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Checksum code in C

Dear experts,

I need to add a checksum to a frame that will be sent from client A to Client B thru protocol. Could someone please show me an example of checksum code to add a checksum to a frame before it is send, on client A side, and calculating the checksum for error detection on the receiver side (client B)?

Please reply asap.
Thank you.

SOLUTION

sunnycoder

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void_main

Or you download the quake II source code from www.idsoftware.com and have a look into crc.c and crc.h. There is networking code for client/server too, but only if you download the full sourcecode (not the "game source")
I think that could help!

SOLUTION

skypalae

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skypalae

Well. the example i've posted is not really using bytes, but half-bytes (nibbles). but you can easily modify it to bytes, words, whatever you want (and can XOR it).
S.

ASKER CERTIFIED SOLUTION

Kent Olsen

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Big_Red_Dog

Kdo forgot to advance the pointer in the buffer...

Here's the corrected code:

/*
ChecksumRegion -- Calculate a checksum over a memory region
Buffer - Start address of region to checksum
Length - Number of bytes to checksum
*/

int ChecksumRegion (void *Buffer, int Length)
{
unsigned char *Ptr;
int idx;
int XORValue;
int SUMValue;

Ptr = (unsigned char *)Buffer;
XORValue = 0;
SUMValue = 0;
for (idx = 1; idx <= Length; ++idx, Ptr++)
{
XORValue ^= *Ptr;
SUMValue += (*Ptr * idx);
}
return (XORValue ^ SumValue);
}