[fpc-devel] bug: Inc(v,i)/Dec(v,i)

Marcel Martin mm10 at ellipsa.net
Thu Jul 7 23:27:13 CEST 2005

Vinzent Hoefler a écrit :
> On Thursday 07 July 2005 05:39, Peter Vreman wrote:
>>>shouldn't it implement inv(v,-1) in exactly the same way it
>>>implements v:=v-1?
>>The problem is what type do you give to -1. In the old situation the
>>-1 was converted to the same type as v -> longword.
> Which should trigger a range check already, because -1 can't be 
> represented as valid longword.
> Personal note: Maybe there was a reason why Borland Pascal didn't do 
> range checks on Inc/Dec.

Yes, there is always a good reason for a bug :-)

To the FPC team.
If ever you changed that, i.e., if you suppressed the overflows
with Inc and Dec, thanks to let us know explicitely (here, for
instance). Personally, I would have to rewrite a few lines of
code, like, for instance, in

procedure XDiv2(X: PBigFloat);
   with X^ do if not IEqu0(Mantissa) then {$Q+} Dec(Exponent); {$Q-}

> The only time I ever used it was a checksum 
> calculation which was modulo anyway. Any other time I use the usual 
> operators. So especially with the "added" overflow check I think, Inc 
> and Dec are pretty useless functions, because the don't do anything you 
> can't accomplish by using "+" or "-" unless you have 
> very_long_and_complex_variable_names and want to save some typing work.

That's a matter of habit. Not sure but I believe that with TP3,
the compiled code was better with "Inc" than with "+".


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