code: func fastLog2Floor(n uint32) uint8 {
  	rv := uint8(0)
  	exponent := uint8(16)
  	for i := 0; i < 5; i++ {
  		if n&log2FloorMasks[i] != 0 {
  			rv += exponent
  			n >>= exponent
  		}
  		exponent >>= 1
  	}
  	return rv
  }
docs: // fastLog2Floor calculates and returns floor(log2(x)) in a constant 5 steps.