format source code [include/c++/14/format]

1	// <format> Formatting -- C++ --
2
3	// Copyright The GNU Toolchain Authors.
4	//
5	// This file is part of the GNU ISO C++ Library. This library is free
6	// software; you can redistribute it and/or modify it under the
7	// terms of the GNU General Public License as published by the
8	// Free Software Foundation; either version 3, or (at your option)
9	// any later version.
10
11	// This library is distributed in the hope that it will be useful,
12	// but WITHOUT ANY WARRANTY; without even the implied warranty of
13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14	// GNU General Public License for more details.
15
16	// Under Section 7 of GPL version 3, you are granted additional
17	// permissions described in the GCC Runtime Library Exception, version
18	// 3.1, as published by the Free Software Foundation.
19
20	// You should have received a copy of the GNU General Public License and
21	// a copy of the GCC Runtime Library Exception along with this program;
22	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23	// <http://www.gnu.org/licenses/>.
24
25	/* @file include/format*
26	* This is a Standard C++ Library header.
27	*/
28
29	#ifndef _GLIBCXX_FORMAT
30	#define _GLIBCXX_FORMAT 1
31
32	#pragma GCC system_header
33
34	#include <bits/requires_hosted.h> // for std::string
35
36	#define __glibcxx_want_format
37	#define __glibcxx_want_format_ranges
38	#define __glibcxx_want_format_uchar
39	#include <bits/version.h>
40
41	#ifdef __cpp_lib_format // C++ >= 20 && HOSTED
42
43	#include <array>
44	#include <charconv>
45	#include <concepts>
46	#include <limits>
47	#include <locale>
48	#include <optional>
49	#include <span>
50	#include <string_view>
51	#include <string>
52	#include <variant> // monostate (TODO: move to bits/utility.h?)
53	#include <bits/ranges_base.h> // input_range, range_reference_t
54	#include <bits/ranges_util.h> // subrange
55	#include <bits/ranges_algobase.h> // ranges::copy
56	#include <bits/stl_iterator.h> // back_insert_iterator
57	#include <bits/stl_pair.h> // __is_pair
58	#include <bits/unicode.h> // __is_scalar_value, _Utf_view, etc.
59	#include <bits/utility.h> // tuple_size_v
60	#include <ext/numeric_traits.h> // __int_traits
61
62	#if !__has_builtin(__builtin_toupper)
63	# include <cctype>
64	#endif
65
66	namespace std _GLIBCXX_VISIBILITY(default)
67	{
68	_GLIBCXX_BEGIN_NAMESPACE_VERSION
69
70	// [format.context], class template basic_format_context
71	template<typename _Out, typename _CharT> class basic_format_context;
72
73	// [format.fmt.string], class template basic_format_string
74	template<typename _CharT, typename... _Args> struct basic_format_string;
75
76	/// @cond undocumented
77	namespace __format
78	{
79	// Type-erased character sink.
80	template<typename _CharT> class _Sink;
81	// Output iterator that writes to a type-erase character sink.
82	template<typename _CharT>
83	class _Sink_iter;
84
85	template<typename _CharT>
86	using __format_context = basic_format_context<_Sink_iter<_CharT>, _CharT>;
87
88	template<typename _CharT>
89	struct _Runtime_format_string
90	{
91	[[__gnu__::__always_inline__]]
92	_Runtime_format_string(basic_string_view<_CharT> __s) noexcept
93	: _M_str(__s) { }
94
95	_Runtime_format_string(const _Runtime_format_string&) = delete;
96	void operator=(const _Runtime_format_string&) = delete;
97
98	private:
99	basic_string_view<_CharT> _M_str;
100
101	template<typename, typename...> friend struct std::basic_format_string;
102	};
103	} // namespace __format
104	/// @endcond
105
106	using format_context = __format::__format_context<char>;
107	#ifdef _GLIBCXX_USE_WCHAR_T
108	using wformat_context = __format::__format_context<wchar_t>;
109	#endif
110
111	// [format.args], class template basic_format_args
112	template<typename _Context> class basic_format_args;
113	using format_args = basic_format_args<format_context>;
114	#ifdef _GLIBCXX_USE_WCHAR_T
115	using wformat_args = basic_format_args<wformat_context>;
116	#endif
117
118	// [format.arguments], arguments
119	// [format.arg], class template basic_format_arg
120	template<typename _Context>
121	class basic_format_arg;
122
123	/* A compile-time checked format string for the specified argument types.*
124	*
125	* @since C++23 but available as an extension in C++20.
126	*/
127	template<typename _CharT, typename... _Args>
128	struct basic_format_string
129	{
130	template<typename _Tp>
131	requires convertible_to<const _Tp&, basic_string_view<_CharT>>
132	consteval
133	basic_format_string(const _Tp& __s);
134
135	[[__gnu__::__always_inline__]]
136	basic_format_string(__format::_Runtime_format_string<_CharT> __s) noexcept
137	: _M_str(__s._M_str)
138	{ }
139
140	[[__gnu__::__always_inline__]]
141	constexpr basic_string_view<_CharT>
142	get() const noexcept
143	{ return _M_str; }
144
145	private:
146	basic_string_view<_CharT> _M_str;
147	};
148
149	template<typename... _Args>
150	using format_string = basic_format_string<char, type_identity_t<_Args>...>;
151
152	#ifdef _GLIBCXX_USE_WCHAR_T
153	template<typename... _Args>
154	using wformat_string
155	= basic_format_string<wchar_t, type_identity_t<_Args>...>;
156	#endif
157
158	#if __cplusplus > 202302L
159	[[__gnu__::__always_inline__]]
160	inline __format::_Runtime_format_string<char>
161	runtime_format(string_view __fmt) noexcept
162	{ return __fmt; }
163
164	#ifdef _GLIBCXX_USE_WCHAR_T
165	[[__gnu__::__always_inline__]]
166	inline __format::_Runtime_format_string<wchar_t>
167	runtime_format(wstring_view __fmt) noexcept
168	{ return __fmt; }
169	#endif
170	#endif // C++26
171
172	// [format.formatter], formatter
173
174	/// The primary template of std::formatter is disabled.
175	template<typename _Tp, typename _CharT = char>
176	struct formatter
177	{
178	formatter() = delete; // No std::formatter specialization for this type.
179	formatter(const formatter&) = delete;
180	formatter& operator=(const formatter&) = delete;
181	};
182
183	// [format.error], class format_error
184	class format_error : public runtime_error
185	{
186	public:
187	explicit format_error(const string& __what) : runtime_error (__what) { }
188	explicit format_error(const char* __what) : runtime_error (__what) { }
189	};
190
191	/// @cond undocumented
192	[[noreturn]]
193	inline void
194	__throw_format_error(const char* __what)
195	{ _GLIBCXX_THROW_OR_ABORT(format_error (__what)); }
196
197	namespace __format
198	{
199	// XXX use named functions for each constexpr error?
200
201	[[noreturn]]
202	inline void
203	__unmatched_left_brace_in_format_string()
204	{ __throw_format_error(what: "format error: unmatched '{' in format string"); }
205
206	[[noreturn]]
207	inline void
208	__unmatched_right_brace_in_format_string()
209	{ __throw_format_error(what: "format error: unmatched '}' in format string"); }
210
211	[[noreturn]]
212	inline void
213	__conflicting_indexing_in_format_string()
214	{ __throw_format_error(what: "format error: conflicting indexing style in format string"); }
215
216	[[noreturn]]
217	inline void
218	__invalid_arg_id_in_format_string()
219	{ __throw_format_error(what: "format error: invalid arg-id in format string"); }
220
221	[[noreturn]]
222	inline void
223	__failed_to_parse_format_spec()
224	{ __throw_format_error(what: "format error: failed to parse format-spec"); }
225	} // namespace __format
226	/// @endcond
227
228	// [format.parse.ctx], class template basic_format_parse_context
229	template<typename _CharT> class basic_format_parse_context;
230	using format_parse_context = basic_format_parse_context<char>;
231	#ifdef _GLIBCXX_USE_WCHAR_T
232	using wformat_parse_context = basic_format_parse_context<wchar_t>;
233	#endif
234
235	template<typename _CharT>
236	class basic_format_parse_context
237	{
238	public:
239	using char_type = _CharT;
240	using const_iterator = typename basic_string_view<_CharT>::const_iterator;
241	using iterator = const_iterator;
242
243	constexpr explicit
244	basic_format_parse_context(basic_string_view<_CharT> __fmt,
245	size_t __num_args = `0`) noexcept
246	: _M_begin(__fmt.begin()), _M_end(__fmt.end()), _M_num_args(__num_args)
247	{ }
248
249	basic_format_parse_context(const basic_format_parse_context&) = delete;
250	void operator=(const basic_format_parse_context&) = delete;
251
252	constexpr const_iterator begin() const noexcept { return _M_begin; }
253	constexpr const_iterator end() const noexcept { return _M_end; }
254
255	constexpr void
256	advance_to(const_iterator __it) noexcept
257	{ _M_begin = __it; }
258
259	constexpr size_t
260	next_arg_id()
261	{
262	if (_M_indexing == _Manual)
263	__format::__conflicting_indexing_in_format_string();
264	_M_indexing = _Auto;
265
266	// _GLIBCXX_RESOLVE_LIB_DEFECTS
267	// 3825. Missing compile-time argument id check in next_arg_id
268	if (std::is_constant_evaluated())
269	if (_M_next_arg_id == _M_num_args)
270	__format::__invalid_arg_id_in_format_string();
271	return _M_next_arg_id++;
272	}
273
274	constexpr void
275	check_arg_id(size_t __id)
276	{
277	if (_M_indexing == _Auto)
278	__format::__conflicting_indexing_in_format_string();
279	_M_indexing = _Manual;
280
281	if (std::is_constant_evaluated())
282	if (__id >= _M_num_args)
283	__format::__invalid_arg_id_in_format_string();
284	}
285
286	private:
287	iterator _M_begin;
288	iterator _M_end;
289	enum _Indexing { _Unknown, _Manual, _Auto };
290	_Indexing _M_indexing = _Unknown;
291	size_t _M_next_arg_id = `0`;
292	size_t _M_num_args;
293	};
294
295	/// @cond undocumented
296	template<typename _Tp, template<typename...> class _Class>
297	static constexpr bool __is_specialization_of = false;
298	template<template<typename...> class _Class, typename... _Args>
299	static constexpr bool __is_specialization_of<_Class<_Args...>, _Class>
300	= true;
301
302	namespace __format
303	{
304	// pre: first != last
305	template<typename _CharT>
306	constexpr pair<unsigned short, const _CharT*>
307	__parse_integer(const _CharT* __first, const _CharT* __last)
308	{
309	if (__first == __last)
310	__builtin_unreachable();
311
312	if constexpr (is_same_v<_CharT, char>)
313	{
314	const auto __start = __first;
315	unsigned short __val = `0`;
316	// N.B. std::from_chars is not constexpr in C++20.
317	if (__detail::__from_chars_alnum<true>(__first, __last, __val, `10`)
318	&& __first != __start) [[likely]]
319	return {__val, __first};
320	}
321	else
322	{
323	constexpr int __n = `32`;
324	char __buf[__n]{};
325	for (int __i = `0`; __i < __n && (__first + __i) != __last; ++__i)
326	__buf[__i] = __first[__i];
327	auto [__v, __ptr] = __format::__parse_integer(first: __buf, last: __buf + __n);
328	if (__ptr) [[likely]]
329	return {__v, __first + (__ptr - __buf)};
330	}
331	return {`0`, nullptr};
332	}
333
334	template<typename _CharT>
335	constexpr pair<unsigned short, const _CharT*>
336	__parse_arg_id(const _CharT* __first, const _CharT* __last)
337	{
338	if (__first == __last)
339	__builtin_unreachable();
340
341	if (*__first == `'0'`)
342	return {`0`, __first + `1`}; // No leading zeros allowed, so '0...' == 0
343
344	if (`'1'` <= __first && __first <= `'9'`)
345	{
346	const unsigned short __id = *__first - `'0'`;
347	const auto __next = __first + `1`;
348	// Optimize for most likely case of single digit arg-id.
349	if (__next == __last \|\| !(`'0'` <= __next && __next <= `'9'`))
350	return {__id, __next};
351	else
352	return __format::__parse_integer(__first, __last);
353	}
354	return {`0`, nullptr};
355	}
356
357	enum _Pres_type {
358	_Pres_none = `0`, // Default type (not valid for integer presentation types).
359	// Presentation types for integral types (including bool and charT).
360	_Pres_d = `1`, _Pres_b, _Pres_B, _Pres_o, _Pres_x, _Pres_X, _Pres_c,
361	// Presentation types for floating-point types.
362	_Pres_a = `1`, _Pres_A, _Pres_e, _Pres_E, _Pres_f, _Pres_F, _Pres_g, _Pres_G,
363	_Pres_p = `0`, _Pres_P, // For pointers.
364	_Pres_s = `0`, // For strings and bool.
365	_Pres_esc = `0xf`, // For strings and charT.
366	};
367
368	enum _Align {
369	_Align_default,
370	_Align_left,
371	_Align_right,
372	_Align_centre,
373	};
374
375	enum _Sign {
376	_Sign_default,
377	_Sign_plus,
378	_Sign_minus, // XXX does this need to be distinct from _Sign_default?
379	_Sign_space,
380	};
381
382	enum _WidthPrec {
383	_WP_none, // No width/prec specified.
384	_WP_value, // Fixed width/prec specified.
385	_WP_from_arg // Use a formatting argument for width/prec.
386	};
387
388	template<typename _Context>
389	size_t
390	__int_from_arg(const basic_format_arg<_Context>& __arg);
391
392	constexpr bool __is_digit(char __c)
393	{ return std::__detail::__from_chars_alnum_to_val(__c) < `10`; }
394
395	constexpr bool __is_xdigit(char __c)
396	{ return std::__detail::__from_chars_alnum_to_val(__c) < `16`; }
397
398	template<typename _CharT>
399	struct _Spec
400	{
401	_Align _M_align : `2`;
402	_Sign _M_sign : `2`;
403	unsigned _M_alt : `1`;
404	unsigned _M_localized : `1`;
405	unsigned _M_zero_fill : `1`;
406	_WidthPrec _M_width_kind : `2`;
407	_WidthPrec _M_prec_kind : `2`;
408	_Pres_type _M_type : `4`;
409	unsigned _M_reserved : `1`;
410	unsigned _M_reserved2 : `16`;
411	unsigned short _M_width;
412	unsigned short _M_prec;
413	char32_t _M_fill = `' '`;
414
415	using iterator = typename basic_string_view<_CharT>::iterator;
416
417	static constexpr _Align
418	_S_align(_CharT __c) noexcept
419	{
420	switch (__c)
421	{
422	case `'<'`: return _Align_left;
423	case `'>'`: return _Align_right;
424	case `'^'`: return _Align_centre;
425	default: return _Align_default;
426	}
427	}
428
429	// pre: __first != __last
430	constexpr iterator
431	_M_parse_fill_and_align(iterator __first, iterator __last) noexcept
432	{
433	if (*__first != `'{'`)
434	{
435	using namespace __unicode;
436	if constexpr (__literal_encoding_is_unicode<_CharT>())
437	{
438	// Accept any UCS scalar value as fill character.
439	_Utf32_view<ranges::subrange<iterator>> __uv({__first, __last});
440	if (!__uv.empty())
441	{
442	auto __beg = __uv.begin();
443	char32_t __c = *__beg++;
444	if (__is_scalar_value(__c))
445	if (auto __next = __beg.base(); __next != __last)
446	if (_Align __align = _S_align(c: *__next))
447	{
448	_M_fill = __c;
449	_M_align = __align;
450	return ++__next;
451	}
452	}
453	}
454	else if (__last - __first >= `2`)
455	if (_Align __align = _S_align(c: __first[`1`]))
456	{
457	_M_fill = *__first;
458	_M_align = __align;
459	return __first + `2`;
460	}
461
462	if (_Align __align = _S_align(c: __first[`0`]))
463	{
464	_M_fill = `' '`;
465	_M_align = __align;
466	return __first + `1`;
467	}
468	}
469	return __first;
470	}
471
472	static constexpr _Sign
473	_S_sign(_CharT __c) noexcept
474	{
475	switch (__c)
476	{
477	case `'+'`: return _Sign_plus;
478	case `'-'`: return _Sign_minus;
479	case `' '`: return _Sign_space;
480	default: return _Sign_default;
481	}
482	}
483
484	// pre: __first != __last
485	constexpr iterator
486	_M_parse_sign(iterator __first, iterator) noexcept
487	{
488	if (_Sign __sign = _S_sign(c: *__first))
489	{
490	_M_sign = __sign;
491	return __first + `1`;
492	}
493	return __first;
494	}
495
496	// pre: __first is valid*
497	constexpr iterator
498	_M_parse_alternate_form(iterator __first, iterator) noexcept
499	{
500	if (*__first == `'#'`)
501	{
502	_M_alt = true;
503	++__first;
504	}
505	return __first;
506	}
507
508	// pre: __first != __last
509	constexpr iterator
510	_M_parse_zero_fill(iterator __first, iterator / __last /) noexcept
511	{
512	if (*__first == `'0'`)
513	{
514	_M_zero_fill = true;
515	++__first;
516	}
517	return __first;
518	}
519
520	// pre: __first != __last
521	static constexpr iterator
522	_S_parse_width_or_precision(iterator __first, iterator __last,
523	unsigned short& __val, bool& __arg_id,
524	basic_format_parse_context<_CharT>& __pc)
525	{
526	if (__format::__is_digit(c: *__first))
527	{
528	auto [__v, __ptr] = __format::__parse_integer(__first, __last);
529	if (!__ptr)
530	__throw_format_error(what: "format error: invalid width or precision "
531	"in format-spec");
532	__first = __ptr;
533	__val = __v;
534	}
535	else if (*__first == `'{'`)
536	{
537	__arg_id = true;
538	++__first;
539	if (__first == __last)
540	__format::__unmatched_left_brace_in_format_string();
541	if (*__first == `'}'`)
542	__val = __pc.next_arg_id();
543	else
544	{
545	auto [__v, __ptr] = __format::__parse_arg_id(__first, __last);
546	if (__ptr == nullptr \|\| __ptr == __last \|\| *__ptr != `'}'`)
547	__format::__invalid_arg_id_in_format_string();
548	__first = __ptr;
549	__pc.check_arg_id(__v);
550	__val = __v;
551	}
552	++__first; // past the '}'
553	}
554	return __first;
555	}
556
557	// pre: __first != __last
558	constexpr iterator
559	_M_parse_width(iterator __first, iterator __last,
560	basic_format_parse_context<_CharT>& __pc)
561	{
562	bool __arg_id = false;
563	if (*__first == `'0'`)
564	__throw_format_error(what: "format error: width must be non-zero in "
565	"format string");
566	auto __next = _S_parse_width_or_precision(__first, __last, val&: _M_width,
567	__arg_id, __pc);
568	if (__next != __first)
569	_M_width_kind = __arg_id ? _WP_from_arg : _WP_value;
570	return __next;
571	}
572
573	// pre: __first != __last
574	constexpr iterator
575	_M_parse_precision(iterator __first, iterator __last,
576	basic_format_parse_context<_CharT>& __pc)
577	{
578	if (__first[`0`] != `'.'`)
579	return __first;
580
581	iterator __next = ++__first;
582	bool __arg_id = false;
583	if (__next != __last)
584	__next = _S_parse_width_or_precision(__first, __last, val&: _M_prec,
585	__arg_id, __pc);
586	if (__next == __first)
587	__throw_format_error(what: "format error: missing precision after '.' in "
588	"format string");
589	_M_prec_kind = __arg_id ? _WP_from_arg : _WP_value;
590	return __next;
591	}
592
593	// pre: __first != __last
594	constexpr iterator
595	_M_parse_locale(iterator __first, iterator / __last /) noexcept
596	{
597	if (*__first == `'L'`)
598	{
599	_M_localized = true;
600	++__first;
601	}
602	return __first;
603	}
604
605	template<typename _Context>
606	size_t
607	_M_get_width(_Context& __ctx) const
608	{
609	size_t __width = `0`;
610	if (_M_width_kind == _WP_value)
611	__width = _M_width;
612	else if (_M_width_kind == _WP_from_arg)
613	__width = __format::__int_from_arg(__ctx.arg(_M_width));
614	return __width;
615	}
616
617	template<typename _Context>
618	size_t
619	_M_get_precision(_Context& __ctx) const
620	{
621	size_t __prec = -`1`;
622	if (_M_prec_kind == _WP_value)
623	__prec = _M_prec;
624	else if (_M_prec_kind == _WP_from_arg)
625	__prec = __format::__int_from_arg(__ctx.arg(_M_prec));
626	return __prec;
627	}
628	};
629
630	template<typename _Int>
631	inline char*
632	__put_sign(_Int __i, _Sign __sign, char* __dest) noexcept
633	{
634	if (__i < `0`)
635	*__dest = `'-'`;
636	else if (__sign == _Sign_plus)
637	*__dest = `'+'`;
638	else if (__sign == _Sign_space)
639	*__dest = `' '`;
640	else
641	++__dest;
642	return __dest;
643	}
644
645	// Write STR to OUT (and do so efficiently if OUT is a _Sink_iter).
646	template<typename _Out, typename _CharT>
647	requires output_iterator<_Out, const _CharT&>
648	inline _Out
649	__write(_Out __out, basic_string_view<_CharT> __str)
650	{
651	if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
652	{
653	if (__str.size())
654	__out = __str;
655	}
656	else
657	for (_CharT __c : __str)
658	*__out++ = __c;
659	return __out;
660	}
661
662	// Write STR to OUT with NFILL copies of FILL_CHAR specified by ALIGN.
663	// pre: __align != _Align_default
664	template<typename _Out, typename _CharT>
665	_Out
666	__write_padded(_Out __out, basic_string_view<_CharT> __str,
667	_Align __align, size_t __nfill, char32_t __fill_char)
668	{
669	const size_t __buflen = `0x20`;
670	_CharT __padding_chars[__buflen];
671	__padding_chars[`0`] = _CharT();
672	basic_string_view<_CharT> __padding{__padding_chars, __buflen};
673
674	auto __pad = [&__padding] (size_t __n, _Out& __o) {
675	if (__n == `0`)
676	return;
677	while (__n > __padding.size())
678	{
679	__o = __format::__write(std::move(__o), __padding);
680	__n -= __padding.size();
681	}
682	if (__n != `0`)
683	__o = __format::__write(std::move(__o), __padding.substr(`0`, __n));
684	};
685
686	size_t __l, __r, __max;
687	if (__align == _Align_centre)
688	{
689	__l = __nfill / `2`;
690	__r = __l + (__nfill & `1`);
691	__max = __r;
692	}
693	else if (__align == _Align_right)
694	{
695	__l = __nfill;
696	__r = `0`;
697	__max = __l;
698	}
699	else
700	{
701	__l = `0`;
702	__r = __nfill;
703	__max = __r;
704	}
705
706	using namespace __unicode;
707	if constexpr (__literal_encoding_is_unicode<_CharT>())
708	if (!__is_single_code_unit<_CharT>(__fill_char)) [[unlikely]]
709	{
710	// Encode fill char as multiple code units of type _CharT.
711	const char32_t __arr[`1`]{ __fill_char };
712	_Utf_view<_CharT, const char32_t(&)[`1`]> __v(__arr);
713	basic_string<_CharT> __padstr(__v.begin(), __v.end());
714	__padding = __padstr;
715	while (__l-- > `0`)
716	__out = __format::__write(std::move(__out), __padding);
717	__out = __format::__write(std::move(__out), __str);
718	while (__r-- > `0`)
719	__out = __format::__write(std::move(__out), __padding);
720	return __out;
721	}
722
723	if (__max < __buflen)
724	__padding.remove_suffix(__buflen - __max);
725	else
726	__max = __buflen;
727
728	char_traits<_CharT>::assign(__padding_chars, __max, __fill_char);
729	__pad(__l, __out);
730	__out = __format::__write(std::move(__out), __str);
731	__pad(__r, __out);
732
733	return __out;
734	}
735
736	// Write STR to OUT, with alignment and padding as determined by SPEC.
737	// pre: __spec._M_align != _Align_default \|\| __align != _Align_default
738	template<typename _CharT, typename _Out>
739	_Out
740	__write_padded_as_spec(basic_string_view<type_identity_t<_CharT>> __str,
741	size_t __estimated_width,
742	basic_format_context<_Out, _CharT>& __fc,
743	const _Spec<_CharT>& __spec,
744	_Align __align = _Align_left)
745	{
746	size_t __width = __spec._M_get_width(__fc);
747
748	if (__width <= __estimated_width)
749	return __format::__write(__fc.out(), __str);
750
751	const size_t __nfill = __width - __estimated_width;
752
753	if (__spec._M_align)
754	__align = __spec._M_align;
755
756	return __format::__write_padded(__fc.out(), __str, __align, __nfill,
757	__spec._M_fill);
758	}
759
760	// A lightweight optional<locale>.
761	struct _Optional_locale
762	{
763	[[__gnu__::__always_inline__]]
764	_Optional_locale() : _M_dummy(), _M_hasval(false) { }
765
766	_Optional_locale(const locale& __loc) noexcept
767	: _M_loc (__loc), _M_hasval(true)
768	{ }
769
770	_Optional_locale(const _Optional_locale& __l) noexcept
771	: _M_dummy(), _M_hasval(__l._M_hasval)
772	{
773	if (_M_hasval)
774	std::construct_at(location: &_M_loc, args: __l._M_loc);
775	}
776
777	_Optional_locale&
778	operator=(const _Optional_locale& __l) noexcept
779	{
780	if (_M_hasval)
781	{
782	if (__l._M_hasval)
783	_M_loc = __l._M_loc;
784	else
785	{
786	_M_loc.~locale();
787	_M_hasval = false;
788	}
789	}
790	else if (__l._M_hasval)
791	{
792	std::construct_at(location: &_M_loc, args: __l._M_loc);
793	_M_hasval = true;
794	}
795	return *this;
796	}
797
798	~_Optional_locale() { if (_M_hasval) _M_loc.~locale(); }
799
800	_Optional_locale&
801	operator=(locale&& __loc) noexcept
802	{
803	if (_M_hasval)
804	_M_loc = std::move(__loc);
805	else
806	{
807	std::construct_at(location: &_M_loc, args: std::move(__loc));
808	_M_hasval = true;
809	}
810	return *this;
811	}
812
813	const locale&
814	value() noexcept
815	{
816	if (!_M_hasval)
817	{
818	std::construct_at(location: &_M_loc);
819	_M_hasval = true;
820	}
821	return _M_loc;
822	}
823
824	bool has_value() const noexcept { return _M_hasval; }
825
826	union {
827	char _M_dummy = `'\0'`;
828	std::locale _M_loc;
829	};
830	bool _M_hasval = false;
831	};
832
833	#ifdef _GLIBCXX_USE_WCHAR_T
834	template<typename _CharT>
835	concept __char = same_as<_CharT, char> \|\| same_as<_CharT, wchar_t>;
836	#else
837	template<typename _CharT>
838	concept __char = same_as<_CharT, char>;
839	#endif
840
841	template<__char _CharT>
842	struct __formatter_str
843	{
844	constexpr typename basic_format_parse_context<_CharT>::iterator
845	parse(basic_format_parse_context<_CharT>& __pc)
846	{
847	auto __first = __pc.begin();
848	const auto __last = __pc.end();
849	_Spec<_CharT> __spec{};
850
851	auto __finalize = [this, &__spec] {
852	_M_spec = __spec;
853	};
854
855	auto __finished = [&] {
856	if (__first == __last \|\| *__first == `'}'`)
857	{
858	__finalize();
859	return true;
860	}
861	return false;
862	};
863
864	if (__finished())
865	return __first;
866
867	__first = __spec._M_parse_fill_and_align(__first, __last);
868	if (__finished())
869	return __first;
870
871	__first = __spec._M_parse_width(__first, __last, __pc);
872	if (__finished())
873	return __first;
874
875	__first = __spec._M_parse_precision(__first, __last, __pc);
876	if (__finished())
877	return __first;
878
879	if (*__first == `'s'`)
880	++__first;
881	#if __cpp_lib_format_ranges
882	else if (*__first == `'?'`)
883	{
884	__spec._M_type = _Pres_esc;
885	++__first;
886	}
887	#endif
888
889	if (__finished())
890	return __first;
891
892	__format::__failed_to_parse_format_spec();
893	}
894
895	template<typename _Out>
896	_Out
897	format(basic_string_view<_CharT> __s,
898	basic_format_context<_Out, _CharT>& __fc) const
899	{
900	if (_M_spec._M_type == _Pres_esc)
901	{
902	// TODO: C++23 escaped string presentation
903	}
904
905	if (_M_spec._M_width_kind == _WP_none
906	&& _M_spec._M_prec_kind == _WP_none)
907	return __format::__write(__fc.out(), __s);
908
909	size_t __estimated_width;
910	if constexpr (__unicode::__literal_encoding_is_unicode<_CharT>())
911	{
912	if (_M_spec._M_prec_kind != _WP_none)
913	{
914	size_t __prec = _M_spec._M_get_precision(__fc);
915	__estimated_width = __unicode::__truncate(__s, __prec);
916	}
917	else
918	__estimated_width = __unicode::__field_width(__s);
919	}
920	else
921	{
922	__s = __s.substr(`0`, _M_spec._M_get_precision(__fc));
923	__estimated_width = __s.size();
924	}
925
926	return __format::__write_padded_as_spec(__s, __estimated_width,
927	__fc, _M_spec);
928	}
929
930	#if __cpp_lib_format_ranges
931	constexpr void
932	set_debug_format() noexcept
933	{ _M_spec._M_type = _Pres_esc; }
934	#endif
935
936	private:
937	_Spec<_CharT> _M_spec{};
938	};
939
940	template<__char _CharT>
941	struct __formatter_int
942	{
943	// If no presentation type is specified, meaning of "none" depends
944	// whether we are formatting an integer or a char or a bool.
945	static constexpr _Pres_type _AsInteger = _Pres_d;
946	static constexpr _Pres_type _AsBool = _Pres_s;
947	static constexpr _Pres_type _AsChar = _Pres_c;
948
949	constexpr typename basic_format_parse_context<_CharT>::iterator
950	_M_do_parse(basic_format_parse_context<_CharT>& __pc, _Pres_type __type)
951	{
952	_Spec<_CharT> __spec{};
953	__spec._M_type = __type;
954
955	const auto __last = __pc.end();
956	auto __first = __pc.begin();
957
958	auto __finalize = [this, &__spec] {
959	_M_spec = __spec;
960	};
961
962	auto __finished = [&] {
963	if (__first == __last \|\| *__first == `'}'`)
964	{
965	__finalize();
966	return true;
967	}
968	return false;
969	};
970
971	if (__finished())
972	return __first;
973
974	__first = __spec._M_parse_fill_and_align(__first, __last);
975	if (__finished())
976	return __first;
977
978	__first = __spec._M_parse_sign(__first, __last);
979	if (__finished())
980	return __first;
981
982	__first = __spec._M_parse_alternate_form(__first, __last);
983	if (__finished())
984	return __first;
985
986	__first = __spec._M_parse_zero_fill(__first, __last);
987	if (__finished())
988	return __first;
989
990	__first = __spec._M_parse_width(__first, __last, __pc);
991	if (__finished())
992	return __first;
993
994	__first = __spec._M_parse_locale(__first, __last);
995	if (__finished())
996	return __first;
997
998	switch (*__first)
999	{
1000	case `'b'`:
1001	__spec._M_type = _Pres_b;
1002	++__first;
1003	break;
1004	case `'B'`:
1005	__spec._M_type = _Pres_B;
1006	++__first;
1007	break;
1008	case `'c'`:
1009	// _GLIBCXX_RESOLVE_LIB_DEFECTS
1010	// 3586. format should not print bool with 'c'
1011	if (__type != _AsBool)
1012	{
1013	__spec._M_type = _Pres_c;
1014	++__first;
1015	}
1016	break;
1017	case `'d'`:
1018	__spec._M_type = _Pres_d;
1019	++__first;
1020	break;
1021	case `'o'`:
1022	__spec._M_type = _Pres_o;
1023	++__first;
1024	break;
1025	case `'x'`:
1026	__spec._M_type = _Pres_x;
1027	++__first;
1028	break;
1029	case `'X'`:
1030	__spec._M_type = _Pres_X;
1031	++__first;
1032	break;
1033	case `'s'`:
1034	if (__type == _AsBool)
1035	{
1036	__spec._M_type = _Pres_s; // same value (and meaning) as "none"
1037	++__first;
1038	}
1039	break;
1040	#if __cpp_lib_format_ranges
1041	case `'?'`:
1042	if (__type == _AsChar)
1043	{
1044	__spec._M_type = _Pres_esc;
1045	++__first;
1046	}
1047	#endif
1048	break;
1049	}
1050
1051	if (__finished())
1052	return __first;
1053
1054	__format::__failed_to_parse_format_spec();
1055	}
1056
1057	template<typename _Tp>
1058	constexpr typename basic_format_parse_context<_CharT>::iterator
1059	_M_parse(basic_format_parse_context<_CharT>& __pc)
1060	{
1061	if constexpr (is_same_v<_Tp, bool>)
1062	{
1063	auto __end = _M_do_parse(__pc, type: _AsBool);
1064	if (_M_spec._M_type == _Pres_s)
1065	if (_M_spec._M_sign \|\| _M_spec._M_alt \|\| _M_spec._M_zero_fill)
1066	__throw_format_error(what: "format error: format-spec contains "
1067	"invalid formatting options for "
1068	"'bool'");
1069	return __end;
1070	}
1071	else if constexpr (__char<_Tp>)
1072	{
1073	auto __end = _M_do_parse(__pc, type: _AsChar);
1074	if (_M_spec._M_type == _Pres_c \|\| _M_spec._M_type == _Pres_esc)
1075	if (_M_spec._M_sign \|\| _M_spec._M_alt \|\| _M_spec._M_zero_fill
1076	/ XXX should be invalid? \|\| _M_spec._M_localized /)
1077	__throw_format_error(what: "format error: format-spec contains "
1078	"invalid formatting options for "
1079	"'charT'");
1080	return __end;
1081	}
1082	else
1083	return _M_do_parse(__pc, type: _AsInteger);
1084	}
1085
1086	template<typename _Int, typename _Out>
1087	typename basic_format_context<_Out, _CharT>::iterator
1088	format(_Int __i, basic_format_context<_Out, _CharT>& __fc) const
1089	{
1090	if (_M_spec._M_type == _Pres_c)
1091	return _M_format_character(_S_to_character(__i), __fc);
1092
1093	char __buf[sizeof(_Int) * __CHAR_BIT__ + `3`];
1094	to_chars_result __res{};
1095
1096	string_view __base_prefix;
1097	make_unsigned_t<_Int> __u;
1098	if (__i < `0`)
1099	__u = -static_cast<make_unsigned_t<_Int>>(__i);
1100	else
1101	__u = __i;
1102
1103	char* __start = __buf + `3`;
1104	char* const __end = __buf + sizeof(__buf);
1105	char* const __start_digits = __start;
1106
1107	switch (_M_spec._M_type)
1108	{
1109	case _Pres_b:
1110	case _Pres_B:
1111	__base_prefix = _M_spec._M_type == _Pres_b ? "0b" : "0B";
1112	__res = to_chars(__start, __end, __u, `2`);
1113	break;
1114	#if 0
1115	case _Pres_c:
1116	return _M_format_character(_S_to_character(__i), __fc);
1117	#endif
1118	case _Pres_none:
1119	// Should not reach here with _Pres_none for bool or charT, so:
1120	[[fallthrough]];
1121	case _Pres_d:
1122	__res = to_chars(__start, __end, __u, `10`);
1123	break;
1124	case _Pres_o:
1125	if (__i != `0`)
1126	__base_prefix = "0";
1127	__res = to_chars(__start, __end, __u, `8`);
1128	break;
1129	case _Pres_x:
1130	case _Pres_X:
1131	__base_prefix = _M_spec._M_type == _Pres_x ? "0x" : "0X";
1132	__res = to_chars(__start, __end, __u, `16`);
1133	if (_M_spec._M_type == _Pres_X)
1134	for (auto __p = __start; __p != __res.ptr; ++__p)
1135	#if __has_builtin(__builtin_toupper)
1136	__p = __builtin_toupper(__p);
1137	#else
1138	__p = std::toupper(c: __p);
1139	#endif
1140	break;
1141	default:
1142	__builtin_unreachable();
1143	}
1144
1145	if (_M_spec._M_alt && __base_prefix.size())
1146	{
1147	__start -= __base_prefix.size();
1148	__builtin_memcpy(__start, __base_prefix.data(),
1149	__base_prefix.size());
1150	}
1151	__start = __format::__put_sign(__i, _M_spec._M_sign, __start - `1`);
1152
1153	return _M_format_int(string_view (__start, __res.ptr - __start),
1154	__start_digits - __start, __fc);
1155	}
1156
1157	template<typename _Out>
1158	typename basic_format_context<_Out, _CharT>::iterator
1159	format(bool __i, basic_format_context<_Out, _CharT>& __fc) const
1160	{
1161	if (_M_spec._M_type == _Pres_c)
1162	return _M_format_character(static_cast<unsigned char>(__i), __fc);
1163	if (_M_spec._M_type != _Pres_s)
1164	return format(static_cast<unsigned char>(__i), __fc);
1165
1166	basic_string<_CharT> __s;
1167	size_t __est_width;
1168	if (_M_spec._M_localized) [[unlikely]]
1169	{
1170	auto& __np = std::use_facet<numpunct<_CharT>>(__fc.locale());
1171	__s = __i ? __np.truename() : __np.falsename();
1172	__est_width = __s.size(); // TODO Unicode-aware estimate
1173	}
1174	else
1175	{
1176	if constexpr (is_same_v<char, _CharT>)
1177	__s = __i ? "true" : "false";
1178	else
1179	__s = __i ? L"true" : L"false";
1180	__est_width = __s.size();
1181	}
1182
1183	return __format::__write_padded_as_spec(__s, __est_width, __fc,
1184	_M_spec);
1185	}
1186
1187	template<typename _Out>
1188	typename basic_format_context<_Out, _CharT>::iterator
1189	_M_format_character(_CharT __c,
1190	basic_format_context<_Out, _CharT>& __fc) const
1191	{
1192	return __format::__write_padded_as_spec({&__c, `1u`}, `1`, __fc, _M_spec);
1193	}
1194
1195	template<typename _Int>
1196	static _CharT
1197	_S_to_character(_Int __i)
1198	{
1199	using _Traits = __gnu_cxx::__int_traits<_CharT>;
1200	if constexpr (is_signed_v<_Int> == is_signed_v<_CharT>)
1201	{
1202	if (_Traits::__min <= __i && __i <= _Traits::__max)
1203	return static_cast<_CharT>(__i);
1204	}
1205	else if constexpr (is_signed_v<_Int>)
1206	{
1207	if (__i >= `0` && make_unsigned_t<_Int>(__i) <= _Traits::__max)
1208	return static_cast<_CharT>(__i);
1209	}
1210	else if (__i <= make_unsigned_t<_CharT>(_Traits::__max))
1211	return static_cast<_CharT>(__i);
1212	__throw_format_error(what: "format error: integer not representable as "
1213	"character");
1214	}
1215
1216	template<typename _Out>
1217	typename basic_format_context<_Out, _CharT>::iterator
1218	_M_format_int(string_view __narrow_str, size_t __prefix_len,
1219	basic_format_context<_Out, _CharT>& __fc) const
1220	{
1221	size_t __width = _M_spec._M_get_width(__fc);
1222
1223	basic_string_view<_CharT> __str;
1224	if constexpr (is_same_v<char, _CharT>)
1225	__str = __narrow_str;
1226	#ifdef _GLIBCXX_USE_WCHAR_T
1227	else
1228	{
1229	size_t __n = __narrow_str.size();
1230	auto __p = (_CharT)__builtin_alloca(__n sizeof(_CharT));
1231	std::__to_wstring_numeric(__narrow_str.data(), __n, __p);
1232	__str = {__p, __n};
1233	}
1234	#endif
1235
1236	if (_M_spec._M_localized)
1237	{
1238	const auto& __l = __fc.locale();
1239	if (__l.name() != "C")
1240	{
1241	auto& __np = use_facet<numpunct<_CharT>>(__l);
1242	string __grp = __np.grouping();
1243	if (!__grp.empty())
1244	{
1245	size_t __n = __str.size() - __prefix_len;
1246	auto __p = (_CharT)__builtin_alloca(`2` __n
1247	* sizeof(_CharT)
1248	+ __prefix_len);
1249	auto __s = __str.data();
1250	char_traits<_CharT>::copy(__p, __s, __prefix_len);
1251	__s += __prefix_len;
1252	auto __end = std::__add_grouping(__p + __prefix_len,
1253	__np.thousands_sep(),
1254	__grp.data(),
1255	__grp.size(),
1256	__s, __s + __n);
1257	__str = {__p, size_t(__end - __p)};
1258	}
1259	}
1260	}
1261
1262	if (__width <= __str.size())
1263	return __format::__write(__fc.out(), __str);
1264
1265	char32_t __fill_char = _M_spec._M_fill;
1266	_Align __align = _M_spec._M_align;
1267
1268	size_t __nfill = __width - __str.size();
1269	auto __out = __fc.out();
1270	if (__align == _Align_default)
1271	{
1272	__align = _Align_right;
1273	if (_M_spec._M_zero_fill)
1274	{
1275	__fill_char = _CharT(`'0'`);
1276	// Write sign and base prefix before zero filling.
1277	if (__prefix_len != `0`)
1278	{
1279	__out = __format::__write(std::move(__out),
1280	__str.substr(`0`, __prefix_len));
1281	__str.remove_prefix(__prefix_len);
1282	}
1283	}
1284	else
1285	__fill_char = _CharT(`' '`);
1286	}
1287	return __format::__write_padded(std::move(__out), __str,
1288	__align, __nfill, __fill_char);
1289	}
1290
1291	#if defined __SIZEOF_INT128__ && defined __STRICT_ANSI__
1292	template<typename _Tp>
1293	using make_unsigned_t
1294	= typename __conditional_t<(sizeof(_Tp) <= sizeof(long long)),
1295	std::make_unsigned<_Tp>,
1296	type_identity<unsigned __int128>>::type;
1297
1298	// std::to_chars is not overloaded for int128 in strict mode.
1299	template<typename _Int>
1300	static to_chars_result
1301	to_chars(char* __first, char* __last, _Int __value, int __base)
1302	{ return std::__to_chars_i<_Int>(__first, __last, __value, __base); }
1303	#endif
1304
1305	_Spec<_CharT> _M_spec{};
1306	};
1307
1308	// Decide how 128-bit floating-point types should be formatted (or not).
1309	// When supported, the typedef __format::__float128_t is the type that
1310	// format arguments should be converted to for storage in basic_format_arg.
1311	// Define the macro _GLIBCXX_FORMAT_F128 to say they're supported.
1312	// _GLIBCXX_FORMAT_F128=1 means __float128, _Float128 etc. will be formatted
1313	// by converting them to long double (or __ieee128 for powerpc64le).
1314	// _GLIBCXX_FORMAT_F128=2 means basic_format_arg needs to enable explicit
1315	// support for _Float128, rather than formatting it as another type.
1316	#undef _GLIBCXX_FORMAT_F128
1317
1318	#ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
1319
1320	// Format 128-bit floating-point types using __ieee128.
1321	using __float128_t = __ieee128;
1322	# define _GLIBCXX_FORMAT_F128 1
1323
1324	#ifdef __LONG_DOUBLE_IEEE128__
1325	// These overloads exist in the library, but are not declared.
1326	// Make them available as std::__format::to_chars.
1327	to_chars_result
1328	to_chars(char, char, __ibm128) noexcept**
1329	__asm("_ZSt8to_charsPcS_e");
1330
1331	to_chars_result
1332	to_chars(char, char, __ibm128, chars_format) noexcept**
1333	__asm("_ZSt8to_charsPcS_eSt12chars_format");
1334
1335	to_chars_result
1336	to_chars(char, char, __ibm128*, chars_format, int) noexcept*
1337	__asm("_ZSt8to_charsPcS_eSt12chars_formati");
1338	#elif __cplusplus == 202002L
1339	to_chars_result
1340	to_chars(char, char, __ieee128) noexcept**
1341	__asm("_ZSt8to_charsPcS_u9__ieee128");
1342
1343	to_chars_result
1344	to_chars(char, char, __ieee128, chars_format) noexcept**
1345	__asm("_ZSt8to_charsPcS_u9__ieee128St12chars_format");
1346
1347	to_chars_result
1348	to_chars(char, char*, __ieee128, chars_format, int) noexcept*
1349	__asm("_ZSt8to_charsPcS_u9__ieee128St12chars_formati");
1350	#endif
1351
1352	#elif defined _GLIBCXX_LDOUBLE_IS_IEEE_BINARY128
1353
1354	// Format 128-bit floating-point types using long double.
1355	using __float128_t = long double;
1356	# define _GLIBCXX_FORMAT_F128 1
1357
1358	#elif __FLT128_DIG__ && defined(_GLIBCXX_HAVE_FLOAT128_MATH)
1359
1360	// Format 128-bit floating-point types using _Float128.
1361	using __float128_t = _Float128;
1362	# define _GLIBCXX_FORMAT_F128 2
1363
1364	# if __cplusplus == 202002L
1365	// These overloads exist in the library, but are not declared for C++20.
1366	// Make them available as std::__format::to_chars.
1367	to_chars_result
1368	to_chars(char, char, _Float128) noexcept**
1369	# if _GLIBCXX_INLINE_VERSION
1370	__asm("_ZNSt3__88to_charsEPcS0_DF128_");
1371	# else
1372	__asm("_ZSt8to_charsPcS_DF128_");
1373	# endif
1374
1375	to_chars_result
1376	to_chars(char, char, _Float128, chars_format) noexcept**
1377	# if _GLIBCXX_INLINE_VERSION
1378	__asm("_ZNSt3__88to_charsEPcS0_DF128_NS_12chars_formatE");
1379	# else
1380	__asm("_ZSt8to_charsPcS_DF128_St12chars_format");
1381	# endif
1382
1383	to_chars_result
1384	to_chars(char, char*, _Float128, chars_format, int) noexcept*
1385	# if _GLIBCXX_INLINE_VERSION
1386	__asm("_ZNSt3__88to_charsEPcS0_DF128_NS_12chars_formatEi");
1387	# else
1388	__asm("_ZSt8to_charsPcS_DF128_St12chars_formati");
1389	# endif
1390	# endif
1391	#endif
1392
1393	using std::to_chars;
1394
1395	// We can format a floating-point type iff it is usable with to_chars.
1396	template<typename _Tp>
1397	concept __formattable_float
1398	= is_same_v<remove_cv_t<_Tp>, _Tp> && requires (_Tp __t, char* __p)
1399	{ __format::to_chars(__p, __p, __t, chars_format::scientific, `6`); };
1400
1401	template<__char _CharT>
1402	struct __formatter_fp
1403	{
1404	constexpr typename basic_format_parse_context<_CharT>::iterator
1405	parse(basic_format_parse_context<_CharT>& __pc)
1406	{
1407	_Spec<_CharT> __spec{};
1408	const auto __last = __pc.end();
1409	auto __first = __pc.begin();
1410
1411	auto __finalize = [this, &__spec] {
1412	_M_spec = __spec;
1413	};
1414
1415	auto __finished = [&] {
1416	if (__first == __last \|\| *__first == `'}'`)
1417	{
1418	__finalize();
1419	return true;
1420	}
1421	return false;
1422	};
1423
1424	if (__finished())
1425	return __first;
1426
1427	__first = __spec._M_parse_fill_and_align(__first, __last);
1428	if (__finished())
1429	return __first;
1430
1431	__first = __spec._M_parse_sign(__first, __last);
1432	if (__finished())
1433	return __first;
1434
1435	__first = __spec._M_parse_alternate_form(__first, __last);
1436	if (__finished())
1437	return __first;
1438
1439	__first = __spec._M_parse_zero_fill(__first, __last);
1440	if (__finished())
1441	return __first;
1442
1443	if (__first[`0`] != `'.'`)
1444	{
1445	__first = __spec._M_parse_width(__first, __last, __pc);
1446	if (__finished())
1447	return __first;
1448	}
1449
1450	__first = __spec._M_parse_precision(__first, __last, __pc);
1451	if (__finished())
1452	return __first;
1453
1454	__first = __spec._M_parse_locale(__first, __last);
1455	if (__finished())
1456	return __first;
1457
1458	switch (*__first)
1459	{
1460	case `'a'`:
1461	__spec._M_type = _Pres_a;
1462	++__first;
1463	break;
1464	case `'A'`:
1465	__spec._M_type = _Pres_A;
1466	++__first;
1467	break;
1468	case `'e'`:
1469	__spec._M_type = _Pres_e;
1470	++__first;
1471	break;
1472	case `'E'`:
1473	__spec._M_type = _Pres_E;
1474	++__first;
1475	break;
1476	case `'f'`:
1477	__spec._M_type = _Pres_f;
1478	++__first;
1479	break;
1480	case `'F'`:
1481	__spec._M_type = _Pres_F;
1482	++__first;
1483	break;
1484	case `'g'`:
1485	__spec._M_type = _Pres_g;
1486	++__first;
1487	break;
1488	case `'G'`:
1489	__spec._M_type = _Pres_G;
1490	++__first;
1491	break;
1492	}
1493
1494	if (__finished())
1495	return __first;
1496
1497	__format::__failed_to_parse_format_spec();
1498	}
1499
1500	template<typename _Fp, typename _Out>
1501	typename basic_format_context<_Out, _CharT>::iterator
1502	format(_Fp __v, basic_format_context<_Out, _CharT>& __fc) const
1503	{
1504	std::string __dynbuf;
1505	char __buf[`128`];
1506	to_chars_result __res{};
1507
1508	size_t __prec = `6`;
1509	bool __use_prec = _M_spec._M_prec_kind != _WP_none;
1510	if (__use_prec)
1511	__prec = _M_spec._M_get_precision(__fc);
1512
1513	char* __start = __buf + `1`; // reserve space for sign
1514	char* __end = __buf + sizeof(__buf);
1515
1516	chars_format __fmt{};
1517	bool __upper = false;
1518	bool __trailing_zeros = false;
1519	char __expc = `'e'`;
1520
1521	switch (_M_spec._M_type)
1522	{
1523	case _Pres_A:
1524	__upper = true;
1525	__expc = `'P'`;
1526	[[fallthrough]];
1527	case _Pres_a:
1528	if (_M_spec._M_type != _Pres_A)
1529	__expc = `'p'`;
1530	__fmt = chars_format::hex;
1531	break;
1532	case _Pres_E:
1533	__upper = true;
1534	__expc = `'E'`;
1535	[[fallthrough]];
1536	case _Pres_e:
1537	__use_prec = true;
1538	__fmt = chars_format::scientific;
1539	break;
1540	case _Pres_F:
1541	__upper = true;
1542	[[fallthrough]];
1543	case _Pres_f:
1544	__use_prec = true;
1545	__fmt = chars_format::fixed;
1546	break;
1547	case _Pres_G:
1548	__upper = true;
1549	__expc = `'E'`;
1550	[[fallthrough]];
1551	case _Pres_g:
1552	__trailing_zeros = true;
1553	__use_prec = true;
1554	__fmt = chars_format::general;
1555	break;
1556	case _Pres_none:
1557	if (__use_prec)
1558	__fmt = chars_format::general;
1559	break;
1560	default:
1561	__builtin_unreachable();
1562	}
1563
1564	// Write value into buffer using std::to_chars.
1565	auto __to_chars = [&](char* __b, char* __e) {
1566	if (__use_prec)
1567	return __format::to_chars(__b, __e, __v, __fmt, __prec);
1568	else if (__fmt != chars_format{})
1569	return __format::to_chars(__b, __e, __v, __fmt);
1570	else
1571	return __format::to_chars(__b, __e, __v);
1572	};
1573
1574	// First try using stack buffer.
1575	__res = __to_chars(__start, __end);
1576
1577	if (__builtin_expect(__res.ec == errc::value_too_large, `0`))
1578	{
1579	// If the buffer is too small it's probably because of a large
1580	// precision, or a very large value in fixed format.
1581	size_t __guess = `8` + __prec;
1582	if (__fmt == chars_format::fixed) // +ddd.prec
1583	{
1584	if constexpr (is_same_v<_Fp, float> \|\| is_same_v<_Fp, double>
1585	\|\| is_same_v<_Fp, long double>)
1586	{
1587	// The number of digits to the left of the decimal point
1588	// is floor(log10(max(abs(__v),1)))+1
1589	int __exp{};
1590	if constexpr (is_same_v<_Fp, float>)
1591	__builtin_frexpf(__v, &__exp);
1592	else if constexpr (is_same_v<_Fp, double>)
1593	__builtin_frexp(__v, &__exp);
1594	else if constexpr (is_same_v<_Fp, long double>)
1595	__builtin_frexpl(__v, &__exp);
1596	if (__exp > `0`)
1597	__guess += `1U` + __exp * `4004U` / `13301U`; // log10(2) approx.
1598	}
1599	else
1600	__guess += numeric_limits<_Fp>::max_exponent10;
1601	}
1602	if (__guess <= sizeof(__buf)) [[unlikely]]
1603	__guess = sizeof(__buf) * `2`;
1604	__dynbuf.reserve(res: __guess);
1605
1606	do
1607	{
1608	auto __overwrite = [&__to_chars, &__res] (char* __p, size_t __n)
1609	{
1610	__res = __to_chars(__p + `1`, __p + __n - `1`);
1611	return __res.ec == errc{} ? __res.ptr - __p : `0`;
1612	};
1613
1614	__dynbuf.__resize_and_overwrite(__dynbuf.capacity() * `2`,
1615	__overwrite);
1616	__start = __dynbuf.data() + `1`; // reserve space for sign
1617	__end = __dynbuf.data() + __dynbuf.size();
1618	}
1619	while (__builtin_expect(__res.ec == errc::value_too_large, `0`));
1620	}
1621
1622	// Use uppercase for 'A', 'E', and 'G' formats.
1623	if (__upper)
1624	{
1625	for (char* __p = __start; __p != __res.ptr; ++__p)
1626	__p = std::toupper(c: __p);
1627	}
1628
1629	bool __have_sign = true;
1630	// Add sign for non-negative values.
1631	if (!__builtin_signbit(__v))
1632	{
1633	if (_M_spec._M_sign == _Sign_plus)
1634	*--__start = `'+'`;
1635	else if (_M_spec._M_sign == _Sign_space)
1636	*--__start = `' '`;
1637	else
1638	__have_sign = false;
1639	}
1640
1641	string_view __narrow_str(__start, __res.ptr - __start);
1642
1643	// Use alternate form. Ensure decimal point is always present,
1644	// and add trailing zeros (up to precision) for g and G forms.
1645	if (_M_spec._M_alt && __builtin_isfinite(__v))
1646	{
1647	string_view __s = __narrow_str;
1648	size_t __sigfigs; // Number of significant figures.
1649	size_t __z = `0`; // Number of trailing zeros to add.
1650	size_t __p; // Position of the exponent character (if any).
1651	size_t __d = __s.find(c: `'.'`); // Position of decimal point.
1652	if (__d != __s.npos) // Found decimal point.
1653	{
1654	__p = __s.find(c: __expc, pos: __d + `1`);
1655	if (__p == __s.npos)
1656	__p = __s.size();
1657
1658	// If presentation type is g or G we might need to add zeros.
1659	if (__trailing_zeros)
1660	{
1661	// Find number of digits after first significant figure.
1662	if (__s [__have_sign] != `'0'`)
1663	// A string like "D.D" or "-D.DDD"
1664	__sigfigs = __p - __have_sign - `1`;
1665	else
1666	// A string like "0.D" or "-0.0DD".
1667	// Safe to assume there is a non-zero digit, because
1668	// otherwise there would be no decimal point.
1669	__sigfigs = __p - __s.find_first_not_of(c: `'0'`, pos: __d + `1`);
1670	}
1671	}
1672	else // No decimal point, we need to insert one.
1673	{
1674	__p = __s.find(c: __expc); // Find the exponent, if present.
1675	if (__p == __s.npos)
1676	__p = __s.size();
1677	__d = __p; // Position where '.' should be inserted.
1678	__sigfigs = __d - __have_sign;
1679	}
1680
1681	if (__trailing_zeros && __prec != `0`)
1682	{
1683	// For g and G presentation types std::to_chars produces
1684	// no more than prec significant figures. Insert this many
1685	// zeros so the result has exactly prec significant figures.
1686	__z = __prec - __sigfigs;
1687	}
1688
1689	if (size_t __extras = int(__d == __p) + __z) // How many to add.
1690	{
1691	if (__dynbuf.empty() && __extras <= size_t(__end - __res.ptr))
1692	{
1693	// The stack buffer is large enough for the result.
1694	// Move exponent to make space for extra chars.
1695	__builtin_memmove(__start + __p + __extras,
1696	__start + __p,
1697	__s.size() - __p);
1698	if (__d == __p)
1699	__start[__p++] = `'.'`;
1700	__builtin_memset(__start + __p, `'0'`, __z);
1701	__narrow_str = {__s.data(), __s.size() + __extras};
1702	}
1703	else // Need to switch to the dynamic buffer.
1704	{
1705	__dynbuf.reserve(res: __s.size() + __extras);
1706	if (__dynbuf.empty())
1707	{
1708	__dynbuf = __s.substr(pos: `0`, n: __p);
1709	if (__d == __p)
1710	__dynbuf += `'.'`;
1711	if (__z)
1712	__dynbuf.append(n: __z, c: `'0'`);
1713	__dynbuf.append(svt: __s.substr(pos: __p));
1714	}
1715	else
1716	{
1717	__dynbuf.insert(pos: __p, n: __extras, c: `'0'`);
1718	if (__d == __p)
1719	__dynbuf [__p] = `'.'`;
1720	}
1721	__narrow_str = __dynbuf;
1722	}
1723	}
1724	}
1725
1726	basic_string<_CharT> __wstr;
1727	basic_string_view<_CharT> __str;
1728	if constexpr (is_same_v<_CharT, char>)
1729	__str = __narrow_str;
1730	#ifdef _GLIBCXX_USE_WCHAR_T
1731	else
1732	{
1733	__wstr = std::__to_wstring_numeric(s: __narrow_str);
1734	__str = __wstr;
1735	}
1736	#endif
1737
1738	if (_M_spec._M_localized && __builtin_isfinite(__v))
1739	{
1740	__wstr = _M_localize(__str, __expc, loc: __fc.locale());
1741	if (!__wstr.empty())
1742	__str = __wstr;
1743	}
1744
1745	size_t __width = _M_spec._M_get_width(__fc);
1746
1747	if (__width <= __str.size())
1748	return __format::__write(__fc.out(), __str);
1749
1750	char32_t __fill_char = _M_spec._M_fill;
1751	_Align __align = _M_spec._M_align;
1752
1753	size_t __nfill = __width - __str.size();
1754	auto __out = __fc.out();
1755	if (__align == _Align_default)
1756	{
1757	__align = _Align_right;
1758	if (_M_spec._M_zero_fill && __builtin_isfinite(__v))
1759	{
1760	__fill_char = _CharT(`'0'`);
1761	// Write sign before zero filling.
1762	if (!__format::__is_xdigit(c: __narrow_str [`0`]))
1763	{
1764	*__out++ = __str[`0`];
1765	__str.remove_prefix(`1`);
1766	}
1767	}
1768	else
1769	__fill_char = _CharT(`' '`);
1770	}
1771	return __format::__write_padded(std::move(__out), __str,
1772	__align, __nfill, __fill_char);
1773	}
1774
1775	// Locale-specific format.
1776	basic_string<_CharT>
1777	_M_localize(basic_string_view<_CharT> __str, char __expc,
1778	const locale& __loc) const
1779	{
1780	basic_string<_CharT> __lstr;
1781
1782	if (__loc == locale::classic())
1783	return __lstr; // Nothing to do.
1784
1785	const auto& __np = use_facet<numpunct<_CharT>>(__loc);
1786	const _CharT __point = __np.decimal_point();
1787	const string __grp = __np.grouping();
1788
1789	_CharT __dot, __exp;
1790	if constexpr (is_same_v<_CharT, char>)
1791	{
1792	__dot = `'.'`;
1793	__exp = __expc;
1794	}
1795	else
1796	{
1797	__dot = L`'.'`;
1798	switch (__expc)
1799	{
1800	case `'e'`:
1801	__exp = L`'e'`;
1802	break;
1803	case `'E'`:
1804	__exp = L`'E'`;
1805	break;
1806	case `'p'`:
1807	__exp = L`'p'`;
1808	break;
1809	case `'P'`:
1810	__exp = L`'P'`;
1811	break;
1812	default:
1813	__builtin_unreachable();
1814	}
1815	}
1816
1817	if (__grp.empty() && __point == __dot)
1818	return __lstr; // Locale uses '.' and no grouping.
1819
1820	size_t __d = __str.find(__dot);
1821	size_t __e = min(__d, __str.find(__exp));
1822	if (__e == __str.npos)
1823	__e = __str.size();
1824	const size_t __r = __str.size() - __e;
1825	auto __overwrite = [&](_CharT* __p, size_t) {
1826	auto __end = std::__add_grouping(__p, __np.thousands_sep(),
1827	__grp.data(), __grp.size(),
1828	__str.data(), __str.data() + __e);
1829	if (__r)
1830	{
1831	if (__d != __str.npos)
1832	{
1833	*__end = __point;
1834	++__end;
1835	++__e;
1836	}
1837	if (__r > `1`)
1838	__end += __str.copy(__end, __str.npos, __e);
1839	}
1840	return (__end - __p);
1841	};
1842	__lstr.__resize_and_overwrite(__e * `2` + __r, __overwrite);
1843	return __lstr;
1844	}
1845
1846	_Spec<_CharT> _M_spec{};
1847	};
1848
1849	} // namespace __format
1850	/// @endcond
1851
1852	/// Format a character.
1853	template<__format::__char _CharT>
1854	struct formatter<_CharT, _CharT>
1855	{
1856	formatter() = default;
1857
1858	constexpr typename basic_format_parse_context<_CharT>::iterator
1859	parse(basic_format_parse_context<_CharT>& __pc)
1860	{
1861	return _M_f.template _M_parse<_CharT>(__pc);
1862	}
1863
1864	template<typename _Out>
1865	typename basic_format_context<_Out, _CharT>::iterator
1866	format(_CharT __u, basic_format_context<_Out, _CharT>& __fc) const
1867	{
1868	if (_M_f._M_spec._M_type == __format::_Pres_none
1869	\|\| _M_f._M_spec._M_type == __format::_Pres_c)
1870	return _M_f._M_format_character(__u, __fc);
1871	else if (_M_f._M_spec._M_type == __format::_Pres_esc)
1872	{
1873	// TODO
1874	return __fc.out();
1875	}
1876	else
1877	return _M_f.format(static_cast<make_unsigned_t<_CharT>>(__u), __fc);
1878	}
1879
1880	#if __cpp_lib_format_ranges
1881	constexpr void
1882	set_debug_format() noexcept
1883	{ _M_f._M_spec._M_type = __format::_Pres_esc; }
1884	#endif
1885
1886	private:
1887	__format::__formatter_int<_CharT> _M_f;
1888	};
1889
1890	#ifdef _GLIBCXX_USE_WCHAR_T
1891	/// Format a char value for wide character output.
1892	template<>
1893	struct formatter<char, wchar_t>
1894	{
1895	formatter() = default;
1896
1897	constexpr typename basic_format_parse_context<wchar_t>::iterator
1898	parse(basic_format_parse_context<wchar_t>& __pc)
1899	{
1900	return _M_f._M_parse<char>(__pc);
1901	}
1902
1903	template<typename _Out>
1904	typename basic_format_context<_Out, wchar_t>::iterator
1905	format(char __u, basic_format_context<_Out, wchar_t>& __fc) const
1906	{
1907	if (_M_f._M_spec._M_type == __format::_Pres_none
1908	\|\| _M_f._M_spec._M_type == __format::_Pres_c)
1909	return _M_f._M_format_character(__u, __fc);
1910	else if (_M_f._M_spec._M_type == __format::_Pres_esc)
1911	{
1912	// TODO
1913	return __fc.out();
1914	}
1915	else
1916	return _M_f.format(static_cast<unsigned char>(__u), __fc);
1917	}
1918
1919	#if __cpp_lib_format_ranges
1920	constexpr void
1921	set_debug_format() noexcept
1922	{ _M_f._M_spec._M_type = __format::_Pres_esc; }
1923	#endif
1924
1925	private:
1926	__format::__formatter_int<wchar_t> _M_f;
1927	};
1928	#endif // USE_WCHAR_T
1929
1930	/* Format a string.*
1931	* @{
1932	*/
1933	template<__format::__char _CharT>
1934	struct formatter<_CharT*, _CharT>
1935	{
1936	formatter() = default;
1937
1938	[[__gnu__::__always_inline__]]
1939	constexpr typename basic_format_parse_context<_CharT>::iterator
1940	parse(basic_format_parse_context<_CharT>& __pc)
1941	{ return _M_f.parse(__pc); }
1942
1943	template<typename _Out>
1944	[[__gnu__::__nonnull__]]
1945	typename basic_format_context<_Out, _CharT>::iterator
1946	format(_CharT* __u, basic_format_context<_Out, _CharT>& __fc) const
1947	{ return _M_f.format(__u, __fc); }
1948
1949	#if __cpp_lib_format_ranges
1950	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
1951	#endif
1952
1953	private:
1954	__format::__formatter_str<_CharT> _M_f;
1955	};
1956
1957	template<__format::__char _CharT>
1958	struct formatter<const _CharT*, _CharT>
1959	{
1960	formatter() = default;
1961
1962	[[__gnu__::__always_inline__]]
1963	constexpr typename basic_format_parse_context<_CharT>::iterator
1964	parse(basic_format_parse_context<_CharT>& __pc)
1965	{ return _M_f.parse(__pc); }
1966
1967	template<typename _Out>
1968	[[__gnu__::__nonnull__]]
1969	typename basic_format_context<_Out, _CharT>::iterator
1970	format(const _CharT* __u,
1971	basic_format_context<_Out, _CharT>& __fc) const
1972	{ return _M_f.format(__u, __fc); }
1973
1974	#if __cpp_lib_format_ranges
1975	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
1976	#endif
1977
1978	private:
1979	__format::__formatter_str<_CharT> _M_f;
1980	};
1981
1982	template<__format::__char _CharT, size_t _Nm>
1983	struct formatter<_CharT[_Nm], _CharT>
1984	{
1985	formatter() = default;
1986
1987	[[__gnu__::__always_inline__]]
1988	constexpr typename basic_format_parse_context<_CharT>::iterator
1989	parse(basic_format_parse_context<_CharT>& __pc)
1990	{ return _M_f.parse(__pc); }
1991
1992	template<typename _Out>
1993	typename basic_format_context<_Out, _CharT>::iterator
1994	format(const _CharT (&__u)[_Nm],
1995	basic_format_context<_Out, _CharT>& __fc) const
1996	{ return _M_f.format({__u, _Nm}, __fc); }
1997
1998	#if __cpp_lib_format_ranges
1999	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2000	#endif
2001
2002	private:
2003	__format::__formatter_str<_CharT> _M_f;
2004	};
2005
2006	template<typename _Traits, typename _Alloc>
2007	struct formatter<basic_string<char, _Traits, _Alloc>, char>
2008	{
2009	formatter() = default;
2010
2011	[[__gnu__::__always_inline__]]
2012	constexpr typename basic_format_parse_context<char>::iterator
2013	parse(basic_format_parse_context<char>& __pc)
2014	{ return _M_f.parse(__pc); }
2015
2016	template<typename _Out>
2017	typename basic_format_context<_Out, char>::iterator
2018	format(const basic_string<char, _Traits, _Alloc>& __u,
2019	basic_format_context<_Out, char>& __fc) const
2020	{ return _M_f.format(__u, __fc); }
2021
2022	#if __cpp_lib_format_ranges
2023	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2024	#endif
2025
2026	private:
2027	__format::__formatter_str<char> _M_f;
2028	};
2029
2030	#ifdef _GLIBCXX_USE_WCHAR_T
2031	template<typename _Traits, typename _Alloc>
2032	struct formatter<basic_string<wchar_t, _Traits, _Alloc>, wchar_t>
2033	{
2034	formatter() = default;
2035
2036	[[__gnu__::__always_inline__]]
2037	constexpr typename basic_format_parse_context<wchar_t>::iterator
2038	parse(basic_format_parse_context<wchar_t>& __pc)
2039	{ return _M_f.parse(__pc); }
2040
2041	template<typename _Out>
2042	typename basic_format_context<_Out, wchar_t>::iterator
2043	format(const basic_string<wchar_t, _Traits, _Alloc>& __u,
2044	basic_format_context<_Out, wchar_t>& __fc) const
2045	{ return _M_f.format(__u, __fc); }
2046
2047	#if __cpp_lib_format_ranges
2048	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2049	#endif
2050
2051	private:
2052	__format::__formatter_str<wchar_t> _M_f;
2053	};
2054	#endif // USE_WCHAR_T
2055
2056	template<typename _Traits>
2057	struct formatter<basic_string_view<char, _Traits>, char>
2058	{
2059	formatter() = default;
2060
2061	[[__gnu__::__always_inline__]]
2062	constexpr typename basic_format_parse_context<char>::iterator
2063	parse(basic_format_parse_context<char>& __pc)
2064	{ return _M_f.parse(__pc); }
2065
2066	template<typename _Out>
2067	typename basic_format_context<_Out, char>::iterator
2068	format(basic_string_view<char, _Traits> __u,
2069	basic_format_context<_Out, char>& __fc) const
2070	{ return _M_f.format(__u, __fc); }
2071
2072	#if __cpp_lib_format_ranges
2073	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2074	#endif
2075
2076	private:
2077	__format::__formatter_str<char> _M_f;
2078	};
2079
2080	#ifdef _GLIBCXX_USE_WCHAR_T
2081	template<typename _Traits>
2082	struct formatter<basic_string_view<wchar_t, _Traits>, wchar_t>
2083	{
2084	formatter() = default;
2085
2086	[[__gnu__::__always_inline__]]
2087	constexpr typename basic_format_parse_context<wchar_t>::iterator
2088	parse(basic_format_parse_context<wchar_t>& __pc)
2089	{ return _M_f.parse(__pc); }
2090
2091	template<typename _Out>
2092	typename basic_format_context<_Out, wchar_t>::iterator
2093	format(basic_string_view<wchar_t, _Traits> __u,
2094	basic_format_context<_Out, wchar_t>& __fc) const
2095	{ return _M_f.format(__u, __fc); }
2096
2097	#if __cpp_lib_format_ranges
2098	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2099	#endif
2100
2101	private:
2102	__format::__formatter_str<wchar_t> _M_f;
2103	};
2104	#endif // USE_WCHAR_T
2105	/// @}
2106
2107	/// @cond undocumented
2108	namespace __format
2109	{
2110	// each cv-unqualified arithmetic type ArithmeticT other than
2111	// char, wchar_t, char8_t, char16_t, or char32_t
2112	template<typename _Tp>
2113	constexpr bool __is_formattable_integer = __is_integer<_Tp>::__value;
2114
2115	#if defined __SIZEOF_INT128__
2116	template<> inline constexpr bool __is_formattable_integer<__int128> = true;
2117	template<> inline constexpr bool __is_formattable_integer<unsigned __int128>
2118	= true;
2119	#endif
2120
2121	template<> inline constexpr bool __is_formattable_integer<char> = false;
2122	template<> inline constexpr bool __is_formattable_integer<wchar_t> = false;
2123	#ifdef _GLIBCXX_USE_CHAR8_T
2124	template<> inline constexpr bool __is_formattable_integer<char8_t> = false;
2125	#endif
2126	template<> inline constexpr bool __is_formattable_integer<char16_t> = false;
2127	template<> inline constexpr bool __is_formattable_integer<char32_t> = false;
2128	}
2129	/// @endcond
2130
2131	/// Format an integer.
2132	template<typename _Tp, __format::__char _CharT>
2133	requires __format::__is_formattable_integer<_Tp>
2134	struct formatter<_Tp, _CharT>
2135	{
2136	formatter() = default;
2137
2138	[[__gnu__::__always_inline__]]
2139	constexpr typename basic_format_parse_context<_CharT>::iterator
2140	parse(basic_format_parse_context<_CharT>& __pc)
2141	{
2142	return _M_f.template _M_parse<_Tp>(__pc);
2143	}
2144
2145	template<typename _Out>
2146	typename basic_format_context<_Out, _CharT>::iterator
2147	format(_Tp __u, basic_format_context<_Out, _CharT>& __fc) const
2148	{ return _M_f.format(__u, __fc); }
2149
2150	private:
2151	__format::__formatter_int<_CharT> _M_f;
2152	};
2153
2154	#if defined __glibcxx_to_chars
2155	/// Format a floating-point value.
2156	template<__format::__formattable_float _Tp, __format::__char _CharT>
2157	struct formatter<_Tp, _CharT>
2158	{
2159	formatter() = default;
2160
2161	[[__gnu__::__always_inline__]]
2162	constexpr typename basic_format_parse_context<_CharT>::iterator
2163	parse(basic_format_parse_context<_CharT>& __pc)
2164	{ return _M_f.parse(__pc); }
2165
2166	template<typename _Out>
2167	typename basic_format_context<_Out, _CharT>::iterator
2168	format(_Tp __u, basic_format_context<_Out, _CharT>& __fc) const
2169	{ return _M_f.format(__u, __fc); }
2170
2171	private:
2172	__format::__formatter_fp<_CharT> _M_f;
2173	};
2174
2175	#if __LDBL_MANT_DIG__ == __DBL_MANT_DIG__
2176	// Reuse __formatter_fp<C>::format<double, Out> for long double.
2177	template<__format::__char _CharT>
2178	struct formatter<long double, _CharT>
2179	{
2180	formatter() = default;
2181
2182	[[__gnu__::__always_inline__]]
2183	constexpr typename basic_format_parse_context<_CharT>::iterator
2184	parse(basic_format_parse_context<_CharT>& __pc)
2185	{ return _M_f.parse(__pc); }
2186
2187	template<typename _Out>
2188	typename basic_format_context<_Out, _CharT>::iterator
2189	format(long double __u, basic_format_context<_Out, _CharT>& __fc) const
2190	{ return _M_f.format((double)__u, __fc); }
2191
2192	private:
2193	__format::__formatter_fp<_CharT> _M_f;
2194	};
2195	#endif
2196
2197	#ifdef __STDCPP_FLOAT16_T__
2198	// Reuse __formatter_fp<C>::format<float, Out> for _Float16.
2199	template<__format::__char _CharT>
2200	struct formatter<_Float16, _CharT>
2201	{
2202	formatter() = default;
2203
2204	[[__gnu__::__always_inline__]]
2205	constexpr typename basic_format_parse_context<_CharT>::iterator
2206	parse(basic_format_parse_context<_CharT>& __pc)
2207	{ return _M_f.parse(__pc); }
2208
2209	template<typename _Out>
2210	typename basic_format_context<_Out, _CharT>::iterator
2211	format(_Float16 __u, basic_format_context<_Out, _CharT>& __fc) const
2212	{ return _M_f.format((float)__u, __fc); }
2213
2214	private:
2215	__format::__formatter_fp<_CharT> _M_f;
2216	};
2217	#endif
2218
2219	#if defined(__FLT32_DIG__)
2220	// Reuse __formatter_fp<C>::format<float, Out> for _Float32.
2221	template<__format::__char _CharT>
2222	struct formatter<_Float32, _CharT>
2223	{
2224	formatter() = default;
2225
2226	[[__gnu__::__always_inline__]]
2227	constexpr typename basic_format_parse_context<_CharT>::iterator
2228	parse(basic_format_parse_context<_CharT>& __pc)
2229	{ return _M_f.parse(__pc); }
2230
2231	template<typename _Out>
2232	typename basic_format_context<_Out, _CharT>::iterator
2233	format(_Float32 __u, basic_format_context<_Out, _CharT>& __fc) const
2234	{ return _M_f.format((float)__u, __fc); }
2235
2236	private:
2237	__format::__formatter_fp<_CharT> _M_f;
2238	};
2239	#endif
2240
2241	#if defined(__FLT64_DIG__)
2242	// Reuse __formatter_fp<C>::format<double, Out> for _Float64.
2243	template<__format::__char _CharT>
2244	struct formatter<_Float64, _CharT>
2245	{
2246	formatter() = default;
2247
2248	[[__gnu__::__always_inline__]]
2249	constexpr typename basic_format_parse_context<_CharT>::iterator
2250	parse(basic_format_parse_context<_CharT>& __pc)
2251	{ return _M_f.parse(__pc); }
2252
2253	template<typename _Out>
2254	typename basic_format_context<_Out, _CharT>::iterator
2255	format(_Float64 __u, basic_format_context<_Out, _CharT>& __fc) const
2256	{ return _M_f.format((double)__u, __fc); }
2257
2258	private:
2259	__format::__formatter_fp<_CharT> _M_f;
2260	};
2261	#endif
2262
2263	#if defined(__FLT128_DIG__) && _GLIBCXX_FORMAT_F128 == 1
2264	// Reuse __formatter_fp<C>::format<__float128_t, Out> for _Float128.
2265	template<__format::__char _CharT>
2266	struct formatter<_Float128, _CharT>
2267	{
2268	formatter() = default;
2269
2270	[[__gnu__::__always_inline__]]
2271	constexpr typename basic_format_parse_context<_CharT>::iterator
2272	parse(basic_format_parse_context<_CharT>& __pc)
2273	{ return _M_f.parse(__pc); }
2274
2275	template<typename _Out>
2276	typename basic_format_context<_Out, _CharT>::iterator
2277	format(_Float128 __u, basic_format_context<_Out, _CharT>& __fc) const
2278	{ return _M_f.format((__format::__float128_t)__u, __fc); }
2279
2280	private:
2281	__format::__formatter_fp<_CharT> _M_f;
2282	};
2283	#endif
2284
2285	#ifdef __STDCPP_BFLOAT16_T__
2286	// Reuse __formatter_fp<C>::format<float, Out> for bfloat16_t.
2287	template<__format::__char _CharT>
2288	struct formatter<__gnu_cxx::__bfloat16_t, _CharT>
2289	{
2290	formatter() = default;
2291
2292	[[__gnu__::__always_inline__]]
2293	constexpr typename basic_format_parse_context<_CharT>::iterator
2294	parse(basic_format_parse_context<_CharT>& __pc)
2295	{ return _M_f.parse(__pc); }
2296
2297	template<typename _Out>
2298	typename basic_format_context<_Out, _CharT>::iterator
2299	format(__gnu_cxx::__bfloat16_t __u,
2300	basic_format_context<_Out, _CharT>& __fc) const
2301	{ return _M_f.format((float)__u, __fc); }
2302
2303	private:
2304	__format::__formatter_fp<_CharT> _M_f;
2305	};
2306	#endif
2307	#endif // __cpp_lib_to_chars
2308
2309	/* Format a pointer.*
2310	* @{
2311	*/
2312	template<__format::__char _CharT>
2313	struct formatter<const void*, _CharT>
2314	{
2315	formatter() = default;
2316
2317	constexpr typename basic_format_parse_context<_CharT>::iterator
2318	parse(basic_format_parse_context<_CharT>& __pc)
2319	{
2320	__format::_Spec<_CharT> __spec{};
2321	const auto __last = __pc.end();
2322	auto __first = __pc.begin();
2323
2324	auto __finalize = [this, &__spec] {
2325	_M_spec = __spec;
2326	};
2327
2328	auto __finished = [&] {
2329	if (__first == __last \|\| *__first == `'}'`)
2330	{
2331	__finalize();
2332	return true;
2333	}
2334	return false;
2335	};
2336
2337	if (__finished())
2338	return __first;
2339
2340	__first = __spec._M_parse_fill_and_align(__first, __last);
2341	if (__finished())
2342	return __first;
2343
2344	// _GLIBCXX_RESOLVE_LIB_DEFECTS
2345	// P2510R3 Formatting pointers
2346	#if __cplusplus > 202302L \|\| ! defined __STRICT_ANSI__
2347	#define _GLIBCXX_P2518R3 1
2348	#else
2349	#define _GLIBCXX_P2518R3 0
2350	#endif
2351
2352	#if _GLIBCXX_P2518R3
2353	__first = __spec._M_parse_zero_fill(__first, __last);
2354	if (__finished())
2355	return __first;
2356	#endif
2357
2358	__first = __spec._M_parse_width(__first, __last, __pc);
2359
2360	if (__first != __last)
2361	{
2362	if (*__first == `'p'`)
2363	++__first;
2364	#if _GLIBCXX_P2518R3
2365	else if (*__first == `'P'`)
2366	{
2367	// _GLIBCXX_RESOLVE_LIB_DEFECTS
2368	// P2510R3 Formatting pointers
2369	__spec._M_type = __format::_Pres_P;
2370	++__first;
2371	}
2372	#endif
2373	}
2374
2375	if (__finished())
2376	return __first;
2377
2378	__format::__failed_to_parse_format_spec();
2379	}
2380
2381	template<typename _Out>
2382	typename basic_format_context<_Out, _CharT>::iterator
2383	format(const void* __v, basic_format_context<_Out, _CharT>& __fc) const
2384	{
2385	auto __u = reinterpret_cast<__UINTPTR_TYPE__>(__v);
2386	char __buf[`2` + sizeof(__v) * `2`];
2387	auto [__ptr, __ec] = std::to_chars(first: __buf + `2`, last: std::end(arr&: __buf),
2388	value: __u, base: `16`);
2389	int __n = __ptr - __buf;
2390	__buf[`0`] = `'0'`;
2391	__buf[`1`] = `'x'`;
2392	#if _GLIBCXX_P2518R3
2393	if (_M_spec._M_type == __format::_Pres_P)
2394	{
2395	__buf[`1`] = `'X'`;
2396	for (auto __p = __buf + `2`; __p != __ptr; ++__p)
2397	#if __has_builtin(__builtin_toupper)
2398	__p = __builtin_toupper(__p);
2399	#else
2400	__p = std::toupper(__p);
2401	#endif
2402	}
2403	#endif
2404
2405	basic_string_view<_CharT> __str;
2406	if constexpr (is_same_v<_CharT, char>)
2407	__str = string_view (__buf, __n);
2408	#ifdef _GLIBCXX_USE_WCHAR_T
2409	else
2410	{
2411	auto __p = (_CharT)__builtin_alloca(__n sizeof(_CharT));
2412	std::__to_wstring_numeric(__buf, __n, __p);
2413	__str = wstring_view(__p, __n);
2414	}
2415	#endif
2416
2417	#if _GLIBCXX_P2518R3
2418	if (_M_spec._M_zero_fill)
2419	{
2420	size_t __width = _M_spec._M_get_width(__fc);
2421	if (__width <= __str.size())
2422	return __format::__write(__fc.out(), __str);
2423
2424	auto __out = __fc.out();
2425	// Write "0x" or "0X" prefix before zero-filling.
2426	__out = __format::__write(std::move(__out), __str.substr(`0`, `2`));
2427	__str.remove_prefix(`2`);
2428	size_t __nfill = __width - __n;
2429	return __format::__write_padded(std::move(__out), __str,
2430	__format::_Align_right,
2431	__nfill, _CharT(`'0'`));
2432	}
2433	#endif
2434
2435	return __format::__write_padded_as_spec(__str, __n, __fc, _M_spec,
2436	__format::_Align_right);
2437	}
2438
2439	private:
2440	__format::_Spec<_CharT> _M_spec{};
2441	};
2442
2443	template<__format::__char _CharT>
2444	struct formatter<void*, _CharT>
2445	{
2446	formatter() = default;
2447
2448	[[__gnu__::__always_inline__]]
2449	constexpr typename basic_format_parse_context<_CharT>::iterator
2450	parse(basic_format_parse_context<_CharT>& __pc)
2451	{ return _M_f.parse(__pc); }
2452
2453	template<typename _Out>
2454	typename basic_format_context<_Out, _CharT>::iterator
2455	format(void* __v, basic_format_context<_Out, _CharT>& __fc) const
2456	{ return _M_f.format(__v, __fc); }
2457
2458	private:
2459	formatter<const void*, _CharT> _M_f;
2460	};
2461
2462	template<__format::__char _CharT>
2463	struct formatter<nullptr_t, _CharT>
2464	{
2465	formatter() = default;
2466
2467	[[__gnu__::__always_inline__]]
2468	constexpr typename basic_format_parse_context<_CharT>::iterator
2469	parse(basic_format_parse_context<_CharT>& __pc)
2470	{ return _M_f.parse(__pc); }
2471
2472	template<typename _Out>
2473	typename basic_format_context<_Out, _CharT>::iterator
2474	format(nullptr_t, basic_format_context<_Out, _CharT>& __fc) const
2475	{ return _M_f.format(nullptr, __fc); }
2476
2477	private:
2478	formatter<const void*, _CharT> _M_f;
2479	};
2480	/// @}
2481
2482	#if defined _GLIBCXX_USE_WCHAR_T && __cpp_lib_format_ranges
2483	// _GLIBCXX_RESOLVE_LIB_DEFECTS
2484	// 3944. Formatters converting sequences of char to sequences of wchar_t
2485
2486	namespace __format { struct __disabled; }
2487
2488	// std::formatter<__disabled, C> uses the primary template, which is disabled.
2489	template<>
2490	struct formatter<char, wchar_t*>
2491	: private formatter<__format::__disabled, wchar_t> { };
2492	template<>
2493	struct formatter<const char, wchar_t*>
2494	: private formatter<__format::__disabled, wchar_t> { };
2495	template<size_t _Nm>
2496	struct formatter<char[_Nm], wchar_t>
2497	: private formatter<__format::__disabled, wchar_t> { };
2498	template<class _Traits, class _Allocator>
2499	struct formatter<basic_string<char, _Traits, _Allocator>, wchar_t>
2500	: private formatter<__format::__disabled, wchar_t> { };
2501	template<class _Traits>
2502	struct formatter<basic_string_view<char, _Traits>, wchar_t>
2503	: private formatter<__format::__disabled, wchar_t> { };
2504	#endif
2505
2506	/// @cond undocumented
2507	namespace __format
2508	{
2509	template<typename _Tp, typename _Context,
2510	typename _Formatter
2511	= typename _Context::template formatter_type<remove_const_t<_Tp>>,
2512	typename _ParseContext
2513	= basic_format_parse_context<typename _Context::char_type>>
2514	concept __parsable_with
2515	= semiregular<_Formatter>
2516	&& requires (_Formatter __f, _ParseContext __pc)
2517	{
2518	{ __f.parse(__pc) } -> same_as<typename _ParseContext::iterator>;
2519	};
2520
2521	template<typename _Tp, typename _Context,
2522	typename _Formatter
2523	= typename _Context::template formatter_type<remove_const_t<_Tp>>,
2524	typename _ParseContext
2525	= basic_format_parse_context<typename _Context::char_type>>
2526	concept __formattable_with
2527	= semiregular<_Formatter>
2528	&& requires (const _Formatter __cf, _Tp&& __t, _Context __fc)
2529	{
2530	{ __cf.format(__t, __fc) } -> same_as<typename _Context::iterator>;
2531	};
2532
2533	// An unspecified output iterator type used in the `formattable` concept.
2534	template<typename _CharT>
2535	using _Iter_for = back_insert_iterator<basic_string<_CharT>>;
2536
2537	template<typename _Tp, typename _CharT,
2538	typename _Context = basic_format_context<_Iter_for<_CharT>, _CharT>>
2539	concept __formattable_impl
2540	= __parsable_with<_Tp, _Context> && __formattable_with<_Tp, _Context>;
2541
2542	} // namespace __format
2543	/// @endcond
2544
2545	// Concept std::formattable was introduced by P2286R8 "Formatting Ranges",
2546	// but we can't guard it with __cpp_lib_format_ranges until we define that!
2547	#if __cplusplus > 202002L
2548	// [format.formattable], concept formattable
2549	template<typename _Tp, typename _CharT>
2550	concept formattable
2551	= __format::__formattable_impl<remove_reference_t<_Tp>, _CharT>;
2552	#endif
2553
2554	#if __cpp_lib_format_ranges
2555	/// @cond undocumented
2556	namespace __format
2557	{
2558	template<typename _Rg, typename _CharT>
2559	concept __const_formattable_range
2560	= ranges::input_range<const _Rg>
2561	&& formattable<ranges::range_reference_t<const _Rg>, _CharT>;
2562
2563	template<typename _Rg, typename _CharT>
2564	using __maybe_const_range
2565	= conditional_t<__const_formattable_range<_Rg, _CharT>, const _Rg, _Rg>;
2566	} // namespace __format
2567	/// @endcond
2568	#endif // format_ranges
2569
2570	/// An iterator after the last character written, and the number of
2571	/// characters that would have been written.
2572	template<typename _Out>
2573	struct format_to_n_result
2574	{
2575	_Out out;
2576	iter_difference_t<_Out> size;
2577	};
2578
2579	_GLIBCXX_BEGIN_NAMESPACE_CONTAINER
2580	template<typename, typename> class vector;
2581	_GLIBCXX_END_NAMESPACE_CONTAINER
2582
2583	/// @cond undocumented
2584	namespace __format
2585	{
2586	template<typename _CharT>
2587	class _Sink_iter
2588	{
2589	_Sink<_CharT>* _M_sink = nullptr;
2590
2591	public:
2592	using iterator_category = output_iterator_tag;
2593	using value_type = void;
2594	using difference_type = ptrdiff_t;
2595	using pointer = void;
2596	using reference = void;
2597
2598	_Sink_iter() = default;
2599	_Sink_iter(const _Sink_iter&) = default;
2600	_Sink_iter& operator=(const _Sink_iter&) = default;
2601
2602	[[__gnu__::__always_inline__]]
2603	explicit constexpr
2604	_Sink_iter(_Sink<_CharT>& __sink) : _M_sink(std::addressof(__sink)) { }
2605
2606	[[__gnu__::__always_inline__]]
2607	constexpr _Sink_iter&
2608	operator=(_CharT __c)
2609	{
2610	_M_sink->_M_write(__c);
2611	return *this;
2612	}
2613
2614	[[__gnu__::__always_inline__]]
2615	constexpr _Sink_iter&
2616	operator=(basic_string_view<_CharT> __s)
2617	{
2618	_M_sink->_M_write(__s);
2619	return *this;
2620	}
2621
2622	[[__gnu__::__always_inline__]]
2623	constexpr _Sink_iter&
2624	operator() { return* *this; }
2625
2626	[[__gnu__::__always_inline__]]
2627	constexpr _Sink_iter&
2628	operator++() { return *this; }
2629
2630	[[__gnu__::__always_inline__]]
2631	constexpr _Sink_iter
2632	operator++(int) { return *this; }
2633
2634	auto
2635	_M_reserve(size_t __n) const
2636	{ return _M_sink->_M_reserve(__n); }
2637	};
2638
2639	// Abstract base class for type-erased character sinks.
2640	// All formatting and output is done via this type's iterator,
2641	// to reduce the number of different template instantiations.
2642	template<typename _CharT>
2643	class _Sink
2644	{
2645	friend class _Sink_iter<_CharT>;
2646
2647	span<_CharT> _M_span;
2648	typename span<_CharT>::iterator _M_next;
2649
2650	// Called when the span is full, to make more space available.
2651	// Precondition: _M_next != _M_span.begin()
2652	// Postcondition: _M_next != _M_span.end()
2653	// TODO: remove the precondition? could make overflow handle it.
2654	virtual void _M_overflow() = `0`;
2655
2656	protected:
2657	// Precondition: __span.size() != 0
2658	[[__gnu__::__always_inline__]]
2659	explicit constexpr
2660	_Sink(span<_CharT> __span) noexcept
2661	: _M_span(__span), _M_next(__span.begin())
2662	{ }
2663
2664	// The portion of the span that has been written to.
2665	[[__gnu__::__always_inline__]]
2666	span<_CharT>
2667	_M_used() const noexcept
2668	{ return _M_span.first(_M_next - _M_span.begin()); }
2669
2670	// The portion of the span that has not been written to.
2671	[[__gnu__::__always_inline__]]
2672	constexpr span<_CharT>
2673	_M_unused() const noexcept
2674	{ return _M_span.subspan(_M_next - _M_span.begin()); }
2675
2676	// Use the start of the span as the next write position.
2677	[[__gnu__::__always_inline__]]
2678	constexpr void
2679	_M_rewind() noexcept
2680	{ _M_next = _M_span.begin(); }
2681
2682	// Replace the current output range.
2683	void
2684	_M_reset(span<_CharT> __s, size_t __pos = `0`) noexcept
2685	{
2686	_M_span = __s;
2687	_M_next = __s.begin() + __pos;
2688	}
2689
2690	// Called by the iterator for it++ = c*
2691	constexpr void
2692	_M_write(_CharT __c)
2693	{
2694	*_M_next++ = __c;
2695	if (_M_next - _M_span.begin() == std::ssize(_M_span)) [[unlikely]]
2696	_M_overflow();
2697	}
2698
2699	constexpr void
2700	_M_write(basic_string_view<_CharT> __s)
2701	{
2702	span __to = _M_unused();
2703	while (__to.size() <= __s.size())
2704	{
2705	__s.copy(__to.data(), __to.size());
2706	_M_next += __to.size();
2707	__s.remove_prefix(__to.size());
2708	_M_overflow();
2709	__to = _M_unused();
2710	}
2711	if (__s.size())
2712	{
2713	__s.copy(__to.data(), __s.size());
2714	_M_next += __s.size();
2715	}
2716	}
2717
2718	// A successful _Reservation can be used to directly write
2719	// up to N characters to the sink to avoid unwanted buffering.
2720	struct _Reservation
2721	{
2722	// True if the reservation was successful, false otherwise.
2723	explicit operator bool() const noexcept { return _M_sink; }
2724	// A pointer to write directly to the sink.
2725	_CharT* get() const noexcept { return _M_sink->_M_next.operator->(); }
2726	// Add n to the _M_next iterator for the sink.
2727	void _M_bump(size_t __n) { _M_sink->_M_bump(__n); }
2728	_Sink* _M_sink;
2729	};
2730
2731	// Attempt to reserve space to write n characters to the sink.
2732	// If anything is written to the reservation then there must be a call
2733	// to _M_bump(N2) before any call to another member function of this,*
2734	// where N2 is the number of characters written.
2735	virtual _Reservation
2736	_M_reserve(size_t __n)
2737	{
2738	if (__n <= _M_unused().size())
2739	return { this };
2740
2741	if (__n <= _M_span.size()) // Cannot meet the request.
2742	{
2743	_M_overflow(); // Make more space available.
2744	if (__n <= _M_unused().size())
2745	return { this };
2746	}
2747	return { nullptr };
2748	}
2749
2750	// Update the next output position after writing directly to the sink.
2751	// pre: no calls to _M_write or _M_overflow since _M_reserve.
2752	virtual void
2753	_M_bump(size_t __n)
2754	{ _M_next += __n; }
2755
2756	public:
2757	_Sink(const _Sink&) = delete;
2758	_Sink& operator=(const _Sink&) = delete;
2759
2760	[[__gnu__::__always_inline__]]
2761	constexpr _Sink_iter<_CharT>
2762	out() noexcept
2763	{ return _Sink_iter<_CharT>(*this); }
2764	};
2765
2766	// A sink with an internal buffer. This is used to implement concrete sinks.
2767	template<typename _CharT>
2768	class _Buf_sink : public _Sink<_CharT>
2769	{
2770	protected:
2771	_CharT _M_buf[`32` * sizeof(void) / sizeof*(_CharT)];
2772
2773	[[__gnu__::__always_inline__]]
2774	constexpr
2775	_Buf_sink() noexcept
2776	: _Sink<_CharT>(_M_buf)
2777	{ }
2778	};
2779
2780	using _GLIBCXX_STD_C::vector;
2781
2782	// A sink that fills a sequence (e.g. std::string, std::vector, std::deque).
2783	// Writes to a buffer then appends that to the sequence when it fills up.
2784	template<typename _Seq>
2785	class _Seq_sink final : public _Buf_sink<typename _Seq::value_type>
2786	{
2787	using _CharT = typename _Seq::value_type;
2788
2789	_Seq _M_seq;
2790
2791	// Transfer buffer contents to the sequence, so buffer can be refilled.
2792	void
2793	_M_overflow() override
2794	{
2795	auto __s = this->_M_used();
2796	if (__s.empty()) [[unlikely]]
2797	return; // Nothing in the buffer to transfer to _M_seq.
2798
2799	// If _M_reserve was called then _M_bump must have been called too.
2800	_GLIBCXX_DEBUG_ASSERT(__s.data() != _M_seq.data());
2801
2802	if constexpr (__is_specialization_of<_Seq, basic_string>)
2803	_M_seq.append(__s.data(), __s.size());
2804	else
2805	_M_seq.insert(_M_seq.end(), __s.begin(), __s.end());
2806
2807	// Make the whole of _M_buf available for the next write:
2808	this->_M_rewind();
2809	}
2810
2811	typename _Sink<_CharT>::_Reservation
2812	_M_reserve(size_t __n) override
2813	{
2814	// We might already have n characters available in this->_M_unused(),
2815	// but the whole point of this function is to be an optimization for
2816	// the std::format("{}", x) case. We want to avoid writing to _M_buf
2817	// and then copying that into a basic_string if possible, so this
2818	// function prefers to create space directly in _M_seq rather than
2819	// using _M_buf.
2820
2821	if constexpr (__is_specialization_of<_Seq, basic_string>
2822	\|\| __is_specialization_of<_Seq, vector>)
2823	{
2824	// Flush the buffer to _M_seq first (should not be needed).
2825	if (this->_M_used().size()) [[unlikely]]
2826	_Seq_sink::_M_overflow();
2827
2828	// Expand _M_seq to make __n new characters available:
2829	const auto __sz = _M_seq.size();
2830	if constexpr (is_same_v<string, _Seq> \|\| is_same_v<wstring, _Seq>)
2831	_M_seq.__resize_and_overwrite(__sz + __n,
2832	[](auto, auto __n2) {
2833	return __n2;
2834	});
2835	else
2836	_M_seq.resize(__sz + __n);
2837
2838	// Set _M_used() to be a span over the original part of _M_seq
2839	// and _M_unused() to be the extra capacity we just created:
2840	this->_M_reset(_M_seq, __sz);
2841	return { this };
2842	}
2843	else // Try to use the base class' buffer.
2844	return _Sink<_CharT>::_M_reserve(__n);
2845	}
2846
2847	void
2848	_M_bump(size_t __n) override
2849	{
2850	if constexpr (__is_specialization_of<_Seq, basic_string>
2851	\|\| __is_specialization_of<_Seq, vector>)
2852	{
2853	auto __s = this->_M_used();
2854	_GLIBCXX_DEBUG_ASSERT(__s.data() == _M_seq.data());
2855	// Truncate the sequence to the part that was actually written to:
2856	_M_seq.resize(__s.size() + __n);
2857	// Switch back to using buffer:
2858	this->_M_reset(this->_M_buf);
2859	}
2860	}
2861
2862	public:
2863	// TODO: for SSO string, use SSO buffer as initial span, then switch
2864	// to _M_buf if it overflows? Or even do that for all unused capacity?
2865
2866	[[__gnu__::__always_inline__]]
2867	_Seq_sink() noexcept(is_nothrow_default_constructible_v<_Seq>)
2868	{ }
2869
2870	_Seq_sink(_Seq&& __s) noexcept(is_nothrow_move_constructible_v<_Seq>)
2871	: _M_seq(std::move(__s))
2872	{ }
2873
2874	using _Sink<_CharT>::out;
2875
2876	_Seq
2877	get() &&
2878	{
2879	if (this->_M_used().size() != `0`)
2880	_Seq_sink::_M_overflow();
2881	return std::move(_M_seq);
2882	}
2883
2884	// A writable span that views everything written to the sink.
2885	// Will be either a view over _M_seq or the used part of _M_buf.
2886	span<_CharT>
2887	view()
2888	{
2889	auto __s = this->_M_used();
2890	if (_M_seq.size())
2891	{
2892	if (__s.size() != `0`)
2893	_Seq_sink::_M_overflow();
2894	return _M_seq;
2895	}
2896	return __s;
2897	}
2898	};
2899
2900	template<typename _CharT, typename _Alloc = allocator<_CharT>>
2901	using _Str_sink
2902	= _Seq_sink<basic_string<_CharT, char_traits<_CharT>, _Alloc>>;
2903
2904	// template<typename _CharT, typename _Alloc = allocator<_CharT>>
2905	// using _Vec_sink = _Seq_sink<vector<_CharT, _Alloc>>;
2906
2907	// A sink that writes to an output iterator.
2908	// Writes to a fixed-size buffer and then flushes to the output iterator
2909	// when the buffer fills up.
2910	template<typename _CharT, typename _OutIter>
2911	class _Iter_sink : public _Buf_sink<_CharT>
2912	{
2913	_OutIter _M_out;
2914	iter_difference_t<_OutIter> _M_max;
2915
2916	protected:
2917	size_t _M_count = `0`;
2918
2919	void
2920	_M_overflow() override
2921	{
2922	auto __s = this->_M_used();
2923	if (_M_max < `0`) // No maximum.
2924	_M_out = ranges::copy(__s, std::move(_M_out)).out;
2925	else if (_M_count < static_cast<size_t>(_M_max))
2926	{
2927	auto __max = _M_max - _M_count;
2928	span<_CharT> __first;
2929	if (__max < __s.size())
2930	__first = __s.first(static_cast<size_t>(__max));
2931	else
2932	__first = __s;
2933	_M_out = ranges::copy(__first, std::move(_M_out)).out;
2934	}
2935	this->_M_rewind();
2936	_M_count += __s.size();
2937	}
2938
2939	public:
2940	[[__gnu__::__always_inline__]]
2941	explicit
2942	_Iter_sink(_OutIter __out, iter_difference_t<_OutIter> __max = -`1`)
2943	: _M_out(std::move(__out)), _M_max(__max)
2944	{ }
2945
2946	using _Sink<_CharT>::out;
2947
2948	format_to_n_result<_OutIter>
2949	_M_finish() &&
2950	{
2951	if (this->_M_used().size() != `0`)
2952	_Iter_sink::_M_overflow();
2953	iter_difference_t<_OutIter> __count(_M_count);
2954	return { std::move(_M_out), __count };
2955	}
2956	};
2957
2958	// Partial specialization for contiguous iterators.
2959	// No buffer is used, characters are written straight to the iterator.
2960	// We do not know the size of the output range, so the span size just grows
2961	// as needed. The end of the span might be an invalid pointer outside the
2962	// valid range, but we never actually call _M_span.end(). This class does
2963	// not introduce any invalid pointer arithmetic or overflows that would not
2964	// have happened anyway.
2965	template<typename _CharT, contiguous_iterator _OutIter>
2966	requires same_as<iter_value_t<_OutIter>, _CharT>
2967	class _Iter_sink<_CharT, _OutIter> : public _Sink<_CharT>
2968	{
2969	_OutIter _M_first;
2970	iter_difference_t<_OutIter> _M_max = -`1`;
2971	protected:
2972	size_t _M_count = `0`;
2973	private:
2974	_CharT _M_buf[`64`]; // Write here after outputting _M_max characters.
2975
2976	protected:
2977	void
2978	_M_overflow() override
2979	{
2980	if (this->_M_unused().size() != `0`)
2981	return; // No need to switch to internal buffer yet.
2982
2983	auto __s = this->_M_used();
2984
2985	if (_M_max >= `0`)
2986	{
2987	_M_count += __s.size();
2988	// Span was already sized for the maximum character count,
2989	// if it overflows then any further output must go to the
2990	// internal buffer, to be discarded.
2991	this->_M_reset(this->_M_buf);
2992	}
2993	else
2994	{
2995	// No maximum character count. Just extend the span to allow
2996	// writing more characters to it.
2997	this->_M_reset({__s.data(), __s.size() + `1024`}, __s.size());
2998	}
2999	}
3000
3001	typename _Sink<_CharT>::_Reservation
3002	_M_reserve(size_t __n) final
3003	{
3004	auto __avail = this->_M_unused();
3005	if (__n > __avail.size())
3006	{
3007	if (_M_max >= `0`)
3008	return {}; // cannot grow
3009
3010	auto __s = this->_M_used();
3011	this->_M_reset({__s.data(), __s.size() + __n}, __s.size());
3012	}
3013	return { this };
3014	}
3015
3016	private:
3017	static span<_CharT>
3018	_S_make_span(_CharT* __ptr, iter_difference_t<_OutIter> __n,
3019	span<_CharT> __buf) noexcept
3020	{
3021	if (__n == `0`)
3022	return __buf; // Only write to the internal buffer.
3023
3024	if (__n > `0`)
3025	{
3026	if constexpr (!is_integral_v<iter_difference_t<_OutIter>>
3027	\|\| sizeof(__n) > sizeof(size_t))
3028	{
3029	// __int128 or __detail::__max_diff_type
3030	auto __m = iter_difference_t<_OutIter>((size_t)-`1`);
3031	if (__n > __m)
3032	__n = __m;
3033	}
3034	return {__ptr, (size_t)__n};
3035	}
3036
3037	#if __has_builtin(__builtin_dynamic_object_size)
3038	if (size_t __bytes = __builtin_dynamic_object_size(__ptr, `2`))
3039	return {__ptr, __bytes / sizeof(_CharT)};
3040	#endif
3041	// Avoid forming a pointer to a different memory page.
3042	const auto __off = reinterpret_cast<__UINTPTR_TYPE__>(__ptr) % `1024`;
3043	__n = (`1024` - __off) / sizeof(_CharT);
3044	if (__n > `0`) [[likely]]
3045	return {__ptr, static_cast<size_t>(__n)};
3046	else // Misaligned/packed buffer of wchar_t?
3047	return {__ptr, `1`};
3048	}
3049
3050	public:
3051	explicit
3052	_Iter_sink(_OutIter __out, iter_difference_t<_OutIter> __n = -`1`) noexcept
3053	: _Sink<_CharT>(_S_make_span(ptr: std::to_address(__out), __n, buf: _M_buf)),
3054	_M_first(__out), _M_max(__n)
3055	{ }
3056
3057	format_to_n_result<_OutIter>
3058	_M_finish() &&
3059	{
3060	auto __s = this->_M_used();
3061	if (__s.data() == _M_buf)
3062	{
3063	// Switched to internal buffer, so must have written _M_max.
3064	iter_difference_t<_OutIter> __count(_M_count + __s.size());
3065	return { _M_first + _M_max, __count };
3066	}
3067	else // Not using internal buffer yet
3068	{
3069	iter_difference_t<_OutIter> __count(__s.size());
3070	return { _M_first + __count, __count };
3071	}
3072	}
3073	};
3074
3075	enum _Arg_t : unsigned char {
3076	_Arg_none, _Arg_bool, _Arg_c, _Arg_i, _Arg_u, _Arg_ll, _Arg_ull,
3077	_Arg_flt, _Arg_dbl, _Arg_ldbl, _Arg_str, _Arg_sv, _Arg_ptr, _Arg_handle,
3078	_Arg_i128, _Arg_u128,
3079	_Arg_bf16, _Arg_f16, _Arg_f32, _Arg_f64, // These are unused.
3080	#ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3081	_Arg_next_value_,
3082	_Arg_f128 = _Arg_ldbl,
3083	_Arg_ibm128 = _Arg_next_value_,
3084	#else
3085	_Arg_f128,
3086	#endif
3087	_Arg_max_
3088	};
3089
3090	template<typename _Context>
3091	struct _Arg_value
3092	{
3093	using _CharT = typename _Context::char_type;
3094
3095	struct _HandleBase
3096	{
3097	const void* _M_ptr;
3098	void (*_M_func)();
3099	};
3100
3101	union
3102	{
3103	monostate _M_none;
3104	bool _M_bool;
3105	_CharT _M_c;
3106	int _M_i;
3107	unsigned _M_u;
3108	long long _M_ll;
3109	unsigned long long _M_ull;
3110	float _M_flt;
3111	double _M_dbl;
3112	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT // No long double if it's ambiguous.
3113	long double _M_ldbl;
3114	#endif
3115	const _CharT* _M_str;
3116	basic_string_view<_CharT> _M_sv;
3117	const void* _M_ptr;
3118	_HandleBase _M_handle;
3119	#ifdef __SIZEOF_INT128__
3120	__int128 _M_i128;
3121	unsigned __int128 _M_u128;
3122	#endif
3123	#ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3124	__ieee128 _M_f128;
3125	__ibm128 _M_ibm128;
3126	#elif _GLIBCXX_FORMAT_F128 == 2
3127	__float128_t _M_f128;
3128	#endif
3129	};
3130
3131	[[__gnu__::__always_inline__]]
3132	_Arg_value() : _M_none () { }
3133
3134	#if 0
3135	template<typename _Tp>
3136	_Arg_value(in_place_type_t<_Tp>, _Tp __val)
3137	{ _S_get<_Tp>() = __val; }
3138	#endif
3139
3140	template<typename _Tp, typename _Self>
3141	[[__gnu__::__always_inline__]]
3142	static auto&
3143	_S_get(_Self& __u) noexcept
3144	{
3145	if constexpr (is_same_v<_Tp, bool>)
3146	return __u._M_bool;
3147	else if constexpr (is_same_v<_Tp, _CharT>)
3148	return __u._M_c;
3149	else if constexpr (is_same_v<_Tp, int>)
3150	return __u._M_i;
3151	else if constexpr (is_same_v<_Tp, unsigned>)
3152	return __u._M_u;
3153	else if constexpr (is_same_v<_Tp, long long>)
3154	return __u._M_ll;
3155	else if constexpr (is_same_v<_Tp, unsigned long long>)
3156	return __u._M_ull;
3157	else if constexpr (is_same_v<_Tp, float>)
3158	return __u._M_flt;
3159	else if constexpr (is_same_v<_Tp, double>)
3160	return __u._M_dbl;
3161	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3162	else if constexpr (is_same_v<_Tp, long double>)
3163	return __u._M_ldbl;
3164	#else
3165	else if constexpr (is_same_v<_Tp, __ieee128>)
3166	return __u._M_f128;
3167	else if constexpr (is_same_v<_Tp, __ibm128>)
3168	return __u._M_ibm128;
3169	#endif
3170	else if constexpr (is_same_v<_Tp, const _CharT*>)
3171	return __u._M_str;
3172	else if constexpr (is_same_v<_Tp, basic_string_view<_CharT>>)
3173	return __u._M_sv;
3174	else if constexpr (is_same_v<_Tp, const void*>)
3175	return __u._M_ptr;
3176	#ifdef __SIZEOF_INT128__
3177	else if constexpr (is_same_v<_Tp, __int128>)
3178	return __u._M_i128;
3179	else if constexpr (is_same_v<_Tp, unsigned __int128>)
3180	return __u._M_u128;
3181	#endif
3182	#if _GLIBCXX_FORMAT_F128 == 2
3183	else if constexpr (is_same_v<_Tp, __float128_t>)
3184	return __u._M_f128;
3185	#endif
3186	else if constexpr (derived_from<_Tp, _HandleBase>)
3187	return static_cast<_Tp&>(__u._M_handle);
3188	// Otherwise, ill-formed.
3189	}
3190
3191	template<typename _Tp>
3192	[[__gnu__::__always_inline__]]
3193	auto&
3194	_M_get() noexcept
3195	{ return _S_get<_Tp>(*this); }
3196
3197	template<typename _Tp>
3198	[[__gnu__::__always_inline__]]
3199	const auto&
3200	_M_get() const noexcept
3201	{ return _S_get<_Tp>(*this); }
3202
3203	template<typename _Tp>
3204	[[__gnu__::__always_inline__]]
3205	void
3206	_M_set(_Tp __v) noexcept
3207	{
3208	if constexpr (derived_from<_Tp, _HandleBase>)
3209	std::construct_at(&_M_handle, __v);
3210	else
3211	_S_get<_Tp>(*this) = __v;
3212	}
3213	};
3214
3215	// [format.arg.store], class template format-arg-store
3216	template<typename _Context, typename... _Args>
3217	class _Arg_store;
3218
3219	} // namespace __format
3220	/// @endcond
3221
3222	template<typename _Context>
3223	class basic_format_arg
3224	{
3225	using _CharT = typename _Context::char_type;
3226
3227	template<typename _Tp>
3228	static constexpr bool __formattable
3229	= __format::__formattable_with<_Tp, _Context>;
3230
3231	public:
3232	class handle : public __format::_Arg_value<_Context>::_HandleBase
3233	{
3234	using _Base = typename __format::_Arg_value<_Context>::_HandleBase;
3235
3236	// Format as const if possible, to reduce instantiations.
3237	template<typename _Tp>
3238	using __maybe_const_t
3239	= __conditional_t<__formattable<const _Tp>, const _Tp, _Tp>;
3240
3241	template<typename _Tq>
3242	static void
3243	_S_format(basic_format_parse_context<_CharT>& __parse_ctx,
3244	_Context& __format_ctx, const void* __ptr)
3245	{
3246	using _Td = remove_const_t<_Tq>;
3247	typename _Context::template formatter_type<_Td> __f;
3248	__parse_ctx.advance_to(__f.parse(__parse_ctx));
3249	_Tq& __val = *const_cast<_Tq>(static_cast<const* _Td*>(__ptr));
3250	__format_ctx.advance_to(__f.format(__val, __format_ctx));
3251	}
3252
3253	template<typename _Tp>
3254	explicit
3255	handle(_Tp& __val) noexcept
3256	{
3257	this->_M_ptr = __builtin_addressof(__val);
3258	auto __func = _S_format<__maybe_const_t<_Tp>>;
3259	this->_M_func = reinterpret_cast<void(*)()>(__func);
3260	}
3261
3262	friend class basic_format_arg<_Context>;
3263
3264	public:
3265	handle(const handle&) = default;
3266	handle& operator=(const handle&) = default;
3267
3268	[[__gnu__::__always_inline__]]
3269	void
3270	format(basic_format_parse_context<_CharT>& __pc, _Context& __fc) const
3271	{
3272	using _Func = void(*)(basic_format_parse_context<_CharT>&,
3273	_Context&, const void*);
3274	auto __f = reinterpret_cast<_Func>(this->_M_func);
3275	__f(__pc, __fc, this->_M_ptr);
3276	}
3277	};
3278
3279	[[__gnu__::__always_inline__]]
3280	basic_format_arg() noexcept : _M_type(__format::_Arg_none) { }
3281
3282	[[nodiscard,__gnu__::__always_inline__]]
3283	explicit operator bool() const noexcept
3284	{ return _M_type != __format::_Arg_none; }
3285
3286	private:
3287	template<typename _Ctx>
3288	friend class basic_format_args;
3289
3290	template<typename _Ctx, typename... _Args>
3291	friend class __format::_Arg_store;
3292
3293	static_assert(is_trivially_copyable_v<__format::_Arg_value<_Context>>);
3294
3295	__format::_Arg_value<_Context> _M_val;
3296	__format::_Arg_t _M_type;
3297
3298	// Transform incoming argument type to the type stored in _Arg_value.
3299	// e.g. short -> int, std::string -> std::string_view,
3300	// char[3] -> const char.*
3301	template<typename _Tp>
3302	static consteval auto
3303	_S_to_arg_type()
3304	{
3305	using _Td = remove_const_t<_Tp>;
3306	if constexpr (is_same_v<_Td, bool>)
3307	return type_identity<bool>();
3308	else if constexpr (is_same_v<_Td, _CharT>)
3309	return type_identity<_CharT>();
3310	else if constexpr (is_same_v<_Td, char> && is_same_v<_CharT, wchar_t>)
3311	return type_identity<_CharT>();
3312	#ifdef __SIZEOF_INT128__ // Check before signed/unsigned integer
3313	else if constexpr (is_same_v<_Td, __int128>)
3314	return type_identity<__int128>();
3315	else if constexpr (is_same_v<_Td, unsigned __int128>)
3316	return type_identity<unsigned __int128>();
3317	#endif
3318	else if constexpr (__is_signed_integer<_Td>::value)
3319	{
3320	if constexpr (sizeof(_Td) <= sizeof(int))
3321	return type_identity<int>();
3322	else if constexpr (sizeof(_Td) <= sizeof(long long))
3323	return type_identity<long long>();
3324	}
3325	else if constexpr (__is_unsigned_integer<_Td>::value)
3326	{
3327	if constexpr (sizeof(_Td) <= sizeof(unsigned))
3328	return type_identity<unsigned>();
3329	else if constexpr (sizeof(_Td) <= sizeof(unsigned long long))
3330	return type_identity<unsigned long long>();
3331	}
3332	else if constexpr (is_same_v<_Td, float>)
3333	return type_identity<float>();
3334	else if constexpr (is_same_v<_Td, double>)
3335	return type_identity<double>();
3336	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3337	else if constexpr (is_same_v<_Td, long double>)
3338	return type_identity<long double>();
3339	#else
3340	else if constexpr (is_same_v<_Td, __ibm128>)
3341	return type_identity<__ibm128>();
3342	else if constexpr (is_same_v<_Td, __ieee128>)
3343	return type_identity<__ieee128>();
3344	#endif
3345
3346	#if defined(__FLT16_DIG__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
3347	else if constexpr (is_same_v<_Td, _Float16>)
3348	return type_identity<float>();
3349	#endif
3350
3351	#if defined(__BFLT16_DIG__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
3352	else if constexpr (is_same_v<_Td, decltype(`0.0bf16`)>)
3353	return type_identity<float>();
3354	#endif
3355
3356	#ifdef __FLT32_DIG__
3357	else if constexpr (is_same_v<_Td, _Float32>)
3358	# ifdef _GLIBCXX_FLOAT_IS_IEEE_BINARY32
3359	return type_identity<float>();
3360	# else
3361	return type_identity<_Float32>();
3362	# endif
3363	#endif
3364	#ifdef __FLT64_DIG__
3365	else if constexpr (is_same_v<_Td, _Float64>)
3366	# ifdef _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
3367	return type_identity<double>();
3368	# else
3369	return type_identity<_Float64>();
3370	# endif
3371	#endif
3372	#if _GLIBCXX_FORMAT_F128
3373	# if __FLT128_DIG__
3374	else if constexpr (is_same_v<_Td, _Float128>)
3375	return type_identity<__format::__float128_t>();
3376	# endif
3377	# if __SIZEOF_FLOAT128__
3378	else if constexpr (is_same_v<_Td, __float128>)
3379	return type_identity<__format::__float128_t>();
3380	# endif
3381	#endif
3382	else if constexpr (__is_specialization_of<_Td, basic_string_view>
3383	\|\| __is_specialization_of<_Td, basic_string>)
3384	{
3385	if constexpr (is_same_v<typename _Td::value_type, _CharT>)
3386	return type_identity<basic_string_view<_CharT>>();
3387	else
3388	return type_identity<handle>();
3389	}
3390	else if constexpr (is_same_v<decay_t<_Td>, const _CharT*>)
3391	return type_identity<const _CharT*>();
3392	else if constexpr (is_same_v<decay_t<_Td>, _CharT*>)
3393	return type_identity<const _CharT*>();
3394	else if constexpr (is_void_v<remove_pointer_t<_Td>>)
3395	return type_identity<const void*>();
3396	else if constexpr (is_same_v<_Td, nullptr_t>)
3397	return type_identity<const void*>();
3398	else
3399	return type_identity<handle>();
3400	}
3401
3402	// Transform a formattable type to the appropriate storage type.
3403	template<typename _Tp>
3404	using _Normalize = typename decltype(_S_to_arg_type<_Tp>())::type;
3405
3406	// Get the _Arg_t value corresponding to a normalized type.
3407	template<typename _Tp>
3408	static consteval __format::_Arg_t
3409	_S_to_enum()
3410	{
3411	using namespace __format;
3412	if constexpr (is_same_v<_Tp, bool>)
3413	return _Arg_bool;
3414	else if constexpr (is_same_v<_Tp, _CharT>)
3415	return _Arg_c;
3416	else if constexpr (is_same_v<_Tp, int>)
3417	return _Arg_i;
3418	else if constexpr (is_same_v<_Tp, unsigned>)
3419	return _Arg_u;
3420	else if constexpr (is_same_v<_Tp, long long>)
3421	return _Arg_ll;
3422	else if constexpr (is_same_v<_Tp, unsigned long long>)
3423	return _Arg_ull;
3424	else if constexpr (is_same_v<_Tp, float>)
3425	return _Arg_flt;
3426	else if constexpr (is_same_v<_Tp, double>)
3427	return _Arg_dbl;
3428	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3429	else if constexpr (is_same_v<_Tp, long double>)
3430	return _Arg_ldbl;
3431	#else
3432	// Don't use _Arg_ldbl for this target, it's ambiguous.
3433	else if constexpr (is_same_v<_Tp, __ibm128>)
3434	return _Arg_ibm128;
3435	else if constexpr (is_same_v<_Tp, __ieee128>)
3436	return _Arg_f128;
3437	#endif
3438	else if constexpr (is_same_v<_Tp, const _CharT*>)
3439	return _Arg_str;
3440	else if constexpr (is_same_v<_Tp, basic_string_view<_CharT>>)
3441	return _Arg_sv;
3442	else if constexpr (is_same_v<_Tp, const void*>)
3443	return _Arg_ptr;
3444	#ifdef __SIZEOF_INT128__
3445	else if constexpr (is_same_v<_Tp, __int128>)
3446	return _Arg_i128;
3447	else if constexpr (is_same_v<_Tp, unsigned __int128>)
3448	return _Arg_u128;
3449	#endif
3450
3451	// N.B. some of these types will never actually be used here,
3452	// because they get normalized to a standard floating-point type.
3453	#if defined __FLT32_DIG__ && ! _GLIBCXX_FLOAT_IS_IEEE_BINARY32
3454	else if constexpr (is_same_v<_Tp, _Float32>)
3455	return _Arg_f32;
3456	#endif
3457	#if defined __FLT64_DIG__ && ! _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
3458	else if constexpr (is_same_v<_Tp, _Float64>)
3459	return _Arg_f64;
3460	#endif
3461	#if _GLIBCXX_FORMAT_F128 == 2
3462	else if constexpr (is_same_v<_Tp, __format::__float128_t>)
3463	return _Arg_f128;
3464	#endif
3465	else if constexpr (is_same_v<_Tp, handle>)
3466	return _Arg_handle;
3467	}
3468
3469	template<typename _Tp>
3470	void
3471	_M_set(_Tp __v) noexcept
3472	{
3473	_M_type = _S_to_enum<_Tp>();
3474	_M_val._M_set(__v);
3475	}
3476
3477	template<typename _Tp>
3478	requires __format::__formattable_with<_Tp, _Context>
3479	explicit
3480	basic_format_arg(_Tp& __v) noexcept
3481	{
3482	using _Td = _Normalize<_Tp>;
3483	if constexpr (is_same_v<_Td, basic_string_view<_CharT>>)
3484	_M_set(_Td{__v.data(), __v.size()});
3485	else if constexpr (is_same_v<remove_const_t<_Tp>, char>
3486	&& is_same_v<_CharT, wchar_t>)
3487	_M_set(static_cast<_Td>(static_cast<unsigned char>(__v)));
3488	else
3489	_M_set(static_cast<_Td>(__v));
3490	}
3491
3492	template<typename _Ctx, typename... _Argz>
3493	friend auto
3494	make_format_args(_Argz&...) noexcept;
3495
3496	template<typename _Visitor, typename _Ctx>
3497	friend decltype(auto)
3498	visit_format_arg(_Visitor&& __vis, basic_format_arg<_Ctx>);
3499
3500	template<typename _Visitor>
3501	decltype(auto)
3502	_M_visit(_Visitor&& __vis, __format::_Arg_t __type)
3503	{
3504	using namespace __format;
3505	switch (__type)
3506	{
3507	case _Arg_none:
3508	return std::forward<_Visitor>(__vis)(_M_val._M_none);
3509	case _Arg_bool:
3510	return std::forward<_Visitor>(__vis)(_M_val._M_bool);
3511	case _Arg_c:
3512	return std::forward<_Visitor>(__vis)(_M_val._M_c);
3513	case _Arg_i:
3514	return std::forward<_Visitor>(__vis)(_M_val._M_i);
3515	case _Arg_u:
3516	return std::forward<_Visitor>(__vis)(_M_val._M_u);
3517	case _Arg_ll:
3518	return std::forward<_Visitor>(__vis)(_M_val._M_ll);
3519	case _Arg_ull:
3520	return std::forward<_Visitor>(__vis)(_M_val._M_ull);
3521	#if __glibcxx_to_chars // FIXME: need to be able to format these types!
3522	case _Arg_flt:
3523	return std::forward<_Visitor>(__vis)(_M_val._M_flt);
3524	case _Arg_dbl:
3525	return std::forward<_Visitor>(__vis)(_M_val._M_dbl);
3526	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3527	case _Arg_ldbl:
3528	return std::forward<_Visitor>(__vis)(_M_val._M_ldbl);
3529	#else
3530	case _Arg_f128:
3531	return std::forward<_Visitor>(__vis)(_M_val._M_f128);
3532	case _Arg_ibm128:
3533	return std::forward<_Visitor>(__vis)(_M_val._M_ibm128);
3534	#endif
3535	#endif
3536	case _Arg_str:
3537	return std::forward<_Visitor>(__vis)(_M_val._M_str);
3538	case _Arg_sv:
3539	return std::forward<_Visitor>(__vis)(_M_val._M_sv);
3540	case _Arg_ptr:
3541	return std::forward<_Visitor>(__vis)(_M_val._M_ptr);
3542	case _Arg_handle:
3543	{
3544	auto& __h = static_cast<handle&>(_M_val._M_handle);
3545	return std::forward<_Visitor>(__vis)(__h);
3546	}
3547	#ifdef __SIZEOF_INT128__
3548	case _Arg_i128:
3549	return std::forward<_Visitor>(__vis)(_M_val._M_i128);
3550	case _Arg_u128:
3551	return std::forward<_Visitor>(__vis)(_M_val._M_u128);
3552	#endif
3553
3554	#if _GLIBCXX_FORMAT_F128 == 2
3555	case _Arg_f128:
3556	return std::forward<_Visitor>(__vis)(_M_val._M_f128);
3557	#endif
3558
3559	default:
3560	// _Arg_f16 etc.
3561	__builtin_unreachable();
3562	}
3563	}
3564	};
3565
3566	template<typename _Visitor, typename _Context>
3567	inline decltype(auto)
3568	visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg)
3569	{
3570	return __arg._M_visit(std::forward<_Visitor>(__vis), __arg._M_type);
3571	}
3572
3573	/// @cond undocumented
3574	namespace __format
3575	{
3576	struct _WidthPrecVisitor
3577	{
3578	template<typename _Tp>
3579	size_t
3580	operator()(_Tp& __arg) const
3581	{
3582	if constexpr (is_same_v<_Tp, monostate>)
3583	__format::__invalid_arg_id_in_format_string();
3584	// _GLIBCXX_RESOLVE_LIB_DEFECTS
3585	// 3720. Restrict the valid types of arg-id for width and precision
3586	// 3721. Allow an arg-id with a value of zero for width
3587	else if constexpr (sizeof(_Tp) <= sizeof(long long))
3588	{
3589	// _GLIBCXX_RESOLVE_LIB_DEFECTS
3590	// 3720. Restrict the valid types of arg-id for width and precision
3591	if constexpr (__is_unsigned_integer<_Tp>::value)
3592	return __arg;
3593	else if constexpr (__is_signed_integer<_Tp>::value)
3594	if (__arg >= `0`)
3595	return __arg;
3596	}
3597	__throw_format_error(what: "format error: argument used for width or "
3598	"precision must be a non-negative integer");
3599	}
3600	};
3601
3602	template<typename _Context>
3603	inline size_t
3604	__int_from_arg(const basic_format_arg<_Context>& __arg)
3605	{ return std::visit_format_arg(_WidthPrecVisitor (), __arg); }
3606
3607	// Pack _Arg_t enum values into a single 60-bit integer.
3608	template<int _Bits, size_t _Nm>
3609	constexpr auto
3610	__pack_arg_types(const array<_Arg_t, _Nm>& __types)
3611	{
3612	__UINT64_TYPE__ __packed_types = `0`;
3613	for (auto __i = __types.rbegin(); __i != __types.rend(); ++__i)
3614	__packed_types = (__packed_types << _Bits) \| *__i;
3615	return __packed_types;
3616	}
3617	} // namespace __format
3618	/// @endcond
3619
3620	template<typename _Context>
3621	class basic_format_args
3622	{
3623	static constexpr int _S_packed_type_bits = `5`; // _Arg_t values [0,20]
3624	static constexpr int _S_packed_type_mask = `0b11111`;
3625	static constexpr int _S_max_packed_args = `12`;
3626
3627	static_assert( __format::_Arg_max_ <= (`1` << _S_packed_type_bits) );
3628
3629	template<typename... _Args>
3630	using _Store = __format::_Arg_store<_Context, _Args...>;
3631
3632	template<typename _Ctx, typename... _Args>
3633	friend class __format::_Arg_store;
3634
3635	using uint64_t = __UINT64_TYPE__;
3636	using _Format_arg = basic_format_arg<_Context>;
3637	using _Format_arg_val = __format::_Arg_value<_Context>;
3638
3639	// If args are packed then the number of args is in _M_packed_size and
3640	// the packed types are in _M_unpacked_size, accessed via _M_type(i).
3641	// If args are not packed then the number of args is in _M_unpacked_size
3642	// and _M_packed_size is zero.
3643	uint64_t _M_packed_size : `4`;
3644	uint64_t _M_unpacked_size : `60`;
3645
3646	union {
3647	const _Format_arg_val* _M_values; // Active when _M_packed_size != 0
3648	const _Format_arg* _M_args; // Active when _M_packed_size == 0
3649	};
3650
3651	size_t
3652	_M_size() const noexcept
3653	{ return _M_packed_size ? _M_packed_size : _M_unpacked_size; }
3654
3655	typename __format::_Arg_t
3656	_M_type(size_t __i) const noexcept
3657	{
3658	uint64_t __t = _M_unpacked_size >> (__i * _S_packed_type_bits);
3659	return static_cast<__format::_Arg_t>(__t & _S_packed_type_mask);
3660	}
3661
3662	template<typename _Ctx, typename... _Args>
3663	friend auto
3664	make_format_args(_Args&...) noexcept;
3665
3666	// An array of _Arg_t enums corresponding to _Args...
3667	template<typename... _Args>
3668	static consteval array<__format::_Arg_t, sizeof...(_Args)>
3669	_S_types_to_pack()
3670	{ return {_Format_arg::template _S_to_enum<_Args>()...}; }
3671
3672	public:
3673	template<typename... _Args>
3674	basic_format_args(const _Store<_Args...>& __store) noexcept;
3675
3676	[[nodiscard,__gnu__::__always_inline__]]
3677	basic_format_arg<_Context>
3678	get(size_t __i) const noexcept
3679	{
3680	basic_format_arg<_Context> __arg;
3681	if (__i < _M_packed_size)
3682	{
3683	__arg._M_type = _M_type(__i);
3684	__arg._M_val = _M_values[__i];
3685	}
3686	else if (_M_packed_size == `0` && __i < _M_unpacked_size)
3687	__arg = _M_args[__i];
3688	return __arg;
3689	}
3690	};
3691
3692	// _GLIBCXX_RESOLVE_LIB_DEFECTS
3693	// 3810. CTAD for std::basic_format_args
3694	template<typename _Context, typename... _Args>
3695	basic_format_args(__format::_Arg_store<_Context, _Args...>)
3696	-> basic_format_args<_Context>;
3697
3698	template<typename _Context, typename... _Args>
3699	auto
3700	make_format_args(_Args&... __fmt_args) noexcept;
3701
3702	// An array of type-erased formatting arguments.
3703	template<typename _Context, typename... _Args>
3704	class __format::_Arg_store
3705	{
3706	friend std::basic_format_args<_Context>;
3707
3708	template<typename _Ctx, typename... _Argz>
3709	friend auto std::
3710	#if _GLIBCXX_INLINE_VERSION
3711	__8:: // Needed for PR c++/59256
3712	#endif
3713	make_format_args(_Argz&...) noexcept;
3714
3715	// For a sufficiently small number of arguments we only store values.
3716	// basic_format_args can get the types from the _Args pack.
3717	static constexpr bool _S_values_only
3718	= sizeof...(_Args) <= basic_format_args<_Context>::_S_max_packed_args;
3719
3720	using _Element_t
3721	= __conditional_t<_S_values_only,
3722	__format::_Arg_value<_Context>,
3723	basic_format_arg<_Context>>;
3724
3725	_Element_t _M_args[sizeof...(_Args)];
3726
3727	template<typename _Tp>
3728	static _Element_t
3729	_S_make_elt(_Tp& __v)
3730	{
3731	using _Tq = remove_const_t<_Tp>;
3732	using _CharT = typename _Context::char_type;
3733	static_assert(is_default_constructible_v<formatter<_Tq, _CharT>>,
3734	"std::formatter must be specialized for the type "
3735	"of each format arg");
3736	using __format::__formattable_with;
3737	if constexpr (is_const_v<_Tp>)
3738	if constexpr (!__formattable_with<_Tp, _Context>)
3739	if constexpr (__formattable_with<_Tq, _Context>)
3740	static_assert(__formattable_with<_Tp, _Context>,
3741	"format arg must be non-const because its "
3742	"std::formatter specialization has a "
3743	"non-const reference parameter");
3744	basic_format_arg<_Context> __arg(__v);
3745	if constexpr (_S_values_only)
3746	return __arg._M_val;
3747	else
3748	return __arg;
3749	}
3750
3751	template<typename... _Tp>
3752	requires (sizeof...(_Tp) == sizeof...(_Args))
3753	[[__gnu__::__always_inline__]]
3754	_Arg_store(_Tp&... __a) noexcept
3755	: _M_args{_S_make_elt(__a)...}
3756	{ }
3757	};
3758
3759	template<typename _Context>
3760	class __format::_Arg_store<_Context>
3761	{ };
3762
3763	template<typename _Context>
3764	template<typename... _Args>
3765	inline
3766	basic_format_args<_Context>::
3767	basic_format_args(const _Store<_Args...>& __store) noexcept
3768	{
3769	if constexpr (sizeof...(_Args) == `0`)
3770	{
3771	_M_packed_size = `0`;
3772	_M_unpacked_size = `0`;
3773	_M_args = nullptr;
3774	}
3775	else if constexpr (sizeof...(_Args) <= _S_max_packed_args)
3776	{
3777	// The number of packed arguments:
3778	_M_packed_size = sizeof...(_Args);
3779	// The packed type enums:
3780	_M_unpacked_size
3781	= __format::__pack_arg_types<_S_packed_type_bits>(_S_types_to_pack<_Args...>());
3782	// The _Arg_value objects.
3783	_M_values = __store._M_args;
3784	}
3785	else
3786	{
3787	// No packed arguments:
3788	_M_packed_size = `0`;
3789	// The number of unpacked arguments:
3790	_M_unpacked_size = sizeof...(_Args);
3791	// The basic_format_arg objects:
3792	_M_args = __store._M_args;
3793	}
3794	}
3795
3796	/// Capture formatting arguments for use by `std::vformat`.
3797	template<typename _Context = format_context, typename... _Args>
3798	[[nodiscard,__gnu__::__always_inline__]]
3799	inline auto
3800	make_format_args(_Args&... __fmt_args) noexcept
3801	{
3802	using _Fmt_arg = basic_format_arg<_Context>;
3803	using _Store = __format::_Arg_store<_Context, typename _Fmt_arg::template
3804	_Normalize<_Args>...>;
3805	return _Store(__fmt_args...);
3806	}
3807
3808	#ifdef _GLIBCXX_USE_WCHAR_T
3809	/// Capture formatting arguments for use by `std::vformat` (for wide output).
3810	template<typename... _Args>
3811	[[nodiscard,__gnu__::__always_inline__]]
3812	inline auto
3813	make_wformat_args(_Args&... __args) noexcept
3814	{ return std::make_format_args<wformat_context>(__args...); }
3815	#endif
3816
3817	/// @cond undocumented
3818	namespace __format
3819	{
3820	template<typename _Out, typename _CharT, typename _Context>
3821	_Out
3822	__do_vformat_to(_Out, basic_string_view<_CharT>,
3823	const basic_format_args<_Context>&,
3824	const locale* = nullptr);
3825	} // namespace __format
3826	/// @endcond
3827
3828	/* Context for std::format and similar functions.*
3829	*
3830	* A formatting context contains an output iterator and locale to use
3831	* for the formatting operations. Most programs will never need to use
3832	* this class template explicitly. For typical uses of `std::format` the
3833	* library will use the specializations `std::format_context` (for `char`)
3834	* and `std::wformat_context` (for `wchar_t`).
3835	*/
3836	template<typename _Out, typename _CharT>
3837	class basic_format_context
3838	{
3839	static_assert( output_iterator<_Out, const _CharT&> );
3840
3841	basic_format_args<basic_format_context> _M_args;
3842	_Out _M_out;
3843	__format::_Optional_locale _M_loc;
3844
3845	basic_format_context(basic_format_args<basic_format_context> __args,
3846	_Out __out)
3847	: _M_args(__args), _M_out(std::move(__out))
3848	{ }
3849
3850	basic_format_context(basic_format_args<basic_format_context> __args,
3851	_Out __out, const std::locale& __loc)
3852	: _M_args(__args), _M_out(std::move(__out)), _M_loc (__loc)
3853	{ }
3854
3855	// _GLIBCXX_RESOLVE_LIB_DEFECTS
3856	// 4061. Should std::basic_format_context be
3857	// default-constructible/copyable/movable?
3858	basic_format_context(const basic_format_context&) = delete;
3859	basic_format_context& operator=(const basic_format_context&) = delete;
3860
3861	template<typename _Out2, typename _CharT2, typename _Context2>
3862	friend _Out2
3863	__format::__do_vformat_to(_Out2, basic_string_view<_CharT2>,
3864	const basic_format_args<_Context2>&,
3865	const locale*);
3866
3867	public:
3868	~basic_format_context() = default;
3869
3870	using iterator = _Out;
3871	using char_type = _CharT;
3872	template<typename _Tp>
3873	using formatter_type = formatter<_Tp, _CharT>;
3874
3875	[[nodiscard]]
3876	basic_format_arg<basic_format_context>
3877	arg(size_t __id) const noexcept
3878	{ return _M_args.get(__id); }
3879
3880	[[nodiscard]]
3881	std::locale locale() { return _M_loc.value(); }
3882
3883	[[nodiscard]]
3884	iterator out() { return std::move(_M_out); }
3885
3886	void advance_to(iterator __it) { _M_out = std::move(__it); }
3887	};
3888
3889
3890	/// @cond undocumented
3891	namespace __format
3892	{
3893	// Abstract base class defining an interface for scanning format strings.
3894	// Scan the characters in a format string, dividing it up into strings of
3895	// ordinary characters, escape sequences, and replacement fields.
3896	// Call virtual functions for derived classes to parse format-specifiers
3897	// or write formatted output.
3898	template<typename _CharT>
3899	struct _Scanner
3900	{
3901	using iterator = typename basic_format_parse_context<_CharT>::iterator;
3902
3903	basic_format_parse_context<_CharT> _M_pc;
3904
3905	constexpr explicit
3906	_Scanner(basic_string_view<_CharT> __str, size_t __nargs = -`1`)
3907	: _M_pc(__str, __nargs)
3908	{ }
3909
3910	constexpr iterator begin() const noexcept { return _M_pc.begin(); }
3911	constexpr iterator end() const noexcept { return _M_pc.end(); }
3912
3913	constexpr void
3914	_M_scan()
3915	{
3916	basic_string_view<_CharT> __fmt = _M_fmt_str();
3917
3918	if (__fmt.size() == `2` && __fmt[`0`] == `'{'` && __fmt[`1`] == `'}'`)
3919	{
3920	_M_pc.advance_to(begin() + `1`);
3921	_M_format_arg(id: _M_pc.next_arg_id());
3922	return;
3923	}
3924
3925	size_t __lbr = __fmt.find(`'{'`);
3926	size_t __rbr = __fmt.find(`'}'`);
3927
3928	while (__fmt.size())
3929	{
3930	auto __cmp = __lbr <=> __rbr;
3931	if (__cmp == `0`)
3932	{
3933	_M_on_chars(end());
3934	_M_pc.advance_to(end());
3935	return;
3936	}
3937	else if (__cmp < `0`)
3938	{
3939	if (__lbr + `1` == __fmt.size()
3940	\|\| (__rbr == __fmt.npos && __fmt[__lbr + `1`] != `'{'`))
3941	__format::__unmatched_left_brace_in_format_string();
3942	const bool __is_escape = __fmt[__lbr + `1`] == `'{'`;
3943	iterator __last = begin() + __lbr + int(__is_escape);
3944	_M_on_chars(__last);
3945	_M_pc.advance_to(__last + `1`);
3946	__fmt = _M_fmt_str();
3947	if (__is_escape)
3948	{
3949	if (__rbr != __fmt.npos)
3950	__rbr -= __lbr + `2`;
3951	__lbr = __fmt.find(`'{'`);
3952	}
3953	else
3954	{
3955	_M_on_replacement_field();
3956	__fmt = _M_fmt_str();
3957	__lbr = __fmt.find(`'{'`);
3958	__rbr = __fmt.find(`'}'`);
3959	}
3960	}
3961	else
3962	{
3963	if (++__rbr == __fmt.size() \|\| __fmt[__rbr] != `'}'`)
3964	__format::__unmatched_right_brace_in_format_string();
3965	iterator __last = begin() + __rbr;
3966	_M_on_chars(__last);
3967	_M_pc.advance_to(__last + `1`);
3968	__fmt = _M_fmt_str();
3969	if (__lbr != __fmt.npos)
3970	__lbr -= __rbr + `1`;
3971	__rbr = __fmt.find(`'}'`);
3972	}
3973	}
3974	}
3975
3976	constexpr basic_string_view<_CharT>
3977	_M_fmt_str() const noexcept
3978	{ return {begin(), end()}; }
3979
3980	constexpr virtual void _M_on_chars(iterator) { }
3981
3982	constexpr void _M_on_replacement_field()
3983	{
3984	auto __next = begin();
3985
3986	size_t __id;
3987	if (*__next == `'}'`)
3988	__id = _M_pc.next_arg_id();
3989	else if (*__next == `':'`)
3990	{
3991	__id = _M_pc.next_arg_id();
3992	_M_pc.advance_to(++__next);
3993	}
3994	else
3995	{
3996	auto [__i, __ptr] = __format::__parse_arg_id(begin(), end());
3997	if (!__ptr \|\| !(__ptr == `'}'` \|\| __ptr == `':'`))
3998	__format::__invalid_arg_id_in_format_string();
3999	_M_pc.check_arg_id(__id = __i);
4000	if (*__ptr == `':'`)
4001	{
4002	_M_pc.advance_to(++__ptr);
4003	}
4004	else
4005	_M_pc.advance_to(__ptr);
4006	}
4007	_M_format_arg(__id);
4008	if (begin() == end() \|\| *begin() != `'}'`)
4009	__format::__unmatched_left_brace_in_format_string();
4010	_M_pc.advance_to(begin() + `1`); // Move past '}'
4011	}
4012
4013	constexpr virtual void _M_format_arg(size_t __id) = `0`;
4014	};
4015
4016	// Process a format string and format the arguments in the context.
4017	template<typename _Out, typename _CharT>
4018	class _Formatting_scanner : public _Scanner<_CharT>
4019	{
4020	public:
4021	_Formatting_scanner(basic_format_context<_Out, _CharT>& __fc,
4022	basic_string_view<_CharT> __str)
4023	: _Scanner<_CharT>(__str), _M_fc(__fc)
4024	{ }
4025
4026	private:
4027	basic_format_context<_Out, _CharT>& _M_fc;
4028
4029	using iterator = typename _Scanner<_CharT>::iterator;
4030
4031	constexpr void
4032	_M_on_chars(iterator __last) override
4033	{
4034	basic_string_view<_CharT> __str(this->begin(), __last);
4035	_M_fc.advance_to(__format::__write(_M_fc.out(), __str));
4036	}
4037
4038	constexpr void
4039	_M_format_arg(size_t __id) override
4040	{
4041	using _Context = basic_format_context<_Out, _CharT>;
4042	using handle = typename basic_format_arg<_Context>::handle;
4043
4044	std::visit_format_arg([this](auto& __arg) {
4045	using _Type = remove_reference_t<decltype(__arg)>;
4046	using _Formatter = typename _Context::template formatter_type<_Type>;
4047	if constexpr (is_same_v<_Type, monostate>)
4048	__format::__invalid_arg_id_in_format_string();
4049	else if constexpr (is_same_v<_Type, handle>)
4050	__arg.format(this->_M_pc, this->_M_fc);
4051	else if constexpr (is_default_constructible_v<_Formatter>)
4052	{
4053	_Formatter __f;
4054	this->_M_pc.advance_to(__f.parse(this->_M_pc));
4055	this->_M_fc.advance_to(__f.format(__arg, this->_M_fc));
4056	}
4057	else
4058	static_assert(__format::__formattable_with<_Type, _Context>);
4059	}, _M_fc.arg(__id));
4060	}
4061	};
4062
4063	// Validate a format string for Args.
4064	template<typename _CharT, typename... _Args>
4065	class _Checking_scanner : public _Scanner<_CharT>
4066	{
4067	static_assert(
4068	(is_default_constructible_v<formatter<_Args, _CharT>> && ...),
4069	"std::formatter must be specialized for each type being formatted");
4070
4071	public:
4072	constexpr
4073	_Checking_scanner(basic_string_view<_CharT> __str)
4074	: _Scanner<_CharT>(__str, sizeof...(_Args))
4075	{ }
4076
4077	private:
4078	constexpr void
4079	_M_format_arg(size_t __id) override
4080	{
4081	if constexpr (sizeof...(_Args) != `0`)
4082	{
4083	if (__id < sizeof...(_Args))
4084	{
4085	_M_parse_format_spec<_Args...>(__id);
4086	return;
4087	}
4088	}
4089	__builtin_unreachable();
4090	}
4091
4092	template<typename _Tp, typename... _OtherArgs>
4093	constexpr void
4094	_M_parse_format_spec(size_t __id)
4095	{
4096	if (__id == `0`)
4097	{
4098	formatter<_Tp, _CharT> __f;
4099	this->_M_pc.advance_to(__f.parse(this->_M_pc));
4100	}
4101	else if constexpr (sizeof...(_OtherArgs) != `0`)
4102	_M_parse_format_spec<_OtherArgs...>(__id - `1`);
4103	else
4104	__builtin_unreachable();
4105	}
4106	};
4107
4108	template<typename _Out, typename _CharT, typename _Context>
4109	inline _Out
4110	__do_vformat_to(_Out __out, basic_string_view<_CharT> __fmt,
4111	const basic_format_args<_Context>& __args,
4112	const locale* __loc)
4113	{
4114	_Iter_sink<_CharT, _Out> __sink(std::move(__out));
4115	_Sink_iter<_CharT> __sink_out;
4116
4117	if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
4118	__sink_out = __out; // Already a sink iterator, safe to use post-move.
4119	else
4120	__sink_out = __sink.out();
4121
4122	if constexpr (is_same_v<_CharT, char>)
4123	// Fast path for "{}" format strings and simple format arg types.
4124	if (__fmt.size() == `2` && __fmt[`0`] == `'{'` && __fmt[`1`] == `'}'`)
4125	{
4126	bool __done = false;
4127	std::visit_format_arg([&](auto& __arg) {
4128	using _Tp = remove_cvref_t<decltype(__arg)>;
4129	if constexpr (is_same_v<_Tp, bool>)
4130	{
4131	size_t __len = `4` + !__arg;
4132	const char* __chars[] = { "false", "true" };
4133	if (auto __res = __sink_out._M_reserve(__len))
4134	{
4135	__builtin_memcpy(__res.get(), __chars[__arg], __len);
4136	__res._M_bump(__len);
4137	__done = true;
4138	}
4139	}
4140	else if constexpr (is_same_v<_Tp, char>)
4141	{
4142	if (auto __res = __sink_out._M_reserve(`1`))
4143	{
4144	*__res.get() = __arg;
4145	__res._M_bump(`1`);
4146	__done = true;
4147	}
4148	}
4149	else if constexpr (is_integral_v<_Tp>)
4150	{
4151	make_unsigned_t<_Tp> __uval;
4152	const bool __neg = __arg < `0`;
4153	if (__neg)
4154	__uval = make_unsigned_t<_Tp>(~__arg) + `1u`;
4155	else
4156	__uval = __arg;
4157	const auto __n = __detail::__to_chars_len(__uval);
4158	if (auto __res = __sink_out._M_reserve(__n + __neg))
4159	{
4160	auto __ptr = __res.get();
4161	*__ptr = `'-'`;
4162	__detail::__to_chars_10_impl(__ptr + (int)__neg, __n,
4163	__uval);
4164	__res._M_bump(__n + __neg);
4165	__done = true;
4166	}
4167	}
4168	else if constexpr (is_convertible_v<_Tp, string_view>)
4169	{
4170	string_view __sv = __arg;
4171	if (auto __res = __sink_out._M_reserve(__sv.size()))
4172	{
4173	__builtin_memcpy(__res.get(), __sv.data(), __sv.size());
4174	__res._M_bump(__sv.size());
4175	__done = true;
4176	}
4177	}
4178	}, __args.get(`0`));
4179
4180	if (__done)
4181	{
4182	if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
4183	return __sink_out;
4184	else
4185	return std::move(__sink)._M_finish().out;
4186	}
4187	}
4188
4189	auto __ctx = __loc == nullptr
4190	? _Context(__args, __sink_out)
4191	: _Context(__args, __sink_out, *__loc);
4192	_Formatting_scanner<_Sink_iter<_CharT>, _CharT> __scanner(__ctx, __fmt);
4193	__scanner._M_scan();
4194
4195	if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
4196	return __ctx.out();
4197	else
4198	return std::move(__sink)._M_finish().out;
4199	}
4200
4201	} // namespace __format
4202	/// @endcond
4203
4204	template<typename _CharT, typename... _Args>
4205	template<typename _Tp>
4206	requires convertible_to<const _Tp&, basic_string_view<_CharT>>
4207	consteval
4208	basic_format_string<_CharT, _Args...>::
4209	basic_format_string(const _Tp& __s)
4210	: _M_str(__s)
4211	{
4212	__format::_Checking_scanner<_CharT, remove_cvref_t<_Args>...>
4213	__scanner(_M_str);
4214	__scanner._M_scan();
4215	}
4216
4217	// [format.functions], formatting functions
4218
4219	template<typename _Out> requires output_iterator<_Out, const char&>
4220	[[__gnu__::__always_inline__]]
4221	inline _Out
4222	vformat_to(_Out __out, string_view __fmt, format_args __args)
4223	{ return __format::__do_vformat_to(std::move(__out), __fmt, __args); }
4224
4225	#ifdef _GLIBCXX_USE_WCHAR_T
4226	template<typename _Out> requires output_iterator<_Out, const wchar_t&>
4227	[[__gnu__::__always_inline__]]
4228	inline _Out
4229	vformat_to(_Out __out, wstring_view __fmt, wformat_args __args)
4230	{ return __format::__do_vformat_to(std::move(__out), __fmt, __args); }
4231	#endif
4232
4233	template<typename _Out> requires output_iterator<_Out, const char&>
4234	[[__gnu__::__always_inline__]]
4235	inline _Out
4236	vformat_to(_Out __out, const locale& __loc, string_view __fmt,
4237	format_args __args)
4238	{
4239	return __format::__do_vformat_to(std::move(__out), __fmt, __args, &__loc);
4240	}
4241
4242	#ifdef _GLIBCXX_USE_WCHAR_T
4243	template<typename _Out> requires output_iterator<_Out, const wchar_t&>
4244	[[__gnu__::__always_inline__]]
4245	inline _Out
4246	vformat_to(_Out __out, const locale& __loc, wstring_view __fmt,
4247	wformat_args __args)
4248	{
4249	return __format::__do_vformat_to(std::move(__out), __fmt, __args, &__loc);
4250	}
4251	#endif
4252
4253	[[nodiscard]]
4254	inline string
4255	vformat(string_view __fmt, format_args __args)
4256	{
4257	__format::_Str_sink<char> __buf;
4258	std::vformat_to(out: __buf.out(), __fmt, __args);
4259	return std::move(__buf).get();
4260	}
4261
4262	#ifdef _GLIBCXX_USE_WCHAR_T
4263	[[nodiscard]]
4264	inline wstring
4265	vformat(wstring_view __fmt, wformat_args __args)
4266	{
4267	__format::_Str_sink<wchar_t> __buf;
4268	std::vformat_to(out: __buf.out(), __fmt, __args);
4269	return std::move(__buf).get();
4270	}
4271	#endif
4272
4273	[[nodiscard]]
4274	inline string
4275	vformat(const locale& __loc, string_view __fmt, format_args __args)
4276	{
4277	__format::_Str_sink<char> __buf;
4278	std::vformat_to(out: __buf.out(), __loc, __fmt, __args);
4279	return std::move(__buf).get();
4280	}
4281
4282	#ifdef _GLIBCXX_USE_WCHAR_T
4283	[[nodiscard]]
4284	inline wstring
4285	vformat(const locale& __loc, wstring_view __fmt, wformat_args __args)
4286	{
4287	__format::_Str_sink<wchar_t> __buf;
4288	std::vformat_to(out: __buf.out(), __loc, __fmt, __args);
4289	return std::move(__buf).get();
4290	}
4291	#endif
4292
4293	template<typename... _Args>
4294	[[nodiscard]]
4295	inline string
4296	format(format_string<_Args...> __fmt, _Args&&... __args)
4297	{ return std::vformat(__fmt.get(), std::make_format_args(__args...)); }
4298
4299	#ifdef _GLIBCXX_USE_WCHAR_T
4300	template<typename... _Args>
4301	[[nodiscard]]
4302	inline wstring
4303	format(wformat_string<_Args...> __fmt, _Args&&... __args)
4304	{ return std::vformat(__fmt.get(), std::make_wformat_args(__args...)); }
4305	#endif
4306
4307	template<typename... _Args>
4308	[[nodiscard]]
4309	inline string
4310	format(const locale& __loc, format_string<_Args...> __fmt,
4311	_Args&&... __args)
4312	{
4313	return std::vformat(__loc, __fmt.get(),
4314	std::make_format_args(__args...));
4315	}
4316
4317	#ifdef _GLIBCXX_USE_WCHAR_T
4318	template<typename... _Args>
4319	[[nodiscard]]
4320	inline wstring
4321	format(const locale& __loc, wformat_string<_Args...> __fmt,
4322	_Args&&... __args)
4323	{
4324	return std::vformat(__loc, __fmt.get(),
4325	std::make_wformat_args(__args...));
4326	}
4327	#endif
4328
4329	template<typename _Out, typename... _Args>
4330	requires output_iterator<_Out, const char&>
4331	inline _Out
4332	format_to(_Out __out, format_string<_Args...> __fmt, _Args&&... __args)
4333	{
4334	return std::vformat_to(std::move(__out), __fmt.get(),
4335	std::make_format_args(__args...));
4336	}
4337
4338	#ifdef _GLIBCXX_USE_WCHAR_T
4339	template<typename _Out, typename... _Args>
4340	requires output_iterator<_Out, const wchar_t&>
4341	inline _Out
4342	format_to(_Out __out, wformat_string<_Args...> __fmt, _Args&&... __args)
4343	{
4344	return std::vformat_to(std::move(__out), __fmt.get(),
4345	std::make_wformat_args(__args...));
4346	}
4347	#endif
4348
4349	template<typename _Out, typename... _Args>
4350	requires output_iterator<_Out, const char&>
4351	inline _Out
4352	format_to(_Out __out, const locale& __loc, format_string<_Args...> __fmt,
4353	_Args&&... __args)
4354	{
4355	return std::vformat_to(std::move(__out), __loc, __fmt.get(),
4356	std::make_format_args(__args...));
4357	}
4358
4359	#ifdef _GLIBCXX_USE_WCHAR_T
4360	template<typename _Out, typename... _Args>
4361	requires output_iterator<_Out, const wchar_t&>
4362	inline _Out
4363	format_to(_Out __out, const locale& __loc, wformat_string<_Args...> __fmt,
4364	_Args&&... __args)
4365	{
4366	return std::vformat_to(std::move(__out), __loc, __fmt.get(),
4367	std::make_wformat_args(__args...));
4368	}
4369	#endif
4370
4371	template<typename _Out, typename... _Args>
4372	requires output_iterator<_Out, const char&>
4373	inline format_to_n_result<_Out>
4374	format_to_n(_Out __out, iter_difference_t<_Out> __n,
4375	format_string<_Args...> __fmt, _Args&&... __args)
4376	{
4377	__format::_Iter_sink<char, _Out> __sink(std::move(__out), __n);
4378	std::vformat_to(__sink.out(), __fmt.get(),
4379	std::make_format_args(__args...));
4380	return std::move(__sink)._M_finish();
4381	}
4382
4383	#ifdef _GLIBCXX_USE_WCHAR_T
4384	template<typename _Out, typename... _Args>
4385	requires output_iterator<_Out, const wchar_t&>
4386	inline format_to_n_result<_Out>
4387	format_to_n(_Out __out, iter_difference_t<_Out> __n,
4388	wformat_string<_Args...> __fmt, _Args&&... __args)
4389	{
4390	__format::_Iter_sink<wchar_t, _Out> __sink(std::move(__out), __n);
4391	std::vformat_to(__sink.out(), __fmt.get(),
4392	std::make_wformat_args(__args...));
4393	return std::move(__sink)._M_finish();
4394	}
4395	#endif
4396
4397	template<typename _Out, typename... _Args>
4398	requires output_iterator<_Out, const char&>
4399	inline format_to_n_result<_Out>
4400	format_to_n(_Out __out, iter_difference_t<_Out> __n, const locale& __loc,
4401	format_string<_Args...> __fmt, _Args&&... __args)
4402	{
4403	__format::_Iter_sink<char, _Out> __sink(std::move(__out), __n);
4404	std::vformat_to(__sink.out(), __loc, __fmt.get(),
4405	std::make_format_args(__args...));
4406	return std::move(__sink)._M_finish();
4407	}
4408
4409	#ifdef _GLIBCXX_USE_WCHAR_T
4410	template<typename _Out, typename... _Args>
4411	requires output_iterator<_Out, const wchar_t&>
4412	inline format_to_n_result<_Out>
4413	format_to_n(_Out __out, iter_difference_t<_Out> __n, const locale& __loc,
4414	wformat_string<_Args...> __fmt, _Args&&... __args)
4415	{
4416	__format::_Iter_sink<wchar_t, _Out> __sink(std::move(__out), __n);
4417	std::vformat_to(__sink.out(), __loc, __fmt.get(),
4418	std::make_wformat_args(__args...));
4419	return std::move(__sink)._M_finish();
4420	}
4421	#endif
4422
4423	/// @cond undocumented
4424	namespace __format
4425	{
4426	#if 1
4427	template<typename _CharT>
4428	class _Counting_sink final : public _Iter_sink<_CharT, _CharT*>
4429	{
4430	public:
4431	_Counting_sink() : _Iter_sink<_CharT, _CharT>(nullptr*, `0`) { }
4432
4433	[[__gnu__::__always_inline__]]
4434	size_t
4435	count() const
4436	{ return this->_M_count + this->_M_used().size(); }
4437	};
4438	#else
4439	template<typename _CharT>
4440	class _Counting_sink : public _Buf_sink<_CharT>
4441	{
4442	size_t _M_count = `0`;
4443
4444	void
4445	_M_overflow() override
4446	{
4447	if (!std::is_constant_evaluated())
4448	_M_count += this->_M_used().size();
4449	this->_M_rewind();
4450	}
4451
4452	public:
4453	_Counting_sink() = default;
4454
4455	[[__gnu__::__always_inline__]]
4456	size_t
4457	count() noexcept
4458	{
4459	_Counting_sink::_M_overflow();
4460	return _M_count;
4461	}
4462	};
4463	#endif
4464	} // namespace __format
4465	/// @endcond
4466
4467	template<typename... _Args>
4468	[[nodiscard]]
4469	inline size_t
4470	formatted_size(format_string<_Args...> __fmt, _Args&&... __args)
4471	{
4472	__format::_Counting_sink<char> __buf;
4473	std::vformat_to(__buf.out(), __fmt.get(),
4474	std::make_format_args(__args...));
4475	return __buf.count();
4476	}
4477
4478	#ifdef _GLIBCXX_USE_WCHAR_T
4479	template<typename... _Args>
4480	[[nodiscard]]
4481	inline size_t
4482	formatted_size(wformat_string<_Args...> __fmt, _Args&&... __args)
4483	{
4484	__format::_Counting_sink<wchar_t> __buf;
4485	std::vformat_to(__buf.out(), __fmt.get(),
4486	std::make_wformat_args(__args...));
4487	return __buf.count();
4488	}
4489	#endif
4490
4491	template<typename... _Args>
4492	[[nodiscard]]
4493	inline size_t
4494	formatted_size(const locale& __loc, format_string<_Args...> __fmt,
4495	_Args&&... __args)
4496	{
4497	__format::_Counting_sink<char> __buf;
4498	std::vformat_to(__buf.out(), __loc, __fmt.get(),
4499	std::make_format_args(__args...));
4500	return __buf.count();
4501	}
4502
4503	#ifdef _GLIBCXX_USE_WCHAR_T
4504	template<typename... _Args>
4505	[[nodiscard]]
4506	inline size_t
4507	formatted_size(const locale& __loc, wformat_string<_Args...> __fmt,
4508	_Args&&... __args)
4509	{
4510	__format::_Counting_sink<wchar_t> __buf;
4511	std::vformat_to(__buf.out(), __loc, __fmt.get(),
4512	std::make_wformat_args(__args...));
4513	return __buf.count();
4514	}
4515	#endif
4516
4517	#if __cpp_lib_format_ranges
4518	// [format.range], formatting of ranges
4519	// [format.range.fmtkind], variable template format_kind
4520	enum class range_format {
4521	disabled,
4522	map,
4523	set,
4524	sequence,
4525	string,
4526	debug_string
4527	};
4528
4529	/// @cond undocumented
4530	template<typename _Rg>
4531	constexpr auto format_kind = not defined(format_kind<_Rg>);
4532
4533	template<typename _Tp>
4534	consteval range_format
4535	__fmt_kind()
4536	{
4537	using _Ref = ranges::range_reference_t<_Tp>;
4538	if constexpr (is_same_v<remove_cvref_t<_Ref>, _Tp>)
4539	return range_format::disabled;
4540	else if constexpr (requires { typename _Tp::key_type; })
4541	{
4542	if constexpr (requires { typename _Tp::mapped_type; })
4543	{
4544	using _Up = remove_cvref_t<_Ref>;
4545	if constexpr (__is_pair<_Up>)
4546	return range_format::map;
4547	else if constexpr (__is_specialization_of<_Up, tuple>)
4548	if constexpr (tuple_size_v<_Up> == `2`)
4549	return range_format::map;
4550	}
4551	return range_format::set;
4552	}
4553	else
4554	return range_format::sequence;
4555	}
4556	/// @endcond
4557
4558	/// A constant determining how a range should be formatted.
4559	template<ranges::input_range _Rg> requires same_as<_Rg, remove_cvref_t<_Rg>>
4560	constexpr range_format format_kind<_Rg> = __fmt_kind<_Rg>();
4561
4562	// [format.range.formatter], class template range_formatter
4563	template<typename _Tp, typename _CharT = char>
4564	requires same_as<remove_cvref_t<_Tp>, _Tp> && formattable<_Tp, _CharT>
4565	class range_formatter; // TODO
4566
4567	/// @cond undocumented
4568	namespace __format
4569	{
4570	// [format.range.fmtdef], class template range-default-formatter
4571	template<range_format _Kind, ranges::input_range _Rg, typename _CharT>
4572	struct __range_default_formatter; // TODO
4573	} // namespace __format
4574	/// @endcond
4575
4576	// [format.range.fmtmap], [format.range.fmtset], [format.range.fmtstr],
4577	// specializations for maps, sets, and strings
4578	template<ranges::input_range _Rg, typename _CharT>
4579	requires (format_kind<_Rg> != range_format::disabled)
4580	&& formattable<ranges::range_reference_t<_Rg>, _CharT>
4581	struct formatter<_Rg, _CharT>
4582	: __format::__range_default_formatter<format_kind<_Rg>, _Rg, _CharT>
4583	{ };
4584	#endif // C++23 formatting ranges
4585
4586	_GLIBCXX_END_NAMESPACE_VERSION
4587	} // namespace std
4588	#endif // __cpp_lib_format
4589	#endif // _GLIBCXX_FORMAT
4590

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