chromium/third_party/libc++/src/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_n.h>
#include <__algorithm/find.h>
#include <__algorithm/max.h>
#include <__algorithm/min.h>
#include <__algorithm/rotate.h>
#include <__algorithm/transform.h>
#include <__assert>
#include <__charconv/chars_format.h>
#include <__charconv/to_chars_floating_point.h>
#include <__charconv/to_chars_result.h>
#include <__concepts/arithmetic.h>
#include <__concepts/same_as.h>
#include <__config>
#include <__format/concepts.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 <__iterator/concepts.h>
#include <__memory/allocator.h>
#include <__system_error/errc.h>
#include <__type_traits/conditional.h>
#include <__utility/move.h>
#include <__utility/unreachable.h>
#include <cmath>
#include <cstddef>

#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 >= 20

namespace __formatter {

template <floating_point _Tp>
_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value) { … }

template <floating_point _Tp>
_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value, chars_format __fmt) { … }

template <floating_point _Tp>
_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value, chars_format __fmt, int __precision) { … }

// https://en.cppreference.com/w/cpp/language/types#cite_note-1
// float             min subnormal: +/-0x1p-149   max: +/- 3.402,823,4 10^38
// double            min subnormal: +/-0x1p-1074  max  +/- 1.797,693,134,862,315,7 10^308
// long double (x86) min subnormal: +/-0x1p-16446 max: +/- 1.189,731,495,357,231,765,021 10^4932
//
// The maximum number of digits required for the integral part is based on the
// maximum's value power of 10. Every power of 10 requires one additional
// decimal digit.
// The maximum number of digits required for the fractional part is based on
// the minimal subnormal hexadecimal output's power of 10. Every division of a
// fraction's binary 1 by 2, requires one additional decimal digit.
//
// The maximum size of a formatted value depends on the selected output format.
// Ignoring the fact the format string can request a precision larger than the
// values maximum required, these values are:
//
// sign                    1 code unit
// __max_integral
// radix point             1 code unit
// __max_fractional
// exponent character      1 code unit
// sign                    1 code unit
// __max_fractional_value
// -----------------------------------
// total                   4 code units extra required.
//
// TODO FMT Optimize the storage to avoid storing digits that are known to be zero.
// https://www.exploringbinary.com/maximum-number-of-decimal-digits-in-binary-floating-point-numbers/

// TODO FMT Add long double specialization when to_chars has proper long double support.
template <class _Tp>
struct __traits;

template <floating_point _Fp>
_LIBCPP_HIDE_FROM_ABI constexpr size_t __float_buffer_size(int __precision) { … }

template <>
struct __traits<float> { … };

template <>
struct __traits<double> { … };

/// Helper class to store the conversion buffer.
///
/// Depending on the maximum size required for a value, the buffer is allocated
/// on the stack or the heap.
template <floating_point _Fp>
class _LIBCPP_TEMPLATE_VIS __float_buffer { … };

struct __float_result { … };

/// Finds the position of the exponent character 'e' at the end of the buffer.
///
/// Assuming there is an exponent the input will terminate with
/// eSdd and eSdddd (S = sign, d = digit)
///
/// \returns a pointer to the exponent or __last when not found.
constexpr inline _LIBCPP_HIDE_FROM_ABI char* __find_exponent(char* __first, char* __last) { … }

template <class _Fp, class _Tp>
_LIBCPP_HIDE_FROM_ABI __float_result
__format_buffer_default(const __float_buffer<_Fp>& __buffer, _Tp __value, char* __integral) { … }

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) { … }

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) { … }

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) { … }

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) { … }

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) { … }

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) { … }

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) { … }

/// 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) { … }

#  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,
    std::locale __loc,
    __format_spec::__parsed_specifications<_CharT> __specs) { … }
#  endif // _LIBCPP_HAS_NO_LOCALIZATION

template <class _OutIt, class _CharT>
_LIBCPP_HIDE_FROM_ABI _OutIt __format_floating_point_non_finite(
    _OutIt __out_it, __format_spec::__parsed_specifications<_CharT> __specs, bool __negative, bool __isnan) { … }

/// 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 _ParserCharT>
_LIBCPP_HIDE_FROM_ABI auto __write_using_trailing_zeros(
    const _CharT* __first,
    const _CharT* __last,
    output_iterator<const _CharT&> auto __out_it,
    __format_spec::__parsed_specifications<_ParserCharT> __specs,
    size_t __size,
    const _CharT* __exponent,
    size_t __num_trailing_zeros) -> decltype(__out_it) { … }

template <floating_point _Tp, class _CharT, class _FormatContext>
_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
__format_floating_point(_Tp __value, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) { … }

} // namespace __formatter

template <__fmt_char_type _CharT>
struct _LIBCPP_TEMPLATE_VIS __formatter_floating_point { … };

formatter<float, _CharT>;
formatter<double, _CharT>;
formatter<long double, _CharT>;

#  if _LIBCPP_STD_VER >= 23
template <>
inline constexpr bool enable_nonlocking_formatter_optimization<float> = true;
template <>
inline constexpr bool enable_nonlocking_formatter_optimization<double> = true;
template <>
inline constexpr bool enable_nonlocking_formatter_optimization<long double> = true;
#  endif // _LIBCPP_STD_VER >= 23
#endif   // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___FORMAT_FORMATTER_FLOATING_POINT_H