feat: precompute king attack tables

3 files changed, 46 insertions, 18 deletions

diff --git a/src/board.c b/src/board.c
index 83fe8ce..a0b1bb7 100644
--- a/src/board.c
+++ b/src/board.c
@@ -18,7 +18,7 @@ void print_bitboard(Bitboard bb) {
 
 void precompute_knight_attack_table(Bitboard attacks[64]) {
   for (int index = 0; index < 64; index++) {
-    U64 position = (U64)1 << index;
+    U64 position = BIT << index;
 
     attacks[index] =
       ((position & notAFile & notBFile) << 6) |
@@ -32,6 +32,17 @@ void precompute_knight_attack_table(Bitboard attacks[64]) {
   }
 }
 
+void precompute_king_attack_table(Bitboard attacks[64]) {
+  for (int index = 0; index < 64; index++) {
+    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;
+  }
+}
+
 Board parse_FEN(char* FEN) {
   Board board;
   for (int i = 0; i < 12; i++) board.pieces[i] = 0;
@@ -42,7 +53,7 @@ Board parse_FEN(char* FEN) {
   for (int k = 0; k < strlen(FEN); k++) {
     int c = FEN[k];
     int index = rank * 8 + file;
-    Bitboard position = (Bitboard)1 << index;
+    Bitboard position = BIT << index;
 
     if (c > '0' && c <= '8') file += c - '0';
     else {
@@ -87,8 +98,6 @@ Board parse_FEN(char* FEN) {
           rank--;
           file = -1; // So that it becomes 0
           break;
-        case ' ': // TODO: parse everything after
-          return board;
       }
       file++;
     }
@@ -103,7 +112,7 @@ void print_board(Board board) {
     printf("%i|", rank + 1);
     for (int file = 0; file < 8; file++) {
       int index = rank * 8 + file;
-      Bitboard position = (Bitboard)1 << index;
+      Bitboard position = BIT << index;
 
       int found = 0;
       for (int piece = 0; piece < 12; piece++) {
diff --git a/src/board.h b/src/board.h
index c9d8153..11b0c71 100644
--- a/src/board.h
+++ b/src/board.h
@@ -11,6 +11,7 @@
 #define KING   0b1010
 
 typedef U64 Bitboard;
+#define BIT (U64)1
 
 typedef struct {
   Bitboard pieces[12];
@@ -56,6 +57,7 @@ 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);
diff --git a/src/main.c b/src/main.c
index 5f19585..c8c82cf 100644
--- a/src/main.c
+++ b/src/main.c
@@ -6,7 +6,16 @@ int main() {
     start_test_section("Bitboards");
     unit_test(pop_count(0b01110) == 3, "Pop count of 01110 is 3");
   }
-
+  {
+    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");
+    // TODO
+    unit_test(board.side == WHITE, "Side to move is white");
+    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");
     Bitboard attacks[64];
@@ -19,25 +28,33 @@ int main() {
     }
     unit_test(max_attacks == 8, "Max amount of knight attacks should be 8");
 
+    unit_test(
+        attacks[b7] == ((BIT << d8) | (BIT << d6) | (BIT << c5) | (BIT << a5)),
+        "Knight on b7 attacks only d8, d6, c5, a5"
+    );
+  }
+  {
+    start_test_section("Test king attacks");
+    Bitboard attacks[64];
+    precompute_king_attack_table(attacks);
+
+    int max_attacks = 0;
+    for (int i = 0; i < 64; i++) {
+      int attack_count = pop_count(attacks[i]);
+      if (attack_count > max_attacks) max_attacks = attack_count;
+    }
+    unit_test(max_attacks == 8, "Max amount of king attacks should be 8");
+
     {
       U64 bit = 1;
       unit_test(
-          attacks[b7] == ((bit << d8) | (bit << d6) | (bit << c5) | (bit << a5)),
-          "Knight on b7 attacks only d8, d6, c5, a5"
+          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("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");
-    // TODO
-    unit_test(board.side == WHITE, "Side to move is white");
-    unit_test(board.castling_rights == 0, "Everyone can castle");
-    unit_test(board.en_passant_square == 0, "No en passant move is avaialble");
-  }
+
 
   report();
   return 0;