+extern Gc_rc gc_hash_open (Gc_hash hash, Gc_hash_mode mode,
+ gc_hash_handle *outhandle);
+extern Gc_rc gc_hash_clone (gc_hash_handle handle, gc_hash_handle *outhandle);
+extern size_t gc_hash_digest_length (Gc_hash hash);
+extern void gc_hash_hmac_setkey (gc_hash_handle handle,
+ size_t len, const char *key);
+extern void gc_hash_write (gc_hash_handle handle,
+ size_t len, const char *data);
+extern const char *gc_hash_read (gc_hash_handle handle);
+extern void gc_hash_close (gc_hash_handle handle);
+