static float unprecise_invSqrt(float x) {
  float xhalf = 0.5f * x;
  int i = Float.floatToIntBits(x);
  i = 0x5f3759df - (i >> 1);
  x = Float.intBitsToFloat(i);
  x *= (1.5f - xhalf * x * x);
  ret x;
}