Re: hash function over IP address

From	Rainer Weikusat <rweikusat@mssgmbh.com>
Newsgroups	comp.programming, comp.unix.programmer
Subject	Re: hash function over IP address
Date	2012-04-05 19:34 +0100
Message-ID	<87hawy3u46.fsf@sapphire.mobileactivedefense.com> (permalink)
References	(5 earlier) <ohkfr.43093$_C5.25998@newsfe09.iad> <87sjgi3xxr.fsf@sapphire.mobileactivedefense.com> <_xkfr.45660$QC3.18854@newsfe16.iad> <87lima3wxi.fsf@sapphire.mobileactivedefense.com> <5flfr.2467$Nk2.1380@newsfe08.iad>

Cross-posted to 2 groups.

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Daniel Pitts <newsgroup.nospam@virtualinfinity.net> writes:
> On 4/5/12 10:34 AM, Rainer Weikusat wrote:
>> Daniel Pitts<newsgroup.nospam@virtualinfinity.net>  writes:
>>> On 4/5/12 10:12 AM, Rainer Weikusat wrote:
>>>> Daniel Pitts<newsgroup.nospam@virtualinfinity.net>   writes:
>>>>> On 4/5/12 4:08 AM, Rainer Weikusat wrote:
>>>>>> blp@cs.stanford.edu (Ben Pfaff) writes:
>>>>>>> Rainer Weikusat<rweikusat@mssgmbh.com>    writes:
>>>>>>>
>>>>>>>> Ben Pfaff<blp@cs.stanford.edu>    writes:
>>>>>>>>> "Mark"<mark_cruzNOTFORSPAM@hotmail.com>    writes:
>>>>>>>>>
>>>>>>>>>> I'm trying to find a way create a hash value over multiple IP addresses (I
>>>>>>>>>> keep a list of IP addresses and its number is variable. The simplest method
>>>>>>>>>> I've found so far is (obviously not the most effective and collision free):
>>>>>>>>>
>>>>>>>>> Why not use one of many available high-quality hash functions?
>>>>>>>>> Three that come to mind without even going to a search engine:
>>>>>>>>> Jenkins lookup3, murmurhash, FNV.
>>>>>>>>
>>>>>>>> The simple answer is these hash functions are designed to be used for
>>>>>>>> large, variable length string keys NOT for small, fixed-size
>>>>>>>> quantities which can be compared with a single machine instruction.
>>>>>>>>
>>>>>>>> http://burtleburtle.net/bob/hash/integer.html
>>>>>>>> http://www.cris.com/~Ttwang/tech/inthash.htm
>>>>>>>
>>>>>>> He has a list of multiple IP addresses.  A hash function for
>>>>>>> variable length keys may well be appropriate.
>>>>>>
>>>>>> Calculating the hash value must be cheaper than the full comparisons
>>>>>> which will be needed for a linear search.
>>>>> Really? How do you hash a string then?
>>>>
>>>> Really. If calculating the hash value is more expensive than the
>>>> comparisons it is supposed to avoid, it obviously buys you nothing.
>>> A single hash is supposed to save you multiple comparisons, not a
>>> single comparison,
>>
>> An the letter 's' following a word, as in comparisonS, is supposed to
>> indicate a plural.
> Yes, I single hash operation is used so that you can avoid multiple
> (meaning plural) comparisons. I said exactly what I meant, and meant
> exactly what I said. My point still stands.  A hash can be slower than
> a comparison, and still save you a significant amount of time.

And so did I, superbrain. Please pester someone else in future.

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hash function over IP address "Mark" <mark_cruzNOTFORSPAM@hotmail.com> - 2012-04-04 16:37 -0400
  Re: hash function over IP address Barry Margolin <barmar@alum.mit.edu> - 2012-04-04 16:49 -0400
    Re: hash function over IP address China Blue Water Navy <chine.bleu@yahoo.com> - 2012-04-04 14:02 -0700
    Re: hash function over IP address "Mark" <mark_cruzNOTFORSPAM@hotmail.com> - 2012-04-04 17:21 -0400
      Re: hash function over IP address Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-04-04 14:47 -0700
  Re: hash function over IP address Ben Pfaff <blp@cs.stanford.edu> - 2012-04-04 14:40 -0700
    Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-04 22:52 +0100
      Re: hash function over IP address blp@cs.stanford.edu (Ben Pfaff) - 2012-04-04 15:35 -0700
        Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 12:08 +0100
          Re: hash function over IP address blp@cs.stanford.edu (Ben Pfaff) - 2012-04-05 07:42 -0700
            Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 16:29 +0100
          Re: hash function over IP address Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-04-05 10:05 -0700
            Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 18:12 +0100
              Re: hash function over IP address Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-04-05 10:23 -0700
                Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 18:34 +0100
                Re: hash function over IP address Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-04-05 11:11 -0700
                Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 19:34 +0100
                Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 19:38 +0100
                Re: hash function over IP address Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-04-05 12:18 -0700
            Re: hash function over IP address scott@slp53.sl.home (Scott Lurndal) - 2012-04-05 18:45 +0000
              Re: hash function over IP address "Mark" <mark_cruzNOTFORSPAM@hotmail.com> - 2012-04-05 15:02 -0400
  Re: hash function over IP address Rick Jones <rick.jones2@hp.com> - 2012-04-04 23:18 +0000
  Re: hash function over IP address William Ahern <william@wilbur.25thandClement.com> - 2012-04-04 16:57 -0700
  Re: hash function over IP address Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-04-04 21:05 -0400
    Re: hash function over IP address Barry Margolin <barmar@alum.mit.edu> - 2012-04-04 22:52 -0400
      Re: hash function over IP address Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-04-05 08:46 -0400
    Re: hash function over IP address "Mark" <mark_cruzNOTFORSPAM@hotmail.com> - 2012-04-05 08:42 -0400
      Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 15:04 +0100
        Re: hash function over IP address "Mark" <mark_cruzNOTFORSPAM@hotmail.com> - 2012-04-05 10:43 -0400
          Re: hash function over IP address Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-04-05 22:24 -0400
          Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-06 17:13 +0100
            Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-06 17:21 +0100
            Re: hash function over IP address "Mark" <mark_cruzNOTFORSPAM@hotmail.com> - 2012-04-09 10:04 -0400
              Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-09 15:54 +0100
  Re: hash function over IP address BGB <cr88192@hotmail.com> - 2012-04-04 20:21 -0700
  Re: hash function over IP address Udit Gangwani <uditg22@gmail.com> - 2012-04-05 00:26 -0700
  Re: hash function over IP address Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-04-05 12:15 +0100
    Re: hash function over IP address Barry Margolin <barmar@alum.mit.edu> - 2012-04-05 07:52 -0400

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