code: func distcmp(target, a, b common.Hash) int {
  	for i := range target {
  		da := a[i] ^ target[i]
  		db := b[i] ^ target[i]
  		if da > db {
  			return 1
  		} else if da < db {
  			return -1
  		}
  	}
  	return 0
  }
docs: // distcmp compares the distances a->target and b->target.
  // Returns -1 if a is closer to target, 1 if b is closer to target
  // and 0 if they are equal.