+/**
+ * This callback function returns the hashcode of a key. The hashcode
+ * is used for indexing into the backing vector for finding the an
+ * item via its key. The same key must map consistently to the same
+ * hashcode while the hashtable contains an item with that key.
+ * Different keys map map to the same hashcode, in which case the
+ * vector placement is made at the first empty or hole slot following
+ * the hashcode index.
+ */
+static unsigned long integeritem_hashcode(void *this,void *key) {