Add magic bitboard generation
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@ -14,7 +14,6 @@ pub struct Magic {
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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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#[allow(unused)] // FIXME: remove once used
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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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74
src/movegen/wizardry/generation.rs
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74
src/movegen/wizardry/generation.rs
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@ -0,0 +1,74 @@
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use crate::board::{Bitboard, Square};
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use crate::movegen::bishop::bishop_moves;
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use crate::movegen::rook::rook_moves;
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use crate::movegen::Magic;
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use super::mask::{generate_bishop_mask, generate_rook_mask};
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/// A trait to represent RNG for u64 values.
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#[allow(unused)] // FIXME: remove when used
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pub(crate) trait RandGen {
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fn gen(&mut self) -> u64;
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}
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type MagicGenerationType = (Vec<Magic>, Vec<Bitboard>);
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#[allow(unused)] // FIXME: remove when used
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pub fn generate_bishop_magics(rng: &mut dyn RandGen) -> MagicGenerationType {
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generate_magics(rng, generate_bishop_mask, bishop_moves)
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}
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#[allow(unused)] // FIXME: remove when used
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pub fn generate_rook_magics(rng: &mut dyn RandGen) -> MagicGenerationType {
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generate_magics(rng, generate_rook_mask, rook_moves)
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}
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fn generate_magics(
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rng: &mut dyn RandGen,
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mask_fn: impl Fn(Square) -> Bitboard,
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moves_fn: impl Fn(Square, Bitboard) -> Bitboard,
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) -> MagicGenerationType {
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let mut magics = Vec::new();
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let mut boards = Vec::new();
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for square in Square::iter() {
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let mask = mask_fn(square);
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let occupancy_to_moves: Vec<_> = mask
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.iter_power_set()
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.map(|occupancy| (occupancy, moves_fn(square, occupancy)))
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.collect();
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'candidate_search: loop {
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let mut candidate = Magic {
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magic: magic_candidate(rng),
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offset: 0,
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mask,
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shift: (64 - mask.count()) as u8,
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};
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let mut candidate_moves = vec![Bitboard::EMPTY; occupancy_to_moves.len()];
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for (occupancy, moves) in occupancy_to_moves.iter().cloned() {
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let index = candidate.get_index(occupancy);
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// Non-constructive collision, try with another candidate
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if !candidate_moves[index].is_empty() && candidate_moves[index] != moves {
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continue 'candidate_search;
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}
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candidate_moves[index] = moves;
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}
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// We have filled all candidate boards, record the correct offset and add the moves
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candidate.offset = boards.len();
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magics.push(candidate);
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boards.append(&mut candidate_moves);
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break;
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}
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}
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(magics, boards)
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}
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fn magic_candidate(rng: &mut dyn RandGen) -> u64 {
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// Few bits makes for better candidates
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rng.gen() & rng.gen() & rng.gen()
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}
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@ -3,7 +3,6 @@ use crate::movegen::bishop::bishop_moves;
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use crate::movegen::rook::rook_moves;
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/// Compute the relevancy mask for a bishop on a given [Square].
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#[allow(unused)] // FIXME: remove once used
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pub fn generate_bishop_mask(square: Square) -> Bitboard {
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let rays = bishop_moves(square, Bitboard::EMPTY);
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@ -16,7 +15,6 @@ pub fn generate_bishop_mask(square: Square) -> Bitboard {
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}
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/// Compute the relevancy mask for a rook on a given [Square].
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#[allow(unused)] // FIXME: remove once used
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pub fn generate_rook_mask(square: Square) -> Bitboard {
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let rays = rook_moves(square, Bitboard::EMPTY);
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@ -1 +1,2 @@
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mod generation;
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mod mask;
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