fusl/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;
}