[WIP][libc++][format] DO NOT REVIEW

[Mordante]

Summary

Contains a new approach of std::format's parser and formatters. This
approach saves over 10KB of the binary size.

This patch is still work-in-progress. This review is to test the CI.

[Mordante]

Trigger CI.

[Mordante]

Fixes linting issues.

[Mordante]

Clang-tidy fixes.

[Mordante]

More CI fixes.

[Mordante]

Attempt to fix several CI issues.

[Mordante]

Add some debug information.

[Mordante]

More CI fixes.

[Mordante]

Attempt more CI fixes.

[Mordante]

Fixes copy-paste error.

[Mordante]

Refactor and polish.

[Mordante]

Fix CI error.

[Mordante]

The changes in this review have been implemented in smaller patches.

libcxx/benchmarks/std_format_spec_string_unicode.bench.cpp

for (int i = 0; i < 100; ++i)
       it = std::copy_n(input, size_, it);
   }
 
   constexpr size_t size() const noexcept { return data_.size(); }
   constexpr const CharT* begin() const noexcept { return data_.begin(); }
   constexpr const CharT* end() const noexcept { return data_.end(); }
 
   void test(benchmark::State& state) const {
+    std::basic_string_view<CharT> sv{data_.begin(), data_.end()};
     for (auto _ : state)
-      benchmark::DoNotOptimize(std::__format_spec::__get_string_alignment(
-          begin(), end(), 1'000'000, 1'000'000));
+      if constexpr (std::same_as<CharT, char>)
+        benchmark::DoNotOptimize(std::formatted_size("{:{}.{}}", sv, 1'000'000, 1'000'000));
+      else
+        benchmark::DoNotOptimize(std::formatted_size(L"{:{}.{}}", sv, 1'000'000, 1'000'000));
+
     state.SetItemsProcessed(state.iterations() * size());
   }
 };
 
-#define TEST(u8)                                                               \
-  if constexpr (std::same_as<CharT, char>) {                                   \
-    constexpr auto p = tester{u8};                                             \
-    p.test(state);                                                             \
-  } else if constexpr (std::same_as<CharT, char16_t>) {                        \
-    constexpr auto p = tester{TEST_CONCAT(u, u8)};                             \
-    p.test(state);                                                             \
-  } else {                                                                     \
-    constexpr auto p = tester{TEST_CONCAT(U, u8)};                             \
-    p.test(state);                                                             \
+#  define TEST(u8)                                                                                                     \
+    if constexpr (std::same_as<CharT, char>) {                                                                         \
+      constexpr auto p = tester{u8};                                                                                   \
+      p.test(state);                                                                                                   \
+    } else {                                                                                                           \
+      constexpr auto p = tester{TEST_CONCAT(L, u8)};                                                                   \
+      p.test(state);                                                                                                   \
     }
 
 template <class CharT>
 static void BM_EstimateLengthNoMultiByte(benchmark::State& state) {
   TEST("The quick brown fox jumps over the lazy dog");
 }
 
 template <class CharT>
 static void BM_EstimateLengthTwoByteDE(benchmark::State& state) {

 BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnLow, char);
 BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnHigh, char);
 BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteDoubleColumn, char);
 BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByte, char);
 BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteSingleColumn, char);
 BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteDoubleColumn, char);
 BENCHMARK_TEMPLATE(BM_EstimateLengthFourByte, char);
 
-BENCHMARK_TEMPLATE(BM_EstimateLengthNoMultiByte, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthTwoByteDE, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthTwoBytePL, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnLow, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnHigh, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteDoubleColumn, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByte, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteSingleColumn, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteDoubleColumn, char16_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthFourByte, char16_t);
-
-BENCHMARK_TEMPLATE(BM_EstimateLengthNoMultiByte, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthTwoByteDE, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthTwoBytePL, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnLow, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnHigh, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteDoubleColumn, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByte, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteSingleColumn, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteDoubleColumn, char32_t);
-BENCHMARK_TEMPLATE(BM_EstimateLengthFourByte, char32_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthNoMultiByte, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthTwoByteDE, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthTwoBytePL, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnLow, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteSingleColumnHigh, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByteDoubleColumn, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthThreeByte, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteSingleColumn, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthFourByteDoubleColumn, wchar_t);
+BENCHMARK_TEMPLATE(BM_EstimateLengthFourByte, wchar_t);
 
 int main(int argc, char** argv) {
   benchmark::Initialize(&argc, argv);
   if (benchmark::ReportUnrecognizedArguments(argc, argv))
     return 1;
 
   benchmark::RunSpecifiedBenchmarks();
 }
 #else
 int main(int, char**) { return 0; }
 #endif

libcxx/include/CMakeLists.txt

set(files
   __format/format_string.h
   __format/format_to_n_result.h
   __format/formatter.h
   __format/formatter_bool.h
   __format/formatter_char.h
   __format/formatter_floating_point.h
   __format/formatter_integer.h
   __format/formatter_integral.h
+  __format/formatter_output.h
   __format/formatter_pointer.h
   __format/formatter_string.h
   __format/parser_std_format_spec.h
   __functional/binary_function.h
   __functional/binary_negate.h
   __functional/bind.h
   __functional/bind_back.h
   __functional/bind_front.h

libcxx/include/__format/buffer.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_BUFFER_H
 #define _LIBCPP___FORMAT_BUFFER_H
 
 #include <__algorithm/copy_n.h>
 #include <__algorithm/unwrap_iter.h>
 #include <__config>
 #include <__format/enable_insertable.h>
-#include <__format/formatter.h> // for __char_type TODO FMT Move the concept?
+#include <__format/format_fwd.h> // for __char_type TODO FMT Move the concept?
 #include <__iterator/back_insert_iterator.h>
 #include <__iterator/concepts.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/wrap_iter.h>
 #include <__utility/move.h>
 #include <concepts>
 #include <cstddef>
 #include <type_traits>

libcxx/include/__format/format_context.h

 #ifndef _LIBCPP___FORMAT_FORMAT_CONTEXT_H
 #define _LIBCPP___FORMAT_FORMAT_CONTEXT_H
 
 #include <__availability>
 #include <__config>
 #include <__format/buffer.h>
 #include <__format/format_args.h>
 #include <__format/format_fwd.h>
+#include <__format/formatter.h>
 #include <__iterator/back_insert_iterator.h>
 #include <__iterator/concepts.h>
 #include <concepts>
 
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION
 #include <locale>
 #include <optional>
 #endif

libcxx/include/__format/format_fwd.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_FORMAT_FWD_H
 #define _LIBCPP___FORMAT_FORMAT_FWD_H
 
 #include <__availability>
+#include <__concepts/same_as.h>
 #include <__config>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
 template <class _Context>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT basic_format_arg;
 
 template <class _Context, class... _Args>
 struct _LIBCPP_TEMPLATE_VIS __format_arg_store;
 
-template <class _Tp, class _CharT = char>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter;
+namespace __formatter {
+
+/** The character types that formatters are specialized for. */
+template <class _CharT>
+concept __char_type = same_as<_CharT, char> || same_as<_CharT, wchar_t>;
+
+} // namespace __formatter
 
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FORMAT_FORMAT_FWD_H

libcxx/include/__format/formatter.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_FORMATTER_H
 #define _LIBCPP___FORMAT_FORMATTER_H
 
-#include <__algorithm/copy.h>
-#include <__algorithm/fill_n.h>
-#include <__algorithm/transform.h>
-#include <__assert>
 #include <__availability>
 #include <__config>
-#include <__format/format_error.h>
-#include <__format/format_fwd.h>
-#include <__format/format_string.h>
-#include <__format/parser_std_format_spec.h>
-#include <__utility/move.h>
-#include <__utility/unreachable.h>
-#include <string_view>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
+template <class _Tp, class _CharT = char>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter;
+
 /// The default formatter template.
 ///
 /// [format.formatter.spec]/5
 /// If F is a disabled specialization of formatter, these values are false:
 /// - is_default_constructible_v<F>,
 /// - is_copy_constructible_v<F>,
 /// - is_move_constructible_v<F>,
 /// - is_copy_assignable<F>, and
 /// - is_move_assignable<F>.
 template <class _Tp, class _CharT>
 struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter {
   formatter() = delete;
   formatter(const formatter&) = delete;
   formatter& operator=(const formatter&) = delete;
 };
 
-namespace __format_spec {
-
-_LIBCPP_HIDE_FROM_ABI inline char* __insert_sign(char* __buf, bool __negative,
-                                                 _Flags::_Sign __sign) {
-  if (__negative)
-    *__buf++ = '-';
-  else
-    switch (__sign) {
-    case _Flags::_Sign::__default:
-    case _Flags::_Sign::__minus:
-      // No sign added.
-      break;
-    case _Flags::_Sign::__plus:
-      *__buf++ = '+';
-      break;
-    case _Flags::_Sign::__space:
-      *__buf++ = ' ';
-      break;
-    }
-
-  return __buf;
-}
-
-_LIBCPP_HIDE_FROM_ABI constexpr char __hex_to_upper(char c) {
-  switch (c) {
-  case 'a':
-    return 'A';
-  case 'b':
-    return 'B';
-  case 'c':
-    return 'C';
-  case 'd':
-    return 'D';
-  case 'e':
-    return 'E';
-  case 'f':
-    return 'F';
-  }
-  return c;
-}
-
-} // namespace __format_spec
-
-namespace __formatter {
-
-/** The character types that formatters are specialized for. */
-template <class _CharT>
-concept __char_type = same_as<_CharT, char> || same_as<_CharT, wchar_t>;
-
-struct _LIBCPP_TEMPLATE_VIS __padding_size_result {
-  size_t __before;
-  size_t __after;
-};
-
-_LIBCPP_HIDE_FROM_ABI constexpr __padding_size_result
-__padding_size(size_t __size, size_t __width,
-               __format_spec::_Flags::_Alignment __align) {
-  _LIBCPP_ASSERT(__width > __size,
-                 "Don't call this function when no padding is required");
-  _LIBCPP_ASSERT(
-      __align != __format_spec::_Flags::_Alignment::__default,
-      "Caller should adjust the default to the value required by the type");
-
-  size_t __fill = __width - __size;
-  switch (__align) {
-  case __format_spec::_Flags::_Alignment::__default:
-    __libcpp_unreachable();
-
-  case __format_spec::_Flags::_Alignment::__left:
-    return {0, __fill};
-
-  case __format_spec::_Flags::_Alignment::__center: {
-    // The extra padding is divided per [format.string.std]/3
-    // __before = floor(__fill, 2);
-    // __after = ceil(__fill, 2);
-    size_t __before = __fill / 2;
-    size_t __after = __fill - __before;
-    return {__before, __after};
-  }
-  case __format_spec::_Flags::_Alignment::__right:
-    return {__fill, 0};
-  }
-  __libcpp_unreachable();
-}
-
-/**
- * Writes the input to the output with the required padding.
- *
- * Since the output column width is specified the function can be used for
- * ASCII and Unicode input.
- *
- * @pre [@a __first, @a __last) is a valid range.
- * @pre @a __size <= @a __width. Using this function when this pre-condition
- *      doesn't hold incurs an unwanted overhead.
- *
- * @param __out_it    The output iterator to write to.
- * @param __first     Pointer to the first element to write.
- * @param __last      Pointer beyond the last element to write.
- * @param __size      The (estimated) output column width. When the elements
- *                    to be written are ASCII the following condition holds
- *                    @a __size == @a __last - @a __first.
- * @param __width     The number of output columns to write.
- * @param __fill      The character used for the alignment of the output.
- *                    TODO FMT Will probably change to support Unicode grapheme
- *                    cluster.
- * @param __alignment The requested alignment.
- *
- * @returns           An iterator pointing beyond the last element written.
- *
- * @note The type of the elements in range [@a __first, @a __last) can differ
- * from the type of @a __fill. Integer output uses @c std::to_chars for its
- * conversion, which means the [@a __first, @a __last) always contains elements
- * of the type @c char.
- */
-template <class _CharT, class _Fill>
-_LIBCPP_HIDE_FROM_ABI auto
-__write(output_iterator<const _CharT&> auto __out_it, const _CharT* __first,
-        const _CharT* __last, size_t __size, size_t __width, _Fill __fill,
-        __format_spec::_Flags::_Alignment __alignment) -> decltype(__out_it) {
-
-  _LIBCPP_ASSERT(__first <= __last, "Not a valid range");
-  _LIBCPP_ASSERT(__size < __width, "Precondition failure");
-
-  __padding_size_result __padding =
-      __padding_size(__size, __width, __alignment);
-  __out_it = _VSTD::fill_n(_VSTD::move(__out_it), __padding.__before, __fill);
-  __out_it = _VSTD::copy(__first, __last, _VSTD::move(__out_it));
-  return _VSTD::fill_n(_VSTD::move(__out_it), __padding.__after, __fill);
-}
-
-/**
- * @overload
- *
- * Writes additional zero's for the precision before the exponent.
- * This is used when the precision requested in the format string is larger
- * than the maximum precision of the floating-point type. These precision
- * digits are always 0.
- *
- * @param __exponent           The location of the exponent character.
- * @param __num_trailing_zeros The number of 0's to write before the exponent
- *                             character.
- */
-template <class _CharT, class _Fill>
-_LIBCPP_HIDE_FROM_ABI auto __write(output_iterator<const _CharT&> auto __out_it, const _CharT* __first,
-                                   const _CharT* __last, size_t __size, size_t __width, _Fill __fill,
-                                   __format_spec::_Flags::_Alignment __alignment, const _CharT* __exponent,
-                                   size_t __num_trailing_zeros) -> decltype(__out_it) {
-  _LIBCPP_ASSERT(__first <= __last, "Not a valid range");
-  _LIBCPP_ASSERT(__num_trailing_zeros > 0, "The overload not writing trailing zeros should have been used");
-
-  __padding_size_result __padding = __padding_size(__size + __num_trailing_zeros, __width, __alignment);
-  __out_it = _VSTD::fill_n(_VSTD::move(__out_it), __padding.__before, __fill);
-  __out_it = _VSTD::copy(__first, __exponent, _VSTD::move(__out_it));
-  __out_it = _VSTD::fill_n(_VSTD::move(__out_it), __num_trailing_zeros, _CharT('0'));
-  __out_it = _VSTD::copy(__exponent, __last, _VSTD::move(__out_it));
-  return _VSTD::fill_n(_VSTD::move(__out_it), __padding.__after, __fill);
-}
-
-/**
- * @overload
- *
- * Uses a transformation operation before writing an element.
- *
- * TODO FMT Fill will probably change to support Unicode grapheme cluster.
- */
-template <class _CharT, class _UnaryOperation, class _Fill>
-_LIBCPP_HIDE_FROM_ABI auto
-__write(output_iterator<const _CharT&> auto __out_it, const _CharT* __first,
-        const _CharT* __last, size_t __size, _UnaryOperation __op,
-        size_t __width, _Fill __fill,
-        __format_spec::_Flags::_Alignment __alignment) -> decltype(__out_it) {
-
-  _LIBCPP_ASSERT(__first <= __last, "Not a valid range");
-  _LIBCPP_ASSERT(__size < __width, "Precondition failure");
-
-  __padding_size_result __padding =
-      __padding_size(__size, __width, __alignment);
-  __out_it = _VSTD::fill_n(_VSTD::move(__out_it), __padding.__before, __fill);
-  __out_it = _VSTD::transform(__first, __last, _VSTD::move(__out_it), __op);
-  return _VSTD::fill_n(_VSTD::move(__out_it), __padding.__after, __fill);
-}
-
-/**
- * Writes Unicode input to the output with the required padding.
- *
- * This function does almost the same as the @ref __write function, but handles
- * the width estimation of the Unicode input.
- *
- * @param __str       The range [@a __first, @a __last).
- * @param __precision The width to truncate the input string to, use @c -1 for
- *                     no limit.
- */
-template <class _CharT, class _Fill>
-_LIBCPP_HIDE_FROM_ABI auto
-__write_unicode(output_iterator<const _CharT&> auto __out_it,
-                basic_string_view<_CharT> __str, ptrdiff_t __width,
-                ptrdiff_t __precision, _Fill __fill,
-                __format_spec::_Flags::_Alignment __alignment)
-    -> decltype(__out_it) {
-
-  // This value changes when there Unicode column width limits the output
-  // size.
-  auto __last = __str.end();
-  if (__width != 0 || __precision != -1) {
-    __format_spec::__string_alignment<_CharT> __format_traits =
-        __format_spec::__get_string_alignment(__str.begin(), __str.end(),
-                                              __width, __precision);
-
-    if (__format_traits.__align)
-      return __write(_VSTD::move(__out_it), __str.begin(),
-                     __format_traits.__last, __format_traits.__size, __width,
-                     __fill, __alignment);
-
-    // No alignment required update the output based on the precision.
-    // This might be the same as __str.end().
-    __last = __format_traits.__last;
-  }
-
-  // Copy the input to the output. The output size might be limited by the
-  // precision.
-  return _VSTD::copy(__str.begin(), __last, _VSTD::move(__out_it));
-}
-
-} // namespace __formatter
-
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FORMAT_FORMATTER_H
+

libcxx/include/__format/formatter_bool.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_FORMATTER_BOOL_H
 #define _LIBCPP___FORMAT_FORMATTER_BOOL_H
 
+#include <__assert>
 #include <__availability>
 #include <__config>
-#include <__format/format_error.h>
 #include <__format/format_fwd.h>
+#include <__format/format_parse_context.h>
 #include <__format/formatter.h>
 #include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
 #include <__format/parser_std_format_spec.h>
-#include <string_view>
-
-#ifndef _LIBCPP_HAS_NO_LOCALIZATION
-#include <locale>
-#endif
+#include <__utility/unreachable.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
-namespace __format_spec {
-
-template <class _CharT>
-class _LIBCPP_TEMPLATE_VIS __parser_bool : public __parser_integral<_CharT> {
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<bool, _CharT> {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(auto& __parse_ctx)
+  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
       -> decltype(__parse_ctx.begin()) {
-    auto __it = __parser_integral<_CharT>::__parse(__parse_ctx);
+    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_integral);
+    __format_spec::__process_parsed_bool(__parser_);
+    return __result;
+  }
 
-    switch (this->__type) {
-    case _Flags::_Type::__default:
-      this->__type = _Flags::_Type::__string;
-      [[fallthrough]];
-    case _Flags::_Type::__string:
-      this->__handle_bool();
-      break;
-
-    case _Flags::_Type::__binary_lower_case:
-    case _Flags::_Type::__binary_upper_case:
-    case _Flags::_Type::__octal:
-    case _Flags::_Type::__decimal:
-    case _Flags::_Type::__hexadecimal_lower_case:
-    case _Flags::_Type::__hexadecimal_upper_case:
-      this->__handle_integer();
-      break;
+  _LIBCPP_HIDE_FROM_ABI auto format(bool __value, auto& __ctx) const -> decltype(__ctx.out()) {
+    switch (__parser_.__type_) {
+    case __format_spec::__type::__string:
+      return __formatter::__format_bool(__value, __ctx, __parser_.__resolve_dynamic_sizes(__ctx));
+
+    case __format_spec::__type::__binary_lower_case:
+    case __format_spec::__type::__binary_upper_case:
+    case __format_spec::__type::__octal:
+    case __format_spec::__type::__decimal:
+    case __format_spec::__type::__hexadecimal_lower_case:
+    case __format_spec::__type::__hexadecimal_upper_case:
+      // Casting this to a formatter more likely being used reduces the binary size.
+      return __formatter::__format_integer(static_cast<unsigned >(__value), __ctx,
+                                           __parser_.__resolve_dynamic_sizes(__ctx));
 
     default:
-      __throw_format_error(
-          "The format-spec type has a type not supported for a bool argument");
+      _LIBCPP_ASSERT(false, "The parse function should have validated the type");
+      __libcpp_unreachable();
     }
-
-    return __it;
   }
-};
-
-template <class _CharT>
-struct _LIBCPP_TEMPLATE_VIS __bool_strings;
 
-template <>
-struct _LIBCPP_TEMPLATE_VIS __bool_strings<char> {
-  static constexpr string_view __true{"true"};
-  static constexpr string_view __false{"false"};
-};
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <>
-struct _LIBCPP_TEMPLATE_VIS __bool_strings<wchar_t> {
-  static constexpr wstring_view __true{L"true"};
-  static constexpr wstring_view __false{L"false"};
-};
-#endif
-
-template <class _CharT>
-using __formatter_bool = __formatter_integral<__parser_bool<_CharT>>;
-
-} //namespace __format_spec
-
-// [format.formatter.spec]/2.3
-// For each charT, for each cv-unqualified arithmetic type ArithmeticT other
-// than char, wchar_t, char8_t, char16_t, or char32_t, a specialization
-
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<bool, _CharT>
-    : public __format_spec::__formatter_bool<_CharT> {
-  using _Base = __format_spec::__formatter_bool<_CharT>;
-
-  _LIBCPP_HIDE_FROM_ABI auto format(bool __value, auto& __ctx)
-      -> decltype(__ctx.out()) {
-    if (this->__type != __format_spec::_Flags::_Type::__string)
-      return _Base::format(static_cast<unsigned char>(__value), __ctx);
-
-    if (this->__width_needs_substitution())
-      this->__substitute_width_arg_id(__ctx.arg(this->__width));
-
-#ifndef _LIBCPP_HAS_NO_LOCALIZATION
-    if (this->__locale_specific_form) {
-      const auto& __np = use_facet<numpunct<_CharT>>(__ctx.locale());
-      basic_string<_CharT> __str = __value ? __np.truename() : __np.falsename();
-      return __formatter::__write_unicode(
-          __ctx.out(), basic_string_view<_CharT>{__str}, this->__width, -1,
-          this->__fill, this->__alignment);
-    }
-#endif
-    basic_string_view<_CharT> __str =
-        __value ? __format_spec::__bool_strings<_CharT>::__true
-                : __format_spec::__bool_strings<_CharT>::__false;
-
-    // The output only uses ASCII so every character is one column.
-    unsigned __size = __str.size();
-    if (__size >= this->__width)
-      return _VSTD::copy(__str.begin(), __str.end(), __ctx.out());
-
-    return __formatter::__write(__ctx.out(), __str.begin(), __str.end(), __size,
-                                this->__width, this->__fill, this->__alignment);
-  }
+  __format_spec::__parser<_CharT> __parser_;
 };
 
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FORMAT_FORMATTER_BOOL_H

libcxx/include/__format/formatter_char.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_FORMATTER_CHAR_H
 #define _LIBCPP___FORMAT_FORMATTER_CHAR_H
 
 #include <__availability>
+#include <__concepts/same_as.h>
 #include <__config>
-#include <__format/format_error.h>
 #include <__format/format_fwd.h>
+#include <__format/format_parse_context.h>
 #include <__format/formatter.h>
 #include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
 #include <__format/parser_std_format_spec.h>
+#include <type_traits> // is_signed_v
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
-namespace __format_spec {
-
-template <class _CharT>
-class _LIBCPP_TEMPLATE_VIS __parser_char : public __parser_integral<_CharT> {
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __formatter_char {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(auto& __parse_ctx)
+  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
       -> decltype(__parse_ctx.begin()) {
-    auto __it = __parser_integral<_CharT>::__parse(__parse_ctx);
-
-    switch (this->__type) {
-    case _Flags::_Type::__default:
-      this->__type = _Flags::_Type::__char;
-      [[fallthrough]];
-    case _Flags::_Type::__char:
-      this->__handle_char();
-      break;
-
-    case _Flags::_Type::__binary_lower_case:
-    case _Flags::_Type::__binary_upper_case:
-    case _Flags::_Type::__octal:
-    case _Flags::_Type::__decimal:
-    case _Flags::_Type::__hexadecimal_lower_case:
-    case _Flags::_Type::__hexadecimal_upper_case:
-      this->__handle_integer();
-      break;
-
-    default:
-      __throw_format_error(
-          "The format-spec type has a type not supported for a char argument");
-    }
+    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_integral);
+    __format_spec::__process_parsed_char(__parser_);
+    return __result;
 
-    return __it;
+  _LIBCPP_HIDE_FROM_ABI auto format(_CharT __value, auto& __ctx) const -> decltype(__ctx.out()) {
+    if (__parser_.__type_ == __format_spec::__type::__char)
+      return __formatter::__format_char(__value, __ctx.out(), __parser_.__resolve_dynamic_sizes(__ctx));
+
+    if constexpr (sizeof(_CharT) <= sizeof(int)) {
+      // Promotes _CharT to an integral type. This reduces the number of
+      // instantiations of __format_integer reducing code size.
+      if constexpr (is_signed_v<_CharT>)
+        return __formatter::__format_integer(static_cast<int>(__value), __ctx,
+                                             __parser_.__resolve_dynamic_sizes(__ctx));
+      else
+        return __formatter::__format_integer(static_cast<unsigned>(__value), __ctx,
+                                             __parser_.__resolve_dynamic_sizes(__ctx));
+    } else
+      return __formatter::__format_integer(__value, __ctx, __parser_.__resolve_dynamic_sizes(__ctx));
   }
-};
 
-template <class _CharT>
-using __formatter_char = __formatter_integral<__parser_char<_CharT>>;
-
-} // namespace __format_spec
+  _LIBCPP_HIDE_FROM_ABI auto format(char __value, auto& __ctx) const -> decltype(__ctx.out())
+    requires(same_as<_CharT, wchar_t>)
+  {
+    return format(static_cast<wchar_t>(__value), __ctx);
+  }
 
-// [format.formatter.spec]/2.1 The specializations
+  __format_spec::__parser<_CharT> __parser_;
+};
 
 template <>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<char, char>
-    : public __format_spec::__formatter_char<char> {};
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<char, char> : public __formatter_char<char> {};
 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+#    ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
 template <>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<char, wchar_t>
-    : public __format_spec::__formatter_char<wchar_t> {
-  using _Base = __format_spec::__formatter_char<wchar_t>;
-
-  _LIBCPP_HIDE_FROM_ABI auto format(char __value, auto& __ctx)
-      -> decltype(__ctx.out()) {
-    return _Base::format(static_cast<wchar_t>(__value), __ctx);
-  }
-};
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<char, wchar_t> : public __formatter_char<wchar_t> {};
 
 template <>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<wchar_t, wchar_t>
-    : public __format_spec::__formatter_char<wchar_t> {};
-#endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<wchar_t, wchar_t> : public __formatter_char<wchar_t> {
+};
+
+#    endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
 
+
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FORMAT_FORMATTER_CHAR_H

libcxx/include/__format/formatter_floating_point.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_FORMATTER_FLOATING_POINT_H
 #define _LIBCPP___FORMAT_FORMATTER_FLOATING_POINT_H
 
-#include <__algorithm/copy.h>
-#include <__algorithm/copy_n.h>
-#include <__algorithm/fill_n.h>
 #include <__algorithm/find.h>
 #include <__algorithm/min.h>
 #include <__algorithm/rotate.h>
 #include <__algorithm/transform.h>
-#include <__assert>
-#include <__concepts/arithmetic.h>
 #include <__config>
-#include <__format/format_error.h>
 #include <__format/format_fwd.h>
-#include <__format/format_string.h>
+#include <__format/format_parse_context.h>
 #include <__format/formatter.h>
 #include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
 #include <__format/parser_std_format_spec.h>
-#include <__utility/move.h>
+#include <__memory/allocator.h>
 #include <__utility/unreachable.h>
 #include <charconv>
-#include <cmath>
 
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION
 #  include <locale>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
-namespace __format_spec {
+namespace __formatter {
 
 template <floating_point _Tp>
 _LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value) {
   to_chars_result __r = _VSTD::to_chars(__first, __last, __value);
   _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
   return __r.ptr;
 }
 
explicit _LIBCPP_HIDE_FROM_ABI __float_buffer(int __precision)
     //   - wchar_t: same argument as char, but additional std::copy won't work.
     //     The input is always a char buffer, so every char in the buffer needs
     //     to be converted from a char to a wchar_t.
     if (__precision_ > _Traits::__max_fractional) {
       __num_trailing_zeros_ = __precision_ - _Traits::__max_fractional;
       __precision_ = _Traits::__max_fractional;
     }
 
-    __size_ = __format_spec::__float_buffer_size<_Fp>(__precision_);
+    __size_ = __formatter::__float_buffer_size<_Fp>(__precision_);
     if (__size_ > _Traits::__stack_buffer_size)
       // The allocated buffer's contents don't need initialization.
       __begin_ = allocator<char>{}.allocate(__size_);
     else
       __begin_ = __buffer_;
   }
 
   _LIBCPP_HIDE_FROM_ABI ~__float_buffer() {
constexpr inline _LIBCPP_HIDE_FROM_ABI char* __find_exponent(char* __first, char* __last) {
   return __last;
 }
 
 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_default(const __float_buffer<_Fp>& __buffer, _Tp __value,
                                                              char* __integral) {
   __float_result __result;
   __result.__integral = __integral;
-  __result.__last = __format_spec::__to_buffer(__integral, __buffer.end(), __value);
+  __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value);
 
-  __result.__exponent = __format_spec::__find_exponent(__result.__integral, __result.__last);
+  __result.__exponent = __formatter::__find_exponent(__result.__integral, __result.__last);
 
   // Constrains:
   // - There's at least one decimal digit before the radix point.
   // - The radix point, when present, is placed before the exponent.
   __result.__radix_point = _VSTD::find(__result.__integral + 1, __result.__exponent, '.');
 
   // When the radix point isn't found its position is the exponent instead of
   // __result.__last.

 
 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_hexadecimal_lower_case(const __float_buffer<_Fp>& __buffer,
                                                                             _Tp __value, int __precision,
                                                                             char* __integral) {
   __float_result __result;
   __result.__integral = __integral;
   if (__precision == -1)
-    __result.__last = __format_spec::__to_buffer(__integral, __buffer.end(), __value, chars_format::hex);
+    __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::hex);
   else
-    __result.__last = __format_spec::__to_buffer(__integral, __buffer.end(), __value, chars_format::hex, __precision);
+    __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::hex, __precision);
 
   // H = one or more hex-digits
   // S = sign
   // D = one or more decimal-digits
   // When the fractional part is zero and no precision the output is 0p+0
   // else the output is                                              0.HpSD
   // So testing the second position can differentiate between these two cases.
   char* __first = __integral + 1;
_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_hexadecimal_lower_case(const __float_buffer<_Fp>& __buffer,
   return __result;
 }
 
 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_hexadecimal_upper_case(const __float_buffer<_Fp>& __buffer,
                                                                             _Tp __value, int __precision,
                                                                             char* __integral) {
   __float_result __result =
-      __format_spec::__format_buffer_hexadecimal_lower_case(__buffer, __value, __precision, __integral);
+      __formatter::__format_buffer_hexadecimal_lower_case(__buffer, __value, __precision, __integral);
   _VSTD::transform(__result.__integral, __result.__exponent, __result.__integral, __hex_to_upper);
   *__result.__exponent = 'P';
   return __result;
 }
 
 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_scientific_lower_case(const __float_buffer<_Fp>& __buffer,
                                                                            _Tp __value, int __precision,
                                                                            char* __integral) {
   __float_result __result;
   __result.__integral = __integral;
   __result.__last =
-      __format_spec::__to_buffer(__integral, __buffer.end(), __value, chars_format::scientific, __precision);
+      __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::scientific, __precision);
 
   char* __first = __integral + 1;
   _LIBCPP_ASSERT(__first != __result.__last, "No exponent present");
   if (*__first == '.') {
     __result.__radix_point = __first;
-    __result.__exponent = __format_spec::__find_exponent(__first + 1, __result.__last);
+    __result.__exponent = __formatter::__find_exponent(__first + 1, __result.__last);
   } else {
     __result.__radix_point = __result.__last;
     __result.__exponent = __first;
   }
 
   // clang-format off
   _LIBCPP_ASSERT((__result.__integral != __result.__last) &&
                  (__result.__radix_point == __result.__last || *__result.__radix_point == '.') &&
                  (__result.__exponent != __result.__last && *__result.__exponent == 'e'),
                  "Post-condition failure.");
   // clang-format on
   return __result;
 }
 
 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_scientific_upper_case(const __float_buffer<_Fp>& __buffer,
                                                                            _Tp __value, int __precision,
                                                                            char* __integral) {
   __float_result __result =
-      __format_spec::__format_buffer_scientific_lower_case(__buffer, __value, __precision, __integral);
+      __formatter::__format_buffer_scientific_lower_case(__buffer, __value, __precision, __integral);
   *__result.__exponent = 'E';
   return __result;
 }
 
 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_fixed(const __float_buffer<_Fp>& __buffer, _Tp __value,
                                                            int __precision, char* __integral) {
   __float_result __result;
   __result.__integral = __integral;
-  __result.__last = __format_spec::__to_buffer(__integral, __buffer.end(), __value, chars_format::fixed, __precision);
+  __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::fixed, __precision);
 
   // When there's no precision there's no radix point.
   // Else the radix point is placed at __precision + 1 from the end.
   // By converting __precision to a bool the subtraction can be done
   // unconditionally.
   __result.__radix_point = __result.__last - (__precision + bool(__precision));
   __result.__exponent = __result.__last;
 

 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_general_lower_case(__float_buffer<_Fp>& __buffer, _Tp __value,
                                                                         int __precision, char* __integral) {
 
   __buffer.__remove_trailing_zeros();
 
   __float_result __result;
   __result.__integral = __integral;
-  __result.__last = __format_spec::__to_buffer(__integral, __buffer.end(), __value, chars_format::general, __precision);
+  __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::general, __precision);
 
   char* __first = __integral + 1;
   if (__first == __result.__last) {
     __result.__radix_point = __result.__last;
     __result.__exponent = __result.__last;
   } else {
-    __result.__exponent = __format_spec::__find_exponent(__first, __result.__last);
+    __result.__exponent = __formatter::__find_exponent(__first, __result.__last);
     if (__result.__exponent != __result.__last)
       // In scientific mode if there's a radix point it will always be after
       // the first digit. (This is the position __first points at).
       __result.__radix_point = *__first == '.' ? __first : __result.__last;
     else {
       // In fixed mode the algorithm truncates trailing spaces and possibly the
       // radix point. There's no good guess for the position of the radix point
       // therefore scan the output after the first digit.
_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_general_lower_case(__float_buffer<_Fp>& __buffer, _Tp __value,
   // clang-format on
 
   return __result;
 }
 
 template <class _Fp, class _Tp>
 _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_general_upper_case(__float_buffer<_Fp>& __buffer, _Tp __value,
                                                                         int __precision, char* __integral) {
-  __float_result __result =
-      __format_spec::__format_buffer_general_lower_case(__buffer, __value, __precision, __integral);
+  __float_result __result = __formatter::__format_buffer_general_lower_case(__buffer, __value, __precision, __integral);
   if (__result.__exponent != __result.__last)
     *__result.__exponent = 'E';
   return __result;
 }
 
+/// Fills the buffer with the data based on the requested formatting.
+///
+/// This function, when needed, turns the characters to upper case and
+/// determines the "interesting" locations which are returned to the caller.
+///
+/// This means the caller never has to convert the contents of the buffer to
+/// upper case or search for radix points and the location of the exponent.
+/// This gives a bit of overhead. The original code didn't do that, but due
+/// to the number of possible additional work needed to turn this number to
+/// the proper output the code was littered with tests for upper cases and
+/// searches for radix points and exponents.
+/// - When a precision larger than the type's precision is selected
+///   additional zero characters need to be written before the exponent.
+/// - alternate form needs to add a radix point when not present.
+/// - localization needs to do grouping in the integral part.
+template <class _Fp, class _Tp>
+// TODO FMT _Fp should just be _Tp when to_chars has proper long double support.
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer(__float_buffer<_Fp>& __buffer, _Tp __value, bool __negative,
+                                                     bool __has_precision, __format_spec::__sign __sign,
+                                                     __format_spec::__type __type) {
+  char* __first = __insert_sign(__buffer.begin(), __negative, __sign);
+  switch (__type) {
+  case __format_spec::__type::__default:
+    return __formatter::__format_buffer_default(__buffer, __value, __first);
+
+  case __format_spec::__type::__float_hexadecimal_lower_case:
+    return __formatter::__format_buffer_hexadecimal_lower_case(__buffer, __value,
+                                                               __has_precision ? __buffer.__precision() : -1, __first);
+
+  case __format_spec::__type::__float_hexadecimal_upper_case:
+    return __formatter::__format_buffer_hexadecimal_upper_case(__buffer, __value,
+                                                               __has_precision ? __buffer.__precision() : -1, __first);
+
+  case __format_spec::__type::__scientific_lower_case:
+    return __formatter::__format_buffer_scientific_lower_case(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__scientific_upper_case:
+    return __formatter::__format_buffer_scientific_upper_case(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__fixed_lower_case:
+  case __format_spec::__type::__fixed_upper_case:
+    return __formatter::__format_buffer_fixed(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__general_lower_case:
+    return __formatter::__format_buffer_general_lower_case(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__general_upper_case:
+    return __formatter::__format_buffer_general_upper_case(__buffer, __value, __buffer.__precision(), __first);
+
+  default:
+    _LIBCPP_ASSERT(false, "The parser should have validated the type");
+    __libcpp_unreachable();
+  }
+}
+
 #    ifndef _LIBCPP_HAS_NO_LOCALIZATION
 template <class _OutIt, class _Fp, class _CharT>
 _LIBCPP_HIDE_FROM_ABI _OutIt __format_locale_specific_form(_OutIt __out_it, const __float_buffer<_Fp>& __buffer,
                                                            const __float_result& __result, _VSTD::locale __loc,
-                                                           size_t __width, _Flags::_Alignment __alignment,
-                                                           _CharT __fill) {
+                                                           __format_spec::__parser<_CharT> __parser) {
   const auto& __np = use_facet<numpunct<_CharT>>(__loc);
   string __grouping = __np.grouping();
   char* __first = __result.__integral;
   // When no radix point or exponent are present __last will be __result.__last.
   char* __last = _VSTD::min(__result.__radix_point, __result.__exponent);
 
   ptrdiff_t __digits = __last - __first;
   if (!__grouping.empty()) {
     if (__digits <= __grouping[0])
       __grouping.clear();
     else
-      __grouping = __determine_grouping(__digits, __grouping);
+      __grouping = __formatter::__determine_grouping(__digits, __grouping);
   }
 
-  size_t __size = __result.__last - __buffer.begin() + // Formatted string
+  ptrdiff_t __size = __result.__last - __buffer.begin() + // Formatted string
                      __buffer.__num_trailing_zeros() +    // Not yet rendered zeros
                      __grouping.size() -                  // Grouping contains one
                      !__grouping.empty();                 // additional character
 
   __formatter::__padding_size_result __padding = {0, 0};
-  bool __zero_padding = __alignment == _Flags::_Alignment::__default;
-  if (__size < __width) {
+  bool __zero_padding = __parser.__alignment_ == __format_spec::__alignment::__default;
+  if (__size < __parser.__width_) {
     if (__zero_padding) {
-      __alignment = _Flags::_Alignment::__right;
-      __fill = _CharT('0');
+      __parser.__alignment_ = __format_spec::__alignment::__right;
+      __parser.__fill_ = _CharT('0');
     }
 
-    __padding = __formatter::__padding_size(__size, __width, __alignment);
+    __padding = __padding_size(__size, __parser.__width_, __parser.__alignment_);
   }
 
   // sign and (zero padding or alignment)
   if (__zero_padding && __first != __buffer.begin())
     *__out_it++ = *__buffer.begin();
-  __out_it = _VSTD::fill_n(_VSTD::move(__out_it), __padding.__before, __fill);
+  __out_it = _VSTD::fill_n(_VSTD::move(__out_it), __padding.__before_, __parser.__fill_);
   if (!__zero_padding && __first != __buffer.begin())
     *__out_it++ = *__buffer.begin();
 
   // integral part
   if (__grouping.empty()) {
     __out_it = _VSTD::copy_n(__first, __digits, _VSTD::move(__out_it));
   } else {
     auto __r = __grouping.rbegin();
if (__result.__radix_point != __result.__last) {
     __out_it = _VSTD::fill_n(_VSTD::move(__out_it), __buffer.__num_trailing_zeros(), _CharT('0'));
   }
 
   // exponent
   if (__result.__exponent != __result.__last)
     __out_it = _VSTD::copy(__result.__exponent, __result.__last, _VSTD::move(__out_it));
 
   // alignment
-  return _VSTD::fill_n(_VSTD::move(__out_it), __padding.__after, __fill);
+  return _VSTD::fill_n(_VSTD::move(__out_it), __padding.__after_, __parser.__fill_);
 }
-
 #    endif // _LIBCPP_HAS_NO_LOCALIZATION
 
-template <__formatter::__char_type _CharT>
-class _LIBCPP_TEMPLATE_VIS __formatter_floating_point : public __parser_floating_point<_CharT> {
-public:
-  template <floating_point _Tp>
-  _LIBCPP_HIDE_FROM_ABI auto format(_Tp __value, auto& __ctx) -> decltype(__ctx.out()) {
-    if (this->__width_needs_substitution())
-      this->__substitute_width_arg_id(__ctx.arg(this->__width));
+template <class _OutIt, class _CharT>
+_LIBCPP_HIDE_FROM_ABI _OutIt __format_floating_point_non_finite(_OutIt __out_it,
+                                                                __format_spec::__parser<_CharT> __parser,
+                                                                bool __negative, bool __isnan) {
+  char __buffer[4];
+  char* __last = __formatter::__insert_sign(__buffer, __negative, __parser.__sign_);
+
+  // to_chars can return inf, infinity, nan, and nan(n-char-sequence).
+  // The format library requires inf and nan.
+  // All in one expression to avoid dangling references.
+  __last =
+      _VSTD::copy_n(&("infnanINFNAN"[6 * (__parser.__type_ == __format_spec::__type::__float_hexadecimal_upper_case ||
+                                          __parser.__type_ == __format_spec::__type::__scientific_upper_case ||
+                                          __parser.__type_ == __format_spec::__type::__fixed_upper_case ||
+                                          __parser.__type_ == __format_spec::__type::__general_upper_case) +
+                                     3 * __isnan]),
+                    3, __last);
+
+  // [format.string.std]/13
+  // A zero (0) character preceding the width field pads the field with
+  // leading zeros (following any indication of sign or base) to the field
+  // width, except when applied to an infinity or NaN.
+  if (__parser.__alignment_ == __format_spec::__alignment::__default)
+    __parser.__alignment_ = __format_spec::__alignment::__right;
+
+  return __formatter::__write(__buffer, __last, _VSTD::move(__out_it), __parser);
+}
+
+template <floating_point _Tp, class _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __format_floating_point(_Tp __value, auto& __ctx, __format_spec::__parser<_CharT> __parser)
+    -> decltype(__ctx.out()) {
 
-    bool __negative = _VSTD::signbit(__value);
 
-    if (!_VSTD::isfinite(__value)) [[unlikely]]
-      return __format_non_finite(__ctx.out(), __negative, _VSTD::isnan(__value));
-
-    bool __has_precision = this->__has_precision_field();
-    if (this->__precision_needs_substitution())
-      this->__substitute_precision_arg_id(__ctx.arg(this->__precision));
+    return __formatter::__format_floating_point_non_finite(__ctx.out(), __parser, __negative, _VSTD::isnan(__value));
 
-    // Depending on the std-format-spec string the sign and the value
-    // might not be outputted together:
-    // - zero-padding may insert additional '0' characters.
-    // Therefore the value is processed as a non negative value.
-    // The function @ref __insert_sign will insert a '-' when the value was
-    // negative.
 
-    if (__negative)
-      __value = _VSTD::copysign(__value, +1.0);
+    __value = -__value;
 
-    // TODO FMT _Fp should just be _Tp when to_chars has proper long double support.
-    using _Fp = conditional_t<same_as<_Tp, long double>, double, _Tp>;
-    // Force the type of the precision to avoid -1 to become an unsigned value.
-    __float_buffer<_Fp> __buffer(__has_precision ? int(this->__precision) : -1);
-    __float_result __result = __format_buffer(__buffer, __value, __negative, __has_precision);
+  __float_buffer<_Fp> __buffer(__parser.__precision_);
+  __float_result __result = __formatter::__format_buffer(__buffer, __value, __negative, (__parser.__has_precision()),
+                                                         __parser.__sign_, __parser.__type_);
 
-    if (this->__alternate_form && __result.__radix_point == __result.__last) {
-      *__result.__last++ = '.';
+  if (__parser.__alternate_form_ && __result.__radix_point == __result.__last) {
 
-      // When there is an exponent the point needs to be moved before the
-      // exponent. When there's no exponent the rotate does nothing. Since
-      // rotate tests whether the operation is a nop, call it unconditionally.
-      _VSTD::rotate(__result.__exponent, __result.__last - 1, __result.__last);
-      __result.__radix_point = __result.__exponent;
 
-      // The radix point is always placed before the exponent.
-      // - No exponent needs to point to the new last.
-      // - An exponent needs to move one position to the right.
-      // So it's safe to increment the value unconditionally.
-      ++__result.__exponent;
-    }
 
 #    ifndef _LIBCPP_HAS_NO_LOCALIZATION
-    if (this->__locale_specific_form)
-      return __format_spec::__format_locale_specific_form(__ctx.out(), __buffer, __result, __ctx.locale(),
-                                                          this->__width, this->__alignment, this->__fill);
+  if (__parser.__locale_specific_form_)
+    return __formatter::__format_locale_specific_form(__ctx.out(), __buffer, __result, __ctx.locale(), __parser);
 #    endif
 
-    ptrdiff_t __size = __result.__last - __buffer.begin();
-    int __num_trailing_zeros = __buffer.__num_trailing_zeros();
-    if (__size + __num_trailing_zeros >= this->__width) {
-      if (__num_trailing_zeros && __result.__exponent != __result.__last)
-        // Insert trailing zeros before exponent character.
-        return _VSTD::copy(__result.__exponent, __result.__last,
-                           _VSTD::fill_n(_VSTD::copy(__buffer.begin(), __result.__exponent, __ctx.out()),
-                                         __num_trailing_zeros, _CharT('0')));
+  if (__size + __num_trailing_zeros >= __parser.__width_) {
 
-      return _VSTD::fill_n(_VSTD::copy(__buffer.begin(), __result.__last, __ctx.out()), __num_trailing_zeros,
-                           _CharT('0'));
-    }
 
-    auto __out_it = __ctx.out();
-    char* __first = __buffer.begin();
-    if (this->__alignment == _Flags::_Alignment::__default) {
-      // When there is a sign output it before the padding. Note the __size
-      // doesn't need any adjustment, regardless whether the sign is written
-      // here or in __formatter::__write.
-      if (__first != __result.__integral)
-        *__out_it++ = *__first++;
-      // After the sign is written, zero padding is the same a right alignment
-      // with '0'.
-      this->__alignment = _Flags::_Alignment::__right;
-      this->__fill = _CharT('0');
-    }
+  if (__parser.__alignment_ == __format_spec::__alignment ::__default) {
+    __parser.__alignment_ = __format_spec::__alignment::__right;
+    __parser.__fill_ = _CharT('0');
 
-    if (__num_trailing_zeros)
-      return __formatter::__write(_VSTD::move(__out_it), __first, __result.__last, __size, this->__width, this->__fill,
-                                  this->__alignment, __result.__exponent, __num_trailing_zeros);
+    return __formatter::__write_using_trailing_zeros(__first, __result.__last, _VSTD::move(__out_it), __parser, __size,
+                                                     __result.__exponent, __num_trailing_zeros);
 
-    return __formatter::__write(_VSTD::move(__out_it), __first, __result.__last, __size, this->__width, this->__fill,
-                                this->__alignment);
-  }
+  return __formatter::__write(__first, __result.__last, _VSTD::move(__out_it), __parser, __size);
 
-private:
-  template <class _OutIt>
-  _LIBCPP_HIDE_FROM_ABI _OutIt __format_non_finite(_OutIt __out_it, bool __negative, bool __isnan) {
-    char __buffer[4];
-    char* __last = __insert_sign(__buffer, __negative, this->__sign);
-
-    // to_char can return inf, infinity, nan, and nan(n-char-sequence).
-    // The format library requires inf and nan.
-    // All in one expression to avoid dangling references.
-    __last = _VSTD::copy_n(&("infnanINFNAN"[6 * (this->__type == _Flags::_Type::__float_hexadecimal_upper_case ||
-                                                 this->__type == _Flags::_Type::__scientific_upper_case ||
-                                                 this->__type == _Flags::_Type::__fixed_upper_case ||
-                                                 this->__type == _Flags::_Type::__general_upper_case) +
-                                            3 * __isnan]),
-                           3, __last);
+} // namespace __formatter
 
-    // [format.string.std]/13
-    // A zero (0) character preceding the width field pads the field with
-    // leading zeros (following any indication of sign or base) to the field
-    // width, except when applied to an infinity or NaN.
-    if (this->__alignment == _Flags::_Alignment::__default)
-      this->__alignment = _Flags::_Alignment::__right;
-
-    ptrdiff_t __size = __last - __buffer;
-    if (__size >= this->__width)
-      return _VSTD::copy_n(__buffer, __size, _VSTD::move(__out_it));
-
-    return __formatter::__write(_VSTD::move(__out_it), __buffer, __last, __size, this->__width, this->__fill,
-                                this->__alignment);
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS __formatter_floating_point {
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
+      -> decltype(__parse_ctx.begin()) {
+    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_floating_point);
+    __format_spec::__process_parsed_floating_point(__parser_);
+    return __result;
   }
 
-  /// Fills the buffer with the data based on the requested formatting.
-  ///
-  /// This function, when needed, turns the characters to upper case and
-  /// determines the "interesting" locations which are returned to the caller.
-  ///
-  /// This means the caller never has to convert the contents of the buffer to
-  /// upper case or search for radix points and the location of the exponent.
-  /// This gives a bit of overhead. The original code didn't do that, but due
-  /// to the number of possible additional work needed to turn this number to
-  /// the proper output the code was littered with tests for upper cases and
-  /// searches for radix points and exponents.
-  /// - When a precision larger than the type's precision is selected
-  ///   additional zero characters need to be written before the exponent.
-  /// - alternate form needs to add a radix point when not present.
-  /// - localization needs to do grouping in the integral part.
-  template <class _Fp, class _Tp>
-  // TODO FMT _Fp should just be _Tp when to_chars has proper long double support.
-  _LIBCPP_HIDE_FROM_ABI __float_result __format_buffer(__float_buffer<_Fp>& __buffer, _Tp __value, bool __negative,
-                                                       bool __has_precision) {
-    char* __first = __insert_sign(__buffer.begin(), __negative, this->__sign);
-    switch (this->__type) {
-    case _Flags::_Type::__default:
-      return __format_spec::__format_buffer_default(__buffer, __value, __first);
-
-    case _Flags::_Type::__float_hexadecimal_lower_case:
-      return __format_spec::__format_buffer_hexadecimal_lower_case(
-          __buffer, __value, __has_precision ? __buffer.__precision() : -1, __first);
-
-    case _Flags::_Type::__float_hexadecimal_upper_case:
-      return __format_spec::__format_buffer_hexadecimal_upper_case(
-          __buffer, __value, __has_precision ? __buffer.__precision() : -1, __first);
-
-    case _Flags::_Type::__scientific_lower_case:
-      return __format_spec::__format_buffer_scientific_lower_case(__buffer, __value, __buffer.__precision(), __first);
-
-    case _Flags::_Type::__scientific_upper_case:
-      return __format_spec::__format_buffer_scientific_upper_case(__buffer, __value, __buffer.__precision(), __first);
-
-    case _Flags::_Type::__fixed_lower_case:
-    case _Flags::_Type::__fixed_upper_case:
-      return __format_spec::__format_buffer_fixed(__buffer, __value, __buffer.__precision(), __first);
-
-    case _Flags::_Type::__general_lower_case:
-      return __format_spec::__format_buffer_general_lower_case(__buffer, __value, __buffer.__precision(), __first);
-
-    case _Flags::_Type::__general_upper_case:
-      return __format_spec::__format_buffer_general_upper_case(__buffer, __value, __buffer.__precision(), __first);
-
-    default:
-      _LIBCPP_ASSERT(false, "The parser should have validated the type");
-      __libcpp_unreachable();
-    }
+  template <floating_point _Tp>
+  _LIBCPP_HIDE_FROM_ABI auto format(_Tp __value, auto& __ctx) const -> decltype(__ctx.out()) {
+    return __formatter::__format_floating_point(__value, __ctx, __parser_.__resolve_dynamic_sizes(__ctx));
   }
-};
 
-} //namespace __format_spec
+  __format_spec::__parser<_CharT> __parser_;
+};
 
 template <__formatter::__char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<float, _CharT>
-    : public __format_spec::__formatter_floating_point<_CharT> {};
+    : public __formatter_floating_point<_CharT> {};
 template <__formatter::__char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<double, _CharT>
-    : public __format_spec::__formatter_floating_point<_CharT> {};
+    : public __formatter_floating_point<_CharT> {};
 template <__formatter::__char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<long double, _CharT>
-    : public __format_spec::__formatter_floating_point<_CharT> {};
+    : public __formatter_floating_point<_CharT> {};
 
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP___FORMAT_FORMATTER_FLOATING_POINT_H

libcxx/include/__format/formatter_integer.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_FORMATTER_INTEGER_H
 #define _LIBCPP___FORMAT_FORMATTER_INTEGER_H
 
 #include <__availability>
+#include <__concepts/arithmetic.h>
 #include <__config>
-#include <__format/format_error.h>
+#include <__format/format_error.h> // TODO FMT Remove after adding 128-bit support
 #include <__format/format_fwd.h>
+#include <__format/format_parse_context.h>
 #include <__format/formatter.h>
 #include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
 #include <__format/parser_std_format_spec.h>
-#include <limits>
+#include <limits> // TODO FMT Remove after adding 128-bit support
+#include <type_traits> // is_signed_v
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
-_LIBCPP_PUSH_MACROS
+_LIBCPP_PUSH_MACROS // TODO FMT Remove after adding 128-bit support
 #include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
-namespace __format_spec {
-
-template <class _CharT>
-class _LIBCPP_TEMPLATE_VIS __parser_integer : public __parser_integral<_CharT> {
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __formatter_integer {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(auto& __parse_ctx)
+  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
       -> decltype(__parse_ctx.begin()) {
-    auto __it = __parser_integral<_CharT>::__parse(__parse_ctx);
-
-    switch (this->__type) {
-    case _Flags::_Type::__default:
-      this->__type = _Flags::_Type::__decimal;
-      [[fallthrough]];
-
-    case _Flags::_Type::__binary_lower_case:
-    case _Flags::_Type::__binary_upper_case:
-    case _Flags::_Type::__octal:
-    case _Flags::_Type::__decimal:
-    case _Flags::_Type::__hexadecimal_lower_case:
-    case _Flags::_Type::__hexadecimal_upper_case:
-      this->__handle_integer();
-      break;
-
-    case _Flags::_Type::__char:
-      this->__handle_char();
-      break;
-
-    default:
-      __throw_format_error("The format-spec type has a type not supported for "
-                           "an integer argument");
-    }
-    return __it;
+    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_integral);
+    __format_spec::__process_parsed_integer(__parser_);
+    return __result;
+
+  // TODO might want to reduce the number of instantiations
+  // but need to measure the size of them (eg 64 bit and 128 bit version)
+  // One formatter integral and char
+  template <integral _Tp>
+  _LIBCPP_HIDE_FROM_ABI auto format(_Tp __value, auto& __ctx) const -> decltype(__ctx.out()) {
+    return format(__value, __ctx, __parser_.__resolve_dynamic_sizes(__ctx));
   }
-};
 
-template <class _CharT>
-using __formatter_integer = __formatter_integral<__parser_integer<_CharT>>;
+  template <integral _Tp>
+  static _LIBCPP_HIDE_FROM_ABI auto format(_Tp __value, auto& __ctx, __format_spec::__parser<_CharT> __parser)
+      -> decltype(__ctx.out()) {
+    if (__parser.__type_ == __format_spec::__type::__char)
+      return __formatter::__format_char(__value, __ctx.out(), __parser);
 
-} // namespace __format_spec
+    // Reduce the number of instantiation of the integer formatter
+    if constexpr (is_signed_v<_Tp>) {
+      if constexpr (sizeof(_Tp) <= sizeof(int))
+        return __formatter::__format_integer(static_cast<int>(__value), __ctx, __parser);
+      else if constexpr (sizeof(_Tp) <= sizeof(long long))
+        return __formatter::__format_integer(static_cast<long long>(__value), __ctx, __parser);
+#    ifndef _LIBCPP_HAS_NO_INT128
+      else if constexpr (sizeof(_Tp) <= sizeof(__int128_t))
+        return __formatter::__format_integer(static_cast<__int128_t>(__value), __ctx, __parser);
+#    endif
+      else
+        static_assert(sizeof(_Tp) == 0, "Unsupported type");
+    } else {
+      if constexpr (sizeof(_Tp) <= sizeof(unsigned))
+        return __formatter::__format_integer(static_cast<unsigned>(__value), __ctx, __parser);
+      else if constexpr (sizeof(_Tp) <= sizeof(unsigned long long))
+        return __formatter::__format_integer(static_cast<unsigned long long>(__value), __ctx, __parser);
+#    ifndef _LIBCPP_HAS_NO_INT128
+      else if constexpr (sizeof(_Tp) <= sizeof(__uint128_t))
+        return __formatter::__format_integer(static_cast<__uint128_t>(__value), __ctx, __parser);
+#    endif
+      else
+        static_assert(sizeof(_Tp) == 0, "Unsupported type");
+    }
+  }
 
-// [format.formatter.spec]/2.3
-// For each charT, for each cv-unqualified arithmetic type ArithmeticT other
-// than char, wchar_t, char8_t, char16_t, or char32_t, a specialization
+  __format_spec::__parser<_CharT> __parser_;
+};
 
 // Signed integral types.
 template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<signed char, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<short, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<int, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<long, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<long long, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-#ifndef _LIBCPP_HAS_NO_INT128
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<signed char, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<short, _CharT> : public __formatter_integer<_CharT> {
+};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<int, _CharT> : public __formatter_integer<_CharT> {};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<long, _CharT> : public __formatter_integer<_CharT> {};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<long long, _CharT>
+    : public __formatter_integer<_CharT> {};
+#    ifndef _LIBCPP_HAS_NO_INT128
 template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<__int128_t, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {
-  using _Base = __format_spec::__formatter_integer<_CharT>;
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<__int128_t, _CharT>
+    : public __formatter_integer<_CharT> {
+  using _Base = __formatter_integer<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI auto format(__int128_t __value, auto& __ctx)
-      -> decltype(__ctx.out()) {
+  _LIBCPP_HIDE_FROM_ABI auto format(__int128_t __value, auto& __ctx) const -> decltype(__ctx.out()) {
     // TODO FMT Implement full 128 bit support.
     using _To = long long;
-    if (__value < numeric_limits<_To>::min() ||
-        __value > numeric_limits<_To>::max())
+    if (__value < numeric_limits<_To>::min() || __value > numeric_limits<_To>::max())
       __throw_format_error("128-bit value is outside of implemented range");
 
     return _Base::format(static_cast<_To>(__value), __ctx);
   }
 };
-#endif
+#    endif
 
 // Unsigned integral types.
 template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<unsigned char, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<unsigned short, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<unsigned, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<unsigned long, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<unsigned long long, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {};
-#ifndef _LIBCPP_HAS_NO_INT128
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<unsigned char, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<unsigned short, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<unsigned, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<unsigned long, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__formatter::__char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<unsigned long long, _CharT>
+    : public __formatter_integer<_CharT> {};
+#    ifndef _LIBCPP_HAS_NO_INT128
 template <__formatter::__char_type _CharT>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
-    formatter<__uint128_t, _CharT>
-    : public __format_spec::__formatter_integer<_CharT> {
-  using _Base = __format_spec::__formatter_integer<_CharT>;
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<__uint128_t, _CharT>
+    : public __formatter_integer<_CharT> {
+  using _Base = __formatter_integer<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI auto format(__uint128_t __value, auto& __ctx)
-      -> decltype(__ctx.out()) {
+  _LIBCPP_HIDE_FROM_ABI auto format(__uint128_t __value, auto& __ctx) const -> decltype(__ctx.out()) {
     // TODO FMT Implement full 128 bit support.
     using _To = unsigned long long;
-    if (__value < numeric_limits<_To>::min() ||
-        __value > numeric_limits<_To>::max())
+    if (__value < numeric_limits<_To>::min() || __value > numeric_limits<_To>::max())
       __throw_format_error("128-bit value is outside of implemented range");
 
     return _Base::format(static_cast<_To>(__value), __ctx);
   }
 };
-#endif
+#    endif
 
+
+
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP___FORMAT_FORMATTER_INTEGER_H

libcxx/include/__format/formatter_integral.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_FORMATTER_INTEGRAL_H
 #define _LIBCPP___FORMAT_FORMATTER_INTEGRAL_H
 
-#include <__algorithm/copy.h>
-#include <__algorithm/copy_n.h>
-#include <__algorithm/fill_n.h>
-#include <__algorithm/transform.h>
-#include <__assert>
 #include <__config>
 #include <__format/format_error.h>
-#include <__format/format_fwd.h>
-#include <__format/formatter.h>
+#include <__format/format_fwd.h> // for __char_type TODO FMT Move the concept?
+#include <__format/formatter_output.h>
 #include <__format/parser_std_format_spec.h>
 #include <__utility/unreachable.h>
-#include <array>
 #include <charconv>
-#include <concepts>
 #include <limits>
-#include <string>
 
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION
-#include <locale>
+#  include <locale>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
-/**
- * Integral formatting classes.
- *
- * There are two types used here:
- * * C++-type, the type as used in C++.
- * * format-type, the output type specified in the std-format-spec.
- *
- * Design of the integral formatters consists of several layers.
- * * @ref __parser_integral The basic std-format-spec parser for all integral
- *   classes. This parser does the basic sanity checks. It also contains some
- *   helper functions that are nice to have available for all parsers.
- * * A C++-type specific parser. These parsers must derive from
- *   @ref __parser_integral. Their task is to validate whether the parsed
- *   std-format-spec is valid for the C++-type and selected format-type. After
- *   validation they need to make sure all members are properly set. For
- *   example, when the alignment hasn't changed it needs to set the proper
- *   default alignment for the format-type. The following parsers are available:
- *   - @ref __parser_integer
- *   - @ref __parser_char
- *   - @ref __parser_bool
- * * A general formatter for all integral types @ref __formatter_integral. This
- *   formatter can handle all formatting of integers and characters. The class
- *   derives from the proper formatter.
- *   Note the boolean string format-type isn't supported in this class.
- * * A typedef C++-type group combining the @ref __formatter_integral with a
- *   parser:
- *   * @ref __formatter_integer
- *   * @ref __formatter_char
- *   * @ref __formatter_bool
- * * Then every C++-type has its own formatter specializations. They inherit
- *   from the C++-type group typedef. Most specializations need nothing else.
- *   Others need some additional specializations in this class.
- */
-namespace __format_spec {
-
-/** Wrapper around @ref to_chars, returning the output pointer. */
-template <integral _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last,
-                                        _Tp __value, int __base) {
-  // TODO FMT Evaluate code overhead due to not calling the internal function
-  // directly. (Should be zero overhead.)
-  to_chars_result __r = _VSTD::to_chars(__first, __last, __value, __base);
-  _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
-  return __r.ptr;
-}
+namespace __formatter {
 
-/**
- * Helper to determine the buffer size to output a integer in Base @em x.
- *
- * There are several overloads for the supported bases. The function uses the
- * base as template argument so it can be used in a constant expression.
- */
-template <unsigned_integral _Tp, size_t _Base>
-_LIBCPP_HIDE_FROM_ABI constexpr size_t __buffer_size() noexcept
-    requires(_Base == 2) {
-  return numeric_limits<_Tp>::digits // The number of binary digits.
-         + 2                         // Reserve space for the '0[Bb]' prefix.
-         + 1;                        // Reserve space for the sign.
-}
-
-template <unsigned_integral _Tp, size_t _Base>
-_LIBCPP_HIDE_FROM_ABI constexpr size_t __buffer_size() noexcept
-    requires(_Base == 8) {
-  return numeric_limits<_Tp>::digits // The number of binary digits.
-             / 3                     // Adjust to octal.
-         + 1                         // Turn floor to ceil.
-         + 1                         // Reserve space for the '0' prefix.
-         + 1;                        // Reserve space for the sign.
-}
+//
+// Generic
+//
 
-template <unsigned_integral _Tp, size_t _Base>
-_LIBCPP_HIDE_FROM_ABI constexpr size_t __buffer_size() noexcept
-    requires(_Base == 10) {
-  return numeric_limits<_Tp>::digits10 // The floored value.
-         + 1                           // Turn floor to ceil.
-         + 1;                          // Reserve space for the sign.
+_LIBCPP_HIDE_FROM_ABI inline char* __insert_sign(char* __buf, bool __negative, __format_spec::__sign __sign) {
+  if (__negative)
+    *__buf++ = '-';
+  else
+    switch (__sign) {
+    case __format_spec::__sign::__default:
+    case __format_spec::__sign::__minus:
+      // No sign added.
+      break;
+    case __format_spec::__sign::__plus:
+      *__buf++ = '+';
+      break;
+    case __format_spec::__sign::__space:
+      *__buf++ = ' ';
+      break;
     }
 
-template <unsigned_integral _Tp, size_t _Base>
-_LIBCPP_HIDE_FROM_ABI constexpr size_t __buffer_size() noexcept
-    requires(_Base == 16) {
-  return numeric_limits<_Tp>::digits // The number of binary digits.
-             / 4                     // Adjust to hexadecimal.
-         + 2                         // Reserve space for the '0[Xx]' prefix.
-         + 1;                        // Reserve space for the sign.
+  return __buf;
 }
 
 /**
  * Determines the required grouping based on the size of the input.
  *
  * The grouping's last element will be repeated. For simplicity this repeating
  * is unwrapped based on the length of the input. (When the input is short some
  * groups are not processed.)
  *
  * @returns The size of the groups to write. This means the number of
  * separator characters written is size() - 1.
  *
  * @note Since zero-sized groups cause issues they are silently ignored.
  *
  * @note The grouping field of the locale is always a @c std::string,
  * regardless whether the @c std::numpunct's type is @c char or @c wchar_t.
  */
-_LIBCPP_HIDE_FROM_ABI inline string
-__determine_grouping(ptrdiff_t __size, const string& __grouping) {
+_LIBCPP_HIDE_FROM_ABI inline string __determine_grouping(ptrdiff_t __size,
+                                                         const string& __grouping) {
   _LIBCPP_ASSERT(!__grouping.empty() && __size > __grouping[0],
                  "The slow grouping formatting is used while there will be no "
                  "separators written");
   string __r;
   auto __end = __grouping.end() - 1;
   auto __ptr = __grouping.begin();
 
   while (true) {
if (__ptr != __end) {
         // Skip grouping with a width of 0.
       } while (*__ptr == 0 && __ptr != __end);
     }
   }
 
   __libcpp_unreachable();
 }
 
-template <class _Parser>
-requires __formatter::__char_type<typename _Parser::char_type>
-class _LIBCPP_TEMPLATE_VIS __formatter_integral : public _Parser {
-public:
-  using _CharT = typename _Parser::char_type;
-
-  template <integral _Tp>
-  _LIBCPP_HIDE_FROM_ABI auto format(_Tp __value, auto& __ctx)
-      -> decltype(__ctx.out()) {
-    if (this->__width_needs_substitution())
-      this->__substitute_width_arg_id(__ctx.arg(this->__width));
-
-    if (this->__type == _Flags::_Type::__char)
-      return __format_as_char(__value, __ctx);
-
-    if constexpr (unsigned_integral<_Tp>)
-      return __format_unsigned_integral(__value, false, __ctx);
-    else {
-      // Depending on the std-format-spec string the sign and the value
-      // might not be outputted together:
-      // - alternate form may insert a prefix string.
-      // - zero-padding may insert additional '0' characters.
-      // Therefore the value is processed as a positive unsigned value.
-      // The function @ref __insert_sign will a '-' when the value was negative.
-      auto __r = __to_unsigned_like(__value);
-      bool __negative = __value < 0;
-      if (__negative)
-        __r = __complement(__r);
-
-      return __format_unsigned_integral(__r, __negative, __ctx);
-    }
-  }
-
-private:
-  /** Generic formatting for format-type c. */
-  _LIBCPP_HIDE_FROM_ABI auto __format_as_char(integral auto __value,
-                                              auto& __ctx)
-      -> decltype(__ctx.out()) {
-    if (this->__alignment == _Flags::_Alignment::__default)
-      this->__alignment = _Flags::_Alignment::__right;
+//
+// Char
+//
 
-    using _Tp = decltype(__value);
-    if constexpr (!same_as<_CharT, _Tp>) {
-      // cmp_less and cmp_greater can't be used for character types.
-      if constexpr (signed_integral<_CharT> == signed_integral<_Tp>) {
-        if (__value < numeric_limits<_CharT>::min() ||
-            __value > numeric_limits<_CharT>::max())
-          __throw_format_error(
-              "Integral value outside the range of the char type");
-      } else if constexpr (signed_integral<_CharT>) {
-        // _CharT is signed _Tp is unsigned
-        if (__value >
-            static_cast<make_unsigned_t<_CharT>>(numeric_limits<_CharT>::max()))
-          __throw_format_error(
-              "Integral value outside the range of the char type");
-      } else {
-        // _CharT is unsigned _Tp is signed
-        if (__value < 0 || static_cast<make_unsigned_t<_Tp>>(__value) >
-                               numeric_limits<_CharT>::max())
-          __throw_format_error(
-              "Integral value outside the range of the char type");
-      }
-    }
+template <__formatter::__char_type _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __format_char(integral auto __value, output_iterator<const _CharT&> auto __out_it,
+                                         __format_spec::__parser<_CharT> __parser) -> decltype(__out_it) {
+      if (__value < numeric_limits<_CharT>::min() || __value > numeric_limits<_CharT>::max())
+        __throw_format_error("Integral value outside the range of the char type");
+      if (__value > static_cast<make_unsigned_t<_CharT>>(numeric_limits<_CharT>::max()))
+        __throw_format_error("Integral value outside the range of the char type");
+      if (__value < 0 || static_cast<make_unsigned_t<_Tp>>(__value) > numeric_limits<_CharT>::max())
+        __throw_format_error("Integral value outside the range of the char type");
 
-    const auto __c = static_cast<_CharT>(__value);
-    return __write(_VSTD::addressof(__c), _VSTD::addressof(__c) + 1,
-                   __ctx.out());
-  }
+  return __formatter::__write(_VSTD::addressof(__c), _VSTD::addressof(__c) + 1, _VSTD::move(__out_it), __parser);
+}
+
+//
+// Integer
+//
+
+/** Wrapper around @ref to_chars, returning the output pointer. */
+template <integral _Tp>
+_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value, int __base) {
+  // TODO FMT Evaluate code overhead due to not calling the internal function
+  // directly. (Should be zero overhead.)
+  to_chars_result __r = _VSTD::to_chars(__first, __last, __value, __base);
+  _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
+  return __r.ptr;
 
-  /**
-   * Generic formatting for format-type bBdoxX.
-   *
-   * This small wrapper allocates a buffer with the required size. Then calls
-   * the real formatter with the buffer and the prefix for the base.
-   */
-  _LIBCPP_HIDE_FROM_ABI auto
-  __format_unsigned_integral(unsigned_integral auto __value, bool __negative,
-                             auto& __ctx) -> decltype(__ctx.out()) {
-    switch (this->__type) {
-    case _Flags::_Type::__binary_lower_case: {
-      array<char, __buffer_size<decltype(__value), 2>()> __array;
-      return __format_unsigned_integral(__array.begin(), __array.end(), __value,
-                                        __negative, 2, __ctx, "0b");
-    }
-    case _Flags::_Type::__binary_upper_case: {
-      array<char, __buffer_size<decltype(__value), 2>()> __array;
-      return __format_unsigned_integral(__array.begin(), __array.end(), __value,
-                                        __negative, 2, __ctx, "0B");
-    }
-    case _Flags::_Type::__octal: {
-      // Octal is special; if __value == 0 there's no prefix.
-      array<char, __buffer_size<decltype(__value), 8>()> __array;
-      return __format_unsigned_integral(__array.begin(), __array.end(), __value,
-                                        __negative, 8, __ctx,
-                                        __value != 0 ? "0" : nullptr);
-    }
-    case _Flags::_Type::__decimal: {
-      array<char, __buffer_size<decltype(__value), 10>()> __array;
-      return __format_unsigned_integral(__array.begin(), __array.end(), __value,
-                                        __negative, 10, __ctx, nullptr);
-    }
-    case _Flags::_Type::__hexadecimal_lower_case: {
-      array<char, __buffer_size<decltype(__value), 16>()> __array;
-      return __format_unsigned_integral(__array.begin(), __array.end(), __value,
-                                        __negative, 16, __ctx, "0x");
-    }
-    case _Flags::_Type::__hexadecimal_upper_case: {
-      array<char, __buffer_size<decltype(__value), 16>()> __array;
-      return __format_unsigned_integral(__array.begin(), __array.end(), __value,
-                                        __negative, 16, __ctx, "0X");
-    }
-    default:
-      _LIBCPP_ASSERT(false, "The parser should have validated the type");
-      __libcpp_unreachable();
-    }
-  }
+ * Helper to determine the buffer size to output a integer in Base @em x.
+ * There are several overloads for the supported bases. The function uses the
+ * base as template argument so it can be used in a constant expression.
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 2)
+{
+  return numeric_limits<_Tp>::digits // The number of binary digits.
+         + 2                         // Reserve space for the '0[Bb]' prefix.
+         + 1;                        // Reserve space for the sign.
+
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 8)
+{
+  return numeric_limits<_Tp>::digits // The number of binary digits.
+             / 3                     // Adjust to octal.
+         + 1                         // Turn floor to ceil.
+         + 1                         // Reserve space for the '0' prefix.
+         + 1;                        // Reserve space for the sign.
+
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 10)
+{
+  return numeric_limits<_Tp>::digits10 // The floored value.
+         + 1                           // Turn floor to ceil.
+         + 1;                          // Reserve space for the sign.
+
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 16)
+{
+  return numeric_limits<_Tp>::digits // The number of binary digits.
+             / 4                     // Adjust to hexadecimal.
+         + 2                         // Reserve space for the '0[Xx]' prefix.
+         + 1;                        // Reserve space for the sign.