ck_ht: Add ck_ht_entry_empty function.

Function returns true if the initialized ck_ht_entry_t
pointed to by its argument does not contain a key-value pair.

include/ck_ht.h

@@ -52,6 +52,9 @@ struct ck_ht_entry {
 } CK_CC_ALIGNED;
 typedef struct ck_ht_entry ck_ht_entry_t;
 
+#define CK_HT_KEY_EMPTY		((uintptr_t)0)
+#define CK_HT_KEY_TOMBSTONE	(~(uintptr_t)0)
+
 struct ck_ht_map;
 struct ck_ht {
 	struct ck_ht_map *map;
@@ -77,6 +80,13 @@ ck_ht_iterator_init(struct ck_ht_iterator *iterator)
 	return;
 }
 
+CK_CC_INLINE static bool
+ck_ht_entry_empty(ck_ht_entry_t *entry)
+{
+
+	return entry->key == CK_HT_KEY_EMPTY;
+}
+
 CK_CC_INLINE static void
 ck_ht_entry_key_set(ck_ht_entry_t *entry, const void *key, uint16_t key_length)
 {

src/ck_ht.c

@@ -56,9 +56,6 @@
 #define CK_HT_PROBE_DEFAULT 64ULL
 #endif
 
-#define CK_HT_KEY_EMPTY       ((uintptr_t)0)
-#define CK_HT_KEY_TOMBSTONE   (~(uintptr_t)0)
-
 struct ck_ht_map {
 	enum ck_ht_mode mode;
 	uint64_t deletions;