How can I avoid “for” loops with an “if” condition inside them with C++?

Question

With almost all code I write, I am often dealing with set reduction problems on collections that ultimately end up with naive \"if\" conditions inside of them. Here\'s a simple

Answer 1

If DoStuff() would be dependent on i somehow in the future then I'd propose this guaranteed branch-free bit-masking variant.

unsigned int times = 0;
const int kSize = sizeof(unsigned int)*8;
for(int i = 0; i < myCollection.size()/kSize; i++){
  unsigned int mask = 0;
  for (int j = 0; j<kSize; j++){
    mask |= (myCollection[i*kSize+j]==SOMETHING) << j;
  }
  times+=popcount(mask);
}

for(int i=0;i<times;i++)
   DoStuff();

Where popcount is any function doing a population count ( count number of bits = 1 ). There will be some freedom to put more advanced constraints with i and their neighbors. If that is not needed we can strip the inner loop and remake the outer loop

for(int i = 0; i < myCollection.size(); i++)
  times += (myCollection[i]==SOMETHING);

followed by a

for(int i=0;i<times;i++)
   DoStuff();