shift a slice rightwards w/o allocating memory

description.txt

RShiftSlice(b = [abc.....], n = 3, padb = '0')
 [ab0....c]
    ^    ^
 [a00...bc]
   ^    ^
 [000..abc]
  ^    ^
 [0000.abc]
     ^
 [00000abc]
      ^

RShiftSlice(b = [abcde...], n = 5, padb = '0')
 [abcd0..e]
      ^  ^
 [abc00.de]
     ^  ^
 [ab000cde]
    ^  ^
 [a000bcde]
   ^  ^
 [000abcde]
  ^  ^

example.go

func main() {
  b := []byte{65,66,67,68,69,0,0,0} // ABCDE...
  RShiftSlice(b, 3, byte(48))
  println(string(b))  // 000ABCDE
}

RShiftSlice.go

func RShiftSlice(b []byte, n uint, padb byte) {
  if n != 0 {
    bz := uint(len(b))
    wi := bz-1
    for ; wi >= n; wi-- {
      b[wi] = b[wi-n]
      b[wi-n] = padb
    }
    zn := bz-n-1
    for ; wi > zn; wi-- {
      b[wi] = padb
    }
  }
}