feat: compute pawn attack table

3 files changed, 44 insertions, 20 deletions

diff --git a/src/board.c b/src/board.c
index a0b1bb7..0c133a8 100644
--- a/src/board.c
+++ b/src/board.c
@@ -37,9 +37,18 @@ void precompute_king_attack_table(Bitboard attacks[64]) {
     U64 position = BIT << index;
 
     attacks[index] =
-      (position & notAFile) << 7  | (position << 8) | (position & notHFile) << 9 |
-      (position & notAFile) >> 1  |                   (position & notHFile) << 1 |
-      (position & notAFile) >> 9  | (position >> 8) | (position & notHFile) >> 7;
+      (position & notAFile) << 7 | (position << 8) | (position & notHFile) << 9 |
+      (position & notAFile) >> 1 |                   (position & notHFile) << 1 |
+      (position & notAFile) >> 9 | (position >> 8) | (position & notHFile) >> 7;
+  }
+}
+
+void precompute_pawn_attack_table(Bitboard attacks[64], BYTE color) {
+  for (int index = 0; index < 64; index++) {
+    U64 position = BIT << index;
+
+    if (color == WHITE) attacks[index] = (position & notAFile) << 7 | (position & notHFile) << 9;
+    else                attacks[index] = (position & notAFile) >> 9 | (position & notHFile) >> 7;
   }
 }
 
diff --git a/src/board.h b/src/board.h
index 11b0c71..cf89794 100644
--- a/src/board.h
+++ b/src/board.h
@@ -56,9 +56,11 @@ static const char* pieces[] = {
   "♚", "♔",
 };
 
-void precompute_knight_attack_table();
-void precompute_king_attack_table();
 void print_bitboard(Bitboard bb);
 int pop_count(Bitboard bb);
 void print_board(Board board);
 Board parse_FEN(char* FEN);
+
+void precompute_knight_attack_table(Bitboard table[64]);
+void precompute_king_attack_table(Bitboard table[64]);
+void precompute_pawn_attack_table(Bitboard table[64], BYTE color);
diff --git a/src/main.c b/src/main.c
index c8c82cf..d6aa2b8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2,12 +2,11 @@
 #include "board.h"
 
 int main() {
-  {
-    start_test_section("Bitboards");
+  start_test_section("Bitboards"); {
     unit_test(pop_count(0b01110) == 3, "Pop count of 01110 is 3");
   }
-  {
-    start_test_section("Default FEN string");
+
+  start_test_section("Default FEN string"); {
     Board board = parse_FEN("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
     unit_test(pop_count(board.pieces[PAWN] | board.pieces[PAWN | BLACK]) == 16, "There are 16 pawns total");
     unit_test(pop_count(board.pieces[ROOK]) == 2, "There are 2 white rooks");
@@ -16,8 +15,8 @@ int main() {
     unit_test(board.castling_rights == 0, "Both sides can castle");
     unit_test(board.en_passant_square == 0, "No en passant move is avaialble");
   }
-  {
-    start_test_section("Test knight attacks");
+
+  start_test_section("Test knight attacks"); {
     Bitboard attacks[64];
     precompute_knight_attack_table(attacks);
 
@@ -33,8 +32,8 @@ int main() {
         "Knight on b7 attacks only d8, d6, c5, a5"
     );
   }
-  {
-    start_test_section("Test king attacks");
+
+  start_test_section("Test king attacks"); {
     Bitboard attacks[64];
     precompute_king_attack_table(attacks);
 
@@ -45,16 +44,30 @@ int main() {
     }
     unit_test(max_attacks == 8, "Max amount of king attacks should be 8");
 
-    {
-      U64 bit = 1;
-      unit_test(
-          attacks[h2] == ((BIT << h1) | (BIT << g1) | (BIT << g2) | (BIT << g3) | (BIT << h3)),
-          "King on h2 attacks only h1, g1, g2, g3, h3"
-      );
-    }
+    unit_test(
+        attacks[h2] == ((BIT << h1) | (BIT << g1) | (BIT << g2) | (BIT << g3) | (BIT << h3)),
+        "King on h2 attacks only h1, g1, g2, g3, h3"
+    );
   }
 
+  start_test_section("Test pawn attacks"); {
+    Bitboard white_attacks[64];
+    Bitboard black_attacks[64];
 
+    precompute_pawn_attack_table(white_attacks, WHITE);
+    precompute_pawn_attack_table(black_attacks, BLACK);
+
+    int is_same = 0;
+    int max_attacks = 0;
+    for (int i = 0; i < 64; i++) {
+      int attack_count = pop_count(white_attacks[i]);
+      if (attack_count > max_attacks) max_attacks = attack_count;
+      if (white_attacks[i] == black_attacks[i]) is_same = 1;
+    }
+    unit_test(max_attacks == 2, "Max amount of pawn attacks should be 2");
+    unit_test(is_same == 0, "Black and white pawns always move differently");
+    unit_test(white_attacks[g2] == (BIT << h3 | BIT << f3), "White pawn on g2 attacks only h3 and f3");
+  }
 
   report();
   return 0;