strncmp.c

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#include <string.h>

/*
 * PJ: my own strncmp implementation
 *
 * strncmp with short-circuit support: very common when you have const strings
 * combined by the compiler.
 * Otherwise we compare the strings as normal
 * We bail out when s1 ends (null-term) or n bytes have been analyzed
 */

int strncmp(const char* s1, const char* s2, size_t n)
{
    int r = -1;

    if(s1 == s2)
    {
        // short circuit - same string
        return 0;
    }

    // I don't want to panic with a NULL ptr - we'll fall through and fail
    if(s1 != NULL && s2 != NULL)
    {
        // iterate through strings until they don't match, s1 ends, or n == 0
        for(; n && *s1 == *s2; ++s1, ++s2, n--)
        {
            if(*s1 == 0)
            {
                r = 0;
                break;
            }
        }

        // handle case where we didn't break early - set return code.
        if(n == 0)
        {
            r = 0;
        }
        else if(r != 0)
        {
            r = *s1 - *s2;
        }
    }

    return r;
}