char *strstr(char *s1, *s2 ) {
    register char *p = s1;
    extern   char *strchr();
    extern   int   strncmp();

    register int len = strlen( s2 );
    for( ; (p = strchr( p, *s2 ) ) != 0; p++ ) {
        if( strncmp( p, s2, len ) == 0 ) {
            return (p);
        }
    }
    return (0);
}