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From: Rainer Weikusat <rweikusat@mssgmbh.com>
Newsgroups: comp.programming,comp.unix.programmer
Subject: Re: hash function over IP address
Date: Mon, 09 Apr 2012 15:54:28 +0100
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"Mark" <mark_cruzNOTFORSPAM@hotmail.com> writes:
> "Rainer Weikusat" <rweikusat@mssgmbh.com> wrote in message 
> news:87ehs0g7nn.fsf@sapphire.mobileactivedefense.com...
>>> Number of next hops is variable, thus anyway it would require to delete 
>>> the
>>> node and re-insert it back with a new key generated, right? (that's not 
>>> an
>>> issue though). How would you suggest to concatenate 32-bit long unsigned
>>> integers, in what form -- convert to strings, concatenate and use such
>>> string as a key?
>>
>> I would consolidate each pair into a 64-bit integer, using 0 in place
>> of a possibly-missing 'second 32-bit number' and then do 'string
>> comparions' on 64-bit integer strings of some length. Whether I would
>> rather store an explicit length together with such a string or use a
>> (64-bit) null terminator would depend on the actual circumstances.
>
> Thanks, this looks reasonable, however I don't understand what do you mean 
> by "each pair"? For instance, given three next hops:
>
> 10.10.10.1
> 20.20.20.1
> 30.30.30.1
>
> this would yield in two 64-bit values:
>
> 10.10.10.1_20.20.20.1
> 30.30.30.1_0.0.0.0

Using another notataion: The three IPv4 addresses

0x0a0a0a01
0x14141401
0x1e1e1e01

would yield the two 64-bit values

0x0a0a0a0114141401
0x1e1e1e0100000000