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Code Issues Releases Wiki Activity

Retire ok_to_do_nullmove()

Browse source 
Has been remained the same from ages also with the FIXME.

Retire for now and rearrange the conditions order for
maximum performance.

Also a small touch at null zugzwang verification.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-06-01 19:49:46 +01:00
parent 7903495b0a
commit 50e094ef8d
1 changed files with 20 additions and 36 deletions
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56
src/search.cpp
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@ -301,7 +301,6 @@ namespace {
bool connected_moves(const Position& pos, Move m1, Move m2);
bool value_is_mate(Value value);
bool move_is_killer(Move m, SearchStack* ss);
bool ok_to_do_nullmove(const Position& pos);
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
bool connected_threat(const Position& pos, Move m, Move threat);
Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
@ -1125,11 +1124,11 @@ namespace {
// Step 6. Razoring (is omitted in PV nodes)
if ( !PvNode
&& depth < RazorDepth
&& !isCheck
&& refinedValue < beta - razor_margin(depth)
&& ttMove == MOVE_NONE
&& (ss-1)->currentMove != MOVE_NULL
&& depth < RazorDepth
&& !isCheck
&& !value_is_mate(beta)
&& !pos.has_pawn_on_7th(pos.side_to_move()))
{
@ -1147,10 +1146,10 @@ namespace {
if ( !PvNode
&& allowNullmove
&& depth < RazorDepth
&& refinedValue >= beta + futility_margin(depth, 0)
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& refinedValue >= beta + futility_margin(depth, 0))
&& pos.non_pawn_material(pos.side_to_move()))
return refinedValue - futility_margin(depth, 0);
// Step 8. Null move search with verification search (is omitted in PV nodes)
@ -1160,10 +1159,10 @@ namespace {
if ( !PvNode
&& allowNullmove
&& depth > OnePly
&& refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
&& pos.non_pawn_material(pos.side_to_move()))
{
ss->currentMove = MOVE_NULL;
@ -1186,14 +1185,13 @@ namespace {
if (nullValue >= value_mate_in(PLY_MAX))
nullValue = beta;
if (depth < 6 * OnePly)
// Do zugzwang verification search at high depths
if ( depth < 6 * OnePly
|| search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, false, threadID) >= beta)
return nullValue;
// Do zugzwang verification search
Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, false, threadID);
if (v >= beta)
return nullValue;
} else {
}
else
{
// The null move failed low, which means that we may be faced with
// some kind of threat. If the previous move was reduced, check if
// the move that refuted the null move was somehow connected to the
@ -1279,11 +1277,11 @@ namespace {
// Step 12. Futility pruning (is omitted in PV nodes)
if ( !PvNode
&& !captureOrPromotion
&& !isCheck
&& !dangerous
&& !captureOrPromotion
&& !move_is_castle(move)
&& move != ttMove)
&& move != ttMove
&& !move_is_castle(move))
{
// Move count based pruning
if ( moveCount >= futility_move_count(depth)
@ -1321,8 +1319,8 @@ namespace {
bool doFullDepthSearch = true;
if ( depth >= 3 * OnePly
&& !dangerous
&& !captureOrPromotion
&& !dangerous
&& !move_is_castle(move)
&& !move_is_killer(move, ss))
{
@ -1387,13 +1385,13 @@ namespace {
}
// Step 18. Check for split
if ( TM.active_threads() > 1
if ( depth >= MinimumSplitDepth
&& TM.active_threads() > 1
&& bestValue < beta
&& depth >= MinimumSplitDepth
&& Iteration <= 99
&& TM.available_thread_exists(threadID)
&& !AbortSearch
&& !TM.thread_should_stop(threadID))
&& !TM.thread_should_stop(threadID)
&& Iteration <= 99)
TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
mateThreat, &moveCount, &mp, threadID, PvNode);
}
@ -1965,20 +1963,6 @@ namespace {
}
// ok_to_do_nullmove() looks at the current position and decides whether
// doing a 'null move' should be allowed. In order to avoid zugzwang
// problems, null moves are not allowed when the side to move has very
// little material left. Currently, the test is a bit too simple: Null
// moves are avoided only when the side to move has only pawns left.
// It's probably a good idea to avoid null moves in at least some more
// complicated endgames, e.g. KQ vs KR. FIXME
bool ok_to_do_nullmove(const Position& pos) {
return pos.non_pawn_material(pos.side_to_move()) != Value(0);
}
// connected_threat() tests whether it is safe to forward prune a move or if
// is somehow coonected to the threat move returned by null search.