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[moves] Remove special handling of EnPassant moves

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Instead of generating e.p. moves in a separate pass, check whether each capture
move (left and right) targets the en passant square. If so, yield an e.p. capture
otherwise just a regular capture.
This commit is contained in:
Eryn Wells 2025-06-08 16:16:05 -07:00
parent bba910090c
commit 428ace13dc
1 changed files with 25 additions and 47 deletions
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72
moves/src/generators/pawn.rs
View file

@ -27,7 +27,6 @@ enum MoveType {
DoublePushes,
LeftCaptures,
RightCaptures,
EnPassant,
}
struct PromotionIterator {
@ -62,10 +61,6 @@ impl PawnMoveGenerator {
let (single_pushes, double_pushes) = Self::pushes(pawns, color, empty);
let (left_captures, right_captures) = Self::captures(pawns, color, enemies | en_passant);
let en_passant = en_passant & (left_captures | right_captures);
let left_captures = left_captures & !en_passant;
let right_captures = right_captures & !en_passant;
Self {
color,
single_pushes,
@ -137,22 +132,6 @@ impl PawnMoveGenerator {
Color::White => target.neighbor(Direction::SouthWest),
Color::Black => target.neighbor(Direction::NorthEast),
},
MoveType::EnPassant => match self.color {
Color::White => {
if (self.en_passant & self.left_captures).is_populated() {
target.neighbor(Direction::SouthEast)
} else {
target.neighbor(Direction::SouthWest)
}
}
Color::Black => {
if (self.en_passant & self.left_captures).is_populated() {
target.neighbor(Direction::NorthWest)
} else {
target.neighbor(Direction::NorthEast)
}
}
},
}
}
@ -165,7 +144,6 @@ impl PawnMoveGenerator {
MoveType::DoublePushes => self.double_pushes,
MoveType::LeftCaptures => self.left_captures,
MoveType::RightCaptures => self.right_captures,
MoveType::EnPassant => self.en_passant,
};
self.target_iterator = next_bitboard.occupied_squares_trailing();
@ -229,12 +207,16 @@ impl std::iter::Iterator for PawnMoveGenerator {
MoveType::DoublePushes => Some(GeneratedMove {
ply: Move::double_push(origin, target),
}),
MoveType::LeftCaptures | MoveType::RightCaptures => Some(GeneratedMove {
ply: Move::capture(origin, target),
}),
MoveType::EnPassant => Some(GeneratedMove {
ply: Move::en_passant_capture(origin, target),
}),
MoveType::LeftCaptures | MoveType::RightCaptures => {
let target_bitboard: BitBoard = target.into();
Some(GeneratedMove {
ply: if (target_bitboard & self.en_passant).is_populated() {
Move::en_passant_capture(origin, target)
} else {
Move::capture(origin, target)
},
})
}
}
} else if self.next_move_type().is_some() {
self.next()
@ -252,8 +234,7 @@ impl MoveType {
MoveType::SinglePushes => Some(MoveType::DoublePushes),
MoveType::DoublePushes => Some(MoveType::LeftCaptures),
MoveType::LeftCaptures => Some(MoveType::RightCaptures),
MoveType::RightCaptures => Some(MoveType::EnPassant),
MoveType::EnPassant => None,
MoveType::RightCaptures => None,
}
}
}
@ -261,8 +242,8 @@ impl MoveType {
#[cfg(test)]
mod tests {
use super::*;
use crate::{assert_move_list, assert_move_list_does_not_contain, ply, Move};
use chessfriend_board::test_board;
use crate::{assert_move_list, assert_move_list_contains, assert_move_list_does_not_contain, ply, Move};
use chessfriend_board::{fen::FromFenStr, test_board};
use chessfriend_core::{Color, Square};
use std::collections::HashSet;
@ -370,20 +351,8 @@ mod tests {
#[test]
fn black_d5_left_captures() {
let black_captures_board = test_board!(Black Pawn on D5, White Queen on E4);
let generated_moves: HashSet<GeneratedMove> =
PawnMoveGenerator::new(&black_captures_board, Some(Color::Black)).collect();
assert_eq!(
generated_moves,
[
GeneratedMove {
ply: Move::capture(Square::D5, Square::E4)
},
GeneratedMove {
ply: Move::quiet(Square::D5, Square::D4)
}
]
.into()
);
let generated_moves = PawnMoveGenerator::new(&black_captures_board, Some(Color::Black));
assert_move_list!(generated_moves, [ply!(D5 x E4), ply!(D5 - D4),]);
}
#[test]
@ -527,7 +496,7 @@ mod tests {
let generated_moves = PawnMoveGenerator::new(&board, None);
assert_move_list!(generated_moves, [ply!(E5 - E6), ply!(E5 x F6 e.p.),]);
assert_move_list!(generated_moves, [ply!(E5 - E6), ply!(E5 x F6 e.p.)]);
}
#[test]
@ -556,4 +525,13 @@ mod tests {
assert_move_list_does_not_contain!(generated_moves, [ply!(B4 x A3 e.p.)]);
}
#[test]
fn black_en_passant_check() {
let board = Board::from_fen_str("8/8/8/2k5/2pP4/8/B7/4K3 b - d3 0 3").expect("invalid fen");
println!("{}", board.display());
let generated_moves: HashSet<_> = PawnMoveGenerator::new(&board, None).collect();
assert_move_list_contains!(generated_moves, [ply!(C4 x D3 e.p.)]);
}
}