Нетипизированный файл. Нужно оптимизировать

program project1;

{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
  Classes
  { you can add units after this };

{$IFDEF WINDOWS}{$R project1.rc}{$ENDIF}
var
  filename: string;
  f: file;
  m1, m2, n: integer;
  buf1, buf2: integer;
  i: integer;
begin
write('Enter file name: '); readln(fileName);
write('Enter begin of first block: '); readln(m1);
write('Enter begin of second block: '); readln(m2);
write('Enter size of blocks (bytes): '); readln(n);
if (abs(m1 - m2) < n) then begin writeln('Blocks are crossing.'); readln; exit; end;
assign(f, fileName);
reset(f, 1);
for i:= 0 to n - 1 do
begin
  seek(f, m1 + i);
  BlockRead(f, buf1, 1);

  seek(f, m2 + i);
  BlockRead(f, buf2, 1);

  seek(f, m2 + i);
  BlockWrite(f, buf1, 1);

  seek(f, m1 + i);
  BlockWrite(f, buf2, 1);

end;
close(f);
writeln('Press any key to continue....'); readln;
end.

for i:= 0 to n - 1 do
begin
  seek(f, m1 + i);
  BlockRead(f, buf1, 1);

  seek(f, m2 + i);
  BlockRead(f, buf2, 1);

  seek(f, m2 + i);
  BlockWrite(f, buf1, 1);

  seek(f, m1 + i);
  BlockWrite(f, buf2, 1);