initial cmath code and minor libm.h update

[libm] / src / math / frexp.c

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