sixel_allocator_unref(
    sixel_allocator_t /* in */ *allocator)  /* allocator object to be unreference */
{
    /* TODO: be thread safe */
    if (allocator) {
        assert(allocator->ref > 0);
        --allocator->ref;
        if (allocator->ref == 0) {
            sixel_allocator_destroy(allocator);
        }
    }
}
sixel_allocator_unref(
    sixel_allocator_t   *allocator)   
{
     
    if (allocator) {
        assert(allocator->ref > 0);
        --allocator->ref;
        if (allocator->ref == 0) {
            sixel_allocator_destroy(allocator);
        }
    }
}