looking for C source for IP Hdr Cksum

[husain at stsusa.com]

	Does anyone have the C source code (or algorithm in ENGLISH!)
 	for calculating the checksum for the IP PDU header??
        (IP = Internet Protocol - ISO 8473)
	The ISO 8473 annex gives a really wierd description of the 
	cksum algorithm using MODULO 255 arithmetic. HELP! What is 
	that ?????               

	Thanks in advance

	kbh
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