split off repr

src/repr/bitboard.rs

@@ -0,0 +1,101 @@
+use crate::repr::board::{BOARD_AREA, BOARD_SIZE};
+use const_fn::const_fn;
+use static_assertions::const_assert;
+
+// quick explanation for the dual-nature of [`BitBoard`]
+// There's both a `bitvec` impl (which is variable length)
+// and a `native` impl which uses a u64 as the backing type
+// the `native` impl is ~15-25% faster (in non-BitBoard specific benchmarks)
+// `bitvec` is only really useful if you're using esoteric board sizes
+
+#[cfg(feature = "bitvec")]
+use bitvec::prelude::*;
+
+#[cfg(feature = "bitvec")]
+type BBBaseType = u64;
+
+#[cfg(feature = "bitvec")]
+pub type BitBoardInner = BitArr!(for BOARD_AREA, in BBBaseType, Lsb0);
+
+#[cfg(not(feature = "bitvec"))]
+pub type BitBoardInner = u64;
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub struct BitBoard(BitBoardInner);
+
+// BitBoard should be big enough to fit all points on the board
+const_assert!(std::mem::size_of::<BitBoard>() * 8 >= BOARD_AREA);
+
+impl Default for BitBoard {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl BitBoard {
+    #[cfg(feature = "bitvec")]
+    pub const fn new() -> Self {
+        Self(bitarr!(BBBaseType, Lsb0; 0; BOARD_AREA))
+    }
+
+    #[cfg(not(feature = "bitvec"))]
+    pub const fn new() -> Self {
+        Self(0)
+    }
+
+    #[cfg(not(feature = "bitvec"))]
+    pub const fn get(&self, row: usize, col: usize) -> bool {
+        ((self.0 >> Self::get_index(row, col)) & 0b1) != 0b0
+    }
+
+    #[cfg(not(feature = "bitvec"))]
+    pub const fn set(&mut self, row: usize, col: usize, value: bool) {
+        let index = Self::get_index(row, col);
+        // PERF! branchless setting of bit (~+3% perf bump)
+        self.0 &= !(0b1 << index); // clear bit
+        self.0 |= (value as BitBoardInner) << index; // set bit (if needed)
+    }
+
+    const fn get_index(row: usize, col: usize) -> usize {
+        row * BOARD_SIZE + col
+    }
+
+    #[cfg(feature = "bitvec")]
+    pub fn get(&self, row: usize, col: usize) -> bool {
+        self.0[Self::get_index(row, col)]
+    }
+
+    #[cfg(feature = "bitvec")]
+    pub fn set(&mut self, row: usize, col: usize, value: bool) {
+        self.0.set(Self::get_index(row, col), value);
+    }
+
+    // works on both `bitvec` and native (const on native)
+    #[const_fn(cfg(not(feature = "bitvec")))]
+    pub const fn count(&self) -> usize {
+        self.0.count_ones() as usize
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn set_and_get() {
+        let mut b = BitBoard::new();
+        for i in 0..BOARD_SIZE {
+            for j in 0..BOARD_SIZE {
+                assert!(
+                    !b.get(i, j),
+                    "A just-initalized BitBoard should be completely empty"
+                )
+            }
+        }
+        assert!(!b.get(2, 4));
+        b.set(2, 4, true);
+        assert!(b.get(2, 4));
+        b.set(2, 4, false);
+        assert!(!b.get(2, 4));
+    }
+}