From 0a890b42e8b701feed27faee4b0caf601f5bb258 Mon Sep 17 00:00:00 2001
From: eug-vs <eugene@eug-vs.xyz>
Date: Sat, 21 Jan 2023 00:38:43 +0300
Subject: refactor: do not wrap Bitboard into struct

---
 src/bitboard.rs | 72 +++++++++++++++++++++++++++++++++++++++------------------
 src/main.rs     |  5 ----
 2 files changed, 49 insertions(+), 28 deletions(-)

diff --git a/src/bitboard.rs b/src/bitboard.rs
index a2d34cb..6aba264 100644
--- a/src/bitboard.rs
+++ b/src/bitboard.rs
@@ -1,42 +1,68 @@
-use std::fmt;
+pub type Bitboard = u64;
 
-pub struct Bitboard(pub u64);
-
-impl fmt::Display for Bitboard {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        for index in 0..64 {
-            f.write_str(if &self.0 >> index & 1 == 1 { "1" } else { "." });
-            if (index + 1) % 8 == 0 {
-                f.write_str("\n");
-            }
+/// Print bitboard on screen in the same way squares appear in memory
+/// (i.e the board is actually flipped along X)
+pub fn print(bb: &Bitboard) {
+    for index in 0..64 {
+        print!("{}", if bb >> index & 1 == 1 { "1" } else { "." });
+        if (index + 1) % 8 == 0 {
+            println!();
         }
-        return write!(f, "\n")
     }
+    return println!();
 }
 
-impl Bitboard {
-    pub fn pop_count(&self) -> i32 {
-        if self.0 == 0 {
-            return 0;
-        }
-        return Bitboard::pop_count(&Bitboard(self.0 >> 1)) + (self.0 & 1) as i32;
+/// Return bitboard cardinality, aka number of elements in the set
+pub fn pop_count(bb: &Bitboard) -> u8 {
+    if bb == &0u64 {
+        return 0;
     }
+    return pop_count(&(bb >> 1)) + (bb & 1) as u8;
+}
+
+/// Return Bitboard with only Least Single Bit
+pub fn ls1b(bb: &Bitboard) -> u64 {
+    bb & !(bb - 1)
 }
 
+/// Log base 2 (aka Trailing Zero Count)
+///
+/// WARNING: Only works for SINGLE Bitboards
+/// Useful for calculating bit-index of LS1B
+pub fn bitscan(bb: &Bitboard) -> u8 {
+    debug_assert!(pop_count(bb) == 1, "Bitscan only works for SINGLE Bitboards!");
+    pop_count(&(bb - 1))
+}
+
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
-    fn test_print() {
-        const bb: Bitboard = Bitboard(127);
-        println!("{}", bb);
+    fn test_pop_count() {
+        assert_eq!(pop_count(&127), 7);
     }
 
     #[test]
-    fn test_pop_count() {
-        const bb: Bitboard = Bitboard(127);
-        assert_eq!(bb.pop_count(), 7);
+    fn test_ls1b() {
+        assert_eq!(ls1b(&38), 2);
+        assert_eq!(ls1b(&16), 16);
+        assert_eq!(ls1b(&20), 4);
+    }
+
+    #[test]
+    fn test_bitscan() {
+        assert_eq!(bitscan(&4), 2);
+        assert_eq!(bitscan(&16), 4);
+        assert_eq!(bitscan(&64), 6);
+        assert_eq!(bitscan(&128), 7);
+    }
+
+    #[test]
+    #[should_panic(expected = "Bitscan only works for SINGLE Bitboards!")]
+    fn test_bitscan_with_non_single_bb() {
+        bitscan(&5);
     }
 }
 
diff --git a/src/main.rs b/src/main.rs
index e0d9912..3555c81 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,10 +1,5 @@
 mod bitboard;
-use bitboard::*;
 
 fn main() {
-    const bb: Bitboard = Bitboard(127);
     println!("Hello, world!");
-    println!("{}", bb);
-    println!("{}", bb.0);
-    println!("{}", bb.pop_count());
 }
-- 
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