add hash.c: zobrist init + pos zobrist calc + tt hash creation

src/hash.h

@@ -0,0 +1,89 @@
+/* hash.h - hash management.
+ *
+ * Copyright (C) 2024 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ *
+ */
+
+#ifndef HASH_H
+#define HASH_H
+
+#include <assert.h>
+
+#include "chessdefs.h"
+
+#define NBUCKETS             4                    /* buckets per hash table entry */
+
+#define HASH_SIZE_DEFAULT   32                    /* default: 32Mb */
+#define HASH_SIZE_MIN        4
+#define HASH_SIZE_MAX    32768                    /* 32Gb */
+
+typedef u64 key;
+
+/**
+ * hentry_t: hashtable bucket.
+ *
+ * Size should be exactly 16 bytes. If impossible to fit necessary data in
+ * 16 bytes in future, it should be updated to be exactly 32 bytes.
+ */
+typedef struct {
+    key key;                                      /* zobrist */
+    union {
+        u64 data;
+        struct {
+            u16 depth;                            /* ply in search */
+            s16 eval;
+            u16 move;
+            u8 flags;                             /* maybe for locking, etc... */
+            u8 filler;
+        };
+    };
+} hentry_t;
+
+typedef struct {
+    hentry_t buckets[NBUCKETS];
+} bucket_t;
+
+typedef struct {
+    bucket_t *keys;                               /* &hashtable entries */
+
+    /* memory size in bytes/mb */
+    size_t bytes;
+    u32  mb;
+
+    /* size in buckets/keys */
+    size_t nbuckets;
+    size_t nkeys;                                 /* nbuckets * NBUCKETS */
+
+    /* internal representation */
+    u32  nbits;                                   /* #buckets in bits, power of 2 */
+    u32  mask;                                    /* nbuckets - 1, key mask */
+
+    /* stats - unsure about usage */
+    size_t used_buckets;
+    size_t used_keys;
+    u64 collisions;
+} hasht_t;
+
+/* hack:
+ *  ep zobrist key index is 0-7 for each en-passant file, 8 for SQUARE_NONE.
+ * To transform :
+ *   - ep == 64 (SQUARE_NONE) to id = 8
+ *   - ep == 0~63 to idx = sq_file(ep), i.e. (ep & 7)
+ * we use the formula:
+ * idx = ( ( ep & SQUARE_NONE ) >> 3 ) | sq_file(ep);
+ */
+#define EP_ZOBRIST_IDX(ep) ( ( (ep) >> 3 ) | sq_file(ep) )
+
+void zobrist_init(void);
+int hash_create(int Mb);
+void hash_clear();
+void hash_delete();
+
+#endif  /* HASH_H */