source: asp3_tinet_ecnl_arm/trunk/musl-1.1.18/src/math/fmod.c@ 352

#include <math.h>
#include <stdint.h>

double fmod(double x, double y)
{
        union {double f; uint64_t i;} ux = {x}, uy = {y};
        int ex = ux.i>>52 & 0x7ff;
        int ey = uy.i>>52 & 0x7ff;
        int sx = ux.i>>63;
        uint64_t i;

        /* in the followings uxi should be ux.i, but then gcc wrongly adds */
        /* float load/store to inner loops ruining performance and code size */
        uint64_t uxi = ux.i;

        if (uy.i<<1 == 0 || isnan(y) || ex == 0x7ff)
                return (x*y)/(x*y);
        if (uxi<<1 <= uy.i<<1) {
                if (uxi<<1 == uy.i<<1)
                        return 0*x;
                return x;
        }

        /* normalize x and y */
        if (!ex) {
                for (i = uxi<<12; i>>63 == 0; ex--, i <<= 1);
                uxi <<= -ex + 1;
        } else {
                uxi &= -1ULL >> 12;
                uxi |= 1ULL << 52;
        }
        if (!ey) {
                for (i = uy.i<<12; i>>63 == 0; ey--, i <<= 1);
                uy.i <<= -ey + 1;
        } else {
                uy.i &= -1ULL >> 12;
                uy.i |= 1ULL << 52;
        }

        /* x mod y */
        for (; ex > ey; ex--) {
                i = uxi - uy.i;
                if (i >> 63 == 0) {
                        if (i == 0)
                                return 0*x;
                        uxi = i;
                }
                uxi <<= 1;
        }
        i = uxi - uy.i;
        if (i >> 63 == 0) {
                if (i == 0)
                        return 0*x;
                uxi = i;
        }
        for (; uxi>>52 == 0; uxi <<= 1, ex--);

        /* scale result */
        if (ex > 0) {
                uxi -= 1ULL << 52;
                uxi |= (uint64_t)ex << 52;
        } else {
                uxi >>= -ex + 1;
        }
        uxi |= (uint64_t)sx << 63;
        ux.i = uxi;
        return ux.f;
}