Question

I have programmed an embedded software (using C of course) and now I’m considering ways to improve the running time of the system. The most important single module in my system is one very large nested for loop module.

That module consists of two nested for loops that loops max 122500 times. That’s not very much yet, but the problem is that inside that nested for loop I have a function call to a function that is in another source file. That specific function consists mostly of two another nested for loops which loops always 22500 times. So now I have to make a function call 122500 times.

I have made that function that is to be called a lot lighter and shorter (yet still works as it should) and now I started to think that would it be faster to rip off that function call and write that process directly inside those first two for loops?

The processor in that system is ARM7TDMI and its frequency is 55MHz. The system itself isn’t very time critical so it doesn’t have to be real time capable. However the faster it can process its duties the better.

Also would it be also faster to use while loops instead of fors? And any piece of advice about how to improve the running time is appreciated.

-zaplec

Answer 1

TRY IT AND SEE!!

It’ll almost certainly make a difference. Function call overhead isn’t usually that much of an issue, but at over 100K repetitions it starts to add up.

…But whether or not it makes any real-world difference is something only you can answer, after trying it and timing the results.

As for for vs while… it shouldn’t matter unless you actually change the behavior when changing the loop. If in doubt, make your compiler spit out assembler code for both and compare… or just change it and time it.