Вопрос по иходному коду

procedure critt(var s:RawByteString; key:integer);
var
  i : Cardinal;
  c, d : Byte;
  a, b : Byte;
begin
  if Length(s)=0 then
    Exit;
  c := Byte(key);
  d := Byte(key shr 20);

  a := $B8;// 10111000b;
  for i := 1 to Length(s) do
    begin
      b := Byte(s[i]) + c;
      b := b xor d;
      b := (b shr 3) or (b shl 5);
      b := b xor a;

      s[i] := AnsiChar(b);
      a := (a shr 3) or (a shl 5);
    end;
end;
procedure decritt(var s:RawByteString; key:integer);
var
  i : Cardinal;
  c, d : Byte;
  a, b : Byte;
begin
  if Length(s)=0 then
    Exit;
  c := Byte(key);
  d := Byte(key shr 20);

  a := $B8;// 10111000b;
  for i := 1 to Length(s) do
    begin
      b := Byte(s[i]) xor a;
      b := (b shl 3) or (b shr 5);
      b := b xor d;
      b := b - c;

      s[i] := AnsiChar(b);
      a := (a shr 3) or (a shl 5);
    end;
end;