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c++performancemathematical-optimization

How to make large calculations program faster


I'm implementing a compression algorithm. Thing is, it is taking a second for a 20 Kib files, so that's not acceptable. I think it's slow because of the calculations.
I need suggestions on how to make it faster. I have some tips already, like shifting bits instead of multiplying, but I really want to be sure of which changes actually help because of the complexity of the program. I also accept suggestions concerning compiler options, I've heard there is a way to make the program do faster mathematical calculations.

Common operations are:

  • pow(...) function of math library
  • large number % 2
  • large number multiplying

Edit: the program has no floating point numbers


Solution

  • The question of how to make things faster should not be asked here to other people, but rather in your environment to a profiler. Use the profiler to determine where most of the time is spent, and that will hint you into which operations need to be improved, then if you don't know how to do it, ask about specific operations. It is almost impossible to say what you need to change without knowing what your original code is, and the question does not provide enough information: pow(...) function: what are the arguments to the function, is the exponent fixed? how much precision do you need? can you change the function for something that will yield a similar result? large number: how large is large in large number? what is number in this context? integers? floating point?