int isqrt(unsigned x) {
  unsigned x1;
  int s, g0, g1;

  if (x <= 1) return x;

  s = 1;
  x1 = x - 1;

  if (x1 > 65535) {s = s + 8; x1 = x1 >> 16;}

  if (x1 > 255) {s = s + 4; x1 = x1 >> 8;}

  if (x1 > 15) {s = s + 2; x1 = x1 >> 4;}

  if (x1 > 3) {s = s + 1;}

  g0 = 1 << s;

  g1 = (g0 + (x >> s)) >> 1;

  while (g1 < g0) {
    g0 = g1;
    g1 = (g0 + (x/g0)) >> 1;
  }

  return g0;
}