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Do not null search when beta is a mate value

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Also do not return unproven mates in null search.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2008-12-15 11:50:01 +01:00
parent 4c294932e7
commit dae2f600d6
1 changed files with 21 additions and 1 deletions
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22
src/search.cpp
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@ -267,6 +267,7 @@ namespace {
void update_pv(SearchStack ss[], int ply);
void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
bool connected_moves(const Position &pos, Move m1, Move m2);
bool value_is_mate(Value value);
bool move_is_killer(Move m, const SearchStack& ss);
Depth extension(const Position &pos, Move m, bool pvNode, bool check, bool singleReply, bool mateThreat, bool* dangerous);
bool ok_to_do_nullmove(const Position &pos);
@ -1176,6 +1177,7 @@ namespace {
if ( allowNullmove
&& depth > OnePly
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& approximateEval >= beta - NullMoveMargin)
{
@ -1201,7 +1203,11 @@ namespace {
pos.undo_null_move(u);
if (nullValue >= beta)
if (value_is_mate(nullValue))
{
/* Do not return unproven mates */
}
else if (nullValue >= beta)
{
if (depth < 6 * OnePly)
return beta;
@ -1298,10 +1304,12 @@ namespace {
&& !moveIsCapture
&& !move_promotion(move))
{
// History pruning. See ok_to_prune() definition.
if ( moveCount >= 2 + int(depth)
&& ok_to_prune(pos, move, ss[ply].threatMove, depth))
continue;
// Value based pruning.
if (depth < 3 * OnePly && approximateEval < beta)
{
if (futilityValue == VALUE_NONE)
@ -2120,6 +2128,18 @@ namespace {
}
// value_is_mate() checks if the given value is a mate one
// eventually compensated for the ply.
bool value_is_mate(Value value) {
assert(abs(value) <= VALUE_INFINITE);
return value <= value_mated_in(PLY_MAX)
|| value >= value_mate_in(PLY_MAX);
}
// move_is_killer() checks if the given move is among the
// killer moves of that ply.