The program has several "encryption" algorithms. This one should blockwise reverse the input. "He|ll|o " becomes "o |ll|He" (block length of 2).

I add two strings, in this case appending the result string to the current "block" string and making that the result. When I add the result first and then the block it works fine and gives me back the original string. But when i try to reverse the order it just gives me the the last "block".

Several other functions that are used for "rotation" are above.

//amount of blocks
function amBl(i1:integer;i2:integer):integer;
begin
  if (i1 mod i2) <> 0 then result := (i1 div i2) else result := (i1 div i2) - 1;
end;

//calculation of block length
function calcBl(keyStr:string):integer;
var i:integer;
begin
  result := 0;
  for i := 1 to Length(keyStr) do
  begin
     result := (result + ord(keyStr[i])) mod 5;
     result := result + 2;
  end;

end;

//desperate try to add strings
function append(s1,s2:string):string;
begin
  insert(s2,s1,Length(s1)+1);
  result := s1;
end;

function rotation(inStr,keyStr:string):string;
var //array of chars -> string
    block,temp:string;
    //position in block  variable
    posB:integer;
    //block length and block count variable
    bl, bc:integer;
    //null character as placeholder
    n : ansiChar;

begin
   //calculating block length 2..6
   bl := calcBl(keyStr);
   setLength(block,bl);
   result := '';
   temp := '';
   {n := #00;}

   for bc := 0 to amBl(Length(inStr),bl) do
     begin
       //filling block with chars starting from back of virtual block (in inStr)
       for posB := 1 to bl do
       begin
       block[posB] := inStr[bc * bl + posB];
       {if inStr[bc * bl + posB] = ' ' then block[posB] := n;}
       end;

       //adding the block in front of the existing result string
       temp := result;
       result := block + temp;
       //result := append(block,temp);
       //result := concat(block,temp);

     end;

end;

(full code http://pastebin.com/6Uarerhk)

After all the loops "result" has the right value, but in the last step (between "result := block + temp" and the "end;" of the function) "block" replaces the content of "result" with itself completely, it doesn't add result at the end anymore. And as you can see I even used a temp variable to try to work around that.. doesnt change anything though.