Integer concatenation c

Question

I'm trying to concatenate two uint32_t and get back a uint64_t. Here's my method

uint64_t concat_int1_int2 (uint32_t int1, uint32_t int2) {
  uint64_t concatenated = int1;
  return concatenated << 32 | int2;
}

This seems to be extremely slow (I need to do it ~1,000,000 times and it is taking ~ 6 minutes). Two questions, why does the bit shift take so long (that seems to be the limiting step), and does anyone have a suggestion for a faster way to do this?

Answer 1

The way you are doing it is correct. It may help to inline the function. Most likely your performance problem is in code you haven't shown us.

Answer 2

Your solution is near optiomal, it can't be much faster. Marking the function as inline may help a very little, but will not make much difference. I made a test here in my machine using your code, it took 10ms to run 1,000,000 iterations of it. Your speed problem is somewhere else.