[GiNaC-list] Bug in GiNaC 1.7.0

[Richard B. Kreckel]

Hi,

On 07/19/2016 08:30 PM, Mario Prausa wrote:
> I found a regression in GiNaC 1.7.0.
> 
> In basic.cpp (function subs_one_level) the lines
> 
>   588         auto it = m.find(*this);
>   589         if (it != m.end())
>   590             return it->second;
>   591         return *this;
> 
> are causing problems. In GiNaC 1.6.7 we have
> 
>  599                 ex thisex = *this;
>  600                 it = m.find(thisex);
>  601                 if (it != m.end())
>  602                         return it->second;
>  603                 return thisex;
> 
> which work properly.
> 
> The problem with the 1.7.0 version is, that the this-pointer is
> dynamically allocated in line 618 (when called from line 629).
> 
> *this is implicitly casted into an ex, both in line 588 and in line
> 591.  As the dynallocated-flag is set, the first cast destroys the
> this-pointer, and the second cast crashes.

Thank you very much for carefully debugging this regression and
explaining it. Such attention and enduringness is highly appreciated!

It was wrong to remove the temporary variable thisex in 1b8bcb06. The
obvious fix is to reinstate the temporary ex. This section definitely
should have a comment explaining what's going on so it doesn't happen
again. (@Ralf: I see that you've independently introduced the same bug
in pynac.)

@Mario, since you found the regression, could you, please, send a small
test case in order to put it into the regression tests?

All my best,
   -richy.
-- 
Richard B. Kreckel
<http://in.terlu.de/~kreckel/>