Re: Challenge for Feeb: dealing with large numbers in C

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: Challenge for Feeb: dealing with large numbers in C
Date	2019-10-22 10:27 +0200
Organization	A noiseless patient Spider
Message-ID	<qomegr$2bk$1@dont-email.me> (permalink)
References	(2 earlier) <Yq9rF.26213$kV2.22694@fx22.iad> <3pkrF.1790269$HWr.573547@fx36.am4> <CdnrF.146403$hL1.58740@fx35.iad> <41orF.3049827$dw4.2946808@fx12.am4> <tNrrF.93850$XA2.69506@fx05.iad>

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On 22/10/2019 02:08, DFS wrote:
> On 10/21/2019 3:53 PM, Bart wrote:
>> On 21/10/2019 19:57, DFS wrote:
>>> On 10/21/2019 11:46 AM, Bart wrote:

>>>>
>>>> But if you just wanted a hash function, just ask that instead.
>>>>
>>>> I have a cheap and cheerful one, but it's one of those things, like
>>>> random number generators, where nothing but perfection will do for
>>>> many people.
>>>
>>> Yeah, other than for crypto reasons, why are hash generators made so
>>> complicated?
>>
>> I don't know. 
> 
> 
> Someone told me it's to minimize the number of collisions.
> 

There are various characteristics that are considered "nice to have" in
a hash function.  Different use-cases place the emphasis differently,
and there are always trade-offs - thus there are many hash functions
that can be useful in different circumstances.  Examples include:

1. Speed of algorithm (possibly also the speed on different types of
processor).

2. Size of output (you want big outputs for things like digital
fingerprints to eliminate collisions, but want small outputs when making
a hashmap structure in a program).

3. Cryptographic security (sometimes you want it, sometimes you don't care).

4. "Avalanche effect" - small changes in the input making big changes to
the output.  Sometimes that is useful, sometimes it does not matter.

5. Avoiding pathological results (such as extra zeros leaving the output
unchanged, or zero in giving zero out).

6. Mathematical guarantees (such as guaranteeing detection of any N bits
changed, or other specific patterns of changes in the input).

7. Perfect hashes - minimal size of output while guaranteeing uniqueness
for a known set of inputs.

Thread

Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-20 18:12 -0400
  Re: Challenge for Feeb: dealing with large numbers in C Barry Schwarz <schwarzb@delq.com> - 2019-10-20 18:33 -0700
    Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-20 23:16 -0400
      Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-21 13:15 +0100
        Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 14:40 -0400
          Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-22 00:54 +0100
            Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-22 10:05 +0200
            Re: Challenge for Feeb: dealing with large numbers in C Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-23 07:18 -0700
          Re: Challenge for Feeb: dealing with large numbers in C Manfred <noname@invalid.add> - 2019-10-26 20:01 +0200
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-26 17:50 -0400
              Re: Challenge for Feeb: dealing with large numbers in C Manfred <noname@add.invalid> - 2019-10-28 16:33 +0100
      Re: Challenge for Feeb: dealing with large numbers in C Barry Schwarz <schwarzb@delq.com> - 2019-10-21 07:56 -0700
      Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 16:46 +0100
        Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 14:57 -0400
          Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 20:53 +0100
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 16:05 -0400
              Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 21:12 +0100
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 20:08 -0400
              Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-22 10:27 +0200
          Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-22 19:45 +0100
            Re: Challenge for Feeb: dealing with large numbers in C Eli the Bearded <*@eli.users.panix.com> - 2019-10-22 19:58 +0000
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-23 11:46 -0400
              Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-23 20:02 +0100
              Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 01:38 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-23 22:10 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ike Naar <ike@sdf.lonestar.org> - 2019-10-24 07:24 +0000
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 09:29 -0400
                Re: Challenge for Feeb: dealing with large numbers in C James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-10-24 08:45 -0700
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 11:56 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-24 09:13 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 18:28 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 10:36 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 09:26 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 18:29 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 14:38 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 21:30 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-24 11:30 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 20:36 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 21:34 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-24 22:42 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 18:59 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-25 02:48 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-26 04:33 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-26 17:21 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-26 18:47 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-26 23:24 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-27 00:29 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-27 01:58 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-27 12:02 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 02:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-10-26 14:29 -0600
                Re: Challenge for Feeb: dealing with large numbers in C Keith Thompson <kst-u@mib.org> - 2019-10-26 13:36 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-26 22:06 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-26 23:04 +0100
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-27 12:49 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-27 18:20 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-27 22:45 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 00:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-27 14:57 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 01:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 01:44 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 02:31 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 10:42 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 12:45 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 17:39 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-28 20:31 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 20:22 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-28 22:07 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 22:22 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-29 10:17 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 11:21 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-28 11:05 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 19:26 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 21:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 21:57 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 23:59 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 00:53 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 01:09 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 01:32 +0000
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-28 22:44 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-29 03:05 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 11:12 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-29 04:19 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 11:47 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-29 05:03 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 13:16 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 17:13 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 17:35 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ike Naar <ike@sdf.lonestar.org> - 2019-10-30 07:19 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 16:19 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 16:50 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-29 10:03 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 17:13 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-29 10:23 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 22:20 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-30 03:04 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-30 15:39 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-30 09:02 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-30 19:35 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-30 14:11 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-31 03:34 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-04 17:02 -0800
                Re: Challenge for Feeb: dealing with large numbers in C Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2019-10-26 12:30 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Robert Wessel <robertwessel2@yahoo.com> - 2019-10-26 12:03 -0500
                Re: Challenge for Feeb: dealing with large numbers in C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-10-26 14:25 -0600
                Re: Challenge for Feeb: dealing with large numbers in C Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-24 18:06 -0700
        Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 22:44 +0100
          Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 19:00 -0400
  Re: Challenge for Feeb: dealing with large numbers in C Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2019-10-21 10:20 +0800
    Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 12:44 +0100
  Re: Challenge for Feeb: dealing with large numbers in C Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2019-10-21 10:24 +0800
    Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-20 23:05 -0400
      Re: Challenge for Feeb: dealing with large numbers in C Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2019-10-21 11:32 +0800
  Re: Challenge for Feeb: dealing with large numbers in C Autist <autist69@gmail.com> - 2019-10-29 15:15 +0100

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