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Simplify pawn moves generator

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This patch simplifies QUIET_CHECKS pawn move generator by merging discovery check
move generator with direct check move generator. It also simplifies emptySquares
instantiation. In addition, I added a comment in generate_moves() to clarify Check
branches.

STC:
LLR: 2.95 (-2.94,2.94) <-2.50,0.50>
Total: 112648 W: 9952 L: 9945 D: 92751
Ptnml(0-2): 369, 7682, 40195, 7729, 349
https://tests.stockfishchess.org/tests/view/6088226895e7f1852abd2978

LTC:
LLR: 2.93 (-2.94,2.94) <-2.50,0.50>
Total: 74656 W: 2797 L: 2765 D: 69094
Ptnml(0-2): 38, 2328, 32554, 2380, 28
https://tests.stockfishchess.org/tests/view/60884e5095e7f1852abd2994

closes https://github.com/official-stockfish/Stockfish/pull/3447

No functional change
This commit is contained in:
bmc4 2021-04-27 19:59:46 -03:00 • committed by Stéphane Nicolet
parent 33a858eaa1
commit 84b42b3ab3
1 changed files with 14 additions and 29 deletions
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43
src/movegen.cpp
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@ -58,19 +58,16 @@ namespace {
constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
const Square ksq = pos.square<KING>(Them);
Bitboard emptySquares;
const Bitboard emptySquares = Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces();
const Bitboard enemies = Type == EVASIONS ? pos.checkers()
: Type == CAPTURES ? target : pos.pieces(Them);
Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
Bitboard enemies = (Type == EVASIONS ? pos.checkers()
: Type == CAPTURES ? target : pos.pieces(Them));
// Single and double pawn pushes, no promotions
if (Type != CAPTURES)
{
emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
@ -82,22 +79,12 @@ namespace {
if (Type == QUIET_CHECKS)
{
b1 &= pawn_attacks_bb(Them, ksq);
b2 &= pawn_attacks_bb(Them, ksq);
// Add pawn pushes which give discovered check. This is possible only
// if the pawn is not on the same file as the enemy king, because we
// don't generate captures. Note that a possible discovered check
// promotion has been already generated amongst the captures.
Bitboard dcCandidateQuiets = pos.blockers_for_king(Them) & pawnsNotOn7;
if (dcCandidateQuiets)
{
Bitboard dc1 = shift<Up>(dcCandidateQuiets) & emptySquares & ~file_bb(ksq);
Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
b1 |= dc1;
b2 |= dc2;
}
// To make a quiet check, you either make a direct check by pushing a pawn
// or push a blocker pawn that is not on the same file as the enemy king.
// Discovered check promotion has been already generated amongst the captures.
Bitboard dcCandidatePawns = pos.blockers_for_king(Them) & ~file_bb(ksq);
b1 &= pawn_attacks_bb(Them, ksq) | shift< Up>(dcCandidatePawns);
b2 &= pawn_attacks_bb(Them, ksq) | shift<Up+Up>(dcCandidatePawns);
}
while (b1)
@ -116,16 +103,13 @@ namespace {
// Promotions and underpromotions
if (pawnsOn7)
{
if (Type == CAPTURES)
emptySquares = ~pos.pieces();
if (Type == EVASIONS)
emptySquares &= target;
Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
if (Type == EVASIONS)
b3 &= target;
while (b1)
moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(b1), ksq);
@ -185,8 +169,9 @@ namespace {
while (bb)
{
Square from = pop_lsb(bb);
Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
// To check, you either move freely a blocker or make a direct check.
if (Checks && (Pt == QUEEN || !(pos.blockers_for_king(~Us) & from)))
b &= pos.check_squares(Pt);