Re: Good hash for pointers

From	Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups	comp.lang.c
Subject	Re: Good hash for pointers
Date	2024-05-26 10:20 -0700
Organization	A noiseless patient Spider
Message-ID	<86ed9ofq14.fsf@linuxsc.com> (permalink)
References	(5 earlier) <v2sudq$2trh1$1@raubtier-asyl.eternal-september.org> <8634q5hjsp.fsf@linuxsc.com> <v2vmhr$3ffjk$1@raubtier-asyl.eternal-september.org> <86le3wfsmd.fsf@linuxsc.com> <v2voe7$3fr50$1@raubtier-asyl.eternal-september.org>

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Bonita Montero <Bonita.Montero@gmail.com> writes:

> Am 26.05.2024 um 18:24 schrieb Tim Rentsch:
>
>> Bonita Montero <Bonita.Montero@gmail.com> writes:
>>
>>> Am 25.05.2024 um 19:40 schrieb Tim Rentsch:
>>>
>>>> Bonita Montero <Bonita.Montero@gmail.com> writes:
>>>>
>>>>> Am 25.05.2024 um 11:12 schrieb Tim Rentsch:
>>>>>
>>>>>> Your hash function is expensive to compute, moreso even
>>>>>> than the "FNV" function shown earlier.  In a case like
>>>>>> this one where the compares are cheap, it's better to
>>>>>> have a dumb-but-fast hash function that might need a
>>>>>> few more looks to find an open slot, because the cost
>>>>>> of looking is so cheap compared to computing the hash
>>>>>> function.
>>>>>
>>>>> A (size_t)pointer * LARGE_PRIME can be sufficient,
>>>>> ignoring the overflow.
>>>>
>>>> Plenty fast but the output quality is poor. ...
>>>
>>> If the prime is large enough there'e no regular distribution.
>>
>> Your conjecture is contradicted by empirical facts.
>
> There are no empirival facts for that since two times the
> taken prime is beyond the 64 bit address space.

You don't listen very well do you?

I say the output quality is poor because I have run tests that
show the poor output quality.  I've done that with a prime of my
own choosing and also with 18446744073709551557, the value you
suggested.  In both cases the test runs show results that are
clearly worse than all the other hash functions tested, including
bart's and malcolm's.  Furthermore the results for your suggested
calculation are worse across the board, on every variety of
dynamic workload in my test suite.

Your proposed hash function is too weak to be taken as a serious
candidate.

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Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-23 12:11 +0100
  Re: Good hash for pointers Richard Harnden <richard.nospam@gmail.invalid> - 2024-05-23 15:37 +0100
    Re: Good hash for pointers Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-05-23 15:51 -0700
      Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-24 00:42 +0100
  Re: Good hash for pointers Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-23 20:34 +0000
  Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-23 15:49 -0700
    Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-24 00:43 +0100
      Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-23 16:52 -0700
        Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-24 01:28 +0100
          Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-23 18:39 -0700
            Re: Good hash for pointers bart <bc@freeuk.com> - 2024-05-24 11:14 +0100
              Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-24 12:05 +0100
                Re: Good hash for pointers "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-05-24 10:49 -0700
                Re: Good hash for pointers "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-05-24 10:51 -0700
              Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-24 06:18 -0700
                Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-24 15:07 +0100
                Re: Good hash for pointers scott@slp53.sl.home (Scott Lurndal) - 2024-05-24 14:51 +0000
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-25 02:49 -0700
              Re: Good hash for pointers David Brown <david.brown@hesbynett.no> - 2024-05-24 17:00 +0200
                Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-24 17:10 +0100
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-05-24 19:27 +0300
          Re: Good hash for pointers David Brown <david.brown@hesbynett.no> - 2024-05-24 09:41 +0200
  Re: Good hash for pointers "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-05-23 17:32 -0700
    Re: Good hash for pointers "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-05-23 18:59 -0700
      Re: Good hash for pointers jak <nospam@please.ty> - 2024-05-24 04:09 +0200
  Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-24 20:28 +0200
    Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-24 19:57 +0100
      Re: Good hash for pointers bart <bc@freeuk.com> - 2024-05-25 00:54 +0100
        Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-25 02:12 -0700
          Re: Good hash for pointers bart <bc@freeuk.com> - 2024-05-25 12:28 +0100
            Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-25 11:12 -0700
              Re: Good hash for pointers bart <bc@freeuk.com> - 2024-05-25 20:31 +0100
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-25 22:54 -0700
          Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-25 17:00 +0200
            Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-25 10:40 -0700
              Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-25 18:56 +0100
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-25 11:23 -0700
                Re: Good hash for pointers Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-25 23:13 +0200
                Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-25 23:07 +0100
                Re: Good hash for pointers bart <bc@freeuk.com> - 2024-05-25 23:42 +0100
                Re: Good hash for pointers Richard Harnden <richard.nospam@gmail.invalid> - 2024-05-26 19:58 +0100
                Re: Good hash for pointers Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-26 22:42 +0000
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 18:05 +0200
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 18:07 +0200
              Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 18:04 +0200
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-26 09:24 -0700
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 18:36 +0200
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-26 10:20 -0700
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 19:39 +0200
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 19:54 +0200
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-27 08:07 +0200
                Re: Good hash for pointers Ben Bacarisse <ben@bsb.me.uk> - 2024-05-28 11:07 +0100
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-30 10:10 +0200
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-30 11:27 +0200
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-30 19:26 -0700
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-05-30 19:27 -0700
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-02 10:45 +0300
                Re: Good hash for pointers "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-02 12:42 -0700
                Re: Good hash for pointers "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-03 12:35 -0700
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-02 16:02 -0700
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-03 10:50 +0300
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-03 18:02 -0700
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-04 11:38 +0300
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-04 22:10 -0700
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-03 16:34 +0200
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-03 17:46 +0300
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-03 17:54 +0200
                Re: Good hash for pointers bart <bc@freeuk.com> - 2024-06-03 17:24 +0100
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-03 20:16 +0300
                Re: Good hash for pointers bart <bc@freeuk.com> - 2024-06-03 19:48 +0100
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-03 22:41 +0300
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-03 22:51 +0300
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-03 16:51 -0700
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-03 17:01 -0700
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-03 20:25 +0200
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-03 19:50 +0300
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-03 20:31 +0200
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-05 00:59 +0300
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-05 11:10 +0200
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-05 12:34 +0300
                Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-05 12:05 +0200
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-05 13:11 +0300
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-05 08:58 -0700
                AES problem (was: Good hash for pointers) Michael S <already5chosen@yahoo.com> - 2024-06-05 19:51 +0300
                Re: AES problem (was: Good hash for pointers) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-05 21:24 -0700
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-05 19:59 +0300
                Re: Good hash for pointers Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-05 21:40 -0700
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-06 11:00 +0300
                Re: Good hash for pointers Michael S <already5chosen@yahoo.com> - 2024-06-06 13:35 +0300
  Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 20:06 +0200
    Re: Good hash for pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-05-26 20:10 +0100
  Re: Good hash for pointers Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-26 20:24 +0200

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