droidfish/DroidFish/jni/stockfish/pawns.cpp

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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
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Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <cassert>
#include "bitboard.h"
#include "bitcount.h"
#include "pawns.h"
#include "position.h"
namespace {
#define S(mg, eg) make_score(mg, eg)
// Doubled pawn penalty by opposed flag and file
const Score DoubledPawnPenalty[2][8] = {
{ S(13, 43), S(20, 48), S(23, 48), S(23, 48),
S(23, 48), S(23, 48), S(20, 48), S(13, 43) },
{ S(13, 43), S(20, 48), S(23, 48), S(23, 48),
S(23, 48), S(23, 48), S(20, 48), S(13, 43) }};
// Isolated pawn penalty by opposed flag and file
const Score IsolatedPawnPenalty[2][8] = {
{ S(37, 45), S(54, 52), S(60, 52), S(60, 52),
S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
{ S(25, 30), S(36, 35), S(40, 35), S(40, 35),
S(40, 35), S(40, 35), S(36, 35), S(25, 30) }};
// Backward pawn penalty by opposed flag and file
const Score BackwardPawnPenalty[2][8] = {
{ S(30, 42), S(43, 46), S(49, 46), S(49, 46),
S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
{ S(20, 28), S(29, 31), S(33, 31), S(33, 31),
S(33, 31), S(33, 31), S(29, 31), S(20, 28) }};
// Pawn chain membership bonus by file
const Score ChainBonus[8] = {
S(11,-1), S(13,-1), S(13,-1), S(14,-1),
S(14,-1), S(13,-1), S(13,-1), S(11,-1)
};
// Candidate passed pawn bonus by rank
const Score CandidateBonus[8] = {
S( 0, 0), S( 6, 13), S(6,13), S(14,29),
S(34,68), S(83,166), S(0, 0), S( 0, 0)
};
const Score PawnStructureWeight = S(233, 201);
#undef S
inline Score apply_weight(Score v, Score w) {
return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
(int(eg_value(v)) * eg_value(w)) / 0x100);
}
}
/// PawnInfoTable::pawn_info() takes a position object as input, computes
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/// a PawnInfo object, and returns a pointer to it. The result is also stored
/// in an hash table, so we don't have to recompute everything when the same
/// pawn structure occurs again.
PawnInfo* PawnInfoTable::pawn_info(const Position& pos) const {
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Key key = pos.pawn_key();
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PawnInfo* pi = probe(key);
// If pi->key matches the position's pawn hash key, it means that we
// have analysed this pawn structure before, and we can simply return
// the information we found the last time instead of recomputing it.
if (pi->key == key)
return pi;
// Initialize PawnInfo entry
pi->key = key;
pi->passedPawns[WHITE] = pi->passedPawns[BLACK] = 0;
pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
pi->halfOpenFiles[WHITE] = pi->halfOpenFiles[BLACK] = 0xFF;
// Calculate pawn attacks
Bitboard wPawns = pos.pieces(PAWN, WHITE);
Bitboard bPawns = pos.pieces(PAWN, BLACK);
pi->pawnAttacks[WHITE] = ((wPawns << 9) & ~FileABB) | ((wPawns << 7) & ~FileHBB);
pi->pawnAttacks[BLACK] = ((bPawns >> 7) & ~FileABB) | ((bPawns >> 9) & ~FileHBB);
// Evaluate pawns for both colors and weight the result
pi->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, pi)
- evaluate_pawns<BLACK>(pos, bPawns, wPawns, pi);
pi->value = apply_weight(pi->value, PawnStructureWeight);
return pi;
}
/// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
template<Color Us>
Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
Bitboard theirPawns, PawnInfo* pi) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
Bitboard b;
Square s;
File f;
Rank r;
bool passed, isolated, doubled, opposed, chain, backward, candidate;
Score value = SCORE_ZERO;
const Square* pl = pos.piece_list(Us, PAWN);
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// Loop through all pawns of the current color and score each pawn
while ((s = *pl++) != SQ_NONE)
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{
assert(pos.piece_on(s) == make_piece(Us, PAWN));
f = file_of(s);
r = rank_of(s);
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// This file cannot be half open
pi->halfOpenFiles[Us] &= ~(1 << f);
// Our rank plus previous one. Used for chain detection
b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
// Flag the pawn as passed, isolated, doubled or member of a pawn
// chain (but not the backward one).
passed = !(theirPawns & passed_pawn_mask(Us, s));
doubled = ourPawns & squares_in_front_of(Us, s);
opposed = theirPawns & squares_in_front_of(Us, s);
isolated = !(ourPawns & neighboring_files_bb(f));
chain = ourPawns & neighboring_files_bb(f) & b;
// Test for backward pawn
backward = false;
// If the pawn is passed, isolated, or member of a pawn chain it cannot
// be backward. If there are friendly pawns behind on neighboring files
// or if can capture an enemy pawn it cannot be backward either.
if ( !(passed | isolated | chain)
&& !(ourPawns & attack_span_mask(Them, s))
&& !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
{
// We now know that there are no friendly pawns beside or behind this
// pawn on neighboring files. We now check whether the pawn is
// backward by looking in the forward direction on the neighboring
// files, and seeing whether we meet a friendly or an enemy pawn first.
b = pos.attacks_from<PAWN>(s, Us);
// Note that we are sure to find something because pawn is not passed
// nor isolated, so loop is potentially infinite, but it isn't.
while (!(b & (ourPawns | theirPawns)))
Us == WHITE ? b <<= 8 : b >>= 8;
// The friendly pawn needs to be at least two ranks closer than the
// enemy pawn in order to help the potentially backward pawn advance.
backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
}
assert(opposed | passed | (attack_span_mask(Us, s) & theirPawns));
// A not passed pawn is a candidate to become passed if it is free to
// advance and if the number of friendly pawns beside or behind this
// pawn on neighboring files is higher or equal than the number of
// enemy pawns in the forward direction on the neighboring files.
candidate = !(opposed | passed | backward | isolated)
&& (b = attack_span_mask(Them, s + pawn_push(Us)) & ourPawns) != 0
&& popcount<Max15>(b) >= popcount<Max15>(attack_span_mask(Us, s) & theirPawns);
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// Passed pawns will be properly scored in evaluation because we need
// full attack info to evaluate passed pawns. Only the frontmost passed
// pawn on each file is considered a true passed pawn.
if (passed && !doubled)
set_bit(&(pi->passedPawns[Us]), s);
// Score this pawn
if (isolated)
value -= IsolatedPawnPenalty[opposed][f];
if (doubled)
value -= DoubledPawnPenalty[opposed][f];
if (backward)
value -= BackwardPawnPenalty[opposed][f];
if (chain)
value += ChainBonus[f];
if (candidate)
value += CandidateBonus[relative_rank(Us, s)];
}
return value;
}
/// PawnInfo::updateShelter() calculates and caches king shelter. It is called
/// only when king square changes, about 20% of total king_shelter() calls.
template<Color Us>
Score PawnInfo::updateShelter(const Position& pos, Square ksq) {
const int Shift = (Us == WHITE ? 8 : -8);
Bitboard pawns;
int r, shelter = 0;
if (relative_rank(Us, ksq) <= RANK_4)
{
pawns = pos.pieces(PAWN, Us) & this_and_neighboring_files_bb(file_of(ksq));
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r = ksq & (7 << 3);
for (int i = 0; i < 3; i++)
{
r += Shift;
shelter += BitCount8Bit[(pawns >> r) & 0xFF] << (6 - i);
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}
}
kingSquares[Us] = ksq;
kingShelters[Us] = make_score(shelter, 0);
return kingShelters[Us];
}
// Explicit template instantiation
template Score PawnInfo::updateShelter<WHITE>(const Position& pos, Square ksq);
template Score PawnInfo::updateShelter<BLACK>(const Position& pos, Square ksq);