src/stdlib/frexp.c

#include <math.h>
#include <inttypes.h>

double frexp(double x, int *e)
{
	union { double d; uint64_t i; } y = { x };
	int ee = y.i>>52 & 0x7ff;

	if (!ee) {
		if (x) {
			x = frexp(x*0x1p64, e);
			*e -= 64;
		} else *e = 0;
		return x;
	} else if (ee == 0x7ff) {
		return x;
	}

	*e = ee - 0x3fe;
	y.i &= 0x800fffffffffffffull;
	y.i |= 0x3fe0000000000000ull;
	return y.d;
}