Author: Will Singleton
Date: 16:00:13 03/11/98
Progress on tt table implementation -
Following advice, I wrote a validate routine to test whether the
incremental hashkey matched a value calculated from scratch. Sure
enough, errors popped up, which were related to ep, promotion and
castling. Those are fixed.
I've done some early data-gathering, resulting in the following
observations:
The percentage of true transpositions appearing in the table, for which
a value can be returned immediately as the true score of the position,
is small. That is, using iterative deepening, a ply 6 search can only
find transpositions within its current search, and none from the
previous ply 5 search. That would hold true for scores which narrow the
window.
The main value of tt tables is to order the search by using moves that
have caused cutoffs in stored positions, and may do so again.
As for specific observations, my node count is down to about 60% of what
it was without tt-tables. The number of tt hits from ply 6 to 7 (in the
table below) increase by a factor of 3, while the overall nodes from ply
6 to 7 increase 20 fold. Doesn't seem right. Amateur's node count is
excessive, but I'm only using killers and transpositions (and some
extensions). Move-ordering is tt-move, killers, good captures, rest of
moves. But even so, compared to Hiarcs especially, the node count seems
pretty high.
Test position results -- 7 plies
r2n1rk1/p4ppp/1qb1p3/4P1B1/1p1Pp1NP/1Pp1Q1P1/P1P2P2/3RR1K1 w - -
---------------------------------------
Amateur -- with tt tables --
thru ply 6 - move=Nh6 score=162 nodes=118302
tt hits=13204 tt cutoffs=11337
thru ply 7 - move=Bf6 score=521 nodes=2068354
tt hits=32687 tt cutoffs=13807
Amateur -- without tt tables --
thru ply 6 - move=Nh6 score=162 nodes=199272
thru ply 7 - move=Bf6 score=553 nodes=3514276
---------------------------------------
Hiarcs --
pv Bf6 h6 Bxg7 f5 Qxh6 fxg4 Qh8+ Kf7 Qxf8+ Kg6 Qf6+ Kh7;
score 631; nodes 120121
---------------------------------------
MacChess --
07/33|00:00:11| Nh6+ Kh8 Be7 Re8 Bxd8 Qb7 Nxf7+ Qxf7 Bg5;
328862 (nodes) tt-hits:11095 tt-cutoffs:7605
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Last modified: Thu, 15 Apr 21 08:11:13 -0700
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