Question

I’m running intensive numerical simulations. I often use long integers, but I realized it would be safe to use integers instead. Would this improve the speed of my simulations significantly?

Answer 1

Depends. If you have lots and lots of numbers consecutively in memory, they’re more likely to fit in the L2 cache, so you have fewer cache misses. L2 cache misses – depending on your platform – can be a significant performance impact, so it’s definitely a good idea to make things fit in cache as much as possible (and prefetch if you can). But don’t expect your code to fly all of a sudden because your types are smaller.

EDIT: One more thing – if you choose an awkward type (like a 16-bit integer on a 32-bit or 64-bit platform), you may end up with worse performance because the CPU will have to surgically extract the 16-bit value and turn it into something it can work with. But typically, ints are a good choice.