AcessViolation em while ao gerar MD5

// Update given Context to include Length bytes of Input
procedure MD5Update(var Context: MD5Context; Input: pChar; Length: longword);
var
   Index: longword;
   PartLen: longword;
   I: longword;
begin
   with Context do begin
      Index := (Count[0] shr 3) and $3f;
      inc(Count[0], Length shl 3);
      if Count[0] < (Length shl 3) then inc(Count[1]);
      inc(Count[1], Length shr 29);
   end;
   PartLen := 64 - Index;
   if Length >= PartLen then begin
      CopyMemory(@Context.Buffer[Index], Input, PartLen);
      Transform(@Context.Buffer, Context.State);

      I := PartLen;
      while I + 63 < Length do begin
         Transform(@Input[I], Context.State);
         inc(I, 64);
      end;
      Index := 0;
   end else I := 0;
   CopyMemory(@Context.Buffer[Index], @Input[I], Length - I);
end;