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Simplify pawn captures #1048

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Merged
codedeliveryservice merged 5 commits into from
May 27, 2026
Merged

Simplify pawn captures #1048

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5c223f1
pawn captures.
protonspring May 26, 2026
b7a117e
more
protonspring May 26, 2026
bfe2852
cleanup
protonspring May 26, 2026
0b0c8eb
cleanup
protonspring May 26, 2026
ce2141f
Cargo formatting.
protonspring May 26, 2026
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28 changes: 12 additions & 16 deletions src/board/movegen.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -103,13 +103,11 @@ impl super::Board {
}
}

fn collect_pawn_captures(
&self, list: &mut MoveList, pawns: Bitboard, dir: i8, target: Bitboard, seventh_rank: Bitboard,
) {
let promos = (pawns & seventh_rank).shift(dir);
list.push_promotion_capture_setwise(dir, promos & target);
let captures = (pawns & !seventh_rank).shift(dir);
list.push_pawns_setwise(dir, captures & target, MoveKind::Capture);
fn collect_pawn_captures(&self, list: &mut MoveList, pawns: Bitboard, dir: i8, target: Bitboard) {
let captures = pawns.shift(dir) & target;
let promos = captures & Bitboard::BOTH_HOME_ROWS;
list.push_promotion_capture_setwise(dir, promos);
list.push_pawns_setwise(dir, captures ^ promos, MoveKind::Capture);

let ep = self.en_passant();
if ep != Square::None && pawns.contains(ep.shift(-dir)) {
Expand All @@ -121,24 +119,22 @@ impl super::Board {
let stm = self.side_to_move();
let up = Square::UP[stm];
let pawns = self.colored_pieces(stm, PieceType::Pawn);
let seventh_rank = Bitboard::SEVENTH_RANK[stm];
let third_rank = Bitboard::THIRD_RANK[stm];
let empty = !self.occupancies();
let king_sq = self.king_square(stm);

let pushable_pawns = pawns & (!pinned | Bitboard::file(king_sq.file()));
let promotions = (pushable_pawns & seventh_rank).shift(up) & empty;
let pushed_pawns = (pawns & (!pinned | Bitboard::file(king_sq.file()))).shift(up) & empty;
let promotions = pushed_pawns & Bitboard::BOTH_HOME_ROWS & target;

if mgkind == MovegenKind::Quiet {
let non_promotions = pushable_pawns & !seventh_rank;
let single_pushes = non_promotions.shift(up) & empty;
let single_pushes = pushed_pawns ^ promotions;
let double_pushes = (single_pushes & third_rank).shift(up) & empty;

list.push_pawns_setwise(up, single_pushes & target, MoveKind::Normal);
list.push_pawns_setwise(up * 2, double_pushes & target, MoveKind::DoublePush);
list.push_pawns_setwise(up, promotions & target, MoveKind::PromotionR);
list.push_pawns_setwise(up, promotions & target, MoveKind::PromotionB);
list.push_pawns_setwise(up, promotions & target, MoveKind::PromotionN);
list.push_pawns_setwise(up, promotions, MoveKind::PromotionR);
list.push_pawns_setwise(up, promotions, MoveKind::PromotionB);
list.push_pawns_setwise(up, promotions, MoveKind::PromotionN);
}

if mgkind == MovegenKind::Noisy {
Expand All @@ -152,7 +148,7 @@ impl super::Board {

for i in 0..2 {
let the_pawns = pawns & (!pinned | pin_masks[i]) & shift_masks[i];
self.collect_pawn_captures(list, the_pawns, dirs[i], target, seventh_rank);
self.collect_pawn_captures(list, the_pawns, dirs[i], target);
}
}
}
Expand Down
2 changes: 1 addition & 1 deletion src/types/bitboard.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ pub struct Bitboard(pub u64);
impl Bitboard {
pub const ALL: Self = Self(0xFFFFFFFFFFFFFFFF);
pub const LIGHT_SQUARES: Self = Self(0x55AA55AA55AA55AA);
pub const SEVENTH_RANK: [Bitboard; 2] = [Self::rank(Rank::R7), Self::rank(Rank::R2)];
pub const BOTH_HOME_ROWS: Self = Self(0xFF000000000000FF);
pub const SIXTH_RANK: [Bitboard; 2] = [Self::rank(Rank::R6), Self::rank(Rank::R3)];
pub const THIRD_RANK: [Bitboard; 2] = [Self::rank(Rank::R3), Self::rank(Rank::R6)];
pub const HOME_ROWS: [Bitboard; 2] = [Self::rank(Rank::R1), Self::rank(Rank::R8)];
Expand Down
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