#include <assert.h>
#include <math.h>
#include <limits.h>

/* Access bit-level representation of floating-point number */
typedef unsigned float_bits;

/* computs 0.5*f.  If f is NaN, then return f. */
float_bits float_half(float_bits uf) {
  float_bits s = uf & 0x80000000, f = uf & 0x007FFFFF, e = (uf >> 23) & 0xFF;

  if (e == 0xFF) {
    return uf;
  }

  if (e > 1) {
    e--;
    return s | (e << 23) | f;
  }

  if (e == 1) {
    f |= 1 << 23;
    e = 0;
  }
  int t = f;
  f >>= 1;
  if (t & f & 1) {
    f++;
  }
  return s | (e << 23) | f;
}

int main() {
  for (float_bits x = 0; ; x++) {
    float *a = (float*) &x;
    float b = 0.5 * *a;
    float_bits c = float_half(x);
    float *d = (float*) &c;
    assert(b == *d || (isnan(b) && isnan(*d)));

    if (x == UINT_MAX) {
      break;
    }
  }
}