Сравнить бинарные файлы и узнать разницу в процентах

uses Math
 
function CompareFiles(const Filename1, Filename2: String): Integer;
var FileStream1, FileStream2: TFileStream;
    FileSize1, FileSize2, I, II: Int64;
    FileData1, FileData2: TBytes;
    DifferentBytes: Int64;
begin
  Result:= -1;
  if FileExists(Filename1) and FileExists(Filename2) then begin
    try
      FileStream1:= TFileStream.Create(Filename1, fmOpenRead);
      FileStream2:= TFileStream.Create(Filename2, fmOpenRead);
 
      FileSize1:= FileStream1.Size;
      FileSize2:= FileStream2.Size;
 
      SetLength(FileData1, FileSize1);
      SetLength(FileData2, FileSize2);
      FileStream1.Read(FileData1[0], FileSize1);
      FileStream2.Read(FileData2[0], FileSize2);
 
      DifferentBytes:= Abs(FileSize1 - FileSize2);
      II:= Min(FileSize1, FileSize2);
 
      for I := 0 to II-1 do
        if FileData1[i] <> FileData2[i]
          then DifferentBytes:= DifferentBytes + 1;
 
      Result:= Round(DifferentBytes / Max(FileSize1, FileSize2) * 100);
 
    finally
      FileStream1.Free;
      FileStream2.Free;
      SetLength(FileData1, 0);
      SetLength(FileData2, 0);
    end;
  end;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
 if OpenDialog1.Execute then Edit1.Text:= OpenDialog1.FileName;
end;
 
procedure TForm1.Button2Click(Sender: TObject);
begin
  if OpenDialog2.Execute then Edit2.Text:= OpenDialog2.FileName;
end;
 
procedure TForm1.Button3Click(Sender: TObject);
var Percent: Integer;
begin
  Percent:= CompareFiles(Edit1.Text, Edit2.Text);
  if Percent <> -1 then
    ShowMessage('Файлы различны на ' + IntToStr(Percent) + '%');
end;