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From: Rainer Weikusat <rweikusat@mssgmbh.com>
Newsgroups: comp.programming,comp.unix.programmer
Subject: Re: hash function over IP address
Date: Thu, 05 Apr 2012 12:15:40 +0100
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"Mark" <mark_cruzNOTFORSPAM@hotmail.com> writes:
> unsigned long hash_ipaddr(struct in_addr *addr)
> {
>     unsigned long res;
>
>     if (addr == NULL)
>         return 0UL;
>
>     res = (((addr->s_addr >> 24) & 0xff) * 256) + \
>           (((addr->s_addr >> 16) & 0xff) * 256) + \
>           (((addr->s_addr >>  8) & 0xff)* 256) + \
>           (addr->s_addr & 0xff);
>
>     return res;
> }

Unrelated question (Barry Margolin also noticed that but I'd like to
try expressing it somewhat clearer): This function adds the three
highest octets together in the high octet of a 16-bit integer and
then adds the lowest octet of the original address to the lowest octet
of this 16-bit integer whose value was zero before this addition. This
seems rather odd. Is this intentional?