add custom chess engine

2026-06-08 13:58:22 -06:00
parent d2ae34f530
commit c3280aa6d3
42 changed files with 3033 additions and 168 deletions
@@ -0,0 +1,87 @@
+// Bitboard utilities and precomputed attack tables. Sliders use magic
+// bitboards; the tables are built once by init_bitboards() (called from
+// engine_create) and are read-only afterwards.
+#ifndef CHESS_BITBOARD_H
+#define CHESS_BITBOARD_H
+
+#include "types.h"
+
+#if defined(_MSC_VER)
+#include <intrin.h>
+#endif
+
+namespace chess {
+
+constexpr Bitboard FILE_A_BB = 0x0101010101010101ULL;
+constexpr Bitboard FILE_H_BB = 0x8080808080808080ULL;
+constexpr Bitboard RANK_1_BB = 0x00000000000000FFULL;
+constexpr Bitboard RANK_8_BB = 0xFF00000000000000ULL;
+
+inline Bitboard square_bb(Square s) { return 1ULL << s; }
+inline Bitboard file_bb(File f)     { return FILE_A_BB << f; }
+inline Bitboard rank_bb(Rank r)     { return RANK_1_BB << (8 * int(r)); }
+
+inline int popcount(Bitboard b) {
+#if defined(_MSC_VER)
+    return int(__popcnt64(b));
+#else
+    return __builtin_popcountll(b);
+#endif
+}
+
+inline Square lsb(Bitboard b) {
+#if defined(_MSC_VER)
+    unsigned long i;
+    _BitScanForward64(&i, b);
+    return Square(i);
+#else
+    return Square(__builtin_ctzll(b));
+#endif
+}
+
+// Returns the least-significant square and clears it from b.
+inline Square pop_lsb(Bitboard& b) {
+    Square s = lsb(b);
+    b &= b - 1;
+    return s;
+}
+
+inline bool more_than_one(Bitboard b) { return b & (b - 1); }
+
+// Precomputed leaper attacks (filled by init_bitboards).
+extern Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
+extern Bitboard KnightAttacks[SQUARE_NB];
+extern Bitboard KingAttacks[SQUARE_NB];
+
+struct Magic {
+    Bitboard  mask;
+    Bitboard  magic;
+    Bitboard* attacks;
+    unsigned  shift;
+
+    unsigned index(Bitboard occ) const {
+        return unsigned(((occ & mask) * magic) >> shift);
+    }
+};
+
+extern Magic BishopMagics[SQUARE_NB];
+extern Magic RookMagics[SQUARE_NB];
+
+inline Bitboard bishop_attacks(Square s, Bitboard occ) {
+    const Magic& m = BishopMagics[s];
+    return m.attacks[m.index(occ)];
+}
+inline Bitboard rook_attacks(Square s, Bitboard occ) {
+    const Magic& m = RookMagics[s];
+    return m.attacks[m.index(occ)];
+}
+inline Bitboard queen_attacks(Square s, Bitboard occ) {
+    return bishop_attacks(s, occ) | rook_attacks(s, occ);
+}
+
+// Must be called once before any attack query (engine_create does this).
+void init_bitboards();
+
+} // namespace chess
+
+#endif // CHESS_BITBOARD_H