bitmask_get_size
alloc_size = bitmask_get_size(new_idx_items);
alloc_size = bitmask_get_size(new_idx_items);
ptr = malloc(bitmask_get_size(num_items), M_NHOP, M_WAITOK | M_ZERO);
size_t size = bitmask_get_size(items);
size_t bitmask_get_size(uint32_t items);