C++: What is faster - lookup in hashmap or switch statement?

Question

I have a code pattern which translates one integer to another. Just like this:

int t(int value) {
    switch (value) {
        case 1: return const_1;
        ca         


        

Answer 1

The switch will be faster. If it's a small number of cases, as in your example, it will use an if-chain. If a large number of cases, and if they are reasonably compact, it has the option to generate a jump-table, which only takes a few instructions. (BTW you don't have to order the cases.) The hash-map is O(1), but will probably take in the range of 10-40 instructions.