Faster approach to checking for an all-zero buffer in C?

Question

I am searching for a faster method of accomplishing this:

int is_empty(char * buf, int size) 
{
    int i;
    for(i = 0; i < size; i++) {
        if(buf[         


        

Answer 1

You stated in your question that you are looking for a most likely unnecessary micro-optimization. In 'normal' cases the ASM approach by Thomas and others should give you the fastest results.

Still, this is forgetting the big picture. If your buffer is really large, then starting from the start and essential do a linear search is definitely not the fastest way to do this. Assume your cp replacement is quite good at finding large consecutive empty regions but has a few non-empty bytes at the end of the array. All linear searches would require reading the whole array. On the other hand a quicksort inspired algorithm could search for any non-zero elements and abort much faster for a large enough dataset.

So before doing any kind of micro-optimization I would look closely at the data in your buffer and see if that gives you any patterns. For a single '1', randomly distributed in the buffer a linear search (disregarding threading/parallelization) will be the fastest approach, in other cases not necessarily so.