I’m trying to use it in a way that always worked in Turbo Pascal for DOS, I
have no idea how to program in C, I find Pascal much more clear and easy to
follow and C just confuses me, so I never spent much time other than a few
stray projects here and there on C… I’ve always used pascal since the 80s, and
in fact my units that change the for loop variable that run in {$Mode TP} are
the original code from turbo pascal written in the 80s.. over the decades I’ve
modified stuff all around it, but the actual code with for loops with changing
control variables is the exact same code I was running on old 4.7MHz Dos
machines with turbo pascal for DOS… so for nearly 40 years I have never even
known there was some rule against changing the control variable in for loops,
it’s always worked and I’ve always used it.. and it still works if I use {$Mode
TP} it may not work if I try to use Delphi or something else, and there may be
some pascal version even older than turbo pascal for DOS that didn’t act this
way, but from the entire scope of my programming experience, this is something
that has just always worked and I never had a reason not to use it.
James
From: fpc-pascal <fpc-pascal-boun...@lists.freepascal.org> On Behalf Of Markus
Greim
Sent: Monday, September 9, 2019 1:32 PM
To: FPC-Pascal users discussions <fpc-pascal@lists.freepascal.org>
Subject: Re: [fpc-pascal] Illegal counter variable?
James,
not every body is using a GHz machine. I am , for example, programming a 80186
in an embedded system with very limited speed an RAM.
But I understand thats not a general argument.
But look at MISRA C. Its a big set of rules for "real" save C programming, more
or less now the standard in the automobile industry.
Also here are strict rules for counters in for loops.
See:
https://www.misra.org.uk/forum/viewtopic.php?t=272
So what they are doing is writing Pascal programs in C... ;-) And they need
huge and expensive and complex tools to check the C code for
MISRA compatibility!
So we should NOT give up the safety of Pascal for the sloppiness of C!
Kind Regards
Markus
<https://app.frontapp.com/api/1/noauth/companies/schleibinger_geraete_gmbh/seen/msg_3t3yn9e/han_9pzu6a/a2c200f4.gif>
On September 9, 2019, 7:19 PM GMT+2 ja...@productionautomation.net
<mailto:ja...@productionautomation.net> wrote:
Yes, today such limitations do seem too restrictive, I wonder if the reasons
for the restrictions have become obsolete. You would have to have a really slow
computer with very limited resources to optimize loops to the point of reducing
functionality like this, and the tendency with modern pc's is to have a larger
library of much more powerful and more flexible tools, even if they are more
complex and take more memory and resources. For example Case statements used to
only work with characters or integers, but the modern version now also works
with strings, very much added functionality for sure, but also would use more
resources.... but we would all rather have the capability because even a
raspberry pi is blazing fast and has ram to burn compared to our old 8086s It
seems silly to me that I can't so what I used to do with Turbo Pascal for DOS
where I was limited to programs of a few hundred K, due to optimizations that
just can't make much of a difference at all on modern computers. I am happy
that FPC has TP compatibility mode though! It's just I get to a point where I
eventually can't cross units since I can't have a circular unit reference. So I
have to choose for any given unit.. do I want my old for loops and change the
control variables, or do I want cool new case statements... etc.. it would be
nice to have {$Mode everything_the_way_I_want_it}
Since the compiler knows I was trying to change the variable inside the for
loop, could it not just compile in not quite as efficient code (TP MODE for
loop) when it detects this, and use the more efficient optimized code when it
detects that it is able to use it?
James
-----Original Message-----
From: fpc-pascal <fpc-pascal-boun...@lists.freepascal.org
<mailto:fpc-pascal-boun...@lists.freepascal.org> > On Behalf Of Bernd Oppolzer
Sent: Monday, September 9, 2019 10:46 AM
To: FPC-Pascal users discussions <fpc-pascal@lists.freepascal.org
<mailto:fpc-pascal@lists.freepascal.org> >
Subject: Re: [fpc-pascal] Illegal counter variable?
Am 09.09.2019 um 16:11 schrieb James Richters:
> I just don't see why having the limitation, there is no technical
> reason that the for loop couldn't change that I can see.. especially since it
> works in TP mode.
The original reason why some Pascal implementations had this limitation:
for performance or optimization reasons, the loop control variable was
transferred to a register at the beginning of the loop, and changing the
variable (at its storage location) inside the loop simply had no effect,
because the variable was not fetched from there again during loop execution.
Worse: maybe, to make read accesses to the loop control variable valid inside
the loop, they are prepared by storing the control register value into the loop
control variable, thus turning changes to the loop control variable useless.
Forbidding (write) accesses to the loop control variable allows for many
aggressive optimization strategies around loops.
Maybe today such limitations seem too restrictive.
Kind regards
Bernd
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