daw_json_parse_real.h

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// Copyright (c) Darrell Wright
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/beached/daw_json_link
//
 
#pragma once
 
#include "version.h"
 
#include "daw_fp_fallback.h"
#include "daw_json_assert.h"
#include "daw_json_parse_policy_policy_details.h"
#include "daw_json_parse_real_power10.h"
#include "daw_json_parse_unsigned_int.h"
#include "daw_json_skip.h"
#include "daw_json_type_options.h"
 
#include <daw/daw_cxmath.h>
#include <daw/daw_likely.h>
#include <daw/daw_restrict.h>
#include <daw/daw_utility.h>
 
#include <cstddef>
#include <cstdint>
#include <limits>
#include <type_traits>
 
namespace daw::json {
  inline namespace DAW_JSON_VER {
    namespace json_details {
      template<bool skip_end_check, typename Unsigned>
      DAW_ATTRIB_NONNULL( )
      DAW_ATTRIB_FLATINLINE inline constexpr void parse_digits_until_last(
        char const *DAW_RESTRICT first, char const *const DAW_RESTRICT last,
        Unsigned &DAW_RESTRICT v ) {
        Unsigned value = v;
        if constexpr( skip_end_check ) {
          auto dig = parse_digit( *first );
          while( dig < 10U ) {
            value *= 10U;
            value += dig;
            ++first;
            dig = parse_digit( *first );
          }
        } else {
          while( DAW_LIKELY( first < last ) ) {
            value *= 10U;
            value += parse_digit( *first );
            ++first;
          }
        }
        v = value;
      }
 
      template<bool skip_end_check, typename Unsigned, typename CharT>
      [[nodiscard]] DAW_ATTRIB_NONNULL( ) DAW_ATTRIB_FLATINLINE
        inline constexpr CharT *parse_digits_while_number(
          CharT *DAW_RESTRICT first, CharT *const DAW_RESTRICT last,
          Unsigned &DAW_RESTRICT v ) {
 
        // silencing gcc9 unused warning.  last is used inside if constexpr
        // blocks
        (void)last;
 
        Unsigned value = v;
        if constexpr( skip_end_check ) {
          for( auto dig = parse_digit( *first ); dig < 10U;
               ++first, dig = parse_digit( *first ) ) {
            value *= 10U;
            value += dig;
          }
        } else {
          if( first < last ) {
            unsigned dig = parse_digit( *first );
            while( dig < 10U ) {
              ++first;
              value *= 10U;
              value += dig;
              if( DAW_UNLIKELY( first == last ) ) {
                break;
              }
              dig = parse_digit( *first );
            }
          }
        }
        v = value;
        return first;
      }
 
      template<typename ParseState, typename Result,
               typename max_storage_digits, typename CharT>
      DAW_ATTRIB_NONNULL( ( 1, 2 ) )
      [[nodiscard]] inline constexpr bool should_use_strtod(
        CharT *whole_first, CharT *whole_last, CharT *fract_first,
        CharT *fract_last ) {
        if constexpr( std::is_floating_point_v<Result> and
                      ParseState::precise_ieee754 ) {
          return DAW_UNLIKELY(
            ( ( whole_last - whole_first ) +
              ( fract_first ? fract_last - fract_first : 0 ) ) >
            max_storage_digits::value );
        } else {
          // avoid -Wunused-but-set-parameter in gcc warnings
          (void)whole_first;
          (void)whole_last;
          (void)fract_first;
          (void)fract_last;
          return false;
        }
      }
 
      template<typename Result, typename ParseState>
      [[nodiscard]] DAW_ATTRIB_INLINE static constexpr Result
      parse_real_known( ParseState &parse_state ) {
        using CharT = typename ParseState::CharT;
        // [-]WHOLE[.FRACTION][(e|E)[+|-]EXPONENT]
        daw_json_assert_weak(
          parse_state.has_more( ) and
            parse_policy_details::is_number_start( parse_state.front( ) ),
          ErrorReason::InvalidNumberStart, parse_state );
 
        CharT *whole_first = parse_state.first;
        CharT *whole_last = parse_state.class_first ? parse_state.class_first
                                                    : parse_state.class_last;
        CharT *fract_first =
          parse_state.class_first ? parse_state.class_first + 1 : nullptr;
        CharT *fract_last = parse_state.class_last;
        CharT *exp_first =
          parse_state.class_last ? parse_state.class_last + 1 : nullptr;
        CharT *const exp_last = parse_state.last;
 
        if( parse_state.class_first == nullptr ) {
          if( parse_state.class_last == nullptr ) {
            whole_last = parse_state.last;
          } else {
            whole_last = parse_state.class_last;
          }
        } else if( parse_state.class_last == nullptr ) {
          fract_last = parse_state.last;
        }
 
        using max_storage_digits = daw::constant<static_cast<std::ptrdiff_t>(
          daw::numeric_limits<std::uint64_t>::digits10 )>;
 
        bool use_strtod =
          should_use_strtod<ParseState, Result, max_storage_digits>(
            whole_first, whole_last, fract_first, fract_last );
 
        Result const sign = [&] {
          if( *whole_first == '-' ) {
            ++whole_first;
            return static_cast<Result>( -1.0 );
          }
          return static_cast<Result>( 1.0 );
        }( );
        using max_exponent = daw::constant<static_cast<std::ptrdiff_t>(
          daw::numeric_limits<Result>::max_digits10 + 1 )>;
        using unsigned_t =
          daw::conditional_t<max_storage_digits::value >= max_exponent::value,
                             std::uint64_t, Result>;
 
        using signed_t =
          typename daw::conditional_t<std::is_floating_point_v<unsigned_t>,
                                      daw::traits::identity<unsigned_t>,
                                      std::make_signed<unsigned_t>>::type;
        std::intmax_t whole_exponent_available = whole_last - whole_first;
        std::intmax_t fract_exponent_available =
          fract_first ? fract_last - fract_first : 0;
        signed_t exponent = 0;
 
        if( whole_exponent_available > max_exponent::value ) {
          whole_last = whole_first + max_exponent::value;
          whole_exponent_available -= max_exponent::value;
          fract_exponent_available = 0;
          fract_first = nullptr;
          exponent = whole_exponent_available;
        } else {
          whole_exponent_available =
            max_exponent::value - whole_exponent_available;
          if constexpr( ParseState::precise_ieee754 ) {
            use_strtod |= DAW_UNLIKELY( fract_exponent_available >
                                        whole_exponent_available );
          }
          if( whole_exponent_available < fract_exponent_available ) {
            fract_exponent_available = whole_exponent_available;
          }
          exponent = -fract_exponent_available;
          fract_last = fract_first + fract_exponent_available;
        }
 
        unsigned_t significant_digits = 0;
        parse_digits_until_last<( ParseState::is_zero_terminated_string or
                                  ParseState::is_unchecked_input )>(
          whole_first, whole_last, significant_digits );
        if( fract_first ) {
          parse_digits_until_last<( ParseState::is_zero_terminated_string or
                                    ParseState::is_unchecked_input )>(
            fract_first, fract_last, significant_digits );
        }
 
        if( exp_first and ( exp_last - exp_first ) > 0 ) {
          signed_t const exp_sign = [&] {
            switch( *exp_first ) {
            case '-':
              ++exp_first;
              daw_json_assert_weak( exp_first < exp_last,
                                    ErrorReason::InvalidNumber );
              return -1;
            case '+':
              daw_json_assert_weak( exp_first < exp_last,
                                    ErrorReason::InvalidNumber );
              ++exp_first;
              return 1;
            default:
              return 1;
            }
          }( );
          exponent += to_signed(
            [&] {
              unsigned_t exp_result = 0;
              if constexpr( ParseState::is_zero_terminated_string ) {
                auto dig = parse_digit( *exp_first );
                while( dig < 10U ) {
                  ++exp_first;
                  exp_result *= 10U;
                  exp_result += dig;
                  dig = parse_digit( *exp_first );
                }
              } else {
                if( exp_first < exp_last ) {
                  auto dig = parse_digit( *exp_first );
                  do {
                    if( dig >= 10U ) {
                      break;
                    }
                    ++exp_first;
                    exp_result *= 10U;
                    exp_result += dig;
                    if( exp_first >= exp_last ) {
                      break;
                    }
                    dig = parse_digit( *exp_first );
                  } while( true );
                }
              }
              return exp_result;
            }( ),
            exp_sign );
        }
        if constexpr( std::is_floating_point_v<Result> and
                      ParseState::precise_ieee754 ) {
          // On std floating point types, check for conditions that cannot be
          // precisely calculated using the normal method and use the fallback
          // method(usually strtod/from_chars)
          use_strtod |= exponent > 22;
          use_strtod |= exponent < -22;
          use_strtod |= significant_digits > 9007199254740992ULL;
          if constexpr( std::is_same_v<Result, long double> ) {
            return json_details::parse_with_strtod<Result>( parse_state.first,
                                                            parse_state.last );
          } else {
            if( DAW_UNLIKELY( use_strtod ) ) {
              return json_details::parse_with_strtod<Result>(
                parse_state.first, parse_state.last );
            }
          }
        }
        return sign * power10<Result>(
                        ParseState::exec_tag,
                        static_cast<Result>( significant_digits ), exponent );
      }
 
      template<typename Result, typename ParseState>
      [[nodiscard]] DAW_ATTRIB_INLINE static constexpr Result
      parse_real_unknown( ParseState &parse_state ) {
        // [-]WHOLE[.FRACTION][(e|E)[+|-]EXPONENT]
        using CharT = typename ParseState::CharT;
        daw_json_assert_weak(
          parse_state.has_more( ) and
            parse_policy_details::is_number_start( parse_state.front( ) ),
          ErrorReason::InvalidNumberStart, parse_state );
 
        CharT *const orig_first = parse_state.first;
        CharT *const orig_last = parse_state.last;
 
        // silencing gcc9 warning as these are only used when precise ieee is in
        // play.
        (void)orig_first;
        (void)orig_last;
 
        auto const sign = static_cast<Result>(
          parse_policy_details::validate_signed_first( parse_state ) );
 
        using max_storage_digits = daw::constant<static_cast<std::int64_t>(
          daw::numeric_limits<std::uint64_t>::digits10 )>;
        using max_exponent = daw::constant<static_cast<std::int64_t>(
          daw::numeric_limits<Result>::max_digits10 + 1 )>;
        using unsigned_t =
          daw::conditional_t<max_storage_digits::value >= max_exponent::value,
                             std::uint64_t, Result>;
        using signed_t =
          daw::conditional_t<max_storage_digits::value >= max_exponent::value,
                             std::int64_t, Result>;
 
        CharT *first = parse_state.first;
        CharT *const whole_last =
          parse_state.first +
          ( std::min )( parse_state.last - parse_state.first,
                        static_cast<std::ptrdiff_t>( max_exponent::value ) );
 
        unsigned_t significant_digits = 0;
        CharT *last_char =
          parse_digits_while_number<( ParseState::is_zero_terminated_string or
                                      ParseState::is_unchecked_input )>(
            first, whole_last, significant_digits );
        std::ptrdiff_t sig_digit_count = last_char - parse_state.first;
        bool use_strtod =
          std::is_floating_point_v<Result> and ParseState::precise_ieee754 and
          DAW_UNLIKELY( sig_digit_count > max_storage_digits::value );
        signed_t exponent_p1 = [&] {
          if( DAW_UNLIKELY( last_char >= whole_last ) ) {
            if constexpr( std::is_floating_point_v<Result> and
                          ParseState::precise_ieee754 ) {
              use_strtod = true;
            }
            // We have sig digits we cannot parse because there isn't enough
            // room in a std::uint64_t
            CharT *ptr = skip_digits<( ParseState::is_zero_terminated_string or
                                       ParseState::is_unchecked_input )>(
              last_char, parse_state.last );
            auto const diff = ptr - last_char;
 
            last_char = ptr;
            if( significant_digits == 0 ) {
              return signed_t{ 0 };
            }
            return static_cast<signed_t>( diff );
          }
          return signed_t{ 0 };
        }( );
 
        first = last_char;
        if( ( ParseState::is_zero_terminated_string or
              ParseState::is_unchecked_input or
              DAW_LIKELY( first < parse_state.last ) ) and
            *first == '.' ) {
          ++first;
          if( exponent_p1 != 0 ) {
            if( first < parse_state.last ) {
              first = skip_digits<( ParseState::is_zero_terminated_string or
                                    ParseState::is_unchecked_input )>(
                first, parse_state.last );
            }
          } else {
            CharT *fract_last =
              first + ( std::min )( parse_state.last - first,
                                    static_cast<std::ptrdiff_t>(
                                      max_exponent::value -
                                      ( first - parse_state.first ) ) );
 
            last_char = parse_digits_while_number<(
              ParseState::is_zero_terminated_string or
              ParseState::is_unchecked_input )>( first, fract_last,
                                                 significant_digits );
            sig_digit_count += last_char - first;
            exponent_p1 -= static_cast<signed_t>( last_char - first );
            first = last_char;
            if( ( first >= fract_last ) & ( first < parse_state.last ) ) {
              auto new_first =
                skip_digits<( ParseState::is_zero_terminated_string or
                              ParseState::is_unchecked_input )>(
                  first, parse_state.last );
              if constexpr( std::is_floating_point_v<Result> and
                            ParseState::precise_ieee754 ) {
                use_strtod |= new_first > first;
              }
              first = new_first;
            }
          }
        }
 
        signed_t const exponent_p2 = [&] {
          if( ( ParseState::is_unchecked_input or first < parse_state.last ) and
              ( ( *first | 0x20 ) == 'e' ) ) {
            ++first;
            signed_t const exp_sign = [&] {
              daw_json_assert_weak( ( ParseState::is_zero_terminated_string or
                                      first < parse_state.last ),
                                    ErrorReason::UnexpectedEndOfData,
                                    parse_state.copy( first ) );
              switch( *first ) {
              case '+':
                ++first;
                daw_json_assert_weak( ( first < parse_state.last ) and
                                        ( parse_digit( *first ) < 10U ),
                                      ErrorReason::InvalidNumber );
                return signed_t{ 1 };
              case '-':
                ++first;
                daw_json_assert_weak( first < parse_state.last and
                                        parse_digit( *first ) < 10U,
                                      ErrorReason::InvalidNumber );
                return signed_t{ -1 };
              default:
                daw_json_assert_weak( parse_policy_details::is_number( *first ),
                                      ErrorReason::InvalidNumber );
                return signed_t{ 1 };
              }
            }( );
            daw_json_assert_weak( first < parse_state.last,
                                  ErrorReason::UnexpectedEndOfData,
                                  parse_state );
            unsigned_t exp_tmp = 0;
            last_char = parse_digits_while_number<(
              ParseState::is_zero_terminated_string or
              ParseState::is_unchecked_input )>( first, parse_state.last,
                                                 exp_tmp );
            first = last_char;
            return to_signed( exp_tmp, exp_sign );
          }
          return signed_t{ 0 };
        }( );
        signed_t const exponent = [&] {
          if constexpr( ParseState::is_unchecked_input or
                        not std::is_floating_point_v<Result> ) {
            return exponent_p1 + exponent_p2;
          } else {
            if( bool matching_signs =
                  ( exponent_p1 < 0 ) == ( exponent_p2 < 0 );
                not matching_signs ) {
 
              return exponent_p1 + exponent_p2;
            }
            auto const s = exponent_p1 < 0 ? signed_t{ -1 } : signed_t{ 1 };
            if( s < 0 ) {
              if( DAW_UNLIKELY( ( daw::numeric_limits<signed_t>::min( ) -
                                  exponent_p1 ) > exponent_p2 ) ) {
                // We don't have inf, but we can just saturate it to min as it
                // will be 0 anyways for the other result
                return daw::numeric_limits<signed_t>::min( );
              }
              return exponent_p1 + exponent_p2;
            }
            auto r = static_cast<unsigned_t>( exponent_p1 ) +
                     static_cast<unsigned_t>( exponent_p2 );
            if( DAW_UNLIKELY(
                  r > static_cast<unsigned_t>(
                        ( daw::numeric_limits<signed_t>::max )( ) ) ) ) {
              return ( daw::numeric_limits<signed_t>::max )( );
            }
            return static_cast<signed_t>( r );
          }
        }( );
        parse_state.first = first;
 
        if constexpr( std::is_floating_point_v<Result> and
                      ParseState::precise_ieee754 ) {
          use_strtod |= DAW_UNLIKELY( exponent > 22 );
          use_strtod |= DAW_UNLIKELY( exponent < -22 );
          use_strtod |=
            DAW_UNLIKELY( significant_digits > 9007199254740992ULL );
          if( DAW_UNLIKELY( use_strtod ) ) {
            using json_details::parse_with_strtod;
            auto result = parse_with_strtod<Result>( orig_first, orig_last );
            /*auto x =
              fallback_fp<Result>( result, sign, significant_digits, exponent );
            (void)x;*/
            return result;
          }
        }
        return sign * power10<Result>(
                        ParseState::exec_tag,
                        static_cast<Result>( significant_digits ), exponent );
      }
 
      template<typename Result, bool KnownRange, typename ParseState>
      [[nodiscard]] static constexpr Result
      parse_real( ParseState &parse_state ) {
        if constexpr( KnownRange ) {
          return parse_real_known<Result>( parse_state );
        } else {
          return parse_real_unknown<Result>( parse_state );
        }
      }
    } // namespace json_details
  } // namespace DAW_JSON_VER
} // namespace daw::json