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

user_148634 0
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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[i] != 0) return 0;
    }
    return 1;
}

I realize I'm searching for a micro optimization unnecessary except in extreme cases, but I know a faster method exists, and I'm curious what it is.

buffer optimization c performance
19 Answers

What about looping from size to zero (cheaper checks):

int is_empty(char * buf, int size) 
{
    while(size --> 0) {
        if(buf[size] != 0) return 0;
    }
    return 1;
}

It must be noted that we probably cannot outperform the compiler, so enable the most aggressive speed optimization in your compiler and assume that you're likely to not go any faster.

Or handling everything using pointers (not tested, but likely to perform quite good):

int is_empty(char* buf, int size)
{
    char* org = buf;

    if (buf[size-1] == 1)
        return 0;

    buf[size-1] = 1;
    while(! *buf++);
    buf--;

    return buf == org[size-1];
}
user_7270610
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