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Don't update bestValue when pruning

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Simply return a fail-low score

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-12-08 19:12:17 +01:00
parent 14df99130f
commit 3f14ed6602
2 changed files with 13 additions and 8 deletions
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19
src/search.cpp
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@ -948,6 +948,9 @@ split_point_start: // At split points actual search starts from here
{
lock_grab(&(sp->lock));
bestValue = sp->bestValue;
moveCount = sp->moveCount;
assert(bestValue > -VALUE_INFINITE && moveCount > 0);
}
// Step 11. Loop through moves
@ -1065,13 +1068,7 @@ split_point_start: // At split points actual search starts from here
if (futilityValue < beta)
{
if (SpNode)
{
lock_grab(&(sp->lock));
if (futilityValue > sp->bestValue)
sp->bestValue = bestValue = futilityValue;
}
else if (futilityValue > bestValue)
bestValue = futilityValue;
continue;
}
@ -1220,9 +1217,17 @@ split_point_start: // At split points actual search starts from here
// case of StopRequest or thread.cutoff_occurred() are set, but this is
// harmless because return value is discarded anyhow in the parent nodes.
// If we are in a singular extension search then return a fail low score.
if (!SpNode && !moveCount)
if (!moveCount)
return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
// We have pruned all the moves, so return a fail-low score
if (bestValue == -VALUE_INFINITE)
{
assert(!playedMoveCount);
bestValue = alpha;
}
// Step 21. Update tables
// If the search is not aborted, update the transposition table,
// history counters, and killer moves.

2
src/thread.cpp
View file

@ -263,7 +263,7 @@ Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
Value bestValue, Depth depth, Move threatMove,
int moveCount, MovePicker* mp, int nodeType) {
assert(pos.pos_is_ok());
assert(bestValue >= -VALUE_INFINITE);
assert(bestValue > -VALUE_INFINITE);
assert(bestValue <= alpha);
assert(alpha < beta);
assert(beta <= VALUE_INFINITE);