even std::unordered_map is easy to beat on most workloads if you relax the standard's requirements a litte, because the standard more or less requires hashing w

even std::unordered_map is easy to beat on most workloads if you relax the standard's requirements a litte, because the standard more or less requires hashing with chaining ("The elements of an unordered associative container are organized into buckets. Keys with the same hash code appear in the same bucket"). A good linear probing hash table will be faster most of the time, e.g. Google's dense_hash_map.