ck_hs: add convenience hash function wrapper ck_hs_hash.

ck_hs_hash takes two arguments, the hash set and the key, then computes the
hash value. Performance gain from CK_HS_HASH is negligible with most workloads.
Basic test coverage in serial.c.

Shoutout to Theo Schlossnagle <jesus@circonus.com> who provided initial patch.

include/ck_hs.h

@@ -109,6 +109,14 @@ typedef struct ck_hs_iterator ck_hs_iterator_t;
 /* Convenience wrapper to table hash function. */
 #define CK_HS_HASH(T, F, K) F((K), (T)->seed)
 
+/* Computes the hash of n bytes of k for the specified hash map. */
+static inline unsigned long
+ck_hs_hash(const struct ck_hs *hs, const void *k)
+{
+
+	return hs->hf(k, hs->seed);
+}
+
 typedef void *ck_hs_apply_fn_t(void *, void *);
 bool ck_hs_apply(ck_hs_t *, unsigned long, const void *, ck_hs_apply_fn_t *, void *);
 void ck_hs_iterator_init(ck_hs_iterator_t *);

regressions/ck_hs/validate/serial.c

@@ -159,7 +159,14 @@ run_test(unsigned int is, unsigned int ad)
 
 	for (j = 0; j < size; j++) {
 		for (i = 0; i < sizeof(test) / sizeof(*test); i++) {
-			h = test[i][0];
+			unsigned long long h_1;
+
+			h = CK_HS_HASH(&hs[j], hs_hash, test[i]);
+			h_1 = ck_hs_hash(&hs[j], test[i]);
+
+			if (h != h_1)
+				ck_error("h != h_1 (%lu != %lu)\n", h, h_1);
+
 			if (ck_hs_get(&hs[j], h, test[i]) != NULL) {
 				continue;
 			}