daw_json_parse_real_power10.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_json_exec_modes.h"
 
#include <daw/daw_arith_traits.h>
#include <daw/daw_likely.h>
 
#include <cmath>
#include <cstddef>
#include <limits>
#include <type_traits>
 
namespace daw::json {
  inline namespace DAW_JSON_VER {
    namespace json_details {
      inline constexpr double dpow10_tbl[] = {
        1e0,   1e1,   1e2,   1e3,   1e4,   1e5,   1e6,   1e7,   1e8,   1e9,
        1e10,  1e11,  1e12,  1e13,  1e14,  1e15,  1e16,  1e17,  1e18,  1e19,
        1e20,  1e21,  1e22,  1e23,  1e24,  1e25,  1e26,  1e27,  1e28,  1e29,
        1e30,  1e31,  1e32,  1e33,  1e34,  1e35,  1e36,  1e37,  1e38,  1e39,
        1e40,  1e41,  1e42,  1e43,  1e44,  1e45,  1e46,  1e47,  1e48,  1e49,
        1e50,  1e51,  1e52,  1e53,  1e54,  1e55,  1e56,  1e57,  1e58,  1e59,
        1e60,  1e61,  1e62,  1e63,  1e64,  1e65,  1e66,  1e67,  1e68,  1e69,
        1e70,  1e71,  1e72,  1e73,  1e74,  1e75,  1e76,  1e77,  1e78,  1e79,
        1e80,  1e81,  1e82,  1e83,  1e84,  1e85,  1e86,  1e87,  1e88,  1e89,
        1e90,  1e91,  1e92,  1e93,  1e94,  1e95,  1e96,  1e97,  1e98,  1e99,
        1e100, 1e101, 1e102, 1e103, 1e104, 1e105, 1e106, 1e107, 1e108, 1e109,
        1e110, 1e111, 1e112, 1e113, 1e114, 1e115, 1e116, 1e117, 1e118, 1e119,
        1e120, 1e121, 1e122, 1e123, 1e124, 1e125, 1e126, 1e127, 1e128, 1e129,
        1e130, 1e131, 1e132, 1e133, 1e134, 1e135, 1e136, 1e137, 1e138, 1e139,
        1e140, 1e141, 1e142, 1e143, 1e144, 1e145, 1e146, 1e147, 1e148, 1e149,
        1e150, 1e151, 1e152, 1e153, 1e154, 1e155, 1e156, 1e157, 1e158, 1e159,
        1e160, 1e161, 1e162, 1e163, 1e164, 1e165, 1e166, 1e167, 1e168, 1e169,
        1e170, 1e171, 1e172, 1e173, 1e174, 1e175, 1e176, 1e177, 1e178, 1e179,
        1e180, 1e181, 1e182, 1e183, 1e184, 1e185, 1e186, 1e187, 1e188, 1e189,
        1e190, 1e191, 1e192, 1e193, 1e194, 1e195, 1e196, 1e197, 1e198, 1e199,
        1e200, 1e201, 1e202, 1e203, 1e204, 1e205, 1e206, 1e207, 1e208, 1e209,
        1e210, 1e211, 1e212, 1e213, 1e214, 1e215, 1e216, 1e217, 1e218, 1e219,
        1e220, 1e221, 1e222, 1e223, 1e224, 1e225, 1e226, 1e227, 1e228, 1e229,
        1e230, 1e231, 1e232, 1e233, 1e234, 1e235, 1e236, 1e237, 1e238, 1e239,
        1e240, 1e241, 1e242, 1e243, 1e244, 1e245, 1e246, 1e247, 1e248, 1e249,
        1e250, 1e251, 1e252, 1e253, 1e254, 1e255, 1e256, 1e257, 1e258, 1e259,
        1e260, 1e261, 1e262, 1e263, 1e264, 1e265, 1e266, 1e267, 1e268, 1e269,
        1e270, 1e271, 1e272, 1e273, 1e274, 1e275, 1e276, 1e277, 1e278, 1e279,
        1e280, 1e281, 1e282, 1e283, 1e284, 1e285, 1e286, 1e287, 1e288, 1e289,
        1e290, 1e291, 1e292, 1e293, 1e294, 1e295, 1e296, 1e297, 1e298, 1e299,
        1e300, 1e301, 1e302, 1e303, 1e304, 1e305, 1e306, 1e307, 1e308 };
 
      inline constexpr int max_dbl_exp =
        std::numeric_limits<double>::max_exponent10;
 
      template<typename T>
      DAW_ATTRIB_INLINE constexpr T const &Min( T const &l,
                                                T const &r ) noexcept {
        if( l <= r ) {
          return l;
        }
        return r;
      }
 
      template<typename Result>
      inline constexpr int max_exp =
        std::is_same_v<Result, float>
          ? Min( max_dbl_exp, std::numeric_limits<float>::max_exponent10 )
          : max_dbl_exp;
 
      template<typename Result, typename Unsigned>
      DAW_ATTRIB_FLATINLINE static inline constexpr Result
      power10( constexpr_exec_tag, Result result, Unsigned p ) {
        // We only have a double table, of which float is a subset.  Long double
        // will be calculated in terms of that
 
        constexpr auto max_v =
          static_cast<Result>( dpow10_tbl[max_exp<Result>] );
 
        if( DAW_UNLIKELY( p > max_exp<Result> ) ) {
          if constexpr( std::is_floating_point_v<Result> ) {
            if( DAW_UNLIKELY( p >
                              daw::numeric_limits<Result>::max_exponent ) ) {
              return std::numeric_limits<Result>::infinity( );
            }
          }
          Result exp2 = max_v;
          p -= max_exp<Result>;
 
          for( ; p > max_exp<Result>; p -= max_exp<Result> ) {
            exp2 *= max_v;
          }
          return static_cast<Result>( result ) *
                 ( exp2 * static_cast<Result>(
                            dpow10_tbl[static_cast<std::size_t>( p )] ) );
        } else if( DAW_UNLIKELY( p < -max_exp<Result> ) ) {
          if constexpr( std::is_floating_point_v<Result> ) {
            if( DAW_UNLIKELY( p <
                              daw::numeric_limits<Result>::min_exponent ) ) {
              return Result{ 0 };
            }
          }
          Result exp2 = max_v;
          p += max_exp<Result>;
 
          for( ; p < -max_exp<Result>; p += max_exp<Result> ) {
            result /= max_v;
          }
          return ( static_cast<Result>( result ) /
                   static_cast<Result>(
                     dpow10_tbl[static_cast<std::size_t>( -p )] ) ) /
                 exp2;
        }
        if( p < 0 ) {
          return static_cast<Result>( result ) /
                 static_cast<Result>(
                   dpow10_tbl[static_cast<std::size_t>( -p )] );
        }
        return static_cast<Result>( result ) *
               static_cast<Result>( dpow10_tbl[static_cast<std::size_t>( p )] );
      }
 
      template<typename Result, typename Unsigned>
      DAW_ATTRIB_FLATINLINE static inline constexpr Result
      power10( runtime_exec_tag, Result result, Unsigned p ) {
        if constexpr( std::is_same_v<Result, double> or
                      std::is_same_v<Result, float> ) {
          return power10( constexpr_exec_tag{ }, result,
                          static_cast<std::int32_t>( p ) );
        } else {
          // For long double and others fallback to the slower std::pow
          using std::pow;
          return result * pow( static_cast<Result>( 10.0 ), p );
        }
      }
    } // namespace json_details
  }   // namespace DAW_JSON_VER
} // namespace daw::json