RoundUpToPowerOf2

unsigned int RoundUpToPowerOf2(unsigned int x){
  ASSERT(x<=0x80000000u);
  x = x - 1;
  x = x | (x >> 1);
  x = x | (x >> 2);
  x = x | (x >> 4);
  x = x | (x >> 8);
  x = x | (x >> 16);
  return x + 1;
}