C++ Adding 2 arrays together quickly

Question

Given the arrays:

int canvas[10][10];
int addon[10][10];

Where all the values range from 0 - 100, what is the fastest way in C++ to add

Answer 1

The best you're going to do in standard C or C++ is to recast that as a one-dimensional array of 100 numbers and add them in a loop. (Single subscripts will use a bit less processing than double ones, unless the compiler can optimize it out. The only way you're going to know how much of an effect there is, if there is one, is to test.)

You could certainly create a class where the addition would be one simple C++ instruction (canvas += addon;), but that wouldn't speed anything up. All that would happen is that the simple C++ instruction would expand into the loop above.

You would need to get into lower-level processing in order to speed that up. There are additional instructions on many modern CPUs to do such processing that you might be able to use. You might be able to run something like this on a GPU using something like Cuda. You could try making the operation parallel and running on several cores, but on such a small instance you'll have to know how caching works on your CPU.

The alternatives are to improve your algorithm (on a knapsack-type problem, you might be able to use dynamic programming in some way - without more information from you, we can't tell you), or to accept the performance. Tens of millions of operations on a 10 by 10 array turn into hundreds of billions of operations on numbers, and that's not as intimidating as it used to be. Of course, I don't know your usage scenario or performance requirements.