protected static int getValue(char c) {
        if (c >= 'A' && c <= 'Z')
            return c - 'A';
        if (c >= 'a' && c <= 'z')
            return c - 'a' + 26;
        if (c >= '0' && c <= '9')
            return c - '0' + 52;
        if (c == '+')
            return 62;
        if (c == '/')
            return 63;
        if (c == '=')
            return 0;
        return -1;
    }