add-piece-move-cache (#1)

Reviewed-on: #1
Co-authored-by: Josh <josh@joshuaschuett.com>
Co-committed-by: Josh <josh@joshuaschuett.com>

engine/src/bitboard.c

@@ -0,0 +1,61 @@
+#include "bitboard.h"
+
+uint64_t PAWN_ATTACKS[2][64];
+uint64_t KNIGHT_ATTACKS[64];
+uint64_t KING_ATTACKS[64];
+
+void create_knight_attack_cache(void) {
+    for (int sq = 0; sq < 64; sq++) {
+        uint64_t b = 1ULL << sq;
+        uint64_t mask = 0ULL;
+
+        mask |= (b & ~FILE_A)  << 15;
+        mask |= (b & ~FILE_H)  << 17;
+        mask |= (b & ~(FILE_A | FILE_B)) << 6;
+        mask |= (b & ~(FILE_G | FILE_H)) << 10;
+        mask |= (b & ~FILE_A)  >> 17;
+        mask |= (b & ~FILE_H)  >> 15;
+        mask |= (b & ~(FILE_A | FILE_B)) >> 10;
+        mask |= (b & ~(FILE_G | FILE_H)) >> 6;
+
+        KNIGHT_ATTACKS[sq] = mask;
+    }
+}
+
+void create_pawn_attack_cache(void) {
+    for (int sq = 0; sq < 64; sq++) {
+        uint64_t b = 1ULL << sq;
+
+        // White: NE (+9), NW (+7), but never from rank 8
+        uint64_t w  = ((b & ~FILE_H & ~RANK_8) << 9) | ((b & ~FILE_A & ~RANK_8) << 7);
+
+        // Black: SE (-7), SW (-9), but never from rank 1
+        uint64_t bl = ((b & ~FILE_H & ~RANK_1) >> 7) | ((b & ~FILE_A & ~RANK_1) >> 9);
+
+        PAWN_ATTACKS[WHITE][sq] = w;
+        PAWN_ATTACKS[BLACK][sq] = bl;
+    }
+}
+
+void create_king_attack_cache(void) {
+    for (int sq = 0; sq < 64; sq++) {
+        uint64_t b = 1ULL << sq;
+        uint64_t mask = 0ULL;
+
+        // North / South
+        mask |= (b & ~RANK_8) << 8;
+        mask |= (b & ~RANK_1) >> 8;
+
+        // East / West
+        mask |= (b & ~FILE_H) << 1;
+        mask |= (b & ~FILE_A) >> 1;
+
+        // Diagonals
+        mask |= (b & ~FILE_A & ~RANK_8) << 7;
+        mask |= (b & ~FILE_H & ~RANK_8) << 9;
+        mask |= (b & ~FILE_A & ~RANK_1) >> 9;
+        mask |= (b & ~FILE_H & ~RANK_1) >> 7;
+
+        KING_ATTACKS[sq] = mask;
+    }
+}