third_party/ulib/musl/src/math/modf.c

#include "libm.h"

double modf(double x, double* iptr) {
    union {
        double f;
        uint64_t i;
    } u = {x};
    uint64_t mask;
    int e = (int)(u.i >> 52 & 0x7ff) - 0x3ff;

    /* no fractional part */
    if (e >= 52) {
        *iptr = x;
        if (e == 0x400 && u.i << 12 != 0) /* nan */
            return x;
        u.i &= 1ULL << 63;
        return u.f;
    }

    /* no integral part*/
    if (e < 0) {
        u.i &= 1ULL << 63;
        *iptr = u.f;
        return x;
    }

    mask = -1ULL >> 12 >> e;
    if ((u.i & mask) == 0) {
        *iptr = x;
        u.i &= 1ULL << 63;
        return u.f;
    }
    u.i &= ~mask;
    *iptr = u.f;
    return x - u.f;
}