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Re: Tagging programs with git hash. [slightly OT]

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Ben Bacarisse <ben.usenet@bsb.me.uk> wrote:
> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> 
>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>
>>> Git and similar version control systems have an internal version tag,
>>> in git it is the sha-1 hash, which is used to identify the version
>>> within the control system.
>>>
>>> Now it would be nice to tag the executable with this hash, so that if a
>>> user reports a bug, you can ask them to run it in a mode that displays
>>> the hash, then go back to the correct version in the repository to find
>>> the bug.
>>>
>>> But here we have a problem. The hash is created by applying a hash
>>> algorithm to the entire source, which is designed to change every digit
>>> of the hash if even a character of the source is changed. So if we add
>>> the hash to the source, we've changed the hash. So we can't tag an
>>> executable with its version number.
>>
>> Theoretically, this function -- the hash of a hash-containing source --
>> will have a fixed point which would be the solution.  Unfortunately it
>> will be impossible to find!
> 
> It's a sad indictment of my state of mind, but I spent the time walking
> the dog thinking about this and I am not longer sure there will be a
> fixed point.

Yeah, "fixed point" is exactly the phrase that popped into my head
while reading mm's original post (maybe we've both been studying
too much domain theory:). And then, ditto again, the existence
question, and the impracticality certainty.
   And then the further question: is it possible to devise a hash
that guarantees such a fixed point, and where convergence to it
doesn't require an infinite-sequence lub? Or, can you conversely
show that no such (hash) function exists? (Probably outside the
scope of this ng, but when has that ever stopped anybody?:)
-- 
John Forkosh  ( mailto:  j@f.com  where j=john and f=forkosh )

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Thread

Tagging programs with git hash. [slightly OT] Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-05-31 07:02 -0700
  Re: Tagging programs with git hash. [slightly OT] queequeg@trust.no1 (Queequeg) - 2019-05-31 14:27 +0000
    Re: Tagging programs with git hash. [slightly OT] Mateusz Viste <mateusz@wont.tell> - 2019-05-31 16:42 +0000
      Re: Tagging programs with git hash. [slightly OT] Keith Thompson <kst-u@mib.org> - 2019-05-31 13:23 -0700
      Re: Tagging programs with git hash. [slightly OT] queequeg@trust.no1 (Queequeg) - 2019-05-31 21:10 +0000
        Re: Tagging programs with git hash. [slightly OT] Mateusz Viste <mateusz@wont.tell> - 2019-06-01 09:31 +0000
          Re: Tagging programs with git hash. [slightly OT] queequeg@trust.no1 (Queequeg) - 2019-06-01 12:39 +0000
  Re: Tagging programs with git hash. [slightly OT] David Brown <david.brown@hesbynett.no> - 2019-05-31 16:28 +0200
  Re: Tagging programs with git hash. [slightly OT] fir <profesor.fir@gmail.com> - 2019-05-31 07:51 -0700
  Re: Tagging programs with git hash. [slightly OT] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-05-31 15:59 +0100
    Re: Tagging programs with git hash. [slightly OT] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-05-31 22:56 +0100
      Re: Tagging programs with git hash. [slightly OT] John Forkosh <forkosh@panix.com> - 2019-06-01 02:55 +0000
        Re: Tagging programs with git hash. [slightly OT] fir <profesor.fir@gmail.com> - 2019-06-01 04:26 -0700
          Re: Tagging programs with git hash. [slightly OT] fir <profesor.fir@gmail.com> - 2019-06-01 04:35 -0700
      Re: Tagging programs with git hash. [slightly OT] Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-06-01 04:03 -0700
  Re: Tagging programs with git hash. [slightly OT] "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-05-31 13:30 -0700
  Re: Tagging programs with git hash. [slightly OT] Eli the Bearded <*@eli.users.panix.com> - 2019-05-31 21:46 +0000
  Re: Tagging programs with git hash. [slightly OT] Shuggie <shuggie@latepaul.com> - 2019-06-01 11:21 +0100
  Re: Tagging programs with git hash. [slightly OT] Ike Naar <ike@iceland.freeshell.org> - 2019-06-01 21:23 +0000
    Re: Tagging programs with git hash. [slightly OT] Keith Thompson <kst-u@mib.org> - 2019-06-01 14:34 -0700
    Re: Tagging programs with git hash. [slightly OT] Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-06-02 12:36 -0700
      Re: Tagging programs with git hash. [slightly OT] Keith Thompson <kst-u@mib.org> - 2019-06-02 14:35 -0700

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