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

#include "libm.h"

double copysign(double x, double y) {
    union {
        double f;
        uint64_t i;
    } ux = {x}, uy = {y};
    ux.i &= -1ULL / 2;
    ux.i |= uy.i & 1ULL << 63;
    return ux.f;
}