corecrt_internal_fltintrn.h

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//
// corecrt_internal_fltintrn.h
//
//      Copyright (c) Microsoft Corporation. All rights reserved.
//
// Floating point conversion routines for internal use.  This is a C++ header.
//
#pragma once
 
#include <corecrt_internal.h>
#include <float.h>
#include <stdint.h>
#include <stdlib.h>
 
 
 
//-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
// Types
//
//-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
template <typename FloatingType>
struct __acrt_floating_type_traits;
 
template <>
struct __acrt_floating_type_traits<float>
{
    enum : int32_t
    {
        mantissa_bits            = FLT_MANT_DIG,
        exponent_bits            = sizeof(float) * CHAR_BIT - FLT_MANT_DIG,
 
        maximum_binary_exponent  = FLT_MAX_EXP - 1,
        minimum_binary_exponent  = FLT_MIN_EXP - 1,
 
        exponent_bias            = 127
    };
 
    enum : uint32_t
    {
        exponent_mask             = (1u << (exponent_bits    )) - 1,
        normal_mantissa_mask      = (1u << (mantissa_bits    )) - 1,
        denormal_mantissa_mask    = (1u << (mantissa_bits - 1)) - 1,
 
        special_nan_mantissa_mask = (1u << (mantissa_bits - 2))
    };
 
    struct components_type
    {
        uint32_t _mantissa : mantissa_bits - 1;
        uint32_t _exponent : exponent_bits;
        uint32_t _sign     : 1;
    };
 
    static_assert(sizeof(components_type) == sizeof(float), "unexpected components size");
};
 
template <>
struct __acrt_floating_type_traits<double>
{
    enum : int32_t
    {
        mantissa_bits            = DBL_MANT_DIG,
        exponent_bits            = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 
        maximum_binary_exponent  = DBL_MAX_EXP - 1,
        minimum_binary_exponent  = DBL_MIN_EXP - 1,
 
        exponent_bias            = 1023
    };
 
    enum : uint64_t
    {
        exponent_mask             = (1ull << (exponent_bits    )) - 1,
        normal_mantissa_mask      = (1ull << (mantissa_bits    )) - 1,
        denormal_mantissa_mask    = (1ull << (mantissa_bits - 1)) - 1,
 
        special_nan_mantissa_mask = (1ull << (mantissa_bits - 2))
    };
 
    struct components_type
    {
        uint64_t _mantissa : mantissa_bits - 1;
        uint64_t _exponent : exponent_bits;
        uint64_t _sign     : 1;
    };
 
    static_assert(sizeof(components_type) == sizeof(double), "unexpected components size");
};
 
enum class __acrt_fp_class : uint32_t
{
    finite,
    infinity,
    quiet_nan,
    signaling_nan,
    indeterminate,
};
 
enum class __acrt_has_trailing_digits
{
    trailing,
    no_trailing
};
 
// Precision is the number of digits after the decimal point, but
// this has different implications for how many digits need to be
// generated based upon how the number will be formatted.
enum class __acrt_precision_style
{
    fixed,      // 123.456 %f style requires '3' precision to generate 6 digits to format "123.456".
    scientific  // 123.456 %e style requires '5' precision to generate 6 digits to format "1.23456e+02".
};
 
// This rounding mode is used to know if we are using functions like gcvt vs printf
enum class __acrt_rounding_mode
{
    legacy,
    standard
};
 
inline __acrt_fp_class __cdecl __acrt_fp_classify(double const& value) throw()
{
    using floating_traits = __acrt_floating_type_traits<double>;
    using components_type = floating_traits::components_type;
 
    components_type const& components = reinterpret_cast<components_type const&>(value);
 
    bool const value_is_nan_or_infinity = components._exponent == (1u << floating_traits::exponent_bits) - 1;
    if (!value_is_nan_or_infinity)
    {
        return __acrt_fp_class::finite;
    }
    else if (components._mantissa == 0)
    {
        return __acrt_fp_class::infinity;
    }
    else if (components._sign == 1 && components._mantissa == floating_traits::special_nan_mantissa_mask)
    {
        return __acrt_fp_class::indeterminate;
    }
    else if (components._mantissa & floating_traits::special_nan_mantissa_mask) // Quiet NAN
    {
        return __acrt_fp_class::quiet_nan;
    }
    else // Signaling NAN
    {
        return __acrt_fp_class::signaling_nan;
    }
}
 
inline bool __cdecl __acrt_fp_is_negative(double const& value) throw()
{
    using floating_traits = __acrt_floating_type_traits<double>;
    using components_type = floating_traits::components_type;
 
    components_type const& components = reinterpret_cast<components_type const&>(value);
 
    return components._sign == 1;
}
 
struct _strflt
{
    int   sign;     // Zero if positive otherwise negative
    int   decpt;    // Exponent of floating point number
    char* mantissa; // Pointer to mantissa in string form
};
 
typedef _strflt* STRFLT;
 
//-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
// Floating Point Conversion Routines
//
//-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
_CRT_BEGIN_C_HEADER
 
// Result buffer count for __acrt_fp_format has a minimum value that depends on the precision requested.
// This requirement originates and propagates from the fp_format_e_internal function (in convert\cvt.cpp)
// This macro can be used to annotate result_buffer_count in the below functions
#define _In_fits_precision_(precision_arg)                                        \
        _When_(precision_arg <= 0, _Pre_satisfies_(_Curr_ > 9))                   \
        _When_(precision_arg >  0, _Pre_satisfies_(_Curr_ > 9 + precision_arg))
 
_Success_(return == 0)
errno_t __cdecl __acrt_fp_format(
    _In_                                                   double const*          value,
    _Maybe_unsafe_(_Inout_updates_z_, result_buffer_count) char*                  result_buffer,
    _In_fits_precision_(precision)                         size_t                 result_buffer_count,
    _Out_writes_(scratch_buffer_count)                     char*                  scratch_buffer,
    _In_                                                   size_t                 scratch_buffer_count,
    _In_                                                   int                    format,
    _In_                                                   int                    precision,
    _In_                                                   uint64_t               options,
    _In_                                                   __acrt_rounding_mode   rounding_mode,
    _Inout_                                                __crt_cached_ptd_host& ptd
    );
 
errno_t __cdecl __acrt_fp_strflt_to_string(
    _Out_writes_z_(buffer_count) char*  buffer,
    _When_((digits >  0), _In_ _Pre_satisfies_(buffer_count > digits + 1))
    _When_((digits <= 0), _In_ _Pre_satisfies_(buffer_count > 1))
    _In_                         size_t buffer_count,
    _In_                         int    digits,
    _Inout_                      STRFLT value,
    _In_                         __acrt_has_trailing_digits trailing_digits,
    _In_                         __acrt_rounding_mode rounding_mode,
    _Inout_                      __crt_cached_ptd_host& ptd
    );
 
__acrt_has_trailing_digits __cdecl __acrt_fltout(
    _In_                         _CRT_DOUBLE            value,
    _In_                         unsigned               precision,
    _In_                         __acrt_precision_style precision_style,
    _Out_                        STRFLT                 result,
    _Out_writes_z_(buffer_count) char*                  buffer,
    _In_                         size_t                 buffer_count
    );
 
_CRT_END_C_HEADER