Re: Asynch comm

[Patrick Townsend <townsend@xxxxxxxxxxxxxx>]

Here is the C code for calculating a one byte LRC checksum character using XOR:

unsigned char checksum(unsigned char *buf, int len)
{
int                   i;
unsigned char         checksum = 0x00;
unsigned char         *ptr = (unsigned char *) buf;

    /* calculate the XOR value for each byte */

    for (i=0; i < len;  i++)
       checksum = checksum ^ ptr[i];

    return (unsigned char) checksum;
}

Patrick

At 02:50 PM 5/29/2000 -0400, Jim Franz wrote:
>I am working on an AS/400 to a credit card authorization network. 
>Unfortunately no previous AS/400 has previously certified to this network. 
>I'm hoping someone else has seen this requirement for async 
>communications. The specs from the other system call for me to add an LRC 
>code at end of packet, "each record must be immediately followed by an LRC 
>character that is computed by using the XOR function on each character of 
>the record. This is a data integrity check." The network person on the 
>other side is not able to really describe what it is. Sounds like some 
>sort of check digit for the whole packet. Any ideas?
>Jim Franz

---
IBM AS/400 communications, FTP automation, and network security
software and consulting services.

http://www.patownsend.com
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