/* We use the number divided by two as the hash (for lots of
collisions), plus set all the higher bits so we can detect if they
don't get masked out. */
-static size_t hash(const void *elem, void *unused)
+static size_t hash(const void *elem, void *unused UNNEEDED)
{
size_t h = *(uint64_t *)elem / 2;
h |= -1UL << NUM_BITS;