From 6719e247a3e0c75261665eca166fc5c8c8fdaf27 Mon Sep 17 00:00:00 2001
From: eug-vs <eugene@eug-vs.xyz>
Date: Mon, 23 Jan 2023 08:47:23 +0300
Subject: refactor: separately store pawn double pushes

---
 src/attacks.rs | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

(limited to 'src/attacks.rs')

diff --git a/src/attacks.rs b/src/attacks.rs
index 5399c96..6762bb3 100644
--- a/src/attacks.rs
+++ b/src/attacks.rs
@@ -45,6 +45,7 @@ pub struct Attacks {
     /// TODO: compute pawn attacks set-wise
     pub pawn: [AttackTable; 2],
     pub pawn_pushes: [AttackTable; 2],
+    pub pawn_double_pushes: [AttackTable; 2],
 
     pub first_rank_attacks: FirstRankAttacks,
     /// Should be indexed by Direction
@@ -59,13 +60,14 @@ impl Attacks {
         let first_rank_attacks = Self::precompute_first_rank_attacks();
         let ray_attacks = Self::precompute_ray_attacks();
         let pawn = Self::precompute_pawn_attacks();
-        let pawn_pushes = Self::precompute_pawn_pushes();
+        let (pawn_pushes, pawn_double_pushes) = Self::precompute_pawn_pushes();
 
         Self {
             knight,
             king,
             pawn,
             pawn_pushes,
+            pawn_double_pushes,
             first_rank_attacks,
             ray_attacks,
         }
@@ -81,14 +83,19 @@ impl Attacks {
         attacks
     }
 
-    fn precompute_pawn_pushes() -> [AttackTable; 2] {
+    fn precompute_pawn_pushes() -> ([AttackTable; 2], [AttackTable; 2]) {
         let mut pushes = [[0; 64]; 2];
+        let mut double_pushes = [[0; 64]; 2];
+
         for index in 0..64 {
             let square = 1u64 << index;
-            pushes[Color::White as usize][index] = (square << 8) | ((square & RANK_2) << 16);
-            pushes[Color::Black as usize][index] = (square >> 8) | ((square & RANK_6) >> 16);
+            pushes       [Color::White as usize][index] = (square << 8);
+            double_pushes[Color::White as usize][index] = ((square & RANK_2) << 16);
+
+            pushes       [Color::Black as usize][index] = (square >> 8);
+            double_pushes[Color::Black as usize][index] = ((square & RANK_6) >> 16);
         }
-        pushes
+        (pushes, double_pushes)
     }
 
     fn precompute_knight_attacks() -> AttackTable {
@@ -332,11 +339,16 @@ mod tests {
 
     #[test]
     fn test_pawn_pushes() {
-        let pushes = Attacks::precompute_pawn_pushes();
+        let (pushes, double_pushes) = Attacks::precompute_pawn_pushes();
         assert_eq!(pushes[Color::White as usize][Square::E4 as usize], Square::E5.to_bitboard());
-        assert_eq!(pushes[Color::White as usize][Square::A2 as usize], Square::A3.to_bitboard() | Square::A4.to_bitboard());
+        assert_eq!(pushes[Color::White as usize][Square::A2 as usize], Square::A3.to_bitboard());
         assert_eq!(pushes[Color::Black as usize][Square::E4 as usize], Square::E3.to_bitboard());
-        assert_eq!(pushes[Color::Black as usize][Square::H6 as usize], Square::H5.to_bitboard() | Square::H4.to_bitboard());
+        assert_eq!(pushes[Color::Black as usize][Square::H6 as usize], Square::H5.to_bitboard());
+
+        assert_eq!(double_pushes[Color::White as usize][Square::E4 as usize], 0);
+        assert_eq!(double_pushes[Color::White as usize][Square::A2 as usize], Square::A4.to_bitboard());
+        assert_eq!(double_pushes[Color::Black as usize][Square::E4 as usize], 0);
+        assert_eq!(double_pushes[Color::Black as usize][Square::H6 as usize], Square::H4.to_bitboard());
     }
 
     #[test]
-- 
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