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History pruning exponential limit

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Use an exponenital law instead of a linear one for
history pruning.

This should prune more at low depths and a bit less
at high depths.

After 965 games

Mod vs Orig +233 =504 -228 +2 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-11-14 17:38:22 +01:00
parent 0eedf47661
commit 52bca81dcb
1 changed files with 19 additions and 1 deletions
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20
src/search.cpp
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@ -1388,6 +1388,9 @@ namespace {
if (tte && (tte->type() & VALUE_TYPE_EVAL))
futilityValue = value_from_tt(tte->value(), ply) + FutilityMargins[int(depth) - 2];
// Move count pruning limit
const int MCLimit = 3 + (1 << (3*int(depth)/8));
// Loop through all legal moves until no moves remain or a beta cutoff
// occurs.
while ( bestValue < beta
@ -1412,8 +1415,23 @@ namespace {
&& !captureOrPromotion
&& move != ttMove)
{
//std::cout << std::endl;
//for (int d = 2; d <= 14; d+=2)
// std::cout << d / 2 << ", " << 3+(1 << (3*d/8)) << std::endl;
//std::cout << std::endl;
/*
3 + (1 << (3*int(depth)/8))
1 * onePly - > moveCount >= 4
2 * onePly - > moveCount >= 5
3 * onePly - > moveCount >= 7
4 * onePly - > moveCount >= 11
5 * onePly - > moveCount >= 11
6 * onePly - > moveCount >= 19
7 * onePly - > moveCount >= 35
*/
// History pruning. See ok_to_prune() definition
if ( moveCount >= 2 + int(depth)
if ( moveCount >= MCLimit
&& ok_to_prune(pos, move, ss[ply].threatMove, depth)
&& bestValue > value_mated_in(PLY_MAX))
continue;