must be 16 bytes. The return value is 0 (GC_OK) on success, or
another Gc_rc error code. */
extern int
-gc_hash_buffer (int hash, const void *in, size_t inlen, char *out);
+gc_hash_buffer (Gc_hash hash, const void *in, size_t inlen, char *out);
/* One-call interface. */
extern int gc_md5 (const void *in, size_t inlen, void *resbuf);