Making of checksum using XOR

I´m trying to make a checksum of the content in a datapacket struct and want to make sure I get it right. Let´s say that the struct have three variables where on is an array like this:

Code:

---

typedef struct {
  char a;
  char b;
  char c[10];
} DataPacket;

---

Should I then make the checksum like this?

Code:

---

char checksum;

checksum = a ^ b;

for(i = 0; i < sizeof(c); i++){
  checksum ^= c[i];
}

---

Yes, you can. And it will be a slightly "better" checksum than using addition, because all bits have an equal chance of being detected as erroneous. But you can only detect an odd-number of failures for each bit.

An addition checksum fails to detect a double failure of the upper-most bit [assuming the checksum is equal size to the transmission unit, e.g. 1 byte checksum].

--
Mats

Perfect, Thank you.

That's called an LRC.
In practice, both checksum and LRC are inferrior to a good CRC.

Aah, I see. I´m trying to comunicate with a device that uses checksum so I´m stuck with that.
The docs I have says "checksum (exclusive OR of above 124 bytes)" I just wanted to make sure that my approach would work or I would be stuck re-sending the first packet. :-)