/*  same as twotimes(), except that the string specified by the begin
 *  and end pointers MAY contain a null characters ('\0') 
 */
int twotimes2(const char * begin, const char * end) {
    unsigned int len = end - begin;
    if (len % 2 != 0)
	return 0;
    for (const char * m = begin + len/2; m != end; ++m, ++begin)
	if (*begin != *m)
	    return 0;
    return 1;
}

/*  returns TRUE (non-zero) if and only if the input C-string contains
 *  the same string
 */
int twotimes(const char * s) {
    const char * p = s;
    while (*p != 0)
	++p;
    return twotimes2(s, p);
}