Computer Chess Club Archives




Subject: Why not store both a lower and an upper bound in a hashtable?

Author: Leen Ammeraal

Date: 09:45:30 12/06/00

I have the impression that most chess programmers
use their hashtables to store
only one evaluation value, along with a flag
denoting Lower, Upper, or Exact.
Why not store both a lower and an upper bound,
where lower = -inf or upper = +inf if only one
real bound is available? A flag is then
superfluous, since this follows from
the two bound values.
For example:
LB      UB     Flag value (not stored)
-inf    100    Upper
-20     +inf   Lower
30      30     Exact
This also offers the possibility to store
two different bounds at the same time, as in
LB = -50, UB = 70.
This is the way I do it, but, unfortunately,
my program is weaker than most others.
Could this be because this idea of storing
two bounds and no flag is wrong?
Leen Ammeraal

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