+/* Callback function pointer types. */
+
+/* Calculate hash of a table entry. */
+typedef hashval_t (*htab_hash) (const void *);
+
+/* Compare a table entry with a possible entry. The entry already in
+ the table always comes first, so the second element can be of a
+ different type (but in this case htab_find and htab_find_slot
+ cannot be used; instead the variants that accept a hash value
+ must be used). */
+typedef int (*htab_eq) (const void *, const void *);
+
+/* Cleanup function called whenever a live element is removed from
+ the hash table. */
+typedef void (*htab_del) (void *);
+
+/* Function called by htab_traverse for each live element. The first
+ arg is the slot of the element (which can be passed to htab_clear_slot
+ if desired), the second arg is the auxiliary pointer handed to
+ htab_traverse. Return 1 to continue scan, 0 to stop. */
+typedef int (*htab_trav) (void **, void *);
+
+/* Memory-allocation function, with the same functionality as calloc().
+ Iff it returns NULL, the hash table implementation will pass an error
+ code back to the user, so if your code doesn't handle errors,
+ best if you use xcalloc instead. */
+typedef void *(*htab_alloc) (size_t, size_t);
+
+/* We also need a free() routine. */
+typedef void (*htab_free) (void *);
+
+/* Memory allocation and deallocation; variants which take an extra
+ argument. */
+typedef void *(*htab_alloc_with_arg) (void *, size_t, size_t);
+typedef void (*htab_free_with_arg) (void *, void *);
+
+/* This macro defines reserved value for empty table entry. */
+
+#define HTAB_EMPTY_ENTRY ((PTR) 0)
+
+/* This macro defines reserved value for table entry which contained
+ a deleted element. */
+
+#define HTAB_DELETED_ENTRY ((PTR) 1)