rchess 2.3.0

A Chess Library Written In Rust
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245

use crate::defs::*;
use crate::mask_gen::sliders::{get_bishop_attacks_slow, get_rook_attacks_slow};
use crate::table_gen::general::RAYS;
use fastrand::Rng;
use lazy_static::lazy_static;

/// Number of used bits to calculate a bishop magic attack key for a square.
#[rustfmt::skip]
const BISHOP_BITS: [u8; 64] = [
    6, 5, 5, 5, 5, 5, 5, 6,
    5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 7, 7, 7, 7, 5, 5,
    5, 5, 7, 9, 9, 7, 5, 5,
    5, 5, 7, 9, 9, 7, 5, 5,
    5, 5, 7, 7, 7, 7, 5, 5,
    5, 5, 5, 5, 5, 5, 5, 5,
    6, 5, 5, 5, 5, 5, 5, 6,
];

/// Number of used bits to calculate a rook magic attack key for a square.
#[rustfmt::skip]
const ROOK_BITS: [u8; 64] = [
    12, 11, 11, 11, 11, 11, 11, 12,
    11, 10, 10, 10, 10, 10, 10, 11,
    11, 10, 10, 10, 10, 10, 10, 11,
    11, 10, 10, 10, 10, 10, 10, 11,
    11, 10, 10, 10, 10, 10, 10, 11,
    11, 10, 10, 10, 10, 10, 10, 11,
    11, 10, 10, 10, 10, 10, 10, 11,
    12, 11, 11, 11, 11, 11, 11, 12,
];

lazy_static! {
    /// The bishop magic for each square.
    pub static ref BISHOP_MAGICS: (Box<[Magic;64]>, usize) = generate_bishop_magics();

    /// The rook magic for each square.
    pub static ref ROOK_MAGICS: (Box<[Magic;64]>, usize) = generate_rook_magics();

    /// The bishop attack magic table.
    pub static ref BISHOP_ATTACKS: Vec<BitBoard> = generate_bishop_attacks();

    /// The rook attack magic table.
    pub static ref ROOK_ATTACKS: Vec<BitBoard> = generate_rook_attacks();
}

fn generate_bishop_magics() -> (Box<[Magic; 64]>, usize) {
    let mut magics = Vec::with_capacity(64);
    let mut current_offset = 0;
    let mut rng = Rng::with_seed(0xDEADBEEF);

    for square in SQUARES {
        let mut attack_table = [BitBoard::EMPTY; 512];

        let mask = get_bishop_mask(square);
        let shift = 64 - BISHOP_BITS[square.index()];
        let occupancy_attacks = Occupancies::new(mask)
            .into_iter()
            .map(|occupancy| (occupancy, get_bishop_attacks_slow(&RAYS, square, occupancy)))
            .collect::<Vec<_>>();

        let mut candidate;
        let mut max_key;
        loop {
            max_key = 0;
            candidate = get_magic_candidate(&mut rng);
            attack_table.fill(BitBoard::EMPTY);

            let mut is_valid = true;
            for (occupancy, attacks) in &occupancy_attacks {
                let key = Magic::calculate_key(*occupancy, mask, candidate, shift);
                max_key = max_key.max(key);

                if attack_table[key].is_empty() {
                    attack_table[key] = *attacks;
                } else if attack_table[key] != *attacks {
                    is_valid = false;
                    break;
                }
            }

            if is_valid {
                break;
            }
        }

        magics.push(Magic::new(mask, candidate, shift, current_offset));
        current_offset += max_key + 1;
    }

    (Box::new(magics.try_into().unwrap()), current_offset)
}

fn generate_rook_magics() -> (Box<[Magic; 64]>, usize) {
    let mut magics = Vec::with_capacity(64);
    let mut current_offset = 0;
    let mut rng = Rng::with_seed(0xBEEFDEAD);

    for square in SQUARES {
        let mut attack_table = [BitBoard::EMPTY; 4096];

        let shift = 64 - ROOK_BITS[square.index()];
        let mask = get_rook_mask(square);
        let occupancy_attacks = Occupancies::new(mask)
            .into_iter()
            .map(|occupancy| (occupancy, get_rook_attacks_slow(&RAYS, square, occupancy)))
            .collect::<Vec<_>>();

        let mut candidate;
        let mut max_key;
        loop {
            max_key = 0;
            candidate = get_magic_candidate(&mut rng);
            attack_table.fill(BitBoard::EMPTY);

            let mut is_valid = true;
            for (occupancy, attacks) in &occupancy_attacks {
                let key = Magic::calculate_key(*occupancy, mask, candidate, shift);
                max_key = max_key.max(key);

                if attack_table[key].is_empty() {
                    attack_table[key] = *attacks;
                } else if attack_table[key] != *attacks {
                    is_valid = false;
                    break;
                }
            }

            if is_valid {
                break;
            }
        }

        magics.push(Magic::new(mask, candidate, shift, current_offset));
        current_offset += max_key + 1;
    }

    (Box::new(magics.try_into().unwrap()), current_offset)
}

/// Gets a magic number candidate.
fn get_magic_candidate(rng: &mut Rng) -> u64 {
    rng.u64(0..=u64::MAX) & rng.u64(0..=u64::MAX) & rng.u64(0..=u64::MAX)
}

fn generate_bishop_attacks() -> Vec<BitBoard> {
    let mut bishop_attacks = vec![BitBoard::EMPTY; BISHOP_MAGICS.1];

    for square in SQUARES {
        let blocker_occupancies = Occupancies::new(get_bishop_mask(square));
        for occupancy in blocker_occupancies {
            let attacks = get_bishop_attacks_slow(&RAYS, square, occupancy);
            let key = BISHOP_MAGICS.0[square.index()].key(occupancy);
            bishop_attacks[key] = attacks;
        }
    }

    bishop_attacks
}

fn generate_rook_attacks() -> Vec<BitBoard> {
    let mut rook_attacks = vec![BitBoard::EMPTY; ROOK_MAGICS.1];

    for square in SQUARES {
        let blocker_occupancies = Occupancies::new(get_rook_mask(square));
        for occupancy in blocker_occupancies {
            let attacks = get_rook_attacks_slow(&RAYS, square, occupancy);
            let key = ROOK_MAGICS.0[square.index()].key(occupancy);
            rook_attacks[key] = attacks;
        }
    }

    rook_attacks
}

/// Gets the bishop blocker mask.
fn get_bishop_mask(square: Square) -> BitBoard {
    let mut mask = get_bishop_attacks_slow(&RAYS, square, BitBoard::EMPTY);

    mask &= !BitBoard::from_rank(Rank::First);
    mask &= !BitBoard::from_rank(Rank::Eighth);
    mask &= !BitBoard::from_file(File::A);
    mask &= !BitBoard::from_file(File::H);

    mask
}

/// Gets the rook blocker mask.
fn get_rook_mask(square: Square) -> BitBoard {
    let mut mask = get_rook_attacks_slow(&RAYS, square, BitBoard::EMPTY);

    if square.rank() != Rank::First {
        mask &= !BitBoard::from_rank(Rank::First);
    }

    if square.rank() != Rank::Eighth {
        mask &= !BitBoard::from_rank(Rank::Eighth);
    }

    if square.file() != File::A {
        mask &= !BitBoard::from_file(File::A);
    }

    if square.file() != File::H {
        mask &= !BitBoard::from_file(File::H);
    }

    mask
}

/// The [`Occupancies`] struct iterates through all occupancies for a mask.
pub struct Occupancies {
    mask: BitBoard,
    n_combinations: u16,
    current_combination: u16,
}

impl Occupancies {
    /// Creates a new [`Occupancies`] object for a given mask.
    pub fn new(mask: BitBoard) -> Self {
        Self {
            mask,
            n_combinations: 2u16.pow(mask.popcnt() as u32),
            current_combination: 0,
        }
    }
}

impl Iterator for Occupancies {
    type Item = BitBoard;

    fn next(&mut self) -> Option<Self::Item> {
        if self.current_combination == self.n_combinations {
            return None;
        }
        let mut mask_combination = BitBoard::EMPTY;
        for (idx, sq) in self.mask.into_iter().enumerate() {
            if self.current_combination & (1 << idx as u16) != 0 {
                mask_combination |= sq.bitboard();
            }
        }
        self.current_combination += 1;
        Some(mask_combination)
    }
}