code: func leadingZeros(x uint32) (n int) {
  	if x >= 1<<16 {
  		x >>= 16
  		n = 16
  	}
  	if x >= 1<<8 {
  		x >>= 8
  		n += 8
  	}
  	n += int(len8tab[x])
  	return 32 - n
  }
docs: // use https://golang.org/pkg/math/bits/#LeadingZeros32 in the future