RE: Error while generating bearoff database

[Ian Shaw]

You’re right, Øystein.

 

We came across this problem years ago when I tried to generate large databases. The thread is still somewhere in the archives.

 

Cheers,

Ian

 

From: Bug-gnubg [mailto:bug-gnubg-bounces+ian.shaw=riverauto.co.uk@gnu.org] On Behalf Of Øystein Schønning-Johansen
Sent: 06 October 2020 09:00
To: Joaquín Koifman <pamalejo@gmail.com>
Cc: gnubg list <bug-gnubg@gnu.org>
Subject: Re: Error while generating bearoff database

 

Hi,

 

Thanks for your bug report. Let me have a guess.

 

In file makebearoff.c lines 216ff:

216        /* read distributions */
217
218        iOffset = 2 * iOffset;
219
220        nBytes = 2 * (nz + nzg);
221
222        if (fseek(pfTmp, iOffset, SEEK_SET) < 0) {
223            perror("fseek'ing temp file");
224            exit(-1);
225        }

 

Let me guess that iOffset in line 218 overflows. I've not checked this theory with any math, but that is still my theory.

 

Could be (I'm not sure as I have not tried) it helps if we change the type of  iOffset to unsigned long instead of long. Or maybe even type size_t, which is probably the type the fseek() expects.

 

No, answering myself...The above suggested fix is not going to work. Checking the fseek() manual it actually expects long type offset as the argument. This is probably by design, such that you can easily move backwards in a file. Can you make a 64bit build? Maybe that will work.

 

However... (and this is a HUGE "however")

 

Building a full onesided bearoff database to the 14.point (or even lower) is actually not something you should do. It does not play better backgammon if you generate this file. A huge onesided non-contact database like this will misplay a lot of positions. It will hence not be usable for playing or rollouts. The neural network at 2-ply plays better! Use 2-ply neural network!

 

Best regards,

-Øystein

(BTW: I will not fix the bug)

 

 

On Tue, Oct 6, 2020 at 6:56 AM Joaquín Koifman <pamalejo@gmail.com> wrote:

Hi all!

 

When trying to generate a one-sided bearoff database greater than 13 points I get the following error. Do you know if there is any workaround?

 

Thanks in advance