Fast way to split a string into fixed-length parts in Delphi

Question

I need to split a string to a TStringList with fixed-length sub-strings.

Currently I use:

procedure StrToStringList(ASource: string; AList: TStrings; AFixedLen: Integer);
begin
    Assert(Assigned(AList));
    while Length(ASource) > AFixedLen do
    begin
        AList.Add(LeftStr(ASource, AFixedLen));
        Delete(ASource, 1, AFixedLen);
    end;
    AList.Add(ASource);
end;

This works, but seems to be slow. Any better / faster idea?

Edited: Profiling of the results:

The speed gain is quite impressive. Here are the results of my (subjective) profiling.

Data size: 290KB, FixedLen: 100:

• Original code: 58 ms
• Heffernan: 1 ms
• Deltics: 1 ms

Data size: 2805KB, FixedLen: 100:

• Original code: 5803 ms
• Heffernan: 5 ms
• Deltics: 4 ms

Answer 1

I think it is wasteful to modify the input string. Avoid this like this:

var
  Remaining: Integer;
  StartIndex: Integer;
begin
  Remaining := Length(ASource);
  StartIndex := 1;
  while Remaining > 0 do
  begin
    AList.Add(Copy(ASource, StartIndex, AFixedLen));
    inc(StartIndex, AFixedLen);
    dec(Remaining, AFixedLen);
  end;
end;

This will reduce the amount of heap allocation, and the copying.

However, I would not be surprised if you observed little gain in performance. In order to perform any serious optimisation we'd likely need to see some example input data.