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Implement magic bitboards for sliding piece move generation #1

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Implement magic bitboards for sliding piece move generation #1

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106 changes: 17 additions & 89 deletions src/board.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ use crate::{
errors::{BoardMoveError, FenParseError},
piece::Piece,
},
magic,
zobrist::{
zobrist_castling, zobrist_color, zobrist_color_swap, zobrist_en_passant, zobrist_piece,
},
Expand Down Expand Up @@ -1107,51 +1108,16 @@ impl Board {
}

fn rooklike_moves_masks(&self, mask: u64) -> impl Iterator<Item = (u32, u64)> {
let opponent_color = self.active_color.opponent();
let opponent_occupancy = self.occupancy_bits_for(opponent_color);
let self_occupancy = self.occupancy_bits_for(self.active_color);
let occupancy = self_occupancy | opponent_occupancy;

mask.as_bit_index_iter().map(move |index| {
let (rank, _) = Self::rank_file_from_index(index);

let rank_mask = RANK_0_MASK << (8 * (rank - 1));

let mut up_mask = FILE_0_MASK.discarding_shl(64 - index);
let up_mask_occupied = up_mask & occupancy;
if up_mask_occupied > 0 {
// If there are other pieces inside the mask of up-moves:
// Check where the last occupied index is and move up until (and including) there.
// That will include a capture of the piece on that square.
// Then mask with !self_occupancy so we don't capture our own pieces.
// The same method works for down_mask, left_mask and right_mask, although
// reversed for down_mask and right_mask.
up_mask &= ALL_MASK.discarding_shr(63 - up_mask_occupied.trailing_zeros())
& !self_occupancy;
}

let mut down_mask = FILE_0_MASK.discarding_shr(index + 8);
let down_mask_occupied = down_mask & occupancy;
if down_mask_occupied > 0 {
down_mask &= ALL_MASK.discarding_shl(63 - down_mask_occupied.leading_zeros())
& !self_occupancy;
}

let mut left_mask = RANK_0_MASK.discarding_shift_lr((index as i32) - 64) & rank_mask;
let left_mask_occupied = left_mask & occupancy;
if left_mask_occupied > 0 {
left_mask &= ALL_MASK.discarding_shr(63 - left_mask_occupied.trailing_zeros())
& !self_occupancy;
}

let mut right_mask = RANK_0_MASK.discarding_shift_lr((index as i32) - 55) & rank_mask;
let right_mask_occupied = right_mask & occupancy;
if right_mask_occupied > 0 {
right_mask &= ALL_MASK.discarding_shl(63 - right_mask_occupied.leading_zeros())
& !self_occupancy;
}
// Occupancy is already in standard bit ordering (bit 0 = a1, etc.)
let occupancy = self.occupancy_bits();

(index, up_mask | down_mask | left_mask | right_mask)
mask.as_bit_index_iter().map(move |board_index| {
// Convert board index to standard square (board_index 0 = bit 63, board_index 63 = bit 0)
let std_sq = 63 - board_index;
// Get attacks in standard ordering, filter out own pieces
let attacks = magic::get_rook_attacks(std_sq, occupancy) & !self_occupancy;
(board_index, attacks)
})
}

Expand Down Expand Up @@ -1179,54 +1145,16 @@ impl Board {
}

fn bishoplike_moves_masks(&self, mask: u64) -> impl Iterator<Item = (u32, u64)> {
let opponent_color = self.active_color.opponent();
let opponent_occupancy = self.occupancy_bits_for(opponent_color);
let self_occupancy = self.occupancy_bits_for(self.active_color);
let occupancy = self_occupancy | opponent_occupancy;

mask.as_bit_index_iter().map(move |index| {
let (_, file) = Self::rank_file_from_index(index);

let mut up_left_mask = DIAG_TL_MASK.discarding_shl(72 - index)
& (ALL_MASK >> index.saturating_sub(9 * (file - 1)));
let up_left_mask_occupied = up_left_mask & occupancy;
if up_left_mask_occupied > 0 {
up_left_mask &= ALL_MASK
.discarding_shr(63 - up_left_mask_occupied.trailing_zeros())
& !self_occupancy;
}

let mut up_right_mask = DIAG_TR_MASK.discarding_shl(63 - index)
& (ALL_MASK >> index.saturating_sub(7 * (8 - file)));
let up_right_mask_occupied = up_right_mask & occupancy;
if up_right_mask_occupied > 0 {
up_right_mask &= ALL_MASK
.discarding_shr(63 - up_right_mask_occupied.trailing_zeros())
& !self_occupancy;
}

let mut down_left_mask = DIAG_TR_MASK.discarding_shr(index)
& (ALL_MASK << 63u32.saturating_sub(index + 7 * (file - 1)));
let down_left_mask_occupied = down_left_mask & occupancy;
if down_left_mask_occupied > 0 {
down_left_mask &= ALL_MASK
.discarding_shl(63 - down_left_mask_occupied.leading_zeros())
& !self_occupancy;
}

let mut down_right_mask = DIAG_TL_MASK.discarding_shr(index + 9)
& (ALL_MASK << 63u32.saturating_sub(index + 9 * (8 - file)));
let down_right_mask_occupied = down_right_mask & occupancy;
if down_right_mask_occupied > 0 {
down_right_mask &= ALL_MASK
.discarding_shl(63 - down_right_mask_occupied.leading_zeros())
& !self_occupancy;
}
// Occupancy is already in standard bit ordering (bit 0 = a1, etc.)
let occupancy = self.occupancy_bits();

(
index,
up_left_mask | up_right_mask | down_left_mask | down_right_mask,
)
mask.as_bit_index_iter().map(move |board_index| {
// Convert board index to standard square (board_index 0 = bit 63, board_index 63 = bit 0)
let std_sq = 63 - board_index;
// Get attacks in standard ordering, filter out own pieces
let attacks = magic::get_bishop_attacks(std_sq, occupancy) & !self_occupancy;
(board_index, attacks)
})
}

Expand Down
1 change: 1 addition & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ pub mod board;
pub mod book;
pub mod engine;
pub mod evaluator;
pub mod magic;
pub mod score;
pub mod threading;
mod zobrist;
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