code: func Proximity(one, other []byte) (ret int) {
  	b := (MaxPO-1)/8 + 1
  	if b > len(one) {
  		b = len(one)
  	}
  	m := 8
  	for i := 0; i < b; i++ {
  		oxo := one[i] ^ other[i]
  		for j := 0; j < m; j++ {
  			if (oxo>>uint8(7-j))&0x01 != 0 {
  				return i*8 + j
  			}
  		}
  	}
  	return MaxPO
  }
docs: // Proximity returns the proximity order of the MSB distance between x and y
  //
  // The distance metric MSB(x, y) of two equal length byte sequences x an y is the
  // value of the binary integer cast of the x^y, ie., x and y bitwise xor-ed.
  // the binary cast is big endian: most significant bit first (=MSB).
  //
  // Proximity(x, y) is a discrete logarithmic scaling of the MSB distance.
  // It is defined as the reverse rank of the integer part of the base 2
  // logarithm of the distance.
  // It is calculated by counting the number of common leading zeros in the (MSB)
  // binary representation of the x^y.
  //
  // (0 farthest, 255 closest, 256 self)