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Re: [Bug-gnubg] Bug in makebearoff when building db w/o gammons

From: Øystein Johansen
Subject: Re: [Bug-gnubg] Bug in makebearoff when building db w/o gammons
Date: Sun, 01 Mar 2009 11:23:48 +0100
User-agent: Thunderbird (Windows/20081209)

Øystein Johansen (OJOHANS) wrote:
> Hi all!
> There's a bug in makebearoff when building one sided databases without
> gammon distributions.

> ERROR:makebearoff.c:483:BearOff: assertion failed: (iGammonBest >= 0)
> I think it's just a matter of removing the assert() or set iGammonBest
> when building w/o gammon distributions.

I've committed a patch which removes the assert. I've also reduced the
size of each index entry for compressed database w/o gammon
distributions. This means that if someone is using a gammonless onesided
bearoff database (which is not very likely), the database evaluations
will be broken unless they build a new.

For discussion:
For bearoff databases with gammon distributions, the db stores gammon
distributions for _all_ positions in the db. Even those positions where
a gammon is already saved. It uses only 2 bytes for such positions, but
I'm estimating that there is about > 20000 positions where there is no
gammon involved. Making a scheme to check for possible gammon and only
storing those distributions sounds trivial, but is it worth the effort?
If I commit such change, it will break compatibility with existing
bearoff databases, but the memory footprint will be 40-50Kb less. Is it
worth it?


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