C: Which is faster, accessing global variable or passing a pointer to the function

Question

I am currently rewriting one of my programs. It has a heavily recursive function which solves peg-solitaire:

int solve(int draw) {
  if (finished())
    return true;

  //loop over every possible move (about 76 long values)
  //do a move (access the board, which is a long value)
  if (solve(draw + 1))
    return true;

  return false;
}

So i was wondering if it's faster to use solve like this:

solve(int draw, long **moves, long *board) {}

At the moment both moves and board are global variables.

Of course i am going to test it, but if someone tells me that this attempt isn't going to be efficient i will save some time :).

best regards

Answer 1

It probably won't be as efficient, but the only way to know for sure is to profile your code. If the bulk of your execution time is spent doing your actual game logic, then the tiny amount of overhead putting a few arguments on the stack should be negligible.

However, from a design point of view, avoiding global variables is much better. It allows your code to be stateless, and hence potentially re-entrant and thread-safe. However, this may or may not be relevant for your application.