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Move draw by material check

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It is more natural to test this case among
others material distributions.

No functional change.
This commit is contained in:
Marco Costalba 2013-09-08 05:49:04 -07:00
parent 0515ad0fb0
commit 490f67a3f8
3 changed files with 17 additions and 13 deletions
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2
src/endgame.h
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@ -43,7 +43,7 @@ enum EndgameType {
KQKP, // KQ vs KP KQKP, // KQ vs KP
KQKR, // KQ vs KR KQKR, // KQ vs KR
KBBKN, // KBB vs KN KBBKN, // KBB vs KN
KmmKm, // K and two minors vs K and one or two minors KmmKm, // K and one or two minors vs K and zero or one minor
// Scaling functions // Scaling functions

13
src/material.cpp
View file

@ -173,10 +173,18 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
return e; return e;
} }
if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN)) // Draw by insufficient material (trivial draws like KK, KBK and KNK)
if ( !pos.pieces(PAWN)
&& pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) <= BishopValueMg)
{ {
e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
return e;
}
// Minor piece endgame with at least one minor piece per side and // Minor piece endgame with at least one minor piece per side and
// no pawns. Note that the case KmmK is already handled by KXK. // no pawns. Note that the case KmmK is already handled by KXK.
if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
{
assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP))); assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP))); assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
@ -240,8 +248,7 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
} }
} }
// No pawns makes it difficult to win, even with a material advantage. This // No pawns makes it difficult to win, even with a material advantage
// catches some trivial draws like KK, KBK and KNK
if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg) if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
{ {
e->factor[WHITE] = (uint8_t) e->factor[WHITE] = (uint8_t)

13
src/position.cpp
View file

@ -1223,6 +1223,7 @@ Key Position::compute_material_key() const {
/// game and the endgame. These functions are used to initialize the incremental /// game and the endgame. These functions are used to initialize the incremental
/// scores when a new position is set up, and to verify that the scores are correctly /// scores when a new position is set up, and to verify that the scores are correctly
/// updated by do_move and undo_move when the program is running in debug mode. /// updated by do_move and undo_move when the program is running in debug mode.
Score Position::compute_psq_score() const { Score Position::compute_psq_score() const {
Score score = SCORE_ZERO; Score score = SCORE_ZERO;
@ -1254,15 +1255,11 @@ Value Position::compute_non_pawn_material(Color c) const {
} }
/// Position::is_draw() tests whether the position is drawn by material, /// Position::is_draw() tests whether the position is drawn by repetition
/// repetition, or the 50 moves rule. It does not detect stalemates, this /// or the 50 moves rule. It does not detect stalemates, this must be done
/// must be done by the search. /// by the search.
bool Position::is_draw() const {
// Draw by material? bool Position::is_draw() const {
if ( !pieces(PAWN)
&& (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
return true;
// Draw by the 50 moves rule? // Draw by the 50 moves rule?
if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size())) if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))