perf: faster implementation of pop_count

1 files changed, 6 insertions, 4 deletions

diff --git a/src/bitboard.rs b/src/bitboard.rs
index d7a4fdb..3df4902 100644
--- a/src/bitboard.rs
+++ b/src/bitboard.rs
@@ -22,11 +22,13 @@ pub fn print(bb: Bitboard, title: &str) {
 }
 
 /// Return bitboard cardinality, aka number of elements in the set
-pub fn pop_count(bb: Bitboard) -> u8 {
-    if bb == 0 {
-        return 0;
+pub fn pop_count(mut bb: Bitboard) -> u8 {
+    let mut count = 0;
+    while bb > 0 {
+        count += 1;
+        bb &= bb - 1;
     }
-    return pop_count(bb >> 1) + (bb & 1) as u8;
+    return count;
 }
 
 /// Return Bitboard with only Least Single Bit