102 lines
2.8 KiB
Rust
102 lines
2.8 KiB
Rust
use crate::board::{BOARD_AREA, BOARD_SIZE};
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use const_fn::const_fn;
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use static_assertions::const_assert;
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// quick explanation for the dual-nature of [`BitBoard`]
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// There's both a `bitvec` impl (which is variable length)
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// and a `native` impl which uses a u64 as the backing type
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// the `native` impl is ~15-25% faster (in non-BitBoard specific benchmarks)
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// `bitvec` is only really useful if you're using esoteric board sizes
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#[cfg(feature = "bitvec")]
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use bitvec::prelude::*;
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#[cfg(feature = "bitvec")]
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type BBBaseType = u64;
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#[cfg(feature = "bitvec")]
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pub type BitBoardInner = BitArr!(for BOARD_AREA, in BBBaseType, Lsb0);
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#[cfg(not(feature = "bitvec"))]
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pub type BitBoardInner = u64;
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#[derive(Copy, Clone, PartialEq, Eq)]
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pub struct BitBoard(BitBoardInner);
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// BitBoard should be big enough to fit all points on the board
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const_assert!(std::mem::size_of::<BitBoard>() * 8 >= BOARD_AREA);
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impl Default for BitBoard {
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fn default() -> Self {
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Self::new()
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}
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}
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impl BitBoard {
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#[cfg(feature = "bitvec")]
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pub const fn new() -> Self {
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Self(bitarr!(BBBaseType, Lsb0; 0; BOARD_AREA))
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}
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#[cfg(not(feature = "bitvec"))]
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pub const fn new() -> Self {
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Self(0)
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}
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#[cfg(not(feature = "bitvec"))]
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pub const fn get(&self, row: usize, col: usize) -> bool {
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((self.0 >> Self::get_index(row, col)) & 0b1) != 0b0
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}
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#[cfg(not(feature = "bitvec"))]
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pub const fn set(&mut self, row: usize, col: usize, value: bool) {
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let index = Self::get_index(row, col);
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// PERF! branchless setting of bit (~+3% perf bump)
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self.0 &= !(0b1 << index); // clear bit
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self.0 |= (value as BitBoardInner) << index; // set bit (if needed)
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}
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const fn get_index(row: usize, col: usize) -> usize {
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row * BOARD_SIZE + col
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}
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#[cfg(feature = "bitvec")]
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pub fn get(&self, row: usize, col: usize) -> bool {
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self.0[Self::get_index(row, col)]
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}
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#[cfg(feature = "bitvec")]
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pub fn set(&mut self, row: usize, col: usize, value: bool) {
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self.0.set(Self::get_index(row, col), value);
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}
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// works on both `bitvec` and native (const on native)
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#[const_fn(cfg(not(feature = "bitvec")))]
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pub const fn count(&self) -> usize {
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self.0.count_ones() as usize
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}
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}
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn set_and_get() {
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let mut b = BitBoard::new();
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for i in 0..BOARD_SIZE {
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for j in 0..BOARD_SIZE {
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assert!(
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!b.get(i, j),
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"A just-initalized BitBoard should be completely empty"
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)
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}
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}
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assert!(!b.get(2, 4));
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b.set(2, 4, true);
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assert!(b.get(2, 4));
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b.set(2, 4, false);
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assert!(!b.get(2, 4));
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}
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}
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