Function timing

Read up on QueryPerformanceCounter.

Quote:

Original post by VanillaSnake21 Hi, I would like to know the best way to measure the time it takes for the function to run. I want to test out different line drawing algorithms, and see how they compare. I read somewhere that you can use regular windows time functions, but won't the extra function calls interfere with timing? BTW I am using VC6 which does come with a profiler, but I don't think it's accurate. I rerun the same code 5 or 6 times and it's output varies from .24s to .6s. If I'm trying to improve algorithm speed won't every millisecond matter? Thanks.

Any kind of timing measurement will influence the execution speed of your app. If you want to minimize the effect of the calls make sure both algorithms call the timing functions the same number of times.

Windows' performance counter will do the trick. Standard time functions do not have a high enough resolution to do proper profiling.
Take a look at http://support.microsoft.com/kb/172338

If possible, you can also loop over the code multiple times. This helps compensate for the resolution, along with can help give you a more average value.

Pseudo algorithm works something like this:

desired_time = 2500; // let's use millisecondsn_runs = 1;time_taken = 0;do {  time_start = // get current time  for [1 .. n_runs] {    // run whatever you're profiling  }  time_end = // get_current_time;  time_taken = time_end - time_start;  n_runs = n_runs * 2;} while (time_taken < desired_time);average_time = (n_runs/2)/time_taken;

The only parameter here is the desired time to run. Then, the number of runs to achieve that will be dynamically determined. This gives you the convenience of making the code usable for algorithms with variable running times.

Ideally, you'd repeat this whole measurement several times, then choose the best samples, and use average of that.

With such approach, accuracy of timer itself isn't a problem, just set running time to some reasonably large factor of timer resolution. For low resolution timers, you may need to let it run for several seconds.

Thanks guys [smile]