🚀 go-pugleaf

Robert AH Prins [mailto:prinsra@williscorroon.com] decided it was an
auspicious moment for:
>Take this snippet:
>
>const
>  sfile: integer = -1;
>
>procedure open(_file: integer);
>begin
>{$ifdef fast}
>  if _file <> sfile then
>    begin;
>      sfile:= _file;
>{$endif}
>      close(datatout);
>      assign(datatout, files[_file]);
>      settextbuf(datatout, databuf^, 8192);
>
>      if __first_event then
>        begin
>          rewrite(datatout);
>          __first_event:= false;
>        end
>      else
>        append(datatout);
>{$ifdef fast}
>    end;
>{$endif}
>end; {open}
>
>It's used a program in which many procedures can write their results to one
>of two files (a per event file and a summary file). Going through the
>program, I suddenly realized that I had never tracked calls to "open", and
>much to my surprise I discovered that on several occasions it's called with
>the same value for _file on several consecutive invovations. So I added the
>conditionals, and timed again, clean DOS, SMARTDRV with write caching, and
>running both the old and the new versions several times in alternating
>succession. Much to my surprise the old version, which performs the code
>dozens of times more than the the new version, is actually faster! (NB: The
>file is initially opened for summary data in the main program)
>
>Does anyone have an explanation?
>
I initially assumed that you were opening the file if actually needed.
However, re-reading your code with the {$ifdef} more carefully, I see
that the extra code is not actually doing anything that affects the
process so the code is probably a bit slower just due to the extra bits
you've added.

I am assuming the fast option is to prevent reopening the same file and
I have assumed that one of the files will already be open when this
procedure is called. If there is no open file then perhaps you need a
procedure to do the first open that can be separate from this one.

If you change the code to:

const
  sfile: integer = -1;

procedure open(_file: integer);
begin
  if _file <> sfile then
    begin
      sfile:= _file;            

{only close then assign and rewrite/append the file if different to old
one - otherwise you do not actually need to do anything so the if..then
is checking that you have a different file}

      close(datatout);
      assign(datatout, files[_file]);
      settextbuf(datatout, databuf^, 8192);

      if __first_event then
        begin
          rewrite(datatout);
          __first_event:= false;
        end
      else
        append(datatout);
    end;

end; {open}

-- 
Pedt

In Idle village (near Bradford), do they have an Idle Working Mens Club ?