[Cbc] integer overflow in CglGomory.cpp

[John Forrest]

Modified in trunk (can be copied to stable).  Just for now I have left 
it as was unless GOMORY_LONG is defined in configure.  If anyone is 
interested they could see what difference it makes (on my first test it 
was slower - but then invalid cuts can be very powerful!).  There may be 
some connection with queries about accuracy of Gomory cuts in 2015 
(GOMORY_RELAX_NUMBER).

John Forrest


On 16/05/17 10:47, Tobias Stengel wrote:
>
> Hi,
>
> I noticed an integer overflow in CglGomory.cpp / 
> nearestRational(double, int) lines 445 and 446. That specific MIP is 
> solved correctly, but I have no idea whether such an overflow can lead 
> to wrong cuts that e.g. cut off the optimal solution. Anyway integer 
> overflow is undefined behaviour in C/C++ and the returned fractional 
> is not „near“ the input…
>
> 2 parameter sets for nearestRational that lead to overflow can be 
> found in the attached test program. Does anyone know how 
> nearestRational works and how the overflow can be fixed properly?
>
> Thanks
>
> Tobias
>
>
>
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