Fast hashmap

I need a lightning fast hashmap where the key exists of some struct containing enums. (Using it for caching modified images and retrieving them during rendering a game). A simple example: const Key = struct { image_index: u32, modifier: Modifier, style: u8, } const Modifier = enum(u8) { flip_vert, flip_horz, } var map: std.HashMapUnmanaged(Key, Image); How to accomplish a fast hashkey for Key? Are there other know slowdowns in HashMap during hashing / lookup which I sh...