🚀 go-pugleaf

In article <J5r+FNAGY7a2Yw7Y@pedt.demon.co.uk>,
  Pedt Scragg <newsmaster@pedt.demon.co.uk> wrote:
> Robert AH Prins [mailto:prinsra@williscorroon.com] decided it was an
> auspicious moment for:
>
> <opening and closing file if needed>
> >> >
> >> I initially assumed that you were opening the file if actually needed.
> >> However, re-reading your code with the {$ifdef} more carefully, I see
> >> that the extra code is not actually doing anything that affects the
> >> process so the code is probably a bit slower just due to the extra bits
> >> you've added.
> >
> >Yes, but don't you think (that's at least what I did!) that a simple if test
> >should be quite a lot faster than closing a file, and opening another one?
>
> Should definitely be faster. The file opening/closing overhead is
> significant if needed to be called a lot of times in the program.
>
> >{$ifdef fast}
> >  if _file <> sfile then
> >    begin;
> >      sfile:= _file;
> >{$endif}
> >      close(datatout);
> >      assign(datatout, files[_file]);
>
> The problem with your {$ifdef fast}/{$endif} pairs is that they are
> adding the conditional test to the file number but you then run the
> close/assign/open part as well.

No, I don't, as can easily be demonstrated by putting a
"writeln('Close/Open');" in the code between begin & end.

> Leaving the conditionals in but rearranging them and the code slightly
> to use the opposite conditional check (I deleted the conditionals from
> the previous post which in hindsight perhaps I should not have done)
>
> const
>   sfile: integer = -1;
>
> procedure open(_file: integer);
> begin
>
> {$ifdef fast}
>   if _file = sfile then exit else
>     begin
> {$endif}
>       sfile:= _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);
> {$ifdef fast}
>     end;
> {$endif}
> end; {open}

Your code is doing exactly what my code is doing, be it that we use opposite
test to skip the close/open section...

But if you look at the code generated for the if-statement in the two cases,
you'll see that my code is a trifle shorter:

My code:

cs:05AE 55             push   bp
cs:05AF 89E5           mov    bp,sp
cs:05B1 8B4604         mov    ax,[bp+04]
cs:05B4 3B060A2A       cmp    ax,[2A0A]
cs:05B8 7503           jne    05BD
cs:05BA E98000         jmp    063D
cs:05BD 8B4604         mov    ax,[bp+04]
cs:05C0 A30A2A         mov    [2A0A],ax

Your code:

cs:05AE 55             push   bp
cs:05AF 89E5           mov    bp,sp
cs:05B1 8B4604         mov    ax,[bp+04]
cs:05B4 3B060A2A       cmp    ax,[2A0A]
cs:05B8 7506           jne    05C0
cs:05BA E98300         jmp    0640 -+---> Bit silly...
cs:05BD E98000         jmp    0640 -+
cs:05C0 8B4604         mov    ax,[bp+04]
cs:05C3 A30A2A         mov    [2A0A],ax

> > Conditionals have the advantage that you
> >don't have to change your source every time - the code is in an include file,
> >and not a unit.
> >
> Yes, and it is a great advantage. I keep source handy for V5, V5.5, V6
> and V7 and find it invaluable not only for version changes but for
> switching on and off things like stack and range checks. IMHO, the usage
> of conditionals is very underrated.

Robert
--
Robert AH Prins
prinsra@williscorroon.com

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