[Cbc] integer overflow in CglGomory.cpp

[John Forrest]

Tobias,

CglGomory is assuming that if it can get a rational number which is 
within 1.0e-10 of double then that will do.  The trouble is that 
1.0/1.0e-10 overflows an integer.  A very crude solution would be to 
change that to 1.0e-7 but I suspect that would lead to inaccurate cuts.

Changing int to long long int fixes the problem.  I think the solution 
is to be more accurate e.g. 1.0e-12 but convert back to int if possible 
or else say no rational.

Shall I modify to use long long int?

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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