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Code Issues Releases Wiki Activity

Fix description of endgame scaling functions

Browse source 
Triggered by a comment of Eelco on talkchess. Also
a bit of cleanup while there.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-12-10 10:14:25 +01:00
parent 47bcb892af
commit 14df99130f
3 changed files with 66 additions and 86 deletions
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148
src/endgame.cpp
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@ -60,10 +60,6 @@ namespace {
// the two kings in basic endgames.
const int DistanceBonus[8] = { 0, 0, 100, 80, 60, 40, 20, 10 };
// Penalty for big distance between king and knight for the defending king
// and knight in KR vs KN endgames.
const int KRKNKingKnightDistancePenalty[8] = { 0, 0, 4, 10, 20, 32, 48, 70 };
// Build corresponding key code for the opposite color: "KBPKN" -> "KNKBP"
const string swap_colors(const string& keyCode) {
@ -333,14 +329,11 @@ Value Endgame<KRKN>::operator()(const Position& pos) const {
assert(pos.piece_count(weakerSide, PAWN) == 0);
assert(pos.piece_count(weakerSide, KNIGHT) == 1);
Square defendingKSq = pos.king_square(weakerSide);
Square nSq = pos.piece_list(weakerSide, KNIGHT)[0];
int d = square_distance(defendingKSq, nSq);
Value result = Value(10)
+ MateTable[defendingKSq]
+ KRKNKingKnightDistancePenalty[d];
const int penalty[8] = { 0, 10, 14, 20, 30, 42, 58, 80 };
Square bksq = pos.king_square(weakerSide);
Square bnsq = pos.piece_list(weakerSide, KNIGHT)[0];
Value result = Value(MateTable[bksq] + penalty[square_distance(bksq, bnsq)]);
return strongerSide == pos.side_to_move() ? result : -result;
}
@ -408,10 +401,9 @@ Value Endgame<KNNK>::operator()(const Position&) const {
return VALUE_DRAW;
}
/// KBPKScalingFunction scales endgames where the stronger side has king,
/// bishop and one or more pawns. It checks for draws with rook pawns and a
/// bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_ZERO is
/// returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
/// K, bishop and one or more pawns vs K. It checks for draws with rook pawns and
/// a bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_DRAW
/// is returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
/// will be used.
template<>
ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
@ -456,17 +448,15 @@ ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
// is placed somewhere in front of the pawn, it's a draw.
if ( square_distance(kingSq, queeningSq) <= 1
|| relative_rank(strongerSide, kingSq) >= rank)
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
}
}
return SCALE_FACTOR_NONE;
}
/// KQKRPScalingFunction scales endgames where the stronger side has only
/// king and queen, while the weaker side has at least a rook and a pawn.
/// It tests for fortress draws with a rook on the third rank defended by
/// a pawn.
/// K and queen vs K, rook and one or more pawns. It tests for fortress draws with
/// a rook on the third rank defended by a pawn.
template<>
ScaleFactor Endgame<KQKRPs>::operator()(const Position& pos) const {
@ -485,16 +475,15 @@ ScaleFactor Endgame<KQKRPs>::operator()(const Position& pos) const {
{
Square rsq = pos.piece_list(weakerSide, ROOK)[0];
if (pos.attacks_from<PAWN>(rsq, strongerSide) & pos.pieces(PAWN, weakerSide))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
}
return SCALE_FACTOR_NONE;
}
/// KRPKRScalingFunction scales KRP vs KR endgames. This function knows a
/// handful of the most important classes of drawn positions, but is far
/// from perfect. It would probably be a good idea to add more knowledge
/// in the future.
/// K, rook and one pawn vs K and a rook. This function knows a handful of the
/// most important classes of drawn positions, but is far from perfect. It would
/// probably be a good idea to add more knowledge in the future.
///
/// It would also be nice to rewrite the actual code for this function,
/// which is mostly copied from Glaurung 1.x, and not very pretty.
@ -542,7 +531,7 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
&& square_distance(bksq, queeningSq) <= 1
&& wksq <= SQ_H5
&& (rank_of(brsq) == RANK_6 || (r <= RANK_3 && rank_of(wrsq) != RANK_6)))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
// The defending side saves a draw by checking from behind in case the pawn
// has advanced to the 6th rank with the king behind.
@ -550,13 +539,13 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
&& square_distance(bksq, queeningSq) <= 1
&& rank_of(wksq) + tempo <= RANK_6
&& (rank_of(brsq) == RANK_1 || (!tempo && abs(file_of(brsq) - f) >= 3)))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
if ( r >= RANK_6
&& bksq == queeningSq
&& rank_of(brsq) == RANK_1
&& (!tempo || square_distance(wksq, wpsq) >= 2))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
// White pawn on a7 and rook on a8 is a draw if black's king is on g7 or h7
// and the black rook is behind the pawn.
@ -565,7 +554,7 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
&& (bksq == SQ_H7 || bksq == SQ_G7)
&& file_of(brsq) == FILE_A
&& (rank_of(brsq) <= RANK_3 || file_of(wksq) >= FILE_D || rank_of(wksq) <= RANK_5))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
// If the defending king blocks the pawn and the attacking king is too far
// away, it's a draw.
@ -573,7 +562,7 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
&& bksq == wpsq + DELTA_N
&& square_distance(wksq, wpsq) - tempo >= 2
&& square_distance(wksq, brsq) - tempo >= 2)
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
// Pawn on the 7th rank supported by the rook from behind usually wins if the
// attacking king is closer to the queening square than the defending king,
@ -613,8 +602,8 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
}
/// KRPPKRPScalingFunction scales KRPP vs KRP endgames. There is only a
/// single pattern: If the stronger side has no pawns and the defending king
/// K, rook and two pawns vs K, rook and one pawn. There is only a single
/// pattern: If the stronger side has no passed pawns and the defending king
/// is actively placed, the position is drawish.
template<>
ScaleFactor Endgame<KRPPKRP>::operator()(const Position& pos) const {
@ -652,9 +641,8 @@ ScaleFactor Endgame<KRPPKRP>::operator()(const Position& pos) const {
}
/// KPsKScalingFunction scales endgames with king and two or more pawns
/// against king. There is just a single rule here: If all pawns are on
/// the same rook file and are blocked by the defending king, it's a draw.
/// K and two or more pawns vs K. There is just a single rule here: If all pawns
/// are on the same rook file and are blocked by the defending king, it's a draw.
template<>
ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
@ -673,7 +661,7 @@ ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
if ( square_distance(ksq, relative_square(strongerSide, SQ_A8)) <= 1
|| ( file_of(ksq) == FILE_A
&& !in_front_bb(strongerSide, ksq) & pawns))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
}
// Are all pawns on the 'h' file?
else if (!(pawns & ~FileHBB))
@ -682,17 +670,16 @@ ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
if ( square_distance(ksq, relative_square(strongerSide, SQ_H8)) <= 1
|| ( file_of(ksq) == FILE_H
&& !in_front_bb(strongerSide, ksq) & pawns))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
}
return SCALE_FACTOR_NONE;
}
/// KBPKBScalingFunction scales KBP vs KB endgames. There are two rules:
/// If the defending king is somewhere along the path of the pawn, and the
/// square of the king is not of the same color as the stronger side's bishop,
/// it's a draw. If the two bishops have opposite color, it's almost always
/// a draw.
/// K, bishop and a pawn vs K and a bishop. There are two rules: If the defending
/// king is somewhere along the path of the pawn, and the square of the king is
/// not of the same color as the stronger side's bishop, it's a draw. If the two
/// bishops have opposite color, it's almost always a draw.
template<>
ScaleFactor Endgame<KBPKB>::operator()(const Position& pos) const {
@ -713,7 +700,7 @@ ScaleFactor Endgame<KBPKB>::operator()(const Position& pos) const {
&& relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
&& ( opposite_colors(weakerKingSq, strongerBishopSq)
|| relative_rank(strongerSide, weakerKingSq) <= RANK_6))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
// Case 2: Opposite colored bishops
if (opposite_colors(strongerBishopSq, weakerBishopSq))
@ -729,25 +716,25 @@ ScaleFactor Endgame<KBPKB>::operator()(const Position& pos) const {
// reasonably well.
if (relative_rank(strongerSide, pawnSq) <= RANK_5)
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
else
{
Bitboard path = squares_in_front_of(strongerSide, pawnSq);
if (path & pos.pieces(KING, weakerSide))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
if ( (pos.attacks_from<BISHOP>(weakerBishopSq) & path)
&& square_distance(weakerBishopSq, pawnSq) >= 3)
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
}
}
return SCALE_FACTOR_NONE;
}
/// KBPPKBScalingFunction scales KBPP vs KB endgames. It detects a few basic
/// draws with opposite-colored bishops.
/// K, bishop and two pawns vs K and bishop. It detects a few basic draws with
/// opposite-colored bishops.
template<>
ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
@ -790,7 +777,7 @@ ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
if ( file_of(ksq) == file_of(blockSq1)
&& relative_rank(strongerSide, ksq) >= relative_rank(strongerSide, blockSq1)
&& opposite_colors(ksq, wbsq))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
else
return SCALE_FACTOR_NONE;
@ -803,13 +790,13 @@ ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
&& ( bbsq == blockSq2
|| (pos.attacks_from<BISHOP>(blockSq2) & pos.pieces(BISHOP, weakerSide))
|| abs(r1 - r2) >= 2))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
else if ( ksq == blockSq2
&& opposite_colors(ksq, wbsq)
&& ( bbsq == blockSq1
|| (pos.attacks_from<BISHOP>(blockSq1) & pos.pieces(BISHOP, weakerSide))))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
else
return SCALE_FACTOR_NONE;
@ -820,10 +807,9 @@ ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
}
/// KBPKNScalingFunction scales KBP vs KN endgames. There is a single rule:
/// If the defending king is somewhere along the path of the pawn, and the
/// square of the king is not of the same color as the stronger side's bishop,
/// it's a draw.
/// K, bisop and a pawn vs K and knight. There is a single rule: If the defending
/// king is somewhere along the path of the pawn, and the square of the king is
/// not of the same color as the stronger side's bishop, it's a draw.
template<>
ScaleFactor Endgame<KBPKN>::operator()(const Position& pos) const {
@ -842,15 +828,15 @@ ScaleFactor Endgame<KBPKN>::operator()(const Position& pos) const {
&& relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
&& ( opposite_colors(weakerKingSq, strongerBishopSq)
|| relative_rank(strongerSide, weakerKingSq) <= RANK_6))
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
return SCALE_FACTOR_NONE;
}
/// KNPKScalingFunction scales KNP vs K endgames. There is a single rule:
/// If the pawn is a rook pawn on the 7th rank and the defending king prevents
/// the pawn from advancing, the position is drawn.
/// K, knight and a pawn vs K. There is a single rule: If the pawn is a rook pawn
/// on the 7th rank and the defending king prevents the pawn from advancing, the
/// position is drawn.
template<>
ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
@ -865,22 +851,21 @@ ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
if ( pawnSq == relative_square(strongerSide, SQ_A7)
&& square_distance(weakerKingSq, relative_square(strongerSide, SQ_A8)) <= 1)
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
if ( pawnSq == relative_square(strongerSide, SQ_H7)
&& square_distance(weakerKingSq, relative_square(strongerSide, SQ_H8)) <= 1)
return SCALE_FACTOR_ZERO;
return SCALE_FACTOR_DRAW;
return SCALE_FACTOR_NONE;
}
/// KPKPScalingFunction scales KP vs KP endgames. This is done by removing
/// the weakest side's pawn and probing the KP vs K bitbase: If the weakest
/// side has a draw without the pawn, she probably has at least a draw with
/// the pawn as well. The exception is when the stronger side's pawn is far
/// advanced and not on a rook file; in this case it is often possible to win
/// (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
/// K and a pawn vs K and a pawn. This is done by removing the weakest side's
/// pawn and probing the KP vs K bitbase: If the weakest side has a draw without
/// the pawn, she probably has at least a draw with the pawn as well. The exception
/// is when the stronger side's pawn is far advanced and not on a rook file; in
/// this case it is often possible to win (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
template<>
ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
@ -889,22 +874,17 @@ ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
assert(pos.piece_count(WHITE, PAWN) == 1);
assert(pos.piece_count(BLACK, PAWN) == 1);
Square wksq, bksq, wpsq;
Color stm;
Square wksq = pos.king_square(strongerSide);
Square bksq = pos.king_square(weakerSide);
Square wpsq = pos.piece_list(strongerSide, PAWN)[0];
Color stm = pos.side_to_move();
if (strongerSide == WHITE)
if (strongerSide == BLACK)
{
wksq = pos.king_square(WHITE);
bksq = pos.king_square(BLACK);
wpsq = pos.piece_list(WHITE, PAWN)[0];
stm = pos.side_to_move();
}
else
{
wksq = flip(pos.king_square(BLACK));
bksq = flip(pos.king_square(WHITE));
wpsq = flip(pos.piece_list(BLACK, PAWN)[0]);
stm = flip(pos.side_to_move());
wksq = flip(wksq);
bksq = flip(bksq);
wpsq = flip(wpsq);
stm = flip(stm);
}
if (file_of(wpsq) >= FILE_E)
@ -920,7 +900,7 @@ ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
&& file_of(wpsq) != FILE_A)
return SCALE_FACTOR_NONE;
// Probe the KPK bitbase with the weakest side's pawn removed. If it's a
// draw, it's probably at least a draw even with the pawn.
return probe_kpk_bitbase(wksq, wpsq, bksq, stm) ? SCALE_FACTOR_NONE : SCALE_FACTOR_ZERO;
// Probe the KPK bitbase with the weakest side's pawn removed. If it's a draw,
// it's probably at least a draw even with the pawn.
return probe_kpk_bitbase(wksq, wpsq, bksq, stm) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;
}

2
src/material.cpp
View file

@ -143,7 +143,7 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) const {
if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
&& pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
{
mi->evaluationFunction = &EvaluateKmmKm[WHITE];
mi->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
return mi;
}
}

2
src/types.h
View file

@ -287,7 +287,7 @@ enum SquareColor {
};
enum ScaleFactor {
SCALE_FACTOR_ZERO = 0,
SCALE_FACTOR_DRAW = 0,
SCALE_FACTOR_NORMAL = 64,
SCALE_FACTOR_MAX = 128,
SCALE_FACTOR_NONE = 255