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More accurate pawn attack span definition

Browse source 
Tweak the pawn attack span for backward pawns and the zone behind
opponent opposing pawns. This is important in positional play and
one of weaknesses of the engine in recent high level games.

STC
LLR: -2.95 (-2.94,2.94) [0.50,4.50]
Total: 66843 W: 14884 L: 14717 D: 37242
http://tests.stockfishchess.org/tests/view/5d8dcb1b0ebc590f3beb2956

LTC
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 77699 W: 12993 L: 12602 D: 52104
http://tests.stockfishchess.org/tests/view/5d8de9bc0ebc590f3beb3d00

See discussion in https://github.com/official-stockfish/Stockfish/pull/2332

Bench: 4012371
This commit is contained in:
Moez Jellouli 2019-09-27 10:18:22 +02:00 • committed by Stéphane Nicolet
parent 005ad170c1
commit e6f4b5f463
2 changed files with 19 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
src/evaluate.cpp
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@ -135,7 +135,7 @@ namespace {
constexpr Score KnightOnQueen = S( 16, 12); constexpr Score KnightOnQueen = S( 16, 12);
constexpr Score LongDiagonalBishop = S( 45, 0); constexpr Score LongDiagonalBishop = S( 45, 0);
constexpr Score MinorBehindPawn = S( 18, 3); constexpr Score MinorBehindPawn = S( 18, 3);
constexpr Score Outpost = S( 18, 6); constexpr Score Outpost = S( 16, 5);
constexpr Score PassedFile = S( 11, 8); constexpr Score PassedFile = S( 11, 8);
constexpr Score PawnlessFlank = S( 17, 95); constexpr Score PawnlessFlank = S( 17, 95);
constexpr Score RestrictedPiece = S( 7, 7); constexpr Score RestrictedPiece = S( 7, 7);

25
src/pawns.cpp
View file

@ -71,10 +71,10 @@ namespace {
constexpr Color Them = (Us == WHITE ? BLACK : WHITE); constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH); constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
Bitboard neighbours, stoppers, support, phalanx; Bitboard neighbours, stoppers, support, phalanx, opposed;
Bitboard lever, leverPush; Bitboard lever, leverPush;
Square s; Square s;
bool opposed, backward, passed, doubled; bool backward, passed, doubled;
Score score = SCORE_ZERO; Score score = SCORE_ZERO;
const Square* pl = pos.squares<PAWN>(Us); const Square* pl = pos.squares<PAWN>(Us);
@ -94,8 +94,6 @@ namespace {
Rank r = relative_rank(Us, s); Rank r = relative_rank(Us, s);
e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
// Flag the pawn // Flag the pawn
opposed = theirPawns & forward_file_bb(Us, s); opposed = theirPawns & forward_file_bb(Us, s);
stoppers = theirPawns & passed_pawn_span(Us, s); stoppers = theirPawns & passed_pawn_span(Us, s);
@ -112,6 +110,17 @@ namespace {
backward = !(neighbours & forward_ranks_bb(Them, s)) backward = !(neighbours & forward_ranks_bb(Them, s))
&& (stoppers & (leverPush | (s + Up))); && (stoppers & (leverPush | (s + Up)));
// Span of backward pawns and span behind opposing pawns are not included
// in the pawnAttacksSpan bitboard.
if (!backward || phalanx)
{
if (opposed)
e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s) &
~pawn_attack_span(Us, frontmost_sq(Them, opposed));
else
e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
}
// A pawn is passed if one of the three following conditions is true: // A pawn is passed if one of the three following conditions is true:
// (a) there is no stoppers except some levers // (a) there is no stoppers except some levers
// (b) the only stoppers are the leverPush, but we outnumber them // (b) the only stoppers are the leverPush, but we outnumber them
@ -130,17 +139,19 @@ namespace {
// Score this pawn // Score this pawn
if (support | phalanx) if (support | phalanx)
{ {
int v = Connected[r] * (2 + bool(phalanx) - opposed) int v = Connected[r] * (2 + bool(phalanx) - bool(opposed))
+ 21 * popcount(support); + 21 * popcount(support);
score += make_score(v, v * (r - 2) / 4); score += make_score(v, v * (r - 2) / 4);
} }
else if (!neighbours) else if (!neighbours)
score -= Isolated + WeakUnopposed * !opposed; score -= Isolated
+ WeakUnopposed * !opposed;
else if (backward) else if (backward)
score -= Backward + WeakUnopposed * !opposed; score -= Backward
+ WeakUnopposed * !opposed;
if (!support) if (!support)
score -= Doubled * doubled score -= Doubled * doubled