laura_core 0.5.0

A fast and efficient move generator for chess engines.
Documentation 
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/*
    Laura-Core: a fast and efficient move generator for chess engines.

    Copyright (C) 2024-2025 HansTibberio <hanstiberio@proton.me>

    Laura-Core 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.

    Laura-Core 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 Laura-Core. If not, see <https://www.gnu.org/licenses/>.
*/

use core::mem::transmute;

use crate::{BitBoard, Color, File, Rank, Square};

/// Defines the deltas for white pawn attacks. These tuples represent the
/// relative movements a white pawn can make to attack diagonally forward.
const WHITE_PAWN_DELTAS: [(i8, i8); 2] = [(1, -1), (1, 1)];

/// Defines the deltas for black pawn attacks. These tuples represent the
/// relative movements a black pawn can make to attack diagonally forward.
const BLACK_PAWN_DELTAS: [(i8, i8); 2] = [(-1, -1), (-1, 1)];

/// Precomputed pawn attack BitBoards for all squares on the chessboard.
///
/// This constant provides a quick lookup for the possible attack positions
/// for both white and black pawns from each square. It is structured as a
/// 2D array where the first dimension represents the pawn color (0 for
/// white, 1 for black) and the second dimension corresponds to the square
/// index (0 to 63). Each entry in the array contains a BitBoard indicating
/// the squares that the pawn can attack from that position.
pub(crate) const PAWN_ATTACKS: [[BitBoard; Square::NUM_SQUARES]; 2] = [
    [
        BitBoard(512),
        BitBoard(1280),
        BitBoard(2560),
        BitBoard(5120),
        BitBoard(10240),
        BitBoard(20480),
        BitBoard(40960),
        BitBoard(16384),
        BitBoard(131072),
        BitBoard(327680),
        BitBoard(655360),
        BitBoard(1310720),
        BitBoard(2621440),
        BitBoard(5242880),
        BitBoard(10485760),
        BitBoard(4194304),
        BitBoard(33554432),
        BitBoard(83886080),
        BitBoard(167772160),
        BitBoard(335544320),
        BitBoard(671088640),
        BitBoard(1342177280),
        BitBoard(2684354560),
        BitBoard(1073741824),
        BitBoard(8589934592),
        BitBoard(21474836480),
        BitBoard(42949672960),
        BitBoard(85899345920),
        BitBoard(171798691840),
        BitBoard(343597383680),
        BitBoard(687194767360),
        BitBoard(274877906944),
        BitBoard(2199023255552),
        BitBoard(5497558138880),
        BitBoard(10995116277760),
        BitBoard(21990232555520),
        BitBoard(43980465111040),
        BitBoard(87960930222080),
        BitBoard(175921860444160),
        BitBoard(70368744177664),
        BitBoard(562949953421312),
        BitBoard(1407374883553280),
        BitBoard(2814749767106560),
        BitBoard(5629499534213120),
        BitBoard(11258999068426240),
        BitBoard(22517998136852480),
        BitBoard(45035996273704960),
        BitBoard(18014398509481984),
        BitBoard(144115188075855872),
        BitBoard(360287970189639680),
        BitBoard(720575940379279360),
        BitBoard(1441151880758558720),
        BitBoard(2882303761517117440),
        BitBoard(5764607523034234880),
        BitBoard(11529215046068469760),
        BitBoard(4611686018427387904),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
    ],
    [
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(0),
        BitBoard(2),
        BitBoard(5),
        BitBoard(10),
        BitBoard(20),
        BitBoard(40),
        BitBoard(80),
        BitBoard(160),
        BitBoard(64),
        BitBoard(512),
        BitBoard(1280),
        BitBoard(2560),
        BitBoard(5120),
        BitBoard(10240),
        BitBoard(20480),
        BitBoard(40960),
        BitBoard(16384),
        BitBoard(131072),
        BitBoard(327680),
        BitBoard(655360),
        BitBoard(1310720),
        BitBoard(2621440),
        BitBoard(5242880),
        BitBoard(10485760),
        BitBoard(4194304),
        BitBoard(33554432),
        BitBoard(83886080),
        BitBoard(167772160),
        BitBoard(335544320),
        BitBoard(671088640),
        BitBoard(1342177280),
        BitBoard(2684354560),
        BitBoard(1073741824),
        BitBoard(8589934592),
        BitBoard(21474836480),
        BitBoard(42949672960),
        BitBoard(85899345920),
        BitBoard(171798691840),
        BitBoard(343597383680),
        BitBoard(687194767360),
        BitBoard(274877906944),
        BitBoard(2199023255552),
        BitBoard(5497558138880),
        BitBoard(10995116277760),
        BitBoard(21990232555520),
        BitBoard(43980465111040),
        BitBoard(87960930222080),
        BitBoard(175921860444160),
        BitBoard(70368744177664),
        BitBoard(562949953421312),
        BitBoard(1407374883553280),
        BitBoard(2814749767106560),
        BitBoard(5629499534213120),
        BitBoard(11258999068426240),
        BitBoard(22517998136852480),
        BitBoard(45035996273704960),
        BitBoard(18014398509481984),
    ],
];

/// Retrieves the attack `BitBoard` for a pawn of the specified color from a given square.
///
/// This function returns a `BitBoard` that represents all possible attack
/// squares for a pawn positioned on the given square, taking into account the
/// pawn’s color (white or black). The attacks are precomputed and stored in
/// the `PAWN_ATTACKS` array for fast access.
#[inline(always)]
pub fn get_pawn_attacks(color: Color, square: Square) -> BitBoard {
    unsafe {
        *PAWN_ATTACKS
            .get_unchecked(color as usize)
            .get_unchecked(square.to_index())
    }
}

/// Generates the attack tables for both white and black pawns for all squares
/// on the chessboard.
///
/// This function iterates over all squares (0 to 63) and calculates the possible
/// attack moves for both white and black pawns based on their movement deltas.
fn gen_pawn_attacks() -> [[BitBoard; 64]; 2] {
    let mut pawn_attacks: [[BitBoard; 64]; 2] = [[BitBoard::EMPTY; 64]; 2];

    for square in BitBoard::FULL {
        let rank: i8 = square.rank() as i8;
        let file: i8 = square.file() as i8;
        let white: usize = Color::White as usize;
        let black: usize = Color::Black as usize;

        for (dr, df) in WHITE_PAWN_DELTAS.iter() {
            let new_rank: i8 = rank + dr;
            let new_file: i8 = file + df;

            if (0..8).contains(&new_rank) && (0..8).contains(&new_file) {
                let new_square: Square = Square::from_file_rank(
                    unsafe { transmute::<u8, File>(new_file as u8) },
                    unsafe { transmute::<u8, Rank>(new_rank as u8) },
                );
                pawn_attacks[white][square.to_index()] =
                    pawn_attacks[white][square.to_index()].set_square(new_square);
            }
        }

        for (dr, df) in BLACK_PAWN_DELTAS.iter() {
            let new_rank: i8 = rank + dr;
            let new_file: i8 = file + df;

            if (0..8).contains(&new_rank) && (0..8).contains(&new_file) {
                let new_square: Square = Square::from_file_rank(
                    unsafe { transmute::<u8, File>(new_file as u8) },
                    unsafe { transmute::<u8, Rank>(new_rank as u8) },
                );
                pawn_attacks[black][square.to_index()] =
                    pawn_attacks[black][square.to_index()].set_square(new_square);
            }
        }
    }

    pawn_attacks
}