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 = requires (_Tp __t, char* __p)
1398	{ __format::to_chars(__p, __p, __t, chars_format::scientific, `6`); };
1399
1400	template<__char _CharT>
1401	struct __formatter_fp
1402	{
1403	constexpr typename basic_format_parse_context<_CharT>::iterator
1404	parse(basic_format_parse_context<_CharT>& __pc)
1405	{
1406	_Spec<_CharT> __spec{};
1407	const auto __last = __pc.end();
1408	auto __first = __pc.begin();
1409
1410	auto __finalize = [this, &__spec] {
1411	_M_spec = __spec;
1412	};
1413
1414	auto __finished = [&] {
1415	if (__first == __last \|\| *__first == `'}'`)
1416	{
1417	__finalize();
1418	return true;
1419	}
1420	return false;
1421	};
1422
1423	if (__finished())
1424	return __first;
1425
1426	__first = __spec._M_parse_fill_and_align(__first, __last);
1427	if (__finished())
1428	return __first;
1429
1430	__first = __spec._M_parse_sign(__first, __last);
1431	if (__finished())
1432	return __first;
1433
1434	__first = __spec._M_parse_alternate_form(__first, __last);
1435	if (__finished())
1436	return __first;
1437
1438	__first = __spec._M_parse_zero_fill(__first, __last);
1439	if (__finished())
1440	return __first;
1441
1442	if (__first[`0`] != `'.'`)
1443	{
1444	__first = __spec._M_parse_width(__first, __last, __pc);
1445	if (__finished())
1446	return __first;
1447	}
1448
1449	__first = __spec._M_parse_precision(__first, __last, __pc);
1450	if (__finished())
1451	return __first;
1452
1453	__first = __spec._M_parse_locale(__first, __last);
1454	if (__finished())
1455	return __first;
1456
1457	switch (*__first)
1458	{
1459	case `'a'`:
1460	__spec._M_type = _Pres_a;
1461	++__first;
1462	break;
1463	case `'A'`:
1464	__spec._M_type = _Pres_A;
1465	++__first;
1466	break;
1467	case `'e'`:
1468	__spec._M_type = _Pres_e;
1469	++__first;
1470	break;
1471	case `'E'`:
1472	__spec._M_type = _Pres_E;
1473	++__first;
1474	break;
1475	case `'f'`:
1476	__spec._M_type = _Pres_f;
1477	++__first;
1478	break;
1479	case `'F'`:
1480	__spec._M_type = _Pres_F;
1481	++__first;
1482	break;
1483	case `'g'`:
1484	__spec._M_type = _Pres_g;
1485	++__first;
1486	break;
1487	case `'G'`:
1488	__spec._M_type = _Pres_G;
1489	++__first;
1490	break;
1491	}
1492
1493	if (__finished())
1494	return __first;
1495
1496	__format::__failed_to_parse_format_spec();
1497	}
1498
1499	template<typename _Fp, typename _Out>
1500	typename basic_format_context<_Out, _CharT>::iterator
1501	format(_Fp __v, basic_format_context<_Out, _CharT>& __fc) const
1502	{
1503	std::string __dynbuf;
1504	char __buf[`128`];
1505	to_chars_result __res{};
1506
1507	size_t __prec = `6`;
1508	bool __use_prec = _M_spec._M_prec_kind != _WP_none;
1509	if (__use_prec)
1510	__prec = _M_spec._M_get_precision(__fc);
1511
1512	char* __start = __buf + `1`; // reserve space for sign
1513	char* __end = __buf + sizeof(__buf);
1514
1515	chars_format __fmt{};
1516	bool __upper = false;
1517	bool __trailing_zeros = false;
1518	char __expc = `'e'`;
1519
1520	switch (_M_spec._M_type)
1521	{
1522	case _Pres_A:
1523	__upper = true;
1524	__expc = `'P'`;
1525	[[fallthrough]];
1526	case _Pres_a:
1527	if (_M_spec._M_type != _Pres_A)
1528	__expc = `'p'`;
1529	__fmt = chars_format::hex;
1530	break;
1531	case _Pres_E:
1532	__upper = true;
1533	__expc = `'E'`;
1534	[[fallthrough]];
1535	case _Pres_e:
1536	__use_prec = true;
1537	__fmt = chars_format::scientific;
1538	break;
1539	case _Pres_F:
1540	__upper = true;
1541	[[fallthrough]];
1542	case _Pres_f:
1543	__use_prec = true;
1544	__fmt = chars_format::fixed;
1545	break;
1546	case _Pres_G:
1547	__upper = true;
1548	__expc = `'E'`;
1549	[[fallthrough]];
1550	case _Pres_g:
1551	__trailing_zeros = true;
1552	__use_prec = true;
1553	__fmt = chars_format::general;
1554	break;
1555	case _Pres_none:
1556	if (__use_prec)
1557	__fmt = chars_format::general;
1558	break;
1559	default:
1560	__builtin_unreachable();
1561	}
1562
1563	// Write value into buffer using std::to_chars.
1564	auto __to_chars = [&](char* __b, char* __e) {
1565	if (__use_prec)
1566	return __format::to_chars(__b, __e, __v, __fmt, __prec);
1567	else if (__fmt != chars_format{})
1568	return __format::to_chars(__b, __e, __v, __fmt);
1569	else
1570	return __format::to_chars(__b, __e, __v);
1571	};
1572
1573	// First try using stack buffer.
1574	__res = __to_chars(__start, __end);
1575
1576	if (__builtin_expect(__res.ec == errc::value_too_large, `0`))
1577	{
1578	// If the buffer is too small it's probably because of a large
1579	// precision, or a very large value in fixed format.
1580	size_t __guess = `8` + __prec;
1581	if (__fmt == chars_format::fixed) // +ddd.prec
1582	{
1583	if constexpr (is_same_v<_Fp, float> \|\| is_same_v<_Fp, double>
1584	\|\| is_same_v<_Fp, long double>)
1585	{
1586	// The number of digits to the left of the decimal point
1587	// is floor(log10(max(abs(__v),1)))+1
1588	int __exp{};
1589	if constexpr (is_same_v<_Fp, float>)
1590	__builtin_frexpf(__v, &__exp);
1591	else if constexpr (is_same_v<_Fp, double>)
1592	__builtin_frexp(__v, &__exp);
1593	else if constexpr (is_same_v<_Fp, long double>)
1594	__builtin_frexpl(__v, &__exp);
1595	if (__exp > `0`)
1596	__guess += `1U` + __exp * `4004U` / `13301U`; // log10(2) approx.
1597	}
1598	else
1599	__guess += numeric_limits<_Fp>::max_exponent10;
1600	}
1601	if (__guess <= sizeof(__buf)) [[unlikely]]
1602	__guess = sizeof(__buf) * `2`;
1603	__dynbuf.reserve(res: __guess);
1604
1605	do
1606	{
1607	auto __overwrite = [&__to_chars, &__res] (char* __p, size_t __n)
1608	{
1609	__res = __to_chars(__p + `1`, __p + __n - `1`);
1610	return __res.ec == errc{} ? __res.ptr - __p : `0`;
1611	};
1612
1613	__dynbuf.__resize_and_overwrite(__dynbuf.capacity() * `2`,
1614	__overwrite);
1615	__start = __dynbuf.data() + `1`; // reserve space for sign
1616	__end = __dynbuf.data() + __dynbuf.size();
1617	}
1618	while (__builtin_expect(__res.ec == errc::value_too_large, `0`));
1619	}
1620
1621	// Use uppercase for 'A', 'E', and 'G' formats.
1622	if (__upper)
1623	{
1624	for (char* __p = __start; __p != __res.ptr; ++__p)
1625	__p = std::toupper(c: __p);
1626	}
1627
1628	bool __have_sign = true;
1629	// Add sign for non-negative values.
1630	if (!__builtin_signbit(__v))
1631	{
1632	if (_M_spec._M_sign == _Sign_plus)
1633	*--__start = `'+'`;
1634	else if (_M_spec._M_sign == _Sign_space)
1635	*--__start = `' '`;
1636	else
1637	__have_sign = false;
1638	}
1639
1640	string_view __narrow_str(__start, __res.ptr - __start);
1641
1642	// Use alternate form. Ensure decimal point is always present,
1643	// and add trailing zeros (up to precision) for g and G forms.
1644	if (_M_spec._M_alt && __builtin_isfinite(__v))
1645	{
1646	string_view __s = __narrow_str;
1647	size_t __sigfigs; // Number of significant figures.
1648	size_t __z = `0`; // Number of trailing zeros to add.
1649	size_t __p; // Position of the exponent character (if any).
1650	size_t __d = __s.find(c: `'.'`); // Position of decimal point.
1651	if (__d != __s.npos) // Found decimal point.
1652	{
1653	__p = __s.find(c: __expc, pos: __d + `1`);
1654	if (__p == __s.npos)
1655	__p = __s.size();
1656
1657	// If presentation type is g or G we might need to add zeros.
1658	if (__trailing_zeros)
1659	{
1660	// Find number of digits after first significant figure.
1661	if (__s [__have_sign] != `'0'`)
1662	// A string like "D.D" or "-D.DDD"
1663	__sigfigs = __p - __have_sign - `1`;
1664	else
1665	// A string like "0.D" or "-0.0DD".
1666	// Safe to assume there is a non-zero digit, because
1667	// otherwise there would be no decimal point.
1668	__sigfigs = __p - __s.find_first_not_of(c: `'0'`, pos: __d + `1`);
1669	}
1670	}
1671	else // No decimal point, we need to insert one.
1672	{
1673	__p = __s.find(c: __expc); // Find the exponent, if present.
1674	if (__p == __s.npos)
1675	__p = __s.size();
1676	__d = __p; // Position where '.' should be inserted.
1677	__sigfigs = __d - __have_sign;
1678	}
1679
1680	if (__trailing_zeros && __prec != `0`)
1681	{
1682	// For g and G presentation types std::to_chars produces
1683	// no more than prec significant figures. Insert this many
1684	// zeros so the result has exactly prec significant figures.
1685	__z = __prec - __sigfigs;
1686	}
1687
1688	if (size_t __extras = int(__d == __p) + __z) // How many to add.
1689	{
1690	if (__dynbuf.empty() && __extras <= size_t(__end - __res.ptr))
1691	{
1692	// The stack buffer is large enough for the result.
1693	// Move exponent to make space for extra chars.
1694	__builtin_memmove(__start + __p + __extras,
1695	__start + __p,
1696	__s.size() - __p);
1697	if (__d == __p)
1698	__start[__p++] = `'.'`;
1699	__builtin_memset(__start + __p, `'0'`, __z);
1700	__narrow_str = {__s.data(), __s.size() + __extras};
1701	}
1702	else // Need to switch to the dynamic buffer.
1703	{
1704	__dynbuf.reserve(res: __s.size() + __extras);
1705	if (__dynbuf.empty())
1706	{
1707	__dynbuf = __s.substr(pos: `0`, n: __p);
1708	if (__d == __p)
1709	__dynbuf += `'.'`;
1710	if (__z)
1711	__dynbuf.append(n: __z, c: `'0'`);
1712	__dynbuf.append(svt: __s.substr(pos: __p));
1713	}
1714	else
1715	{
1716	__dynbuf.insert(pos: __p, n: __extras, c: `'0'`);
1717	if (__d == __p)
1718	__dynbuf [__p] = `'.'`;
1719	}
1720	__narrow_str = __dynbuf;
1721	}
1722	}
1723	}
1724
1725	basic_string<_CharT> __wstr;
1726	basic_string_view<_CharT> __str;
1727	if constexpr (is_same_v<_CharT, char>)
1728	__str = __narrow_str;
1729	#ifdef _GLIBCXX_USE_WCHAR_T
1730	else
1731	{
1732	__wstr = std::__to_wstring_numeric(s: __narrow_str);
1733	__str = __wstr;
1734	}
1735	#endif
1736
1737	if (_M_spec._M_localized && __builtin_isfinite(__v))
1738	{
1739	__wstr = _M_localize(__str, __expc, loc: __fc.locale());
1740	if (!__wstr.empty())
1741	__str = __wstr;
1742	}
1743
1744	size_t __width = _M_spec._M_get_width(__fc);
1745
1746	if (__width <= __str.size())
1747	return __format::__write(__fc.out(), __str);
1748
1749	char32_t __fill_char = _M_spec._M_fill;
1750	_Align __align = _M_spec._M_align;
1751
1752	size_t __nfill = __width - __str.size();
1753	auto __out = __fc.out();
1754	if (__align == _Align_default)
1755	{
1756	__align = _Align_right;
1757	if (_M_spec._M_zero_fill && __builtin_isfinite(__v))
1758	{
1759	__fill_char = _CharT(`'0'`);
1760	// Write sign before zero filling.
1761	if (!__format::__is_xdigit(c: __narrow_str [`0`]))
1762	{
1763	*__out++ = __str[`0`];
1764	__str.remove_prefix(`1`);
1765	}
1766	}
1767	else
1768	__fill_char = _CharT(`' '`);
1769	}
1770	return __format::__write_padded(std::move(__out), __str,
1771	__align, __nfill, __fill_char);
1772	}
1773
1774	// Locale-specific format.
1775	basic_string<_CharT>
1776	_M_localize(basic_string_view<_CharT> __str, char __expc,
1777	const locale& __loc) const
1778	{
1779	basic_string<_CharT> __lstr;
1780
1781	if (__loc == locale::classic())
1782	return __lstr; // Nothing to do.
1783
1784	const auto& __np = use_facet<numpunct<_CharT>>(__loc);
1785	const _CharT __point = __np.decimal_point();
1786	const string __grp = __np.grouping();
1787
1788	_CharT __dot, __exp;
1789	if constexpr (is_same_v<_CharT, char>)
1790	{
1791	__dot = `'.'`;
1792	__exp = __expc;
1793	}
1794	else
1795	{
1796	__dot = L`'.'`;
1797	switch (__expc)
1798	{
1799	case `'e'`:
1800	__exp = L`'e'`;
1801	break;
1802	case `'E'`:
1803	__exp = L`'E'`;
1804	break;
1805	case `'p'`:
1806	__exp = L`'p'`;
1807	break;
1808	case `'P'`:
1809	__exp = L`'P'`;
1810	break;
1811	default:
1812	__builtin_unreachable();
1813	}
1814	}
1815
1816	if (__grp.empty() && __point == __dot)
1817	return __lstr; // Locale uses '.' and no grouping.
1818
1819	size_t __d = __str.find(__dot);
1820	size_t __e = min(__d, __str.find(__exp));
1821	if (__e == __str.npos)
1822	__e = __str.size();
1823	const size_t __r = __str.size() - __e;
1824	auto __overwrite = [&](_CharT* __p, size_t) {
1825	auto __end = std::__add_grouping(__p, __np.thousands_sep(),
1826	__grp.data(), __grp.size(),
1827	__str.data(), __str.data() + __e);
1828	if (__r)
1829	{
1830	if (__d != __str.npos)
1831	{
1832	*__end = __point;
1833	++__end;
1834	++__e;
1835	}
1836	if (__r > `1`)
1837	__end += __str.copy(__end, __str.npos, __e);
1838	}
1839	return (__end - __p);
1840	};
1841	__lstr.__resize_and_overwrite(__e * `2` + __r, __overwrite);
1842	return __lstr;
1843	}
1844
1845	_Spec<_CharT> _M_spec{};
1846	};
1847
1848	} // namespace __format
1849	/// @endcond
1850
1851	/// Format a character.
1852	template<__format::__char _CharT>
1853	struct formatter<_CharT, _CharT>
1854	{
1855	formatter() = default;
1856
1857	constexpr typename basic_format_parse_context<_CharT>::iterator
1858	parse(basic_format_parse_context<_CharT>& __pc)
1859	{
1860	return _M_f.template _M_parse<_CharT>(__pc);
1861	}
1862
1863	template<typename _Out>
1864	typename basic_format_context<_Out, _CharT>::iterator
1865	format(_CharT __u, basic_format_context<_Out, _CharT>& __fc) const
1866	{
1867	if (_M_f._M_spec._M_type == __format::_Pres_none
1868	\|\| _M_f._M_spec._M_type == __format::_Pres_c)
1869	return _M_f._M_format_character(__u, __fc);
1870	else if (_M_f._M_spec._M_type == __format::_Pres_esc)
1871	{
1872	// TODO
1873	return __fc.out();
1874	}
1875	else
1876	return _M_f.format(static_cast<make_unsigned_t<_CharT>>(__u), __fc);
1877	}
1878
1879	#if __cpp_lib_format_ranges
1880	constexpr void
1881	set_debug_format() noexcept
1882	{ _M_f._M_spec._M_type = __format::_Pres_esc; }
1883	#endif
1884
1885	private:
1886	__format::__formatter_int<_CharT> _M_f;
1887	};
1888
1889	#ifdef _GLIBCXX_USE_WCHAR_T
1890	/// Format a char value for wide character output.
1891	template<>
1892	struct formatter<char, wchar_t>
1893	{
1894	formatter() = default;
1895
1896	constexpr typename basic_format_parse_context<wchar_t>::iterator
1897	parse(basic_format_parse_context<wchar_t>& __pc)
1898	{
1899	return _M_f._M_parse<char>(__pc);
1900	}
1901
1902	template<typename _Out>
1903	typename basic_format_context<_Out, wchar_t>::iterator
1904	format(char __u, basic_format_context<_Out, wchar_t>& __fc) const
1905	{
1906	if (_M_f._M_spec._M_type == __format::_Pres_none
1907	\|\| _M_f._M_spec._M_type == __format::_Pres_c)
1908	return _M_f._M_format_character(__u, __fc);
1909	else if (_M_f._M_spec._M_type == __format::_Pres_esc)
1910	{
1911	// TODO
1912	return __fc.out();
1913	}
1914	else
1915	return _M_f.format(static_cast<unsigned char>(__u), __fc);
1916	}
1917
1918	#if __cpp_lib_format_ranges
1919	constexpr void
1920	set_debug_format() noexcept
1921	{ _M_f._M_spec._M_type = __format::_Pres_esc; }
1922	#endif
1923
1924	private:
1925	__format::__formatter_int<wchar_t> _M_f;
1926	};
1927	#endif // USE_WCHAR_T
1928
1929	/* Format a string.*
1930	* @{
1931	*/
1932	template<__format::__char _CharT>
1933	struct formatter<_CharT*, _CharT>
1934	{
1935	formatter() = default;
1936
1937	[[__gnu__::__always_inline__]]
1938	constexpr typename basic_format_parse_context<_CharT>::iterator
1939	parse(basic_format_parse_context<_CharT>& __pc)
1940	{ return _M_f.parse(__pc); }
1941
1942	template<typename _Out>
1943	[[__gnu__::__nonnull__]]
1944	typename basic_format_context<_Out, _CharT>::iterator
1945	format(_CharT* __u, basic_format_context<_Out, _CharT>& __fc) const
1946	{ return _M_f.format(__u, __fc); }
1947
1948	#if __cpp_lib_format_ranges
1949	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
1950	#endif
1951
1952	private:
1953	__format::__formatter_str<_CharT> _M_f;
1954	};
1955
1956	template<__format::__char _CharT>
1957	struct formatter<const _CharT*, _CharT>
1958	{
1959	formatter() = default;
1960
1961	[[__gnu__::__always_inline__]]
1962	constexpr typename basic_format_parse_context<_CharT>::iterator
1963	parse(basic_format_parse_context<_CharT>& __pc)
1964	{ return _M_f.parse(__pc); }
1965
1966	template<typename _Out>
1967	[[__gnu__::__nonnull__]]
1968	typename basic_format_context<_Out, _CharT>::iterator
1969	format(const _CharT* __u,
1970	basic_format_context<_Out, _CharT>& __fc) const
1971	{ return _M_f.format(__u, __fc); }
1972
1973	#if __cpp_lib_format_ranges
1974	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
1975	#endif
1976
1977	private:
1978	__format::__formatter_str<_CharT> _M_f;
1979	};
1980
1981	template<__format::__char _CharT, size_t _Nm>
1982	struct formatter<_CharT[_Nm], _CharT>
1983	{
1984	formatter() = default;
1985
1986	[[__gnu__::__always_inline__]]
1987	constexpr typename basic_format_parse_context<_CharT>::iterator
1988	parse(basic_format_parse_context<_CharT>& __pc)
1989	{ return _M_f.parse(__pc); }
1990
1991	template<typename _Out>
1992	typename basic_format_context<_Out, _CharT>::iterator
1993	format(const _CharT (&__u)[_Nm],
1994	basic_format_context<_Out, _CharT>& __fc) const
1995	{ return _M_f.format({__u, _Nm}, __fc); }
1996
1997	#if __cpp_lib_format_ranges
1998	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
1999	#endif
2000
2001	private:
2002	__format::__formatter_str<_CharT> _M_f;
2003	};
2004
2005	template<typename _Traits, typename _Alloc>
2006	struct formatter<basic_string<char, _Traits, _Alloc>, char>
2007	{
2008	formatter() = default;
2009
2010	[[__gnu__::__always_inline__]]
2011	constexpr typename basic_format_parse_context<char>::iterator
2012	parse(basic_format_parse_context<char>& __pc)
2013	{ return _M_f.parse(__pc); }
2014
2015	template<typename _Out>
2016	typename basic_format_context<_Out, char>::iterator
2017	format(const basic_string<char, _Traits, _Alloc>& __u,
2018	basic_format_context<_Out, char>& __fc) const
2019	{ return _M_f.format(__u, __fc); }
2020
2021	#if __cpp_lib_format_ranges
2022	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2023	#endif
2024
2025	private:
2026	__format::__formatter_str<char> _M_f;
2027	};
2028
2029	#ifdef _GLIBCXX_USE_WCHAR_T
2030	template<typename _Traits, typename _Alloc>
2031	struct formatter<basic_string<wchar_t, _Traits, _Alloc>, wchar_t>
2032	{
2033	formatter() = default;
2034
2035	[[__gnu__::__always_inline__]]
2036	constexpr typename basic_format_parse_context<wchar_t>::iterator
2037	parse(basic_format_parse_context<wchar_t>& __pc)
2038	{ return _M_f.parse(__pc); }
2039
2040	template<typename _Out>
2041	typename basic_format_context<_Out, wchar_t>::iterator
2042	format(const basic_string<wchar_t, _Traits, _Alloc>& __u,
2043	basic_format_context<_Out, wchar_t>& __fc) const
2044	{ return _M_f.format(__u, __fc); }
2045
2046	#if __cpp_lib_format_ranges
2047	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2048	#endif
2049
2050	private:
2051	__format::__formatter_str<wchar_t> _M_f;
2052	};
2053	#endif // USE_WCHAR_T
2054
2055	template<typename _Traits>
2056	struct formatter<basic_string_view<char, _Traits>, char>
2057	{
2058	formatter() = default;
2059
2060	[[__gnu__::__always_inline__]]
2061	constexpr typename basic_format_parse_context<char>::iterator
2062	parse(basic_format_parse_context<char>& __pc)
2063	{ return _M_f.parse(__pc); }
2064
2065	template<typename _Out>
2066	typename basic_format_context<_Out, char>::iterator
2067	format(basic_string_view<char, _Traits> __u,
2068	basic_format_context<_Out, char>& __fc) const
2069	{ return _M_f.format(__u, __fc); }
2070
2071	#if __cpp_lib_format_ranges
2072	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2073	#endif
2074
2075	private:
2076	__format::__formatter_str<char> _M_f;
2077	};
2078
2079	#ifdef _GLIBCXX_USE_WCHAR_T
2080	template<typename _Traits>
2081	struct formatter<basic_string_view<wchar_t, _Traits>, wchar_t>
2082	{
2083	formatter() = default;
2084
2085	[[__gnu__::__always_inline__]]
2086	constexpr typename basic_format_parse_context<wchar_t>::iterator
2087	parse(basic_format_parse_context<wchar_t>& __pc)
2088	{ return _M_f.parse(__pc); }
2089
2090	template<typename _Out>
2091	typename basic_format_context<_Out, wchar_t>::iterator
2092	format(basic_string_view<wchar_t, _Traits> __u,
2093	basic_format_context<_Out, wchar_t>& __fc) const
2094	{ return _M_f.format(__u, __fc); }
2095
2096	#if __cpp_lib_format_ranges
2097	constexpr void set_debug_format() noexcept { _M_f.set_debug_format(); }
2098	#endif
2099
2100	private:
2101	__format::__formatter_str<wchar_t> _M_f;
2102	};
2103	#endif // USE_WCHAR_T
2104	/// @}
2105
2106	/// Format an integer.
2107	template<integral _Tp, __format::__char _CharT>
2108	requires (!__is_one_of<_Tp, char, wchar_t, char16_t, char32_t>::value)
2109	struct formatter<_Tp, _CharT>
2110	{
2111	formatter() = default;
2112
2113	[[__gnu__::__always_inline__]]
2114	constexpr typename basic_format_parse_context<_CharT>::iterator
2115	parse(basic_format_parse_context<_CharT>& __pc)
2116	{
2117	return _M_f.template _M_parse<_Tp>(__pc);
2118	}
2119
2120	template<typename _Out>
2121	typename basic_format_context<_Out, _CharT>::iterator
2122	format(_Tp __u, basic_format_context<_Out, _CharT>& __fc) const
2123	{ return _M_f.format(__u, __fc); }
2124
2125	private:
2126	__format::__formatter_int<_CharT> _M_f;
2127	};
2128
2129	#if defined __SIZEOF_INT128__ && defined __STRICT_ANSI__
2130	template<typename _Tp, __format::__char _CharT>
2131	requires (__is_one_of<_Tp, __int128, unsigned __int128>::value)
2132	struct formatter<_Tp, _CharT>
2133	{
2134	formatter() = default;
2135
2136	[[__gnu__::__always_inline__]]
2137	constexpr typename basic_format_parse_context<_CharT>::iterator
2138	parse(basic_format_parse_context<_CharT>& __pc)
2139	{
2140	return _M_f.template _M_parse<_Tp>(__pc);
2141	}
2142
2143	template<typename _Out>
2144	typename basic_format_context<_Out, _CharT>::iterator
2145	format(_Tp __u, basic_format_context<_Out, _CharT>& __fc) const
2146	{ return _M_f.format(__u, __fc); }
2147
2148	private:
2149	__format::__formatter_int<_CharT> _M_f;
2150	};
2151	#endif
2152
2153	#if defined __glibcxx_to_chars
2154	/// Format a floating-point value.
2155	template<__format::__formattable_float _Tp, __format::__char _CharT>
2156	struct formatter<_Tp, _CharT>
2157	{
2158	formatter() = default;
2159
2160	[[__gnu__::__always_inline__]]
2161	constexpr typename basic_format_parse_context<_CharT>::iterator
2162	parse(basic_format_parse_context<_CharT>& __pc)
2163	{ return _M_f.parse(__pc); }
2164
2165	template<typename _Out>
2166	typename basic_format_context<_Out, _CharT>::iterator
2167	format(_Tp __u, basic_format_context<_Out, _CharT>& __fc) const
2168	{ return _M_f.format(__u, __fc); }
2169
2170	private:
2171	__format::__formatter_fp<_CharT> _M_f;
2172	};
2173
2174	#if __LDBL_MANT_DIG__ == __DBL_MANT_DIG__
2175	// Reuse __formatter_fp<C>::format<double, Out> for long double.
2176	template<__format::__char _CharT>
2177	struct formatter<long double, _CharT>
2178	{
2179	formatter() = default;
2180
2181	[[__gnu__::__always_inline__]]
2182	constexpr typename basic_format_parse_context<_CharT>::iterator
2183	parse(basic_format_parse_context<_CharT>& __pc)
2184	{ return _M_f.parse(__pc); }
2185
2186	template<typename _Out>
2187	typename basic_format_context<_Out, _CharT>::iterator
2188	format(long double __u, basic_format_context<_Out, _CharT>& __fc) const
2189	{ return _M_f.format((double)__u, __fc); }
2190
2191	private:
2192	__format::__formatter_fp<_CharT> _M_f;
2193	};
2194	#endif
2195
2196	#ifdef __STDCPP_FLOAT16_T__
2197	// Reuse __formatter_fp<C>::format<float, Out> for _Float16.
2198	template<__format::__char _CharT>
2199	struct formatter<_Float16, _CharT>
2200	{
2201	formatter() = default;
2202
2203	[[__gnu__::__always_inline__]]
2204	constexpr typename basic_format_parse_context<_CharT>::iterator
2205	parse(basic_format_parse_context<_CharT>& __pc)
2206	{ return _M_f.parse(__pc); }
2207
2208	template<typename _Out>
2209	typename basic_format_context<_Out, _CharT>::iterator
2210	format(_Float16 __u, basic_format_context<_Out, _CharT>& __fc) const
2211	{ return _M_f.format((float)__u, __fc); }
2212
2213	private:
2214	__format::__formatter_fp<_CharT> _M_f;
2215	};
2216	#endif
2217
2218	#if defined(__FLT32_DIG__)
2219	// Reuse __formatter_fp<C>::format<float, Out> for _Float32.
2220	template<__format::__char _CharT>
2221	struct formatter<_Float32, _CharT>
2222	{
2223	formatter() = default;
2224
2225	[[__gnu__::__always_inline__]]
2226	constexpr typename basic_format_parse_context<_CharT>::iterator
2227	parse(basic_format_parse_context<_CharT>& __pc)
2228	{ return _M_f.parse(__pc); }
2229
2230	template<typename _Out>
2231	typename basic_format_context<_Out, _CharT>::iterator
2232	format(_Float32 __u, basic_format_context<_Out, _CharT>& __fc) const
2233	{ return _M_f.format((float)__u, __fc); }
2234
2235	private:
2236	__format::__formatter_fp<_CharT> _M_f;
2237	};
2238	#endif
2239
2240	#if defined(__FLT64_DIG__)
2241	// Reuse __formatter_fp<C>::format<double, Out> for _Float64.
2242	template<__format::__char _CharT>
2243	struct formatter<_Float64, _CharT>
2244	{
2245	formatter() = default;
2246
2247	[[__gnu__::__always_inline__]]
2248	constexpr typename basic_format_parse_context<_CharT>::iterator
2249	parse(basic_format_parse_context<_CharT>& __pc)
2250	{ return _M_f.parse(__pc); }
2251
2252	template<typename _Out>
2253	typename basic_format_context<_Out, _CharT>::iterator
2254	format(_Float64 __u, basic_format_context<_Out, _CharT>& __fc) const
2255	{ return _M_f.format((double)__u, __fc); }
2256
2257	private:
2258	__format::__formatter_fp<_CharT> _M_f;
2259	};
2260	#endif
2261
2262	#if defined(__FLT128_DIG__) && _GLIBCXX_FORMAT_F128 == 1
2263	// Reuse __formatter_fp<C>::format<__float128_t, Out> for _Float128.
2264	template<__format::__char _CharT>
2265	struct formatter<_Float128, _CharT>
2266	{
2267	formatter() = default;
2268
2269	[[__gnu__::__always_inline__]]
2270	constexpr typename basic_format_parse_context<_CharT>::iterator
2271	parse(basic_format_parse_context<_CharT>& __pc)
2272	{ return _M_f.parse(__pc); }
2273
2274	template<typename _Out>
2275	typename basic_format_context<_Out, _CharT>::iterator
2276	format(_Float128 __u, basic_format_context<_Out, _CharT>& __fc) const
2277	{ return _M_f.format((__format::__float128_t)__u, __fc); }
2278
2279	private:
2280	__format::__formatter_fp<_CharT> _M_f;
2281	};
2282	#endif
2283
2284	#ifdef __STDCPP_BFLOAT16_T__
2285	// Reuse __formatter_fp<C>::format<float, Out> for bfloat16_t.
2286	template<__format::__char _CharT>
2287	struct formatter<__gnu_cxx::__bfloat16_t, _CharT>
2288	{
2289	formatter() = default;
2290
2291	[[__gnu__::__always_inline__]]
2292	constexpr typename basic_format_parse_context<_CharT>::iterator
2293	parse(basic_format_parse_context<_CharT>& __pc)
2294	{ return _M_f.parse(__pc); }
2295
2296	template<typename _Out>
2297	typename basic_format_context<_Out, _CharT>::iterator
2298	format(__gnu_cxx::__bfloat16_t __u,
2299	basic_format_context<_Out, _CharT>& __fc) const
2300	{ return _M_f.format((float)__u, __fc); }
2301
2302	private:
2303	__format::__formatter_fp<_CharT> _M_f;
2304	};
2305	#endif
2306	#endif // __cpp_lib_to_chars
2307
2308	/* Format a pointer.*
2309	* @{
2310	*/
2311	template<__format::__char _CharT>
2312	struct formatter<const void*, _CharT>
2313	{
2314	formatter() = default;
2315
2316	constexpr typename basic_format_parse_context<_CharT>::iterator
2317	parse(basic_format_parse_context<_CharT>& __pc)
2318	{
2319	__format::_Spec<_CharT> __spec{};
2320	const auto __last = __pc.end();
2321	auto __first = __pc.begin();
2322
2323	auto __finalize = [this, &__spec] {
2324	_M_spec = __spec;
2325	};
2326
2327	auto __finished = [&] {
2328	if (__first == __last \|\| *__first == `'}'`)
2329	{
2330	__finalize();
2331	return true;
2332	}
2333	return false;
2334	};
2335
2336	if (__finished())
2337	return __first;
2338
2339	__first = __spec._M_parse_fill_and_align(__first, __last);
2340	if (__finished())
2341	return __first;
2342
2343	// _GLIBCXX_RESOLVE_LIB_DEFECTS
2344	// P2510R3 Formatting pointers
2345	#if __cplusplus > 202302L \|\| ! defined __STRICT_ANSI__
2346	#define _GLIBCXX_P2518R3 1
2347	#else
2348	#define _GLIBCXX_P2518R3 0
2349	#endif
2350
2351	#if _GLIBCXX_P2518R3
2352	__first = __spec._M_parse_zero_fill(__first, __last);
2353	if (__finished())
2354	return __first;
2355	#endif
2356
2357	__first = __spec._M_parse_width(__first, __last, __pc);
2358
2359	if (__first != __last)
2360	{
2361	if (*__first == `'p'`)
2362	++__first;
2363	#if _GLIBCXX_P2518R3
2364	else if (*__first == `'P'`)
2365	{
2366	// _GLIBCXX_RESOLVE_LIB_DEFECTS
2367	// P2510R3 Formatting pointers
2368	__spec._M_type = __format::_Pres_P;
2369	++__first;
2370	}
2371	#endif
2372	}
2373
2374	if (__finished())
2375	return __first;
2376
2377	__format::__failed_to_parse_format_spec();
2378	}
2379
2380	template<typename _Out>
2381	typename basic_format_context<_Out, _CharT>::iterator
2382	format(const void* __v, basic_format_context<_Out, _CharT>& __fc) const
2383	{
2384	auto __u = reinterpret_cast<__UINTPTR_TYPE__>(__v);
2385	char __buf[`2` + sizeof(__v) * `2`];
2386	auto [__ptr, __ec] = std::to_chars(first: __buf + `2`, last: std::end(arr&: __buf),
2387	value: __u, base: `16`);
2388	int __n = __ptr - __buf;
2389	__buf[`0`] = `'0'`;
2390	__buf[`1`] = `'x'`;
2391	#if _GLIBCXX_P2518R3
2392	if (_M_spec._M_type == __format::_Pres_P)
2393	{
2394	__buf[`1`] = `'X'`;
2395	for (auto __p = __buf + `2`; __p != __ptr; ++__p)
2396	#if __has_builtin(__builtin_toupper)
2397	__p = __builtin_toupper(__p);
2398	#else
2399	__p = std::toupper(__p);
2400	#endif
2401	}
2402	#endif
2403
2404	basic_string_view<_CharT> __str;
2405	if constexpr (is_same_v<_CharT, char>)
2406	__str = string_view (__buf, __n);
2407	#ifdef _GLIBCXX_USE_WCHAR_T
2408	else
2409	{
2410	auto __p = (_CharT)__builtin_alloca(__n sizeof(_CharT));
2411	std::__to_wstring_numeric(__buf, __n, __p);
2412	__str = wstring_view(__p, __n);
2413	}
2414	#endif
2415
2416	#if _GLIBCXX_P2518R3
2417	if (_M_spec._M_zero_fill)
2418	{
2419	size_t __width = _M_spec._M_get_width(__fc);
2420	if (__width <= __str.size())
2421	return __format::__write(__fc.out(), __str);
2422
2423	auto __out = __fc.out();
2424	// Write "0x" or "0X" prefix before zero-filling.
2425	__out = __format::__write(std::move(__out), __str.substr(`0`, `2`));
2426	__str.remove_prefix(`2`);
2427	size_t __nfill = __width - __n;
2428	return __format::__write_padded(std::move(__out), __str,
2429	__format::_Align_right,
2430	__nfill, _CharT(`'0'`));
2431	}
2432	#endif
2433
2434	return __format::__write_padded_as_spec(__str, __n, __fc, _M_spec,
2435	__format::_Align_right);
2436	}
2437
2438	private:
2439	__format::_Spec<_CharT> _M_spec{};
2440	};
2441
2442	template<__format::__char _CharT>
2443	struct formatter<void*, _CharT>
2444	{
2445	formatter() = default;
2446
2447	[[__gnu__::__always_inline__]]
2448	constexpr typename basic_format_parse_context<_CharT>::iterator
2449	parse(basic_format_parse_context<_CharT>& __pc)
2450	{ return _M_f.parse(__pc); }
2451
2452	template<typename _Out>
2453	typename basic_format_context<_Out, _CharT>::iterator
2454	format(void* __v, basic_format_context<_Out, _CharT>& __fc) const
2455	{ return _M_f.format(__v, __fc); }
2456
2457	private:
2458	formatter<const void*, _CharT> _M_f;
2459	};
2460
2461	template<__format::__char _CharT>
2462	struct formatter<nullptr_t, _CharT>
2463	{
2464	formatter() = default;
2465
2466	[[__gnu__::__always_inline__]]
2467	constexpr typename basic_format_parse_context<_CharT>::iterator
2468	parse(basic_format_parse_context<_CharT>& __pc)
2469	{ return _M_f.parse(__pc); }
2470
2471	template<typename _Out>
2472	typename basic_format_context<_Out, _CharT>::iterator
2473	format(nullptr_t, basic_format_context<_Out, _CharT>& __fc) const
2474	{ return _M_f.format(nullptr, __fc); }
2475
2476	private:
2477	formatter<const void*, _CharT> _M_f;
2478	};
2479	/// @}
2480
2481	#if defined _GLIBCXX_USE_WCHAR_T && __cpp_lib_format_ranges
2482	// _GLIBCXX_RESOLVE_LIB_DEFECTS
2483	// 3944. Formatters converting sequences of char to sequences of wchar_t
2484
2485	namespace __format { struct __disabled; }
2486
2487	// std::formatter<__disabled, C> uses the primary template, which is disabled.
2488	template<>
2489	struct formatter<char, wchar_t*>
2490	: private formatter<__format::__disabled, wchar_t> { };
2491	template<>
2492	struct formatter<const char, wchar_t*>
2493	: private formatter<__format::__disabled, wchar_t> { };
2494	template<size_t _Nm>
2495	struct formatter<char[_Nm], wchar_t>
2496	: private formatter<__format::__disabled, wchar_t> { };
2497	template<class _Traits, class _Allocator>
2498	struct formatter<basic_string<char, _Traits, _Allocator>, wchar_t>
2499	: private formatter<__format::__disabled, wchar_t> { };
2500	template<class _Traits>
2501	struct formatter<basic_string_view<char, _Traits>, wchar_t>
2502	: private formatter<__format::__disabled, wchar_t> { };
2503	#endif
2504
2505	/// @cond undocumented
2506	namespace __format
2507	{
2508	template<typename _Tp, typename _Context,
2509	typename _Formatter
2510	= typename _Context::template formatter_type<remove_const_t<_Tp>>,
2511	typename _ParseContext
2512	= basic_format_parse_context<typename _Context::char_type>>
2513	concept __parsable_with
2514	= semiregular<_Formatter>
2515	&& requires (_Formatter __f, _ParseContext __pc)
2516	{
2517	{ __f.parse(__pc) } -> same_as<typename _ParseContext::iterator>;
2518	};
2519
2520	template<typename _Tp, typename _Context,
2521	typename _Formatter
2522	= typename _Context::template formatter_type<remove_const_t<_Tp>>,
2523	typename _ParseContext
2524	= basic_format_parse_context<typename _Context::char_type>>
2525	concept __formattable_with
2526	= semiregular<_Formatter>
2527	&& requires (const _Formatter __cf, _Tp&& __t, _Context __fc)
2528	{
2529	{ __cf.format(__t, __fc) } -> same_as<typename _Context::iterator>;
2530	};
2531
2532	// An unspecified output iterator type used in the `formattable` concept.
2533	template<typename _CharT>
2534	using _Iter_for = back_insert_iterator<basic_string<_CharT>>;
2535
2536	template<typename _Tp, typename _CharT,
2537	typename _Context = basic_format_context<_Iter_for<_CharT>, _CharT>>
2538	concept __formattable_impl
2539	= __parsable_with<_Tp, _Context> && __formattable_with<_Tp, _Context>;
2540
2541	} // namespace __format
2542	/// @endcond
2543
2544	#if __cplusplus > 202002L
2545	// [format.formattable], concept formattable
2546	template<typename _Tp, typename _CharT>
2547	concept formattable
2548	= __format::__formattable_impl<remove_reference_t<_Tp>, _CharT>;
2549	#endif
2550
2551	#if __cpp_lib_format_ranges
2552	/// @cond undocumented
2553	namespace __format
2554	{
2555	template<typename _Rg, typename _CharT>
2556	concept __const_formattable_range
2557	= ranges::input_range<const _Rg>
2558	&& formattable<ranges::range_reference_t<const _Rg>, _CharT>;
2559
2560	template<typename _Rg, typename _CharT>
2561	using __maybe_const_range
2562	= conditional_t<__const_formattable_range<_Rg, _CharT>, const _Rg, _Rg>;
2563	} // namespace __format
2564	/// @endcond
2565	#endif // format_ranges
2566
2567	/// An iterator after the last character written, and the number of
2568	/// characters that would have been written.
2569	template<typename _Out>
2570	struct format_to_n_result
2571	{
2572	_Out out;
2573	iter_difference_t<_Out> size;
2574	};
2575
2576	_GLIBCXX_BEGIN_NAMESPACE_CONTAINER
2577	template<typename, typename> class vector;
2578	_GLIBCXX_END_NAMESPACE_CONTAINER
2579
2580	/// @cond undocumented
2581	namespace __format
2582	{
2583	template<typename _CharT>
2584	class _Sink_iter
2585	{
2586	_Sink<_CharT>* _M_sink = nullptr;
2587
2588	public:
2589	using iterator_category = output_iterator_tag;
2590	using value_type = void;
2591	using difference_type = ptrdiff_t;
2592	using pointer = void;
2593	using reference = void;
2594
2595	_Sink_iter() = default;
2596	_Sink_iter(const _Sink_iter&) = default;
2597	_Sink_iter& operator=(const _Sink_iter&) = default;
2598
2599	[[__gnu__::__always_inline__]]
2600	explicit constexpr
2601	_Sink_iter(_Sink<_CharT>& __sink) : _M_sink(std::addressof(__sink)) { }
2602
2603	[[__gnu__::__always_inline__]]
2604	constexpr _Sink_iter&
2605	operator=(_CharT __c)
2606	{
2607	_M_sink->_M_write(__c);
2608	return *this;
2609	}
2610
2611	[[__gnu__::__always_inline__]]
2612	constexpr _Sink_iter&
2613	operator=(basic_string_view<_CharT> __s)
2614	{
2615	_M_sink->_M_write(__s);
2616	return *this;
2617	}
2618
2619	[[__gnu__::__always_inline__]]
2620	constexpr _Sink_iter&
2621	operator() { return* *this; }
2622
2623	[[__gnu__::__always_inline__]]
2624	constexpr _Sink_iter&
2625	operator++() { return *this; }
2626
2627	[[__gnu__::__always_inline__]]
2628	constexpr _Sink_iter
2629	operator++(int) { return *this; }
2630
2631	auto
2632	_M_reserve(size_t __n) const
2633	{ return _M_sink->_M_reserve(__n); }
2634	};
2635
2636	// Abstract base class for type-erased character sinks.
2637	// All formatting and output is done via this type's iterator,
2638	// to reduce the number of different template instantiations.
2639	template<typename _CharT>
2640	class _Sink
2641	{
2642	friend class _Sink_iter<_CharT>;
2643
2644	span<_CharT> _M_span;
2645	typename span<_CharT>::iterator _M_next;
2646
2647	// Called when the span is full, to make more space available.
2648	// Precondition: _M_next != _M_span.begin()
2649	// Postcondition: _M_next != _M_span.end()
2650	// TODO: remove the precondition? could make overflow handle it.
2651	virtual void _M_overflow() = `0`;
2652
2653	protected:
2654	// Precondition: __span.size() != 0
2655	[[__gnu__::__always_inline__]]
2656	explicit constexpr
2657	_Sink(span<_CharT> __span) noexcept
2658	: _M_span(__span), _M_next(__span.begin())
2659	{ }
2660
2661	// The portion of the span that has been written to.
2662	[[__gnu__::__always_inline__]]
2663	span<_CharT>
2664	_M_used() const noexcept
2665	{ return _M_span.first(_M_next - _M_span.begin()); }
2666
2667	// The portion of the span that has not been written to.
2668	[[__gnu__::__always_inline__]]
2669	constexpr span<_CharT>
2670	_M_unused() const noexcept
2671	{ return _M_span.subspan(_M_next - _M_span.begin()); }
2672
2673	// Use the start of the span as the next write position.
2674	[[__gnu__::__always_inline__]]
2675	constexpr void
2676	_M_rewind() noexcept
2677	{ _M_next = _M_span.begin(); }
2678
2679	// Replace the current output range.
2680	void
2681	_M_reset(span<_CharT> __s, size_t __pos = `0`) noexcept
2682	{
2683	_M_span = __s;
2684	_M_next = __s.begin() + __pos;
2685	}
2686
2687	// Called by the iterator for it++ = c*
2688	constexpr void
2689	_M_write(_CharT __c)
2690	{
2691	*_M_next++ = __c;
2692	if (_M_next - _M_span.begin() == std::ssize(_M_span)) [[unlikely]]
2693	_M_overflow();
2694	}
2695
2696	constexpr void
2697	_M_write(basic_string_view<_CharT> __s)
2698	{
2699	span __to = _M_unused();
2700	while (__to.size() <= __s.size())
2701	{
2702	__s.copy(__to.data(), __to.size());
2703	_M_next += __to.size();
2704	__s.remove_prefix(__to.size());
2705	_M_overflow();
2706	__to = _M_unused();
2707	}
2708	if (__s.size())
2709	{
2710	__s.copy(__to.data(), __s.size());
2711	_M_next += __s.size();
2712	}
2713	}
2714
2715	// A successful _Reservation can be used to directly write
2716	// up to N characters to the sink to avoid unwanted buffering.
2717	struct _Reservation
2718	{
2719	// True if the reservation was successful, false otherwise.
2720	explicit operator bool() const noexcept { return _M_sink; }
2721	// A pointer to write directly to the sink.
2722	_CharT* get() const noexcept { return _M_sink->_M_next.operator->(); }
2723	// Add n to the _M_next iterator for the sink.
2724	void _M_bump(size_t __n) { _M_sink->_M_bump(__n); }
2725	_Sink* _M_sink;
2726	};
2727
2728	// Attempt to reserve space to write n characters to the sink.
2729	// If anything is written to the reservation then there must be a call
2730	// to _M_bump(N2) before any call to another member function of this,*
2731	// where N2 is the number of characters written.
2732	virtual _Reservation
2733	_M_reserve(size_t __n)
2734	{
2735	if (__n <= _M_unused().size())
2736	return { this };
2737
2738	if (__n <= _M_span.size()) // Cannot meet the request.
2739	{
2740	_M_overflow(); // Make more space available.
2741	if (__n <= _M_unused().size())
2742	return { this };
2743	}
2744	return { nullptr };
2745	}
2746
2747	// Update the next output position after writing directly to the sink.
2748	// pre: no calls to _M_write or _M_overflow since _M_reserve.
2749	virtual void
2750	_M_bump(size_t __n)
2751	{ _M_next += __n; }
2752
2753	public:
2754	_Sink(const _Sink&) = delete;
2755	_Sink& operator=(const _Sink&) = delete;
2756
2757	[[__gnu__::__always_inline__]]
2758	constexpr _Sink_iter<_CharT>
2759	out() noexcept
2760	{ return _Sink_iter<_CharT>(*this); }
2761	};
2762
2763	// A sink with an internal buffer. This is used to implement concrete sinks.
2764	template<typename _CharT>
2765	class _Buf_sink : public _Sink<_CharT>
2766	{
2767	protected:
2768	_CharT _M_buf[`32` * sizeof(void) / sizeof*(_CharT)];
2769
2770	[[__gnu__::__always_inline__]]
2771	constexpr
2772	_Buf_sink() noexcept
2773	: _Sink<_CharT>(_M_buf)
2774	{ }
2775	};
2776
2777	using _GLIBCXX_STD_C::vector;
2778
2779	// A sink that fills a sequence (e.g. std::string, std::vector, std::deque).
2780	// Writes to a buffer then appends that to the sequence when it fills up.
2781	template<typename _Seq>
2782	class _Seq_sink final : public _Buf_sink<typename _Seq::value_type>
2783	{
2784	using _CharT = typename _Seq::value_type;
2785
2786	_Seq _M_seq;
2787
2788	// Transfer buffer contents to the sequence, so buffer can be refilled.
2789	void
2790	_M_overflow() override
2791	{
2792	auto __s = this->_M_used();
2793	if (__s.empty()) [[unlikely]]
2794	return; // Nothing in the buffer to transfer to _M_seq.
2795
2796	// If _M_reserve was called then _M_bump must have been called too.
2797	_GLIBCXX_DEBUG_ASSERT(__s.data() != _M_seq.data());
2798
2799	if constexpr (__is_specialization_of<_Seq, basic_string>)
2800	_M_seq.append(__s.data(), __s.size());
2801	else
2802	_M_seq.insert(_M_seq.end(), __s.begin(), __s.end());
2803
2804	// Make the whole of _M_buf available for the next write:
2805	this->_M_rewind();
2806	}
2807
2808	typename _Sink<_CharT>::_Reservation
2809	_M_reserve(size_t __n) override
2810	{
2811	// We might already have n characters available in this->_M_unused(),
2812	// but the whole point of this function is to be an optimization for
2813	// the std::format("{}", x) case. We want to avoid writing to _M_buf
2814	// and then copying that into a basic_string if possible, so this
2815	// function prefers to create space directly in _M_seq rather than
2816	// using _M_buf.
2817
2818	if constexpr (__is_specialization_of<_Seq, basic_string>
2819	\|\| __is_specialization_of<_Seq, vector>)
2820	{
2821	// Flush the buffer to _M_seq first (should not be needed).
2822	if (this->_M_used().size()) [[unlikely]]
2823	_Seq_sink::_M_overflow();
2824
2825	// Expand _M_seq to make __n new characters available:
2826	const auto __sz = _M_seq.size();
2827	if constexpr (is_same_v<string, _Seq> \|\| is_same_v<wstring, _Seq>)
2828	_M_seq.__resize_and_overwrite(__sz + __n,
2829	[](auto, auto __n2) {
2830	return __n2;
2831	});
2832	else
2833	_M_seq.resize(__sz + __n);
2834
2835	// Set _M_used() to be a span over the original part of _M_seq
2836	// and _M_unused() to be the extra capacity we just created:
2837	this->_M_reset(_M_seq, __sz);
2838	return { this };
2839	}
2840	else // Try to use the base class' buffer.
2841	return _Sink<_CharT>::_M_reserve(__n);
2842	}
2843
2844	void
2845	_M_bump(size_t __n) override
2846	{
2847	if constexpr (__is_specialization_of<_Seq, basic_string>
2848	\|\| __is_specialization_of<_Seq, vector>)
2849	{
2850	auto __s = this->_M_used();
2851	_GLIBCXX_DEBUG_ASSERT(__s.data() == _M_seq.data());
2852	// Truncate the sequence to the part that was actually written to:
2853	_M_seq.resize(__s.size() + __n);
2854	// Switch back to using buffer:
2855	this->_M_reset(this->_M_buf);
2856	}
2857	}
2858
2859	public:
2860	// TODO: for SSO string, use SSO buffer as initial span, then switch
2861	// to _M_buf if it overflows? Or even do that for all unused capacity?
2862
2863	[[__gnu__::__always_inline__]]
2864	_Seq_sink() noexcept(is_nothrow_default_constructible_v<_Seq>)
2865	{ }
2866
2867	_Seq_sink(_Seq&& __s) noexcept(is_nothrow_move_constructible_v<_Seq>)
2868	: _M_seq(std::move(__s))
2869	{ }
2870
2871	using _Sink<_CharT>::out;
2872
2873	_Seq
2874	get() &&
2875	{
2876	if (this->_M_used().size() != `0`)
2877	_Seq_sink::_M_overflow();
2878	return std::move(_M_seq);
2879	}
2880
2881	// A writable span that views everything written to the sink.
2882	// Will be either a view over _M_seq or the used part of _M_buf.
2883	span<_CharT>
2884	view()
2885	{
2886	auto __s = this->_M_used();
2887	if (_M_seq.size())
2888	{
2889	if (__s.size() != `0`)
2890	_Seq_sink::_M_overflow();
2891	return _M_seq;
2892	}
2893	return __s;
2894	}
2895	};
2896
2897	template<typename _CharT, typename _Alloc = allocator<_CharT>>
2898	using _Str_sink
2899	= _Seq_sink<basic_string<_CharT, char_traits<_CharT>, _Alloc>>;
2900
2901	// template<typename _CharT, typename _Alloc = allocator<_CharT>>
2902	// using _Vec_sink = _Seq_sink<vector<_CharT, _Alloc>>;
2903
2904	// A sink that writes to an output iterator.
2905	// Writes to a fixed-size buffer and then flushes to the output iterator
2906	// when the buffer fills up.
2907	template<typename _CharT, typename _OutIter>
2908	class _Iter_sink : public _Buf_sink<_CharT>
2909	{
2910	_OutIter _M_out;
2911	iter_difference_t<_OutIter> _M_max;
2912
2913	protected:
2914	size_t _M_count = `0`;
2915
2916	void
2917	_M_overflow() override
2918	{
2919	auto __s = this->_M_used();
2920	if (_M_max < `0`) // No maximum.
2921	_M_out = ranges::copy(__s, std::move(_M_out)).out;
2922	else if (_M_count < static_cast<size_t>(_M_max))
2923	{
2924	auto __max = _M_max - _M_count;
2925	span<_CharT> __first;
2926	if (__max < __s.size())
2927	__first = __s.first(static_cast<size_t>(__max));
2928	else
2929	__first = __s;
2930	_M_out = ranges::copy(__first, std::move(_M_out)).out;
2931	}
2932	this->_M_rewind();
2933	_M_count += __s.size();
2934	}
2935
2936	public:
2937	[[__gnu__::__always_inline__]]
2938	explicit
2939	_Iter_sink(_OutIter __out, iter_difference_t<_OutIter> __max = -`1`)
2940	: _M_out(std::move(__out)), _M_max(__max)
2941	{ }
2942
2943	using _Sink<_CharT>::out;
2944
2945	format_to_n_result<_OutIter>
2946	_M_finish() &&
2947	{
2948	if (this->_M_used().size() != `0`)
2949	_Iter_sink::_M_overflow();
2950	iter_difference_t<_OutIter> __count(_M_count);
2951	return { std::move(_M_out), __count };
2952	}
2953	};
2954
2955	// Partial specialization for contiguous iterators.
2956	// No buffer is used, characters are written straight to the iterator.
2957	// We do not know the size of the output range, so the span size just grows
2958	// as needed. The end of the span might be an invalid pointer outside the
2959	// valid range, but we never actually call _M_span.end(). This class does
2960	// not introduce any invalid pointer arithmetic or overflows that would not
2961	// have happened anyway.
2962	template<typename _CharT, contiguous_iterator _OutIter>
2963	requires same_as<iter_value_t<_OutIter>, _CharT>
2964	class _Iter_sink<_CharT, _OutIter> : public _Sink<_CharT>
2965	{
2966	_OutIter _M_first;
2967	iter_difference_t<_OutIter> _M_max = -`1`;
2968	protected:
2969	size_t _M_count = `0`;
2970	private:
2971	_CharT _M_buf[`64`]; // Write here after outputting _M_max characters.
2972
2973	protected:
2974	void
2975	_M_overflow() override
2976	{
2977	if (this->_M_unused().size() != `0`)
2978	return; // No need to switch to internal buffer yet.
2979
2980	auto __s = this->_M_used();
2981
2982	if (_M_max >= `0`)
2983	{
2984	_M_count += __s.size();
2985	// Span was already sized for the maximum character count,
2986	// if it overflows then any further output must go to the
2987	// internal buffer, to be discarded.
2988	this->_M_reset(this->_M_buf);
2989	}
2990	else
2991	{
2992	// No maximum character count. Just extend the span to allow
2993	// writing more characters to it.
2994	this->_M_reset({__s.data(), __s.size() + `1024`}, __s.size());
2995	}
2996	}
2997
2998	typename _Sink<_CharT>::_Reservation
2999	_M_reserve(size_t __n) final
3000	{
3001	auto __avail = this->_M_unused();
3002	if (__n > __avail.size())
3003	{
3004	if (_M_max >= `0`)
3005	return {}; // cannot grow
3006
3007	auto __s = this->_M_used();
3008	this->_M_reset({__s.data(), __s.size() + __n}, __s.size());
3009	}
3010	return { this };
3011	}
3012
3013	private:
3014	static span<_CharT>
3015	_S_make_span(_CharT* __ptr, iter_difference_t<_OutIter> __n,
3016	span<_CharT> __buf) noexcept
3017	{
3018	if (__n == `0`)
3019	return __buf; // Only write to the internal buffer.
3020
3021	if (__n > `0`)
3022	{
3023	if constexpr (!is_integral_v<iter_difference_t<_OutIter>>
3024	\|\| sizeof(__n) > sizeof(size_t))
3025	{
3026	// __int128 or __detail::__max_diff_type
3027	auto __m = iter_difference_t<_OutIter>((size_t)-`1`);
3028	if (__n > __m)
3029	__n = __m;
3030	}
3031	return {__ptr, (size_t)__n};
3032	}
3033
3034	#if __has_builtin(__builtin_dynamic_object_size)
3035	if (size_t __bytes = __builtin_dynamic_object_size(__ptr, `2`))
3036	return {__ptr, __bytes / sizeof(_CharT)};
3037	#endif
3038	// Avoid forming a pointer to a different memory page.
3039	const auto __off = reinterpret_cast<__UINTPTR_TYPE__>(__ptr) % `1024`;
3040	__n = (`1024` - __off) / sizeof(_CharT);
3041	if (__n > `0`) [[likely]]
3042	return {__ptr, static_cast<size_t>(__n)};
3043	else // Misaligned/packed buffer of wchar_t?
3044	return {__ptr, `1`};
3045	}
3046
3047	public:
3048	explicit
3049	_Iter_sink(_OutIter __out, iter_difference_t<_OutIter> __n = -`1`) noexcept
3050	: _Sink<_CharT>(_S_make_span(ptr: std::to_address(__out), __n, buf: _M_buf)),
3051	_M_first(__out), _M_max(__n)
3052	{ }
3053
3054	format_to_n_result<_OutIter>
3055	_M_finish() &&
3056	{
3057	auto __s = this->_M_used();
3058	if (__s.data() == _M_buf)
3059	{
3060	// Switched to internal buffer, so must have written _M_max.
3061	iter_difference_t<_OutIter> __count(_M_count + __s.size());
3062	return { _M_first + _M_max, __count };
3063	}
3064	else // Not using internal buffer yet
3065	{
3066	iter_difference_t<_OutIter> __count(__s.size());
3067	return { _M_first + __count, __count };
3068	}
3069	}
3070	};
3071
3072	enum _Arg_t : unsigned char {
3073	_Arg_none, _Arg_bool, _Arg_c, _Arg_i, _Arg_u, _Arg_ll, _Arg_ull,
3074	_Arg_flt, _Arg_dbl, _Arg_ldbl, _Arg_str, _Arg_sv, _Arg_ptr, _Arg_handle,
3075	_Arg_i128, _Arg_u128,
3076	_Arg_bf16, _Arg_f16, _Arg_f32, _Arg_f64, // These are unused.
3077	#ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3078	_Arg_next_value_,
3079	_Arg_f128 = _Arg_ldbl,
3080	_Arg_ibm128 = _Arg_next_value_,
3081	#else
3082	_Arg_f128,
3083	#endif
3084	_Arg_max_
3085	};
3086
3087	template<typename _Context>
3088	struct _Arg_value
3089	{
3090	using _CharT = typename _Context::char_type;
3091
3092	struct _HandleBase
3093	{
3094	const void* _M_ptr;
3095	void (*_M_func)();
3096	};
3097
3098	union
3099	{
3100	monostate _M_none;
3101	bool _M_bool;
3102	_CharT _M_c;
3103	int _M_i;
3104	unsigned _M_u;
3105	long long _M_ll;
3106	unsigned long long _M_ull;
3107	float _M_flt;
3108	double _M_dbl;
3109	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT // No long double if it's ambiguous.
3110	long double _M_ldbl;
3111	#endif
3112	const _CharT* _M_str;
3113	basic_string_view<_CharT> _M_sv;
3114	const void* _M_ptr;
3115	_HandleBase _M_handle;
3116	#ifdef __SIZEOF_INT128__
3117	__int128 _M_i128;
3118	unsigned __int128 _M_u128;
3119	#endif
3120	#ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3121	__ieee128 _M_f128;
3122	__ibm128 _M_ibm128;
3123	#elif _GLIBCXX_FORMAT_F128 == 2
3124	__float128_t _M_f128;
3125	#endif
3126	};
3127
3128	[[__gnu__::__always_inline__]]
3129	_Arg_value() : _M_none () { }
3130
3131	#if 0
3132	template<typename _Tp>
3133	_Arg_value(in_place_type_t<_Tp>, _Tp __val)
3134	{ _S_get<_Tp>() = __val; }
3135	#endif
3136
3137	template<typename _Tp, typename _Self>
3138	[[__gnu__::__always_inline__]]
3139	static auto&
3140	_S_get(_Self& __u) noexcept
3141	{
3142	if constexpr (is_same_v<_Tp, bool>)
3143	return __u._M_bool;
3144	else if constexpr (is_same_v<_Tp, _CharT>)
3145	return __u._M_c;
3146	else if constexpr (is_same_v<_Tp, int>)
3147	return __u._M_i;
3148	else if constexpr (is_same_v<_Tp, unsigned>)
3149	return __u._M_u;
3150	else if constexpr (is_same_v<_Tp, long long>)
3151	return __u._M_ll;
3152	else if constexpr (is_same_v<_Tp, unsigned long long>)
3153	return __u._M_ull;
3154	else if constexpr (is_same_v<_Tp, float>)
3155	return __u._M_flt;
3156	else if constexpr (is_same_v<_Tp, double>)
3157	return __u._M_dbl;
3158	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3159	else if constexpr (is_same_v<_Tp, long double>)
3160	return __u._M_ldbl;
3161	#else
3162	else if constexpr (is_same_v<_Tp, __ieee128>)
3163	return __u._M_f128;
3164	else if constexpr (is_same_v<_Tp, __ibm128>)
3165	return __u._M_ibm128;
3166	#endif
3167	else if constexpr (is_same_v<_Tp, const _CharT*>)
3168	return __u._M_str;
3169	else if constexpr (is_same_v<_Tp, basic_string_view<_CharT>>)
3170	return __u._M_sv;
3171	else if constexpr (is_same_v<_Tp, const void*>)
3172	return __u._M_ptr;
3173	#ifdef __SIZEOF_INT128__
3174	else if constexpr (is_same_v<_Tp, __int128>)
3175	return __u._M_i128;
3176	else if constexpr (is_same_v<_Tp, unsigned __int128>)
3177	return __u._M_u128;
3178	#endif
3179	#if _GLIBCXX_FORMAT_F128 == 2
3180	else if constexpr (is_same_v<_Tp, __float128_t>)
3181	return __u._M_f128;
3182	#endif
3183	else if constexpr (derived_from<_Tp, _HandleBase>)
3184	return static_cast<_Tp&>(__u._M_handle);
3185	// Otherwise, ill-formed.
3186	}
3187
3188	template<typename _Tp>
3189	[[__gnu__::__always_inline__]]
3190	auto&
3191	_M_get() noexcept
3192	{ return _S_get<_Tp>(*this); }
3193
3194	template<typename _Tp>
3195	[[__gnu__::__always_inline__]]
3196	const auto&
3197	_M_get() const noexcept
3198	{ return _S_get<_Tp>(*this); }
3199
3200	template<typename _Tp>
3201	[[__gnu__::__always_inline__]]
3202	void
3203	_M_set(_Tp __v) noexcept
3204	{
3205	if constexpr (derived_from<_Tp, _HandleBase>)
3206	std::construct_at(&_M_handle, __v);
3207	else
3208	_S_get<_Tp>(*this) = __v;
3209	}
3210	};
3211
3212	// [format.arg.store], class template format-arg-store
3213	template<typename _Context, typename... _Args>
3214	class _Arg_store;
3215
3216	} // namespace __format
3217	/// @endcond
3218
3219	template<typename _Context>
3220	class basic_format_arg
3221	{
3222	using _CharT = typename _Context::char_type;
3223
3224	template<typename _Tp>
3225	static constexpr bool __formattable
3226	= __format::__formattable_with<_Tp, _Context>;
3227
3228	public:
3229	class handle : public __format::_Arg_value<_Context>::_HandleBase
3230	{
3231	using _Base = typename __format::_Arg_value<_Context>::_HandleBase;
3232
3233	// Format as const if possible, to reduce instantiations.
3234	template<typename _Tp>
3235	using __maybe_const_t
3236	= __conditional_t<__formattable<const _Tp>, const _Tp, _Tp>;
3237
3238	template<typename _Tq>
3239	static void
3240	_S_format(basic_format_parse_context<_CharT>& __parse_ctx,
3241	_Context& __format_ctx, const void* __ptr)
3242	{
3243	using _Td = remove_const_t<_Tq>;
3244	typename _Context::template formatter_type<_Td> __f;
3245	__parse_ctx.advance_to(__f.parse(__parse_ctx));
3246	_Tq& __val = *const_cast<_Tq>(static_cast<const* _Td*>(__ptr));
3247	__format_ctx.advance_to(__f.format(__val, __format_ctx));
3248	}
3249
3250	template<typename _Tp>
3251	explicit
3252	handle(_Tp& __val) noexcept
3253	{
3254	this->_M_ptr = __builtin_addressof(__val);
3255	auto __func = _S_format<__maybe_const_t<_Tp>>;
3256	this->_M_func = reinterpret_cast<void(*)()>(__func);
3257	}
3258
3259	friend class basic_format_arg<_Context>;
3260
3261	public:
3262	handle(const handle&) = default;
3263	handle& operator=(const handle&) = default;
3264
3265	[[__gnu__::__always_inline__]]
3266	void
3267	format(basic_format_parse_context<_CharT>& __pc, _Context& __fc) const
3268	{
3269	using _Func = void(*)(basic_format_parse_context<_CharT>&,
3270	_Context&, const void*);
3271	auto __f = reinterpret_cast<_Func>(this->_M_func);
3272	__f(__pc, __fc, this->_M_ptr);
3273	}
3274	};
3275
3276	[[__gnu__::__always_inline__]]
3277	basic_format_arg() noexcept : _M_type(__format::_Arg_none) { }
3278
3279	[[nodiscard,__gnu__::__always_inline__]]
3280	explicit operator bool() const noexcept
3281	{ return _M_type != __format::_Arg_none; }
3282
3283	private:
3284	template<typename _Ctx>
3285	friend class basic_format_args;
3286
3287	template<typename _Ctx, typename... _Args>
3288	friend class __format::_Arg_store;
3289
3290	static_assert(is_trivially_copyable_v<__format::_Arg_value<_Context>>);
3291
3292	__format::_Arg_value<_Context> _M_val;
3293	__format::_Arg_t _M_type;
3294
3295	// Transform incoming argument type to the type stored in _Arg_value.
3296	// e.g. short -> int, std::string -> std::string_view,
3297	// char[3] -> const char.*
3298	template<typename _Tp>
3299	static consteval auto
3300	_S_to_arg_type()
3301	{
3302	using _Td = remove_const_t<_Tp>;
3303	if constexpr (is_same_v<_Td, bool>)
3304	return type_identity<bool>();
3305	else if constexpr (is_same_v<_Td, _CharT>)
3306	return type_identity<_CharT>();
3307	else if constexpr (is_same_v<_Td, char> && is_same_v<_CharT, wchar_t>)
3308	return type_identity<_CharT>();
3309	#ifdef __SIZEOF_INT128__ // Check before signed/unsigned integer
3310	else if constexpr (is_same_v<_Td, __int128>)
3311	return type_identity<__int128>();
3312	else if constexpr (is_same_v<_Td, unsigned __int128>)
3313	return type_identity<unsigned __int128>();
3314	#endif
3315	else if constexpr (__is_signed_integer<_Td>::value)
3316	{
3317	if constexpr (sizeof(_Td) <= sizeof(int))
3318	return type_identity<int>();
3319	else if constexpr (sizeof(_Td) <= sizeof(long long))
3320	return type_identity<long long>();
3321	}
3322	else if constexpr (__is_unsigned_integer<_Td>::value)
3323	{
3324	if constexpr (sizeof(_Td) <= sizeof(unsigned))
3325	return type_identity<unsigned>();
3326	else if constexpr (sizeof(_Td) <= sizeof(unsigned long long))
3327	return type_identity<unsigned long long>();
3328	}
3329	else if constexpr (is_same_v<_Td, float>)
3330	return type_identity<float>();
3331	else if constexpr (is_same_v<_Td, double>)
3332	return type_identity<double>();
3333	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3334	else if constexpr (is_same_v<_Td, long double>)
3335	return type_identity<long double>();
3336	#else
3337	else if constexpr (is_same_v<_Td, __ibm128>)
3338	return type_identity<__ibm128>();
3339	else if constexpr (is_same_v<_Td, __ieee128>)
3340	return type_identity<__ieee128>();
3341	#endif
3342
3343	#if defined(__FLT16_DIG__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
3344	else if constexpr (is_same_v<_Td, _Float16>)
3345	return type_identity<float>();
3346	#endif
3347
3348	#if defined(__BFLT16_DIG__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
3349	else if constexpr (is_same_v<_Td, decltype(`0.0bf16`)>)
3350	return type_identity<float>();
3351	#endif
3352
3353	#ifdef __FLT32_DIG__
3354	else if constexpr (is_same_v<_Td, _Float32>)
3355	# ifdef _GLIBCXX_FLOAT_IS_IEEE_BINARY32
3356	return type_identity<float>();
3357	# else
3358	return type_identity<_Float32>();
3359	# endif
3360	#endif
3361	#ifdef __FLT64_DIG__
3362	else if constexpr (is_same_v<_Td, _Float64>)
3363	# ifdef _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
3364	return type_identity<double>();
3365	# else
3366	return type_identity<_Float64>();
3367	# endif
3368	#endif
3369	#if _GLIBCXX_FORMAT_F128
3370	# if __FLT128_DIG__
3371	else if constexpr (is_same_v<_Td, _Float128>)
3372	return type_identity<__format::__float128_t>();
3373	# endif
3374	# if __SIZEOF_FLOAT128__
3375	else if constexpr (is_same_v<_Td, __float128>)
3376	return type_identity<__format::__float128_t>();
3377	# endif
3378	#endif
3379	else if constexpr (__is_specialization_of<_Td, basic_string_view>
3380	\|\| __is_specialization_of<_Td, basic_string>)
3381	{
3382	if constexpr (is_same_v<typename _Td::value_type, _CharT>)
3383	return type_identity<basic_string_view<_CharT>>();
3384	else
3385	return type_identity<handle>();
3386	}
3387	else if constexpr (is_same_v<decay_t<_Td>, const _CharT*>)
3388	return type_identity<const _CharT*>();
3389	else if constexpr (is_same_v<decay_t<_Td>, _CharT*>)
3390	return type_identity<const _CharT*>();
3391	else if constexpr (is_void_v<remove_pointer_t<_Td>>)
3392	return type_identity<const void*>();
3393	else if constexpr (is_same_v<_Td, nullptr_t>)
3394	return type_identity<const void*>();
3395	else
3396	return type_identity<handle>();
3397	}
3398
3399	// Transform a formattable type to the appropriate storage type.
3400	template<typename _Tp>
3401	using _Normalize = typename decltype(_S_to_arg_type<_Tp>())::type;
3402
3403	// Get the _Arg_t value corresponding to a normalized type.
3404	template<typename _Tp>
3405	static consteval __format::_Arg_t
3406	_S_to_enum()
3407	{
3408	using namespace __format;
3409	if constexpr (is_same_v<_Tp, bool>)
3410	return _Arg_bool;
3411	else if constexpr (is_same_v<_Tp, _CharT>)
3412	return _Arg_c;
3413	else if constexpr (is_same_v<_Tp, int>)
3414	return _Arg_i;
3415	else if constexpr (is_same_v<_Tp, unsigned>)
3416	return _Arg_u;
3417	else if constexpr (is_same_v<_Tp, long long>)
3418	return _Arg_ll;
3419	else if constexpr (is_same_v<_Tp, unsigned long long>)
3420	return _Arg_ull;
3421	else if constexpr (is_same_v<_Tp, float>)
3422	return _Arg_flt;
3423	else if constexpr (is_same_v<_Tp, double>)
3424	return _Arg_dbl;
3425	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3426	else if constexpr (is_same_v<_Tp, long double>)
3427	return _Arg_ldbl;
3428	#else
3429	// Don't use _Arg_ldbl for this target, it's ambiguous.
3430	else if constexpr (is_same_v<_Tp, __ibm128>)
3431	return _Arg_ibm128;
3432	else if constexpr (is_same_v<_Tp, __ieee128>)
3433	return _Arg_f128;
3434	#endif
3435	else if constexpr (is_same_v<_Tp, const _CharT*>)
3436	return _Arg_str;
3437	else if constexpr (is_same_v<_Tp, basic_string_view<_CharT>>)
3438	return _Arg_sv;
3439	else if constexpr (is_same_v<_Tp, const void*>)
3440	return _Arg_ptr;
3441	#ifdef __SIZEOF_INT128__
3442	else if constexpr (is_same_v<_Tp, __int128>)
3443	return _Arg_i128;
3444	else if constexpr (is_same_v<_Tp, unsigned __int128>)
3445	return _Arg_u128;
3446	#endif
3447
3448	// N.B. some of these types will never actually be used here,
3449	// because they get normalized to a standard floating-point type.
3450	#if defined __FLT32_DIG__ && ! _GLIBCXX_FLOAT_IS_IEEE_BINARY32
3451	else if constexpr (is_same_v<_Tp, _Float32>)
3452	return _Arg_f32;
3453	#endif
3454	#if defined __FLT64_DIG__ && ! _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
3455	else if constexpr (is_same_v<_Tp, _Float64>)
3456	return _Arg_f64;
3457	#endif
3458	#if _GLIBCXX_FORMAT_F128 == 2
3459	else if constexpr (is_same_v<_Tp, __format::__float128_t>)
3460	return _Arg_f128;
3461	#endif
3462	else if constexpr (is_same_v<_Tp, handle>)
3463	return _Arg_handle;
3464	}
3465
3466	template<typename _Tp>
3467	void
3468	_M_set(_Tp __v) noexcept
3469	{
3470	_M_type = _S_to_enum<_Tp>();
3471	_M_val._M_set(__v);
3472	}
3473
3474	template<typename _Tp>
3475	requires __format::__formattable_with<_Tp, _Context>
3476	explicit
3477	basic_format_arg(_Tp& __v) noexcept
3478	{
3479	using _Td = _Normalize<_Tp>;
3480	if constexpr (is_same_v<_Td, basic_string_view<_CharT>>)
3481	_M_set(_Td{__v.data(), __v.size()});
3482	else if constexpr (is_same_v<remove_const_t<_Tp>, char>
3483	&& is_same_v<_CharT, wchar_t>)
3484	_M_set(static_cast<_Td>(static_cast<unsigned char>(__v)));
3485	else
3486	_M_set(static_cast<_Td>(__v));
3487	}
3488
3489	template<typename _Ctx, typename... _Argz>
3490	friend auto
3491	make_format_args(_Argz&...) noexcept;
3492
3493	template<typename _Visitor, typename _Ctx>
3494	friend decltype(auto)
3495	visit_format_arg(_Visitor&& __vis, basic_format_arg<_Ctx>);
3496
3497	template<typename _Visitor>
3498	decltype(auto)
3499	_M_visit(_Visitor&& __vis, __format::_Arg_t __type)
3500	{
3501	using namespace __format;
3502	switch (__type)
3503	{
3504	case _Arg_none:
3505	return std::forward<_Visitor>(__vis)(_M_val._M_none);
3506	case _Arg_bool:
3507	return std::forward<_Visitor>(__vis)(_M_val._M_bool);
3508	case _Arg_c:
3509	return std::forward<_Visitor>(__vis)(_M_val._M_c);
3510	case _Arg_i:
3511	return std::forward<_Visitor>(__vis)(_M_val._M_i);
3512	case _Arg_u:
3513	return std::forward<_Visitor>(__vis)(_M_val._M_u);
3514	case _Arg_ll:
3515	return std::forward<_Visitor>(__vis)(_M_val._M_ll);
3516	case _Arg_ull:
3517	return std::forward<_Visitor>(__vis)(_M_val._M_ull);
3518	#if __glibcxx_to_chars // FIXME: need to be able to format these types!
3519	case _Arg_flt:
3520	return std::forward<_Visitor>(__vis)(_M_val._M_flt);
3521	case _Arg_dbl:
3522	return std::forward<_Visitor>(__vis)(_M_val._M_dbl);
3523	#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
3524	case _Arg_ldbl:
3525	return std::forward<_Visitor>(__vis)(_M_val._M_ldbl);
3526	#else
3527	case _Arg_f128:
3528	return std::forward<_Visitor>(__vis)(_M_val._M_f128);
3529	case _Arg_ibm128:
3530	return std::forward<_Visitor>(__vis)(_M_val._M_ibm128);
3531	#endif
3532	#endif
3533	case _Arg_str:
3534	return std::forward<_Visitor>(__vis)(_M_val._M_str);
3535	case _Arg_sv:
3536	return std::forward<_Visitor>(__vis)(_M_val._M_sv);
3537	case _Arg_ptr:
3538	return std::forward<_Visitor>(__vis)(_M_val._M_ptr);
3539	case _Arg_handle:
3540	{
3541	auto& __h = static_cast<handle&>(_M_val._M_handle);
3542	return std::forward<_Visitor>(__vis)(__h);
3543	}
3544	#ifdef __SIZEOF_INT128__
3545	case _Arg_i128:
3546	return std::forward<_Visitor>(__vis)(_M_val._M_i128);
3547	case _Arg_u128:
3548	return std::forward<_Visitor>(__vis)(_M_val._M_u128);
3549	#endif
3550
3551	#if _GLIBCXX_FORMAT_F128 == 2
3552	case _Arg_f128:
3553	return std::forward<_Visitor>(__vis)(_M_val._M_f128);
3554	#endif
3555
3556	default:
3557	// _Arg_f16 etc.
3558	__builtin_unreachable();
3559	}
3560	}
3561	};
3562
3563	template<typename _Visitor, typename _Context>
3564	inline decltype(auto)
3565	visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg)
3566	{
3567	return __arg._M_visit(std::forward<_Visitor>(__vis), __arg._M_type);
3568	}
3569
3570	/// @cond undocumented
3571	namespace __format
3572	{
3573	struct _WidthPrecVisitor
3574	{
3575	template<typename _Tp>
3576	size_t
3577	operator()(_Tp& __arg) const
3578	{
3579	if constexpr (is_same_v<_Tp, monostate>)
3580	__format::__invalid_arg_id_in_format_string();
3581	// _GLIBCXX_RESOLVE_LIB_DEFECTS
3582	// 3720. Restrict the valid types of arg-id for width and precision
3583	// 3721. Allow an arg-id with a value of zero for width
3584	else if constexpr (sizeof(_Tp) <= sizeof(long long))
3585	{
3586	// _GLIBCXX_RESOLVE_LIB_DEFECTS
3587	// 3720. Restrict the valid types of arg-id for width and precision
3588	if constexpr (__is_unsigned_integer<_Tp>::value)
3589	return __arg;
3590	else if constexpr (__is_signed_integer<_Tp>::value)
3591	if (__arg >= `0`)
3592	return __arg;
3593	}
3594	__throw_format_error(what: "format error: argument used for width or "
3595	"precision must be a non-negative integer");
3596	}
3597	};
3598
3599	template<typename _Context>
3600	inline size_t
3601	__int_from_arg(const basic_format_arg<_Context>& __arg)
3602	{ return std::visit_format_arg(_WidthPrecVisitor (), __arg); }
3603
3604	// Pack _Arg_t enum values into a single 60-bit integer.
3605	template<int _Bits, size_t _Nm>
3606	constexpr auto
3607	__pack_arg_types(const array<_Arg_t, _Nm>& __types)
3608	{
3609	__UINT64_TYPE__ __packed_types = `0`;
3610	for (auto __i = __types.rbegin(); __i != __types.rend(); ++__i)
3611	__packed_types = (__packed_types << _Bits) \| *__i;
3612	return __packed_types;
3613	}
3614	} // namespace __format
3615	/// @endcond
3616
3617	template<typename _Context>
3618	class basic_format_args
3619	{
3620	static constexpr int _S_packed_type_bits = `5`; // _Arg_t values [0,20]
3621	static constexpr int _S_packed_type_mask = `0b11111`;
3622	static constexpr int _S_max_packed_args = `12`;
3623
3624	static_assert( __format::_Arg_max_ <= (`1` << _S_packed_type_bits) );
3625
3626	template<typename... _Args>
3627	using _Store = __format::_Arg_store<_Context, _Args...>;
3628
3629	template<typename _Ctx, typename... _Args>
3630	friend class __format::_Arg_store;
3631
3632	using uint64_t = __UINT64_TYPE__;
3633	using _Format_arg = basic_format_arg<_Context>;
3634	using _Format_arg_val = __format::_Arg_value<_Context>;
3635
3636	// If args are packed then the number of args is in _M_packed_size and
3637	// the packed types are in _M_unpacked_size, accessed via _M_type(i).
3638	// If args are not packed then the number of args is in _M_unpacked_size
3639	// and _M_packed_size is zero.
3640	uint64_t _M_packed_size : `4`;
3641	uint64_t _M_unpacked_size : `60`;
3642
3643	union {
3644	const _Format_arg_val* _M_values; // Active when _M_packed_size != 0
3645	const _Format_arg* _M_args; // Active when _M_packed_size == 0
3646	};
3647
3648	size_t
3649	_M_size() const noexcept
3650	{ return _M_packed_size ? _M_packed_size : _M_unpacked_size; }
3651
3652	typename __format::_Arg_t
3653	_M_type(size_t __i) const noexcept
3654	{
3655	uint64_t __t = _M_unpacked_size >> (__i * _S_packed_type_bits);
3656	return static_cast<__format::_Arg_t>(__t & _S_packed_type_mask);
3657	}
3658
3659	template<typename _Ctx, typename... _Args>
3660	friend auto
3661	make_format_args(_Args&...) noexcept;
3662
3663	// An array of _Arg_t enums corresponding to _Args...
3664	template<typename... _Args>
3665	static consteval array<__format::_Arg_t, sizeof...(_Args)>
3666	_S_types_to_pack()
3667	{ return {_Format_arg::template _S_to_enum<_Args>()...}; }
3668
3669	public:
3670	basic_format_args() noexcept = default;
3671
3672	template<typename... _Args>
3673	basic_format_args(const _Store<_Args...>& __store) noexcept;
3674
3675	[[nodiscard,__gnu__::__always_inline__]]
3676	basic_format_arg<_Context>
3677	get(size_t __i) const noexcept
3678	{
3679	basic_format_arg<_Context> __arg;
3680	if (__i < _M_packed_size)
3681	{
3682	__arg._M_type = _M_type(__i);
3683	__arg._M_val = _M_values[__i];
3684	}
3685	else if (_M_packed_size == `0` && __i < _M_unpacked_size)
3686	__arg = _M_args[__i];
3687	return __arg;
3688	}
3689	};
3690
3691	// _GLIBCXX_RESOLVE_LIB_DEFECTS
3692	// 3810. CTAD for std::basic_format_args
3693	template<typename _Context, typename... _Args>
3694	basic_format_args(__format::_Arg_store<_Context, _Args...>)
3695	-> basic_format_args<_Context>;
3696
3697	template<typename _Context, typename... _Args>
3698	auto
3699	make_format_args(_Args&... __fmt_args) noexcept;
3700
3701	// An array of type-erased formatting arguments.
3702	template<typename _Context, typename... _Args>
3703	class __format::_Arg_store
3704	{
3705	friend std::basic_format_args<_Context>;
3706
3707	template<typename _Ctx, typename... _Argz>
3708	friend auto std::
3709	#if _GLIBCXX_INLINE_VERSION
3710	__8:: // Needed for PR c++/59256
3711	#endif
3712	make_format_args(_Argz&...) noexcept;
3713
3714	// For a sufficiently small number of arguments we only store values.
3715	// basic_format_args can get the types from the _Args pack.
3716	static constexpr bool _S_values_only
3717	= sizeof...(_Args) <= basic_format_args<_Context>::_S_max_packed_args;
3718
3719	using _Element_t
3720	= __conditional_t<_S_values_only,
3721	__format::_Arg_value<_Context>,
3722	basic_format_arg<_Context>>;
3723
3724	_Element_t _M_args[sizeof...(_Args)];
3725
3726	template<typename _Tp>
3727	static _Element_t
3728	_S_make_elt(_Tp& __v)
3729	{
3730	using _Tq = remove_const_t<_Tp>;
3731	using _CharT = typename _Context::char_type;
3732	static_assert(is_default_constructible_v<formatter<_Tq, _CharT>>,
3733	"std::formatter must be specialized for the type "
3734	"of each format arg");
3735	using __format::__formattable_with;
3736	if constexpr (is_const_v<_Tp>)
3737	if constexpr (!__formattable_with<_Tp, _Context>)
3738	if constexpr (__formattable_with<_Tq, _Context>)
3739	static_assert(__formattable_with<_Tp, _Context>,
3740	"format arg must be non-const because its "
3741	"std::formatter specialization has a "
3742	"non-const reference parameter");
3743	basic_format_arg<_Context> __arg(__v);
3744	if constexpr (_S_values_only)
3745	return __arg._M_val;
3746	else
3747	return __arg;
3748	}
3749
3750	template<typename... _Tp>
3751	requires (sizeof...(_Tp) == sizeof...(_Args))
3752	[[__gnu__::__always_inline__]]
3753	_Arg_store(_Tp&... __a) noexcept
3754	: _M_args{_S_make_elt(__a)...}
3755	{ }
3756	};
3757
3758	template<typename _Context>
3759	class __format::_Arg_store<_Context>
3760	{ };
3761
3762	template<typename _Context>
3763	template<typename... _Args>
3764	inline
3765	basic_format_args<_Context>::
3766	basic_format_args(const _Store<_Args...>& __store) noexcept
3767	{
3768	if constexpr (sizeof...(_Args) == `0`)
3769	{
3770	_M_packed_size = `0`;
3771	_M_unpacked_size = `0`;
3772	_M_args = nullptr;
3773	}
3774	else if constexpr (sizeof...(_Args) <= _S_max_packed_args)
3775	{
3776	// The number of packed arguments:
3777	_M_packed_size = sizeof...(_Args);
3778	// The packed type enums:
3779	_M_unpacked_size
3780	= __format::__pack_arg_types<_S_packed_type_bits>(_S_types_to_pack<_Args...>());
3781	// The _Arg_value objects.
3782	_M_values = __store._M_args;
3783	}
3784	else
3785	{
3786	// No packed arguments:
3787	_M_packed_size = `0`;
3788	// The number of unpacked arguments:
3789	_M_unpacked_size = sizeof...(_Args);
3790	// The basic_format_arg objects:
3791	_M_args = __store._M_args;
3792	}
3793	}
3794
3795	/// Capture formatting arguments for use by `std::vformat`.
3796	template<typename _Context = format_context, typename... _Args>
3797	[[nodiscard,__gnu__::__always_inline__]]
3798	inline auto
3799	make_format_args(_Args&... __fmt_args) noexcept
3800	{
3801	using _Fmt_arg = basic_format_arg<_Context>;
3802	using _Store = __format::_Arg_store<_Context, typename _Fmt_arg::template
3803	_Normalize<_Args>...>;
3804	return _Store(__fmt_args...);
3805	}
3806
3807	#ifdef _GLIBCXX_USE_WCHAR_T
3808	/// Capture formatting arguments for use by `std::vformat` (for wide output).
3809	template<typename... _Args>
3810	[[nodiscard,__gnu__::__always_inline__]]
3811	inline auto
3812	make_wformat_args(_Args&... __args) noexcept
3813	{ return std::make_format_args<wformat_context>(__args...); }
3814	#endif
3815
3816	/// @cond undocumented
3817	namespace __format
3818	{
3819	template<typename _Out, typename _CharT, typename _Context>
3820	_Out
3821	__do_vformat_to(_Out, basic_string_view<_CharT>,
3822	const basic_format_args<_Context>&,
3823	const locale* = nullptr);
3824	} // namespace __format
3825	/// @endcond
3826
3827	/* Context for std::format and similar functions.*
3828	*
3829	* A formatting context contains an output iterator and locale to use
3830	* for the formatting operations. Most programs will never need to use
3831	* this class template explicitly. For typical uses of `std::format` the
3832	* library will use the specializations `std::format_context` (for `char`)
3833	* and `std::wformat_context` (for `wchar_t`).
3834	*/
3835	template<typename _Out, typename _CharT>
3836	class basic_format_context
3837	{
3838	static_assert( output_iterator<_Out, const _CharT&> );
3839
3840	basic_format_args<basic_format_context> _M_args;
3841	_Out _M_out;
3842	__format::_Optional_locale _M_loc;
3843
3844	basic_format_context(basic_format_args<basic_format_context> __args,
3845	_Out __out)
3846	: _M_args(__args), _M_out(std::move(__out))
3847	{ }
3848
3849	basic_format_context(basic_format_args<basic_format_context> __args,
3850	_Out __out, const std::locale& __loc)
3851	: _M_args(__args), _M_out(std::move(__out)), _M_loc (__loc)
3852	{ }
3853
3854	template<typename _Out2, typename _CharT2, typename _Context2>
3855	friend _Out2
3856	__format::__do_vformat_to(_Out2, basic_string_view<_CharT2>,
3857	const basic_format_args<_Context2>&,
3858	const locale*);
3859
3860	public:
3861	basic_format_context() = default;
3862	~basic_format_context() = default;
3863
3864	using iterator = _Out;
3865	using char_type = _CharT;
3866	template<typename _Tp>
3867	using formatter_type = formatter<_Tp, _CharT>;
3868
3869	[[nodiscard]]
3870	basic_format_arg<basic_format_context>
3871	arg(size_t __id) const noexcept
3872	{ return _M_args.get(__id); }
3873
3874	[[nodiscard]]
3875	std::locale locale() { return _M_loc.value(); }
3876
3877	[[nodiscard]]
3878	iterator out() { return std::move(_M_out); }
3879
3880	void advance_to(iterator __it) { _M_out = std::move(__it); }
3881	};
3882
3883
3884	/// @cond undocumented
3885	namespace __format
3886	{
3887	// Abstract base class defining an interface for scanning format strings.
3888	// Scan the characters in a format string, dividing it up into strings of
3889	// ordinary characters, escape sequences, and replacement fields.
3890	// Call virtual functions for derived classes to parse format-specifiers
3891	// or write formatted output.
3892	template<typename _CharT>
3893	struct _Scanner
3894	{
3895	using iterator = typename basic_format_parse_context<_CharT>::iterator;
3896
3897	basic_format_parse_context<_CharT> _M_pc;
3898
3899	constexpr explicit
3900	_Scanner(basic_string_view<_CharT> __str, size_t __nargs = -`1`)
3901	: _M_pc(__str, __nargs)
3902	{ }
3903
3904	constexpr iterator begin() const noexcept { return _M_pc.begin(); }
3905	constexpr iterator end() const noexcept { return _M_pc.end(); }
3906
3907	constexpr void
3908	_M_scan()
3909	{
3910	basic_string_view<_CharT> __fmt = _M_fmt_str();
3911
3912	if (__fmt.size() == `2` && __fmt[`0`] == `'{'` && __fmt[`1`] == `'}'`)
3913	{
3914	_M_pc.advance_to(begin() + `1`);
3915	_M_format_arg(id: _M_pc.next_arg_id());
3916	return;
3917	}
3918
3919	size_t __lbr = __fmt.find(`'{'`);
3920	size_t __rbr = __fmt.find(`'}'`);
3921
3922	while (__fmt.size())
3923	{
3924	auto __cmp = __lbr <=> __rbr;
3925	if (__cmp == `0`)
3926	{
3927	_M_on_chars(end());
3928	_M_pc.advance_to(end());
3929	return;
3930	}
3931	else if (__cmp < `0`)
3932	{
3933	if (__lbr + `1` == __fmt.size()
3934	\|\| (__rbr == __fmt.npos && __fmt[__lbr + `1`] != `'{'`))
3935	__format::__unmatched_left_brace_in_format_string();
3936	const bool __is_escape = __fmt[__lbr + `1`] == `'{'`;
3937	iterator __last = begin() + __lbr + int(__is_escape);
3938	_M_on_chars(__last);
3939	_M_pc.advance_to(__last + `1`);
3940	__fmt = _M_fmt_str();
3941	if (__is_escape)
3942	{
3943	if (__rbr != __fmt.npos)
3944	__rbr -= __lbr + `2`;
3945	__lbr = __fmt.find(`'{'`);
3946	}
3947	else
3948	{
3949	_M_on_replacement_field();
3950	__fmt = _M_fmt_str();
3951	__lbr = __fmt.find(`'{'`);
3952	__rbr = __fmt.find(`'}'`);
3953	}
3954	}
3955	else
3956	{
3957	if (++__rbr == __fmt.size() \|\| __fmt[__rbr] != `'}'`)
3958	__format::__unmatched_right_brace_in_format_string();
3959	iterator __last = begin() + __rbr;
3960	_M_on_chars(__last);
3961	_M_pc.advance_to(__last + `1`);
3962	__fmt = _M_fmt_str();
3963	if (__lbr != __fmt.npos)
3964	__lbr -= __rbr + `1`;
3965	__rbr = __fmt.find(`'}'`);
3966	}
3967	}
3968	}
3969
3970	constexpr basic_string_view<_CharT>
3971	_M_fmt_str() const noexcept
3972	{ return {begin(), end()}; }
3973
3974	constexpr virtual void _M_on_chars(iterator) { }
3975
3976	constexpr void _M_on_replacement_field()
3977	{
3978	auto __next = begin();
3979
3980	size_t __id;
3981	if (*__next == `'}'`)
3982	__id = _M_pc.next_arg_id();
3983	else if (*__next == `':'`)
3984	{
3985	__id = _M_pc.next_arg_id();
3986	_M_pc.advance_to(++__next);
3987	}
3988	else
3989	{
3990	auto [__i, __ptr] = __format::__parse_arg_id(begin(), end());
3991	if (!__ptr \|\| !(__ptr == `'}'` \|\| __ptr == `':'`))
3992	__format::__invalid_arg_id_in_format_string();
3993	_M_pc.check_arg_id(__id = __i);
3994	if (*__ptr == `':'`)
3995	{
3996	_M_pc.advance_to(++__ptr);
3997	}
3998	else
3999	_M_pc.advance_to(__ptr);
4000	}
4001	_M_format_arg(__id);
4002	if (begin() == end() \|\| *begin() != `'}'`)
4003	__format::__unmatched_left_brace_in_format_string();
4004	_M_pc.advance_to(begin() + `1`); // Move past '}'
4005	}
4006
4007	constexpr virtual void _M_format_arg(size_t __id) = `0`;
4008	};
4009
4010	// Process a format string and format the arguments in the context.
4011	template<typename _Out, typename _CharT>
4012	class _Formatting_scanner : public _Scanner<_CharT>
4013	{
4014	public:
4015	_Formatting_scanner(basic_format_context<_Out, _CharT>& __fc,
4016	basic_string_view<_CharT> __str)
4017	: _Scanner<_CharT>(__str), _M_fc(__fc)
4018	{ }
4019
4020	private:
4021	basic_format_context<_Out, _CharT>& _M_fc;
4022
4023	using iterator = typename _Scanner<_CharT>::iterator;
4024
4025	constexpr void
4026	_M_on_chars(iterator __last) override
4027	{
4028	basic_string_view<_CharT> __str(this->begin(), __last);
4029	_M_fc.advance_to(__format::__write(_M_fc.out(), __str));
4030	}
4031
4032	constexpr void
4033	_M_format_arg(size_t __id) override
4034	{
4035	using _Context = basic_format_context<_Out, _CharT>;
4036	using handle = typename basic_format_arg<_Context>::handle;
4037
4038	std::visit_format_arg([this](auto& __arg) {
4039	using _Type = remove_reference_t<decltype(__arg)>;
4040	using _Formatter = typename _Context::template formatter_type<_Type>;
4041	if constexpr (is_same_v<_Type, monostate>)
4042	__format::__invalid_arg_id_in_format_string();
4043	else if constexpr (is_same_v<_Type, handle>)
4044	__arg.format(this->_M_pc, this->_M_fc);
4045	else if constexpr (is_default_constructible_v<_Formatter>)
4046	{
4047	_Formatter __f;
4048	this->_M_pc.advance_to(__f.parse(this->_M_pc));
4049	this->_M_fc.advance_to(__f.format(__arg, this->_M_fc));
4050	}
4051	else
4052	static_assert(__format::__formattable_with<_Type, _Context>);
4053	}, _M_fc.arg(__id));
4054	}
4055	};
4056
4057	// Validate a format string for Args.
4058	template<typename _CharT, typename... _Args>
4059	class _Checking_scanner : public _Scanner<_CharT>
4060	{
4061	static_assert(
4062	(is_default_constructible_v<formatter<_Args, _CharT>> && ...),
4063	"std::formatter must be specialized for each type being formatted");
4064
4065	public:
4066	constexpr
4067	_Checking_scanner(basic_string_view<_CharT> __str)
4068	: _Scanner<_CharT>(__str, sizeof...(_Args))
4069	{ }
4070
4071	private:
4072	constexpr void
4073	_M_format_arg(size_t __id) override
4074	{
4075	if constexpr (sizeof...(_Args) != `0`)
4076	{
4077	if (__id < sizeof...(_Args))
4078	{
4079	_M_parse_format_spec<_Args...>(__id);
4080	return;
4081	}
4082	}
4083	__builtin_unreachable();
4084	}
4085
4086	template<typename _Tp, typename... _OtherArgs>
4087	constexpr void
4088	_M_parse_format_spec(size_t __id)
4089	{
4090	if (__id == `0`)
4091	{
4092	formatter<_Tp, _CharT> __f;
4093	this->_M_pc.advance_to(__f.parse(this->_M_pc));
4094	}
4095	else if constexpr (sizeof...(_OtherArgs) != `0`)
4096	_M_parse_format_spec<_OtherArgs...>(__id - `1`);
4097	else
4098	__builtin_unreachable();
4099	}
4100	};
4101
4102	template<typename _Out, typename _CharT, typename _Context>
4103	inline _Out
4104	__do_vformat_to(_Out __out, basic_string_view<_CharT> __fmt,
4105	const basic_format_args<_Context>& __args,
4106	const locale* __loc)
4107	{
4108	_Iter_sink<_CharT, _Out> __sink(std::move(__out));
4109	_Sink_iter<_CharT> __sink_out;
4110
4111	if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
4112	__sink_out = __out; // Already a sink iterator, safe to use post-move.
4113	else
4114	__sink_out = __sink.out();
4115
4116	if constexpr (is_same_v<_CharT, char>)
4117	// Fast path for "{}" format strings and simple format arg types.
4118	if (__fmt.size() == `2` && __fmt[`0`] == `'{'` && __fmt[`1`] == `'}'`)
4119	{
4120	bool __done = false;
4121	std::visit_format_arg([&](auto& __arg) {
4122	using _Tp = remove_cvref_t<decltype(__arg)>;
4123	if constexpr (is_same_v<_Tp, bool>)
4124	{
4125	size_t __len = `4` + !__arg;
4126	const char* __chars[] = { "false", "true" };
4127	if (auto __res = __sink_out._M_reserve(__len))
4128	{
4129	__builtin_memcpy(__res.get(), __chars[__arg], __len);
4130	__res._M_bump(__len);
4131	__done = true;
4132	}
4133	}
4134	else if constexpr (is_same_v<_Tp, char>)
4135	{
4136	if (auto __res = __sink_out._M_reserve(`1`))
4137	{
4138	*__res.get() = __arg;
4139	__res._M_bump(`1`);
4140	__done = true;
4141	}
4142	}
4143	else if constexpr (is_integral_v<_Tp>)
4144	{
4145	make_unsigned_t<_Tp> __uval;
4146	const bool __neg = __arg < `0`;
4147	if (__neg)
4148	__uval = make_unsigned_t<_Tp>(~__arg) + `1u`;
4149	else
4150	__uval = __arg;
4151	const auto __n = __detail::__to_chars_len(__uval);
4152	if (auto __res = __sink_out._M_reserve(__n + __neg))
4153	{
4154	auto __ptr = __res.get();
4155	*__ptr = `'-'`;
4156	__detail::__to_chars_10_impl(__ptr + (int)__neg, __n,
4157	__uval);
4158	__res._M_bump(__n + __neg);
4159	__done = true;
4160	}
4161	}
4162	else if constexpr (is_convertible_v<_Tp, string_view>)
4163	{
4164	string_view __sv = __arg;
4165	if (auto __res = __sink_out._M_reserve(__sv.size()))
4166	{
4167	__builtin_memcpy(__res.get(), __sv.data(), __sv.size());
4168	__res._M_bump(__sv.size());
4169	__done = true;
4170	}
4171	}
4172	}, __args.get(`0`));
4173
4174	if (__done)
4175	{
4176	if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
4177	return __sink_out;
4178	else
4179	return std::move(__sink)._M_finish().out;
4180	}
4181	}
4182
4183	auto __ctx = __loc == nullptr
4184	? _Context(__args, __sink_out)
4185	: _Context(__args, __sink_out, *__loc);
4186	_Formatting_scanner<_Sink_iter<_CharT>, _CharT> __scanner(__ctx, __fmt);
4187	__scanner._M_scan();
4188
4189	if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
4190	return __ctx.out();
4191	else
4192	return std::move(__sink)._M_finish().out;
4193	}
4194
4195	} // namespace __format
4196	/// @endcond
4197
4198	template<typename _CharT, typename... _Args>
4199	template<typename _Tp>
4200	requires convertible_to<const _Tp&, basic_string_view<_CharT>>
4201	consteval
4202	basic_format_string<_CharT, _Args...>::
4203	basic_format_string(const _Tp& __s)
4204	: _M_str(__s)
4205	{
4206	__format::_Checking_scanner<_CharT, remove_cvref_t<_Args>...>
4207	__scanner(_M_str);
4208	__scanner._M_scan();
4209	}
4210
4211	// [format.functions], formatting functions
4212
4213	template<typename _Out> requires output_iterator<_Out, const char&>
4214	[[__gnu__::__always_inline__]]
4215	inline _Out
4216	vformat_to(_Out __out, string_view __fmt, format_args __args)
4217	{ return __format::__do_vformat_to(std::move(__out), __fmt, __args); }
4218
4219	#ifdef _GLIBCXX_USE_WCHAR_T
4220	template<typename _Out> requires output_iterator<_Out, const wchar_t&>
4221	[[__gnu__::__always_inline__]]
4222	inline _Out
4223	vformat_to(_Out __out, wstring_view __fmt, wformat_args __args)
4224	{ return __format::__do_vformat_to(std::move(__out), __fmt, __args); }
4225	#endif
4226
4227	template<typename _Out> requires output_iterator<_Out, const char&>
4228	[[__gnu__::__always_inline__]]
4229	inline _Out
4230	vformat_to(_Out __out, const locale& __loc, string_view __fmt,
4231	format_args __args)
4232	{
4233	return __format::__do_vformat_to(std::move(__out), __fmt, __args, &__loc);
4234	}
4235
4236	#ifdef _GLIBCXX_USE_WCHAR_T
4237	template<typename _Out> requires output_iterator<_Out, const wchar_t&>
4238	[[__gnu__::__always_inline__]]
4239	inline _Out
4240	vformat_to(_Out __out, const locale& __loc, wstring_view __fmt,
4241	wformat_args __args)
4242	{
4243	return __format::__do_vformat_to(std::move(__out), __fmt, __args, &__loc);
4244	}
4245	#endif
4246
4247	[[nodiscard]]
4248	inline string
4249	vformat(string_view __fmt, format_args __args)
4250	{
4251	__format::_Str_sink<char> __buf;
4252	std::vformat_to(out: __buf.out(), __fmt, __args);
4253	return std::move(__buf).get();
4254	}
4255
4256	#ifdef _GLIBCXX_USE_WCHAR_T
4257	[[nodiscard]]
4258	inline wstring
4259	vformat(wstring_view __fmt, wformat_args __args)
4260	{
4261	__format::_Str_sink<wchar_t> __buf;
4262	std::vformat_to(out: __buf.out(), __fmt, __args);
4263	return std::move(__buf).get();
4264	}
4265	#endif
4266
4267	[[nodiscard]]
4268	inline string
4269	vformat(const locale& __loc, string_view __fmt, format_args __args)
4270	{
4271	__format::_Str_sink<char> __buf;
4272	std::vformat_to(out: __buf.out(), __loc, __fmt, __args);
4273	return std::move(__buf).get();
4274	}
4275
4276	#ifdef _GLIBCXX_USE_WCHAR_T
4277	[[nodiscard]]
4278	inline wstring
4279	vformat(const locale& __loc, wstring_view __fmt, wformat_args __args)
4280	{
4281	__format::_Str_sink<wchar_t> __buf;
4282	std::vformat_to(out: __buf.out(), __loc, __fmt, __args);
4283	return std::move(__buf).get();
4284	}
4285	#endif
4286
4287	template<typename... _Args>
4288	[[nodiscard]]
4289	inline string
4290	format(format_string<_Args...> __fmt, _Args&&... __args)
4291	{ return std::vformat(__fmt.get(), std::make_format_args(__args...)); }
4292
4293	#ifdef _GLIBCXX_USE_WCHAR_T
4294	template<typename... _Args>
4295	[[nodiscard]]
4296	inline wstring
4297	format(wformat_string<_Args...> __fmt, _Args&&... __args)
4298	{ return std::vformat(__fmt.get(), std::make_wformat_args(__args...)); }
4299	#endif
4300
4301	template<typename... _Args>
4302	[[nodiscard]]
4303	inline string
4304	format(const locale& __loc, format_string<_Args...> __fmt,
4305	_Args&&... __args)
4306	{
4307	return std::vformat(__loc, __fmt.get(),
4308	std::make_format_args(__args...));
4309	}
4310
4311	#ifdef _GLIBCXX_USE_WCHAR_T
4312	template<typename... _Args>
4313	[[nodiscard]]
4314	inline wstring
4315	format(const locale& __loc, wformat_string<_Args...> __fmt,
4316	_Args&&... __args)
4317	{
4318	return std::vformat(__loc, __fmt.get(),
4319	std::make_wformat_args(__args...));
4320	}
4321	#endif
4322
4323	template<typename _Out, typename... _Args>
4324	requires output_iterator<_Out, const char&>
4325	inline _Out
4326	format_to(_Out __out, format_string<_Args...> __fmt, _Args&&... __args)
4327	{
4328	return std::vformat_to(std::move(__out), __fmt.get(),
4329	std::make_format_args(__args...));
4330	}
4331
4332	#ifdef _GLIBCXX_USE_WCHAR_T
4333	template<typename _Out, typename... _Args>
4334	requires output_iterator<_Out, const wchar_t&>
4335	inline _Out
4336	format_to(_Out __out, wformat_string<_Args...> __fmt, _Args&&... __args)
4337	{
4338	return std::vformat_to(std::move(__out), __fmt.get(),
4339	std::make_wformat_args(__args...));
4340	}
4341	#endif
4342
4343	template<typename _Out, typename... _Args>
4344	requires output_iterator<_Out, const char&>
4345	inline _Out
4346	format_to(_Out __out, const locale& __loc, format_string<_Args...> __fmt,
4347	_Args&&... __args)
4348	{
4349	return std::vformat_to(std::move(__out), __loc, __fmt.get(),
4350	std::make_format_args(__args...));
4351	}
4352
4353	#ifdef _GLIBCXX_USE_WCHAR_T
4354	template<typename _Out, typename... _Args>
4355	requires output_iterator<_Out, const wchar_t&>
4356	inline _Out
4357	format_to(_Out __out, const locale& __loc, wformat_string<_Args...> __fmt,
4358	_Args&&... __args)
4359	{
4360	return std::vformat_to(std::move(__out), __loc, __fmt.get(),
4361	std::make_wformat_args(__args...));
4362	}
4363	#endif
4364
4365	template<typename _Out, typename... _Args>
4366	requires output_iterator<_Out, const char&>
4367	inline format_to_n_result<_Out>
4368	format_to_n(_Out __out, iter_difference_t<_Out> __n,
4369	format_string<_Args...> __fmt, _Args&&... __args)
4370	{
4371	__format::_Iter_sink<char, _Out> __sink(std::move(__out), __n);
4372	std::vformat_to(__sink.out(), __fmt.get(),
4373	std::make_format_args(__args...));
4374	return std::move(__sink)._M_finish();
4375	}
4376
4377	#ifdef _GLIBCXX_USE_WCHAR_T
4378	template<typename _Out, typename... _Args>
4379	requires output_iterator<_Out, const wchar_t&>
4380	inline format_to_n_result<_Out>
4381	format_to_n(_Out __out, iter_difference_t<_Out> __n,
4382	wformat_string<_Args...> __fmt, _Args&&... __args)
4383	{
4384	__format::_Iter_sink<wchar_t, _Out> __sink(std::move(__out), __n);
4385	std::vformat_to(__sink.out(), __fmt.get(),
4386	std::make_wformat_args(__args...));
4387	return std::move(__sink)._M_finish();
4388	}
4389	#endif
4390
4391	template<typename _Out, typename... _Args>
4392	requires output_iterator<_Out, const char&>
4393	inline format_to_n_result<_Out>
4394	format_to_n(_Out __out, iter_difference_t<_Out> __n, const locale& __loc,
4395	format_string<_Args...> __fmt, _Args&&... __args)
4396	{
4397	__format::_Iter_sink<char, _Out> __sink(std::move(__out), __n);
4398	std::vformat_to(__sink.out(), __loc, __fmt.get(),
4399	std::make_format_args(__args...));
4400	return std::move(__sink)._M_finish();
4401	}
4402
4403	#ifdef _GLIBCXX_USE_WCHAR_T
4404	template<typename _Out, typename... _Args>
4405	requires output_iterator<_Out, const wchar_t&>
4406	inline format_to_n_result<_Out>
4407	format_to_n(_Out __out, iter_difference_t<_Out> __n, const locale& __loc,
4408	wformat_string<_Args...> __fmt, _Args&&... __args)
4409	{
4410	__format::_Iter_sink<wchar_t, _Out> __sink(std::move(__out), __n);
4411	std::vformat_to(__sink.out(), __loc, __fmt.get(),
4412	std::make_wformat_args(__args...));
4413	return std::move(__sink)._M_finish();
4414	}
4415	#endif
4416
4417	/// @cond undocumented
4418	namespace __format
4419	{
4420	#if 1
4421	template<typename _CharT>
4422	class _Counting_sink final : public _Iter_sink<_CharT, _CharT*>
4423	{
4424	public:
4425	_Counting_sink() : _Iter_sink<_CharT, _CharT>(nullptr*, `0`) { }
4426
4427	[[__gnu__::__always_inline__]]
4428	size_t
4429	count() const
4430	{ return this->_M_count + this->_M_used().size(); }
4431	};
4432	#else
4433	template<typename _CharT>
4434	class _Counting_sink : public _Buf_sink<_CharT>
4435	{
4436	size_t _M_count = `0`;
4437
4438	void
4439	_M_overflow() override
4440	{
4441	if (!std::is_constant_evaluated())
4442	_M_count += this->_M_used().size();
4443	this->_M_rewind();
4444	}
4445
4446	public:
4447	_Counting_sink() = default;
4448
4449	[[__gnu__::__always_inline__]]
4450	size_t
4451	count() noexcept
4452	{
4453	_Counting_sink::_M_overflow();
4454	return _M_count;
4455	}
4456	};
4457	#endif
4458	} // namespace __format
4459	/// @endcond
4460
4461	template<typename... _Args>
4462	[[nodiscard]]
4463	inline size_t
4464	formatted_size(format_string<_Args...> __fmt, _Args&&... __args)
4465	{
4466	__format::_Counting_sink<char> __buf;
4467	std::vformat_to(__buf.out(), __fmt.get(),
4468	std::make_format_args(__args...));
4469	return __buf.count();
4470	}
4471
4472	#ifdef _GLIBCXX_USE_WCHAR_T
4473	template<typename... _Args>
4474	[[nodiscard]]
4475	inline size_t
4476	formatted_size(wformat_string<_Args...> __fmt, _Args&&... __args)
4477	{
4478	__format::_Counting_sink<wchar_t> __buf;
4479	std::vformat_to(__buf.out(), __fmt.get(),
4480	std::make_wformat_args(__args...));
4481	return __buf.count();
4482	}
4483	#endif
4484
4485	template<typename... _Args>
4486	[[nodiscard]]
4487	inline size_t
4488	formatted_size(const locale& __loc, format_string<_Args...> __fmt,
4489	_Args&&... __args)
4490	{
4491	__format::_Counting_sink<char> __buf;
4492	std::vformat_to(__buf.out(), __loc, __fmt.get(),
4493	std::make_format_args(__args...));
4494	return __buf.count();
4495	}
4496
4497	#ifdef _GLIBCXX_USE_WCHAR_T
4498	template<typename... _Args>
4499	[[nodiscard]]
4500	inline size_t
4501	formatted_size(const locale& __loc, wformat_string<_Args...> __fmt,
4502	_Args&&... __args)
4503	{
4504	__format::_Counting_sink<wchar_t> __buf;
4505	std::vformat_to(__buf.out(), __loc, __fmt.get(),
4506	std::make_wformat_args(__args...));
4507	return __buf.count();
4508	}
4509	#endif
4510
4511	#if __cpp_lib_format_ranges
4512	// [format.range], formatting of ranges
4513	// [format.range.fmtkind], variable template format_kind
4514	enum class range_format {
4515	disabled,
4516	map,
4517	set,
4518	sequence,
4519	string,
4520	debug_string
4521	};
4522
4523	/// @cond undocumented
4524	template<typename _Rg>
4525	constexpr auto format_kind = not defined(format_kind<_Rg>);
4526
4527	template<typename _Tp>
4528	consteval range_format
4529	__fmt_kind()
4530	{
4531	using _Ref = ranges::range_reference_t<_Tp>;
4532	if constexpr (is_same_v<remove_cvref_t<_Ref>, _Tp>)
4533	return range_format::disabled;
4534	else if constexpr (requires { typename _Tp::key_type; })
4535	{
4536	if constexpr (requires { typename _Tp::mapped_type; })
4537	{
4538	using _Up = remove_cvref_t<_Ref>;
4539	if constexpr (__is_pair<_Up>)
4540	return range_format::map;
4541	else if constexpr (__is_specialization_of<_Up, tuple>)
4542	if constexpr (tuple_size_v<_Up> == `2`)
4543	return range_format::map;
4544	}
4545	return range_format::set;
4546	}
4547	else
4548	return range_format::sequence;
4549	}
4550	/// @endcond
4551
4552	/// A constant determining how a range should be formatted.
4553	template<ranges::input_range _Rg> requires same_as<_Rg, remove_cvref_t<_Rg>>
4554	constexpr range_format format_kind<_Rg> = __fmt_kind<_Rg>();
4555
4556	// [format.range.formatter], class template range_formatter
4557	template<typename _Tp, typename _CharT = char>
4558	requires same_as<remove_cvref_t<_Tp>, _Tp> && formattable<_Tp, _CharT>
4559	class range_formatter; // TODO
4560
4561	/// @cond undocumented
4562	namespace __format
4563	{
4564	// [format.range.fmtdef], class template range-default-formatter
4565	template<range_format _Kind, ranges::input_range _Rg, typename _CharT>
4566	struct __range_default_formatter; // TODO
4567	} // namespace __format
4568	/// @endcond
4569
4570	// [format.range.fmtmap], [format.range.fmtset], [format.range.fmtstr],
4571	// specializations for maps, sets, and strings
4572	template<ranges::input_range _Rg, typename _CharT>
4573	requires (format_kind<_Rg> != range_format::disabled)
4574	&& formattable<ranges::range_reference_t<_Rg>, _CharT>
4575	struct formatter<_Rg, _CharT>
4576	: __format::__range_default_formatter<format_kind<_Rg>, _Rg, _CharT>
4577	{ };
4578	#endif // C++23 formatting ranges
4579
4580	_GLIBCXX_END_NAMESPACE_VERSION
4581	} // namespace std
4582	#endif // __cpp_lib_format
4583	#endif // _GLIBCXX_FORMAT
4584

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