From c558800385c39345731697be8cb987d5f616aedb Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sun, 28 Jan 2024 15:53:19 -0800
Subject: [PATCH] [position] Fix a bug in the pawn pushes move generator

---
 position/src/move_generator/pawn.rs | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/position/src/move_generator/pawn.rs b/position/src/move_generator/pawn.rs
index 3d6d5f4..8b9b4cf 100644
--- a/position/src/move_generator/pawn.rs
+++ b/position/src/move_generator/pawn.rs
@@ -3,7 +3,7 @@
 use super::{move_generator_declaration, MoveGeneratorInternal, MoveSet};
 use crate::{MoveBuilder, Position};
 use chessfriend_bitboard::BitBoard;
-use chessfriend_core::{Color, Piece, PlacedPiece, Square};
+use chessfriend_core::{Color, Piece, PlacedPiece, Rank, Square};
 
 #[derive(Debug)]
 struct MoveIterator(usize, usize);
@@ -39,8 +39,20 @@ impl MoveGeneratorInternal for PawnMoveGenerator {
 
 impl PawnMoveGenerator {
     fn pushes(position: &Position, piece: PlacedPiece) -> BitBoard {
+        let square = piece.square();
+        let bitboard: BitBoard = square.into();
+
         let empty_squares = position.empty_squares();
-        BitBoard::pawn_pushes(piece.square(), piece.color()) & empty_squares
+
+        let mut moves = bitboard.shift_north_one() & empty_squares;
+        if !(bitboard
+            & BitBoard::rank(Rank::PAWN_STARTING_RANKS[piece.color() as usize].as_index()))
+        .is_empty()
+        {
+            moves |= moves.shift_north_one() & empty_squares;
+        }
+
+        moves
     }
 
     fn attacks(position: &Position, piece: PlacedPiece) -> BitBoard {