From ecb82b31207a64e26e1e1789540893b147b6f862 Mon Sep 17 00:00:00 2001
From: Paul-Nicolas Madelaine <pnm@pnm.tf>
Date: Wed, 26 Nov 2025 23:03:23 +0100
Subject: [PATCH] update bitboards

---
 src/bitboard.rs | 47 +++++++++++++++++++++++++++++------------------
 1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/src/bitboard.rs b/src/bitboard.rs
index f1b98f5..3ea56da 100644
--- a/src/bitboard.rs
+++ b/src/bitboard.rs
@@ -2,24 +2,24 @@
 
 use crate::board::*;
 
-use core::iter::ExactSizeIterator;
-use core::iter::FusedIterator;
-
 /// A set of squares.
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Bitboard(pub u64);
 
 impl Bitboard {
+    /// Makes a new, empty `Bitboard`.
     #[inline]
     pub const fn new() -> Self {
         Self(0)
     }
 
+    /// Returns `true` if the bitboard contains the given square.
     #[inline]
-    pub const fn is_empty(&self) -> bool {
-        self.0 == 0
+    pub const fn contains(&self, square: Square) -> bool {
+        self.0 & (1 << square as u8) != 0
     }
 
+    /// Returns the first square in the bitboard, if any.
     #[inline]
     pub const fn first(&self) -> Option<Square> {
         let mask = self.0;
@@ -29,19 +29,19 @@ impl Bitboard {
         }
     }
 
+    /// Returns the last square in the bitboard, if any.
     #[inline]
     pub const fn last(&self) -> Option<Square> {
         let mask = self.0;
         match mask {
             0 => None,
-            _ => Some(unsafe {
-                Square::new_unchecked(63_u8.unchecked_sub(mask.leading_zeros() as u8))
-            }),
+            _ => Some(unsafe { Square::new_unchecked(63 ^ mask.leading_zeros() as u8) }),
         }
     }
 
+    /// Removes the first square from the bitboard and returns it, if any.
     #[inline]
-    pub const fn pop(&mut self) -> Option<Square> {
+    pub const fn pop_first(&mut self) -> Option<Square> {
         let mask = &mut self.0;
         let square = match mask {
             0 => None,
@@ -51,21 +51,32 @@ impl Bitboard {
         square
     }
 
+    /// Adds a square to the bitboard.
     #[inline]
     pub const fn insert(&mut self, square: Square) {
         self.0 |= 1 << square as u8;
     }
 
-    #[inline]
-    pub const fn contains(&self, square: Square) -> bool {
-        self.0 & (1 << square as u8) != 0
-    }
-
+    /// Removes a square from the bitboard.
     #[inline]
     pub const fn remove(&mut self, square: Square) {
         self.0 &= !(1 << square as u8);
     }
 
+    /// Returns the number of squares in the bitboard.
+    #[inline]
+    pub const fn len(&self) -> usize {
+        self.0.count_ones() as usize
+    }
+
+    /// Returns `true` if the bitboard contains no squares.
+    #[inline]
+    pub const fn is_empty(&self) -> bool {
+        self.0 == 0
+    }
+
+    /// Returns the mirror image of the bitboard. This is the set of the mirror images of all the
+    /// squares in the bitboard.
     #[inline]
     pub const fn mirror(self) -> Bitboard {
         let [a, b, c, d, e, f, g, h] = self.0.to_le_bytes();
@@ -138,7 +149,7 @@ impl Iterator for Bitboard {
     type Item = Square;
     #[inline]
     fn next(&mut self) -> Option<Self::Item> {
-        self.pop()
+        self.pop_first()
     }
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
@@ -174,11 +185,11 @@ impl Iterator for Bitboard {
         acc
     }
 }
-impl FusedIterator for Bitboard {}
-impl ExactSizeIterator for Bitboard {
+impl core::iter::FusedIterator for Bitboard {}
+impl core::iter::ExactSizeIterator for Bitboard {
     #[inline]
     fn len(&self) -> usize {
-        self.0.count_ones() as usize
+        self.len()
     }
 }