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72 lines
1.7 KiB
C
72 lines
1.7 KiB
C
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/*
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* PROJECT: ReactOS CRT library
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* LICENSE: MIT (https://spdx.org/licenses/MIT)
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* PURPOSE: Implementation of floor
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* COPYRIGHT: Copyright 2021 Timo Kreuzer <timo.kreuzer@reactos.org>
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*/
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#define _USE_MATH_DEFINES
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#include <math.h>
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#include <limits.h>
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#ifdef _MSC_VER
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#pragma function(floor)
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#endif
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double
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__cdecl
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floor(double x)
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{
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/* Load the value as uint64 */
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unsigned long long u64 = *(unsigned long long*)&x;
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/* Check for NAN */
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if ((u64 & ~(1ULL << 63)) > 0x7FF0000000000000ull)
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{
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/* Set error bit */
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u64 |= 0x0008000000000000ull;
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return *(double*)&u64;
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}
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/* Check if x is positive */
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if ((u64 & (1ULL << 63)) == 0)
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{
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/* Check if it fits into an int64 */
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if (x < (double)_I64_MAX)
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{
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/* Just cast to int64, which will truncate towards 0,
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which is what we want here.*/
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return (double)(long long)x;
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}
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else
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{
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/* The exponent is larger than the fraction bits.
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This means the number is already an integer. */
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return x;
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}
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}
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else
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{
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/* Check if it fits into an int64 */
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if (x > (double)_I64_MIN)
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{
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/* Check if it is -0 */
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if (x == -0.)
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{
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return -0.;
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}
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/* Cast to int64 to truncate towards 0. If this matches the
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input, return it as is, otherwise subtract 1 */
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double y = (double)(long long)x;
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return (x == y) ? y : y - 1;
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}
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else
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{
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/* The exponent is larger than the fraction bits.
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This means the number is already an integer. */
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return x;
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}
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}
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}
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