Re: Good hash for pointers

From	Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups	comp.lang.c
Subject	Re: Good hash for pointers
Date	2024-05-25 02:49 -0700
Organization	A noiseless patient Spider
Message-ID	<86bk4ugr1v.fsf@linuxsc.com> (permalink)
References	(4 earlier) <v2omvt$2049k$1@dont-email.me> <86ed9shtsj.fsf@linuxsc.com> <v2ppac$29ca1$1@dont-email.me> <865xv3ic14.fsf@linuxsc.com> <v2q6v0$2br8t$1@dont-email.me>

Show all headers | View raw

Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:

> On 24/05/2024 14:18, Tim Rentsch wrote:
>
>> bart <bc@freeuk.com> writes:
>>
>>> On 24/05/2024 02:39, Tim Rentsch wrote:
>>>
>>>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>>>
>>>>> On 24/05/2024 00:52, Tim Rentsch wrote:
>>>>>
>>>>>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>>>>>
>>>>>>> On 23/05/2024 23:49, Tim Rentsch wrote:
>>>>>>>
>>>>>>>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>>>>>>>
>>>>>>>>> What is a good hash function for pointers to use in portable
>>>>>>>>> ANSI C?
>>>>>>>>
>>>>>>>> I have a preliminary question.  Do you really mean ANSI C, or
>>>>>>>> is C99 acceptable?
>>>>>>>
>>>>>>> C89 is better.
>>>>>>> But the pass has been sold.
>>>>>>
>>>>>> I'm not asking which you think is better.  I'm asking about
>>>>>> what your requirements are.
>>>>>
>>>>> C 89.
>>>>> I don't want to pull in C99 types and so on just for a hash
>>>>> function.
>>>>
>>>> In that case I think you are stuck with using a half-baked
>>>> solution.  The standard integer types available in C89 just
>>>> aren't a good fit in a 64-bit world.
>>>
>>> I assume the C89 implementation is one that can target current 64
>>> bit machines.
>>>
>>> Then char, short, int, long long will almost certainly have widths
>>> of 8, 16, 32 and 64 bits respectively.
>>
>> C89 doesn't have long long.
>>
>>> (I don't know if 'long long' was part of C89, but it sounds like
>>> Malcolm just doesn't want to be bothered with stdint.h, and any
>>> compiler used is like to support it.
>>
>> What he said was C89.  He didn't mention stdint.h.  I take
>> him at his word.  If what he wants is something different,
>> he should say clearly what it is, and not make people guess
>> about it.  (To be clear this recommendation is intended for
>> every questioner, not just Malcolm.)
>
> cJSON.c is C89.  And these additions to the resource compiler were
> inspired by a menntion of cJSON.c here.
>
> So a C89 hash for a pointer to an unsigned int would be ideal.  However
> it might be impossible to write one which is both efficient in terms
> of machine instructions and a good hash function in that it
> distributes the hashes evenly given an uneven distribution of
> keys.  And pointers returned from repeated calls to malloc() are going
> to have an odd distribution of values.

I suggest you look for a way to write and use a hash function that
uses unsigned long long without that causing cJSON.c to need
compiling by a post-C89 ruleset.

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

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 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 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

csiph-web