c - Performance of array of functions over if and switch statements

Question

I am writing a very performance critical part of the code and I had this crazy idea about substituting case statements (or if statements) with array of function pointers.

Let me demonstrate; here goes the normal version:

while(statement)
{
    /* 'option' changes on every iteration */

    switch(option)
    {
        case 0: /* simple task */ break;
        case 1: /* simple task */ break;
        case 2: /* simple task */ break;
        case 3: /* simple task */ break;
    }
}

And here is the "callback function" version:

void task0(void) {
    /* simple task */
}

void task1(void) {
    /* simple task */
}

void task2(void) {
    /* simple task */
}

void task3(void) {
    /* simple task */
}

void (*task[4]) (void);

task[0] = task0;
task[1] = task1;
task[2] = task2;
task[3] = task3;

while(statement)
{
    /* 'option' changes on every iteration */

    /* and now we call the function with 'case' number */
    (*task[option]) ();
}

So which version will be faster? Is the overhead of the function call eliminating speed benefit over normal switch (or if) statement?

Ofcourse the latter version is not so readable but I am looking for all the speed I can get.

I am about to benchmark this when I get things set up but if someone has an answer already, I wont bother.

Answer 1

I think at the end of the day your switch statements will be the fastest, because function pointers have the "overhead" of the lookup of the function and the function call itself. A switch is just a jmp table straight. It of course depends on different things which only testing can give you an answer to. That's my two cent worth.