Patch p = (Patch)ip;
    protected void calculateChecksum(Patch ip, int start, int end, int ofs)    {    		Patch p = (Patch)ip;        int sum = 0;        for (int i = start; i <= end; i++)            sum += p.sysex[i];        p.sysex[ofs] = (byte) (sum & 0x7f);    }