From 5499628be01d8c4efde40b8133fef21279d4165d Mon Sep 17 00:00:00 2001
From: Simon Gardling <titaniumtown@proton.me>
Date: Tue, 18 Feb 2025 21:51:13 -0500
Subject: [PATCH] add dual impl for `bitboard` (bitvec and standard)

---
 Cargo.toml      |  5 +++-
 src/bitboard.rs | 64 +++++++++++++++++++++++++++++++++++++++++++------
 src/board.rs    |  1 +
 3 files changed, 62 insertions(+), 8 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index da379e9..5a88ae9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,9 +18,12 @@ debug = true
 
 lto = true
 
+[features]
+bitvec = [ "dep:bitvec" ]
+
 [dependencies]
 arrayvec = "0.7"
-bitvec = "1"
+bitvec = { version = "1", optional = true }
 either = "1.13"
 indicatif = "0.17"
 lazy_static = "1.5"
diff --git a/src/bitboard.rs b/src/bitboard.rs
index ee79c18..b2b5083 100644
--- a/src/bitboard.rs
+++ b/src/bitboard.rs
@@ -1,16 +1,27 @@
 use crate::board::{BOARD_AREA, BOARD_SIZE};
-use bitvec::prelude::*;
 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% 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")]
+pub type BitBoardInner = BitArr!(for BOARD_AREA, in u64, 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);
 
-/// Backing Type of BitBoard
-type BBBaseType = u64;
-
-#[derive(Copy, Clone, PartialEq, Eq)]
-pub struct BitBoard(BitArr!(for BOARD_AREA, in BBBaseType, Lsb0));
-
 impl Default for BitBoard {
     fn default() -> Self {
         Self::new()
@@ -18,22 +29,61 @@ impl Default for BitBoard {
 }
 
 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)) & 1) != 0
+    }
+
+    #[cfg(not(feature = "bitvec"))]
+    pub const fn set(&mut self, row: usize, col: usize, value: bool) {
+        let index = Self::get_index(row, col);
+        if value {
+            self.set_bit(index); // Set the bit at (row, col) to 1
+        } else {
+            self.clear_bit(index); // Clear the bit at (row, col)
+        }
+    }
+
+    #[cfg(not(feature = "bitvec"))]
+    const fn clear_bit(&mut self, index: usize) {
+        self.0 &= !(1 << index)
+    }
+
+    #[cfg(not(feature = "bitvec"))]
+    const fn set_bit(&mut self, index: usize) {
+        self.0 |= 1 << index
+    }
+
+    #[cfg(not(feature = "bitvec"))]
+    pub const fn count(&self) -> usize {
+        self.0.count_ones() as usize
+    }
+
     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);
     }
 
+    #[cfg(feature = "bitvec")]
     pub fn count(&self) -> usize {
         self.0.count_ones()
     }
diff --git a/src/board.rs b/src/board.rs
index 4721ede..7d4141d 100644
--- a/src/board.rs
+++ b/src/board.rs
@@ -11,6 +11,7 @@ use std::{cmp::Ordering, fmt};
 pub const BOARD_SIZE: usize = 8;
 
 /// Area of the board
+#[allow(dead_code)]
 pub const BOARD_AREA: usize = BOARD_SIZE * BOARD_SIZE;
 
 /// A chain of positions across the board