69 lines
1.2 KiB
C
69 lines
1.2 KiB
C
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#include <math.h>
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#include <stdint.h>
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double fmod(double x, double y)
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{
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union {double f; uint64_t i;} ux = {x}, uy = {y};
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int ex = ux.i>>52 & 0x7ff;
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int ey = uy.i>>52 & 0x7ff;
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int sx = ux.i>>63;
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uint64_t i;
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/* in the followings uxi should be ux.i, but then gcc wrongly adds */
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/* float load/store to inner loops ruining performance and code size */
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uint64_t uxi = ux.i;
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if (uy.i<<1 == 0 || isnan(y) || ex == 0x7ff)
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return (x*y)/(x*y);
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if (uxi<<1 <= uy.i<<1) {
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if (uxi<<1 == uy.i<<1)
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return 0*x;
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return x;
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}
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/* normalize x and y */
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if (!ex) {
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for (i = uxi<<12; i>>63 == 0; ex--, i <<= 1);
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uxi <<= -ex + 1;
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} else {
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uxi &= -1ULL >> 12;
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uxi |= 1ULL << 52;
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}
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if (!ey) {
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for (i = uy.i<<12; i>>63 == 0; ey--, i <<= 1);
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uy.i <<= -ey + 1;
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} else {
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uy.i &= -1ULL >> 12;
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uy.i |= 1ULL << 52;
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}
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/* x mod y */
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for (; ex > ey; ex--) {
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i = uxi - uy.i;
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if (i >> 63 == 0) {
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if (i == 0)
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return 0*x;
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uxi = i;
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}
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uxi <<= 1;
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}
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i = uxi - uy.i;
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if (i >> 63 == 0) {
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if (i == 0)
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return 0*x;
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uxi = i;
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}
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for (; uxi>>52 == 0; uxi <<= 1, ex--);
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/* scale result */
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if (ex > 0) {
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uxi -= 1ULL << 52;
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uxi |= (uint64_t)ex << 52;
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} else {
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uxi >>= -ex + 1;
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}
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uxi |= (uint64_t)sx << 63;
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ux.i = uxi;
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return ux.f;
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}
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