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More tweaks.

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This commit is contained in:
Daniel Lemire 2022-11-16 16:45:01 -05:00
parent 29b1a03d5b
commit bfc0478feb
1 changed files with 12 additions and 1 deletions
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13
include/fast_float/parse_number.h
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@ -60,7 +60,16 @@ from_chars_result parse_infnan(const char *first, const char *last, T &value) n
return answer; return answer;
} }
/**
* Returns true if the floating-pointing rounding mode is to 'nearest'.
* It is the default on most system. This function is meant to be inexpensive.
* Credit : @mwalcott3
*/
fastfloat_really_inline bool rounds_to_nearest() noexcept { fastfloat_really_inline bool rounds_to_nearest() noexcept {
// See
// A fast function to check your floating-point rounding mode
// https://lemire.me/blog/2022/11/16/a-fast-function-to-check-your-floating-point-rounding-mode/
//
// This function is meant to be equivalent to : // This function is meant to be equivalent to :
// prior: #include <cfenv> // prior: #include <cfenv>
// return fegetround() == FE_TONEAREST; // return fegetround() == FE_TONEAREST;
@ -68,6 +77,8 @@ fastfloat_really_inline bool rounds_to_nearest() noexcept {
// function call. // function call.
// //
// volatile prevents the compiler from computing the function at compile-time // volatile prevents the compiler from computing the function at compile-time
// It does not need to be std::numeric_limits<float>::min(), any small
// value so that 1 + x should round to 1 would do.
static volatile float fmin = std::numeric_limits<float>::min(); static volatile float fmin = std::numeric_limits<float>::min();
// //
// Explanation: // Explanation:
@ -135,7 +146,7 @@ from_chars_result from_chars_advanced(const char *first, const char *last,
// We do not have that fegetround() == FE_TONEAREST. // We do not have that fegetround() == FE_TONEAREST.
// Next is a modified Clinger's fast path, inspired by Jakub Jelínek's proposal // Next is a modified Clinger's fast path, inspired by Jakub Jelínek's proposal
if (pns.exponent >= 0 && pns.exponent <= binary_format<T>::max_exponent_fast_path() && pns.mantissa <=binary_format<T>::max_mantissa_fast_path(pns.exponent) && !pns.too_many_digits) { if (pns.exponent >= 0 && pns.exponent <= binary_format<T>::max_exponent_fast_path() && pns.mantissa <=binary_format<T>::max_mantissa_fast_path(pns.exponent) && !pns.too_many_digits) {
#if (defined(_MSC_VER) && defined(__clang__)) #if (defined(_WIN32) && defined(__clang__))
// ClangCL may map 0 to -0.0 when fegetround() == FE_DOWNWARD // ClangCL may map 0 to -0.0 when fegetround() == FE_DOWNWARD
if(pns.mantissa == 0) { if(pns.mantissa == 0) {
value = 0; value = 0;