stock ishex(str[])
{
    //P:3(\"ishex called: \\\"%s\\\"\", str);
    new
        i,
        cur;
    if (str[0] == \'0\' && (str[1] == \'x\' || str[1] == \'X\')) i = 2;
    while (str)
    {
        cur = str[i++];
        if (!((\'0\' <= cur <= \'9\') || (\'A\' <= cur <= \'F\') || (\'a\' <= cur <= \'f\'))) return 0;
    }
    return 1;
}