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Sum bytes in a string?

 
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M0KHZ



Joined: 14 Feb 2008
Posts: 18
Location: Cumbria

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Sum bytes in a string?
PostPosted: Mon Jul 14, 2008 1:56 am     Reply with quote
Maybe just a Monday morning thing Smile but how do I sum all the bytes in a string (mod 256) to enable a check sum to be developed?

Kevin - M0KHZ
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Mon Jul 14, 2008 3:34 am     Reply with quote
Code:
char MyString[] = {"Hello world."};
char *ptr;
int8 Checksum;

Checksum = 0;

ptr = MyString;
while (ptr != 0)
{
  Checksum += *ptr;
}


Instead of a modulo 256 checksum a CRC8 would give a better error detection. For an efficient implementation see
http://www.ccsinfo.com/forum/viewtopic.php?t=26264
Guest
PostPosted: Mon Jul 14, 2008 4:52 am     Reply with quote
Thanks ckielstra, I knew the solution would be straight forward. The reason for mod256 is due to the ‘other end’ of the communication protocol requiring it, the message structure is fixed with a header and footer, I just need to sum the elements of the string.

Kevin – M0KHZ
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