291 lines
7.8 KiB
Rust
291 lines
7.8 KiB
Rust
mod generation;
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pub(super) use generation::*;
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mod mask;
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use crate::board::{Bitboard, Square};
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/// A type representing the magic board indexing a given [crate::board::Square].
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#[derive(Clone, Debug)]
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pub(super) struct Magic {
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/// Magic number.
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pub(self) magic: u64,
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/// Base offset into the magic square table.
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pub(self) offset: usize,
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/// Mask to apply to the blocker board before applying the magic.
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pub(self) mask: Bitboard,
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/// Length of the resulting mask after applying the magic.
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pub(self) shift: u8,
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}
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impl Magic {
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/// Compute the index into the magics database for this set of `blockers`.
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pub fn get_index(&self, blockers: Bitboard) -> usize {
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let relevant_occupancy = (blockers & self.mask).0;
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let base_index = ((relevant_occupancy.wrapping_mul(self.magic)) >> self.shift) as usize;
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base_index + self.offset
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}
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}
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/// A type encapsulating a database of [Magic] bitboard moves.
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#[derive(Clone, Debug)]
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pub(crate) struct MagicMoves {
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magics: Vec<Magic>,
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moves: Vec<Bitboard>,
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}
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impl MagicMoves {
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/// Initialize a new [MagicMoves] given a matching list of [Magic] and its corresponding moves
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/// as a [Bitboard].
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///
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/// # Safety
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///
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/// This should only be called with values generated by [crate::movegen::wizardry::generation].
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pub unsafe fn new(magics: Vec<Magic>, moves: Vec<Bitboard>) -> Self {
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Self { magics, moves }
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}
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/// Get the set of valid moves for a piece standing on a [Square], given a set of blockers.
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pub fn query(&self, square: Square, blockers: Bitboard) -> Bitboard {
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// SAFETY: indices are in range by construction
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unsafe {
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let index = self
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.magics
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.get_unchecked(square.index())
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.get_index(blockers);
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*self.moves.get_unchecked(index)
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}
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}
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}
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// region:sourcegen
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/// A set of magic numbers for bishop move generation.
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pub(crate) const BISHOP_SEED: [u64; 64] = [
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4908958787341189172,
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1157496606860279808,
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289395876198088778,
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649648646467355137,
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19162426089930848,
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564067194896448,
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18586170375029026,
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9185354800693760,
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72172012436987968,
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317226351607872,
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2597178509285688384,
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1162205282238464,
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144154788211329152,
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172197832046936160,
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4625762105940000802,
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1477217245166903296,
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2251937789583872,
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289373902621379585,
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4616200855845409024,
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2251909637357568,
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3532510975437640064,
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563517968228352,
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562953309660434,
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1196005458310201856,
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2350914225914520576,
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2287018679861376,
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13836188353273790593,
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11267795163676832,
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297519119119499264,
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18588344158519552,
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10453428171813953792,
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72128237668534272,
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1298164929055953920,
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865575144395900952,
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9293076573325312,
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108104018148197376,
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578503662094123152,
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4665870505495102224,
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6066493872259301520,
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285877477613857,
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2328941618281318466,
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721165292771739652,
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4899973577790523400,
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75050392749184,
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2305878200632215680,
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11530099074925593616,
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290561512873919880,
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18652187227888000,
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3379933716168704,
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9223409493537718272,
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22273835729926,
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1152921524003672064,
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4647812741240848385,
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1244225087719112712,
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7367907171013001728,
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9263922034316951570,
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300758214358598160,
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4611686331973636096,
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2377900605806479360,
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6958097192913601024,
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864691130877743617,
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703824948904066,
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612700674899317536,
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180742128018784384,
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];
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/// A set of magic numbers for rook move generation.
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pub(crate) const ROOK_SEED: [u64; 64] = [
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2341871943948451840,
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18015635528220736,
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72066665545773824,
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1188959097794342912,
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12141713393631625314,
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720649693658353672,
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36029896538981888,
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36033359356363520,
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140746619355268,
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1158339898446446661,
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36591886560003650,
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578853633228023808,
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2392554490300416,
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140814806160384,
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180706952366596608,
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10696087878779396,
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1153260703948210820,
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310748649170673678,
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36311372044308544,
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9223444604757615104,
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1267187285230592,
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282574622818306,
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18722484274726152,
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2271591090110593,
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1153063519847989248,
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10168327557107712,
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4507998211276833,
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1153203035420233728,
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4631961017139660032,
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2454499182462107776,
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289367288355753288,
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18015815850820609,
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9268726066908758912,
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11547264697673728000,
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2314929519368081536,
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140943655192577,
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20266215511427202,
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180706969441535248,
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1302683805944911874,
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11534000122299940994,
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22676602724843520,
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4639271120198041668,
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1302104069046927376,
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9184220895313928,
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4612249105954373649,
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562984581726212,
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2312678200579457040,
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4647736876550193157,
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3170604524138139776,
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4684447574787096704,
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20283792725901696,
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1152992019380963840,
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117383863558471808,
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1153488854922068096,
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17596884583424,
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90074759127192064,
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4900502436426416706,
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4573968656793901,
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1161084564408385,
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1657887889314811910,
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4614501455660058690,
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4612530729109422081,
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642458506527236,
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1116704154754,
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];
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// endregion:sourcegen
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#[cfg(test)]
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mod test {
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use std::fmt::Write as _;
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use super::*;
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// A simple XOR-shift RNG implementation.
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struct SimpleRng(u64);
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impl SimpleRng {
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pub fn new() -> Self {
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Self(4) // https://xkcd.com/221/
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}
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}
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impl RandGen for SimpleRng {
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fn gen(&mut self) -> u64 {
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self.0 ^= self.0 >> 12;
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self.0 ^= self.0 << 25;
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self.0 ^= self.0 >> 27;
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self.0
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}
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}
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#[test]
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fn rng() {
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let mut rng = SimpleRng::new();
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assert_eq!(rng.gen(), 134217733);
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assert_eq!(rng.gen(), 4504699139039237);
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assert_eq!(rng.gen(), 13512173405898766);
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assert_eq!(rng.gen(), 9225626310854853124);
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assert_eq!(rng.gen(), 29836777971867270);
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}
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fn split_twice<'a>(
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text: &'a str,
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start_marker: &str,
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end_marker: &str,
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) -> Option<(&'a str, &'a str, &'a str)> {
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let (prefix, rest) = text.split_once(start_marker)?;
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let (mid, suffix) = rest.split_once(end_marker)?;
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Some((prefix, mid, suffix))
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}
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fn array_string(piece_type: &str, values: &[Magic]) -> Result<String, std::fmt::Error> {
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let mut res = String::new();
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writeln!(
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&mut res,
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"/// A set of magic numbers for {} move generation.",
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piece_type
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)?;
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writeln!(
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&mut res,
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"pub(crate) const {}_SEED: [u64; 64] = [",
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piece_type.to_uppercase()
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)?;
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for magic in values {
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writeln!(&mut res, " {},", magic.magic)?;
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}
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writeln!(&mut res, "];")?;
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Ok(res)
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}
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#[test]
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#[ignore = "slow"]
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// Regenerates the magic bitboard numbers.
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fn regen_magic_seeds() {
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// We only care about the magics, the moves can be recomputed at runtime ~cheaply.
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let (bishop_magics, _) = generate_bishop_magics(&mut SimpleRng::new());
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let (rook_magics, _) = generate_rook_magics(&mut SimpleRng::new());
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let original_text = std::fs::read_to_string(file!()).unwrap();
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let bishop_array = array_string("bishop", &bishop_magics[..]).unwrap();
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let rook_array = array_string("rook", &rook_magics[..]).unwrap();
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let new_text = {
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let start_marker = "// region:sourcegen\n";
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let end_marker = "// endregion:sourcegen\n";
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let (prefix, _, suffix) =
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split_twice(&original_text, start_marker, end_marker).unwrap();
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format!("{prefix}{start_marker}{bishop_array}\n{rook_array}{end_marker}{suffix}")
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};
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if new_text != original_text {
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std::fs::write(file!(), new_text).unwrap();
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panic!("source was not up-to-date")
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}
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}
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}
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