int isqrt(unsigned x) {
  unsigned m, y, b;

  m = 0x40000000;
  y = 0;

  while(m != 0) {
    b = y | m;
    y = y >> 1;

    if (x >= b) {
      x = x - b;
      y = y | m;
    }

    m = m >> 2;
  }
  return y;
}