Re: Question on How the Checksum is Computed, please help!

[BORBELY Zoltan]

Hi,

On Thu, May 02, 2002 at 10:23:31PM +0800, address@hidden wrote:
>       if (checksum[0] == checksum[1]) {
> 
> I don't get the fact that checksum[0] will always be equal 
> to checksum[1].

IMHO it's a little sloppy, but it works. The correct version is:
    if (checksum[0] == 0 && checksum[1] == 0) {

> to checksum[1]. For example, I received the ff ack dump:
>    :1e:0c:00:7f:00:02:d1:80:cf:f1
> 
> cf = XOR(1e, 00, 00, d1)
> f1 = XOR(0c, 7f, 02, 80)
> 
> I have computed c1 & f1 as correct. But as you see, 
> they are not equal.

You forget to include the checksum bytes in the receiving checksum
calculation. As you can see 0xcf ^ 0xcf == 0 and 0xf1 ^ 0xf1 == 0, so
they are equal.

Bye,
Bozo