Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C]

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c, comp.theory
Subject	Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C]
Followup-To	comp.theory
Date	2020-08-31 02:30 +0100
Organization	A noiseless patient Spider
Message-ID	<87o8mrr48v.fsf@bsb.me.uk> (permalink)
References	<EZudneqAq4Cla9bCnZ2dnUU7-TnNnZ2d@giganews.com> <20200830120314.347@kylheku.com> <87eennswge.fsf@bsb.me.uk> <wr2dnaioYPFtitHCnZ2dnUU7-UXNnZ2d@giganews.com>

Cross-posted to 2 groups.

Followups directed to: comp.theory

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olcott <NoOne@NoWhere.com> writes:

> On 8/30/2020 3:36 PM, Ben Bacarisse wrote:
>> Kaz Kylheku <793-849-0957@kylheku.com> writes:
>>
>>> On 2020-08-30, olcott <NoOne@NoWhere.com> wrote:
>>>> The end goal of this sequence of posts is to show that the basic "C"
>>>> programming language (without the "C" libraries) can be fully mapped to
>>>> an abstract model of computation that is equivalent to a Turing machine
>>>> in such a way that any Turing complete computation can be written in the
>>>> "C" programming language.
>>>
>>> Turing's infinite tape can be mapped to the <stdio.h> facility.
>>> The possible symbols on that tape can be mapped to characters,
>>> and the operations and positioning can be mapped to the available
>>> library operations.
>>
>> I think (but it's hard to get answers) that Peter Olcott is only
>> considering what we'd call freestanding implementations here.
>>
>> But, worse, he's not interested in simply showing that hosted C is
>> Turing complete by simulating a universal TM.  I think he aims to show
>> that "ordinary C" can be made Turing complete just by implementing it on
>> a Turing complete sub-system.
>>
>> (BTW, even a IO-based UTM needs are bit of checking.  Functions like
>> fgetpos need to be allowed to fail.  I think the specification is plenty
>> loose enough for that since it says almost nothing about what failures
>> are permissible.)
>>
>>>> When "C" is mapped to an abstract model of computation that can provide
>>>> an arbitrary number of arbitrary length linked lists, then "C" acquires
>>>
>>> In the absence of I/O, the C storage model is finite, and therefore not
>>> Turing complete. However, perhaps not quite.
>>>
>>> I had a discussion with this with someone who convinced me of the
>>> following: in C we can allocate automatic storage (informally,
>>> "local variables on the stack") via recursion. If we do this without
>>> taking the address of anything, then pointers do not appear in
>>> the program, and thus, in the abstract sense, we don't run into the
>>> issue of pointers being of finite width.  With that restriction, we have
>>> no random access (the program cannot access material in existing
>>> activation frames without returning to them).  Therefore what we have is
>>> a push-down automaton (PDA).  A PDA is strictly less powerful than a
>>> Turing machine. It contains an infinity in that it can push down as far
>>> as it needs to, but there are some computations that can't be carried
>>> out with a universal push down machine.
>>
>> Hmm...  Modern C has threads and therefore more than one stack.  A PDA
>> with two stacks is Turing complete so there may be a way after all.
>> Nice one!
>
> There you go teamwork. Between you and Kaz.

Note "may".  In the end it is likely to come down to how one chooses to
interpret the standard.  It's really not a clear-cut question.  (See my
reply to Mike Terry about that.)

> Now the key of how do you make an unlimited depth stack?
> is directly addressed by the other key implementation detail:
>
> How do you provide a linked-list of unlimited depth that automatically
> scales to whatever memory is available.

It sounds like you don't know what Kaz's friend was saying.

-- 
Ben.

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Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 13:55 -0500
  Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Kaz Kylheku <793-849-0957@kylheku.com> - 2020-08-30 19:19 +0000
    Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Siri Cruise <chine.bleu@yahoo.com> - 2020-08-30 12:30 -0700
      Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 14:40 -0500
      Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Kaz Kylheku <793-849-0957@kylheku.com> - 2020-08-30 19:41 +0000
        Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 15:02 -0500
          Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-08-30 22:05 +0100
        Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Siri Cruise <chine.bleu@yahoo.com> - 2020-08-30 13:35 -0700
          Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 15:59 -0500
        Re: Transforming "C" into a Turing equivalent language 006 [credit to Kaz where credit is due] olcott <NoOne@NoWhere.com> - 2020-09-02 11:48 -0500
    Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 14:57 -0500
    Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-08-30 21:36 +0100
      Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 16:19 -0500
        Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-08-31 02:30 +0100
          Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 21:35 -0500
            Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-08-31 03:53 +0100
              Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-31 10:08 -0500
            Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] olcott <NoOne@NoWhere.com> - 2020-08-30 23:55 -0500
              Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-08-31 06:30 -0700
                Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] olcott <NoOne@NoWhere.com> - 2020-08-31 10:04 -0500
              Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] olcott <NoOne@NoWhere.com> - 2020-09-01 20:38 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] olcott <NoOne@NoWhere.com> - 2020-09-01 21:51 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] olcott <NoOne@NoWhere.com> - 2020-09-03 09:21 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] André G. Isaak <agisaak@gm.invalid> - 2020-09-03 12:05 -0600
                Re: Transforming "C" into a Turing equivalent language 001 [x86 based halt decider] olcott <NoOne@NoWhere.com> - 2020-09-03 16:39 -0500
            Transforming "C" into a Turing equivalent language 002 [Translating C to a unary TM] olcott <NoOne@NoWhere.com> - 2020-08-31 13:00 -0500
            Re: Transforming "C" into a Turing equivalent language 002 [Translating C to a unary TM] olcott <NoOne@NoWhere.com> - 2020-08-31 13:10 -0500
            Re: Transforming "C" into a Turing equivalent language 004 [x86 language mapped to unlimited integers] olcott <NoOne@NoWhere.com> - 2020-09-02 11:44 -0500
      Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-08-31 00:23 +0100
        Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-08-31 02:24 +0100
          Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-31 09:59 -0500
          Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-08-31 20:06 +0100
            Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-31 14:28 -0500
              Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-08-31 22:51 +0100
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-31 17:49 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-09-01 02:42 +0100
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-31 23:30 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-09-01 15:30 +0100
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-09-01 09:51 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-31 23:32 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-09-01 16:15 +0100
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-09-01 10:53 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [x86_UTM trace] olcott <NoOne@NoWhere.com> - 2020-08-31 23:24 -0500
            Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-08-31 20:46 +0100
              Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-31 15:05 -0500
              Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-09-01 21:39 +0100
                Re: Transforming "C" into a Turing equivalent language 002 [HP proof refutation] olcott <NoOne@NoWhere.com> - 2020-09-01 17:00 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-09-01 17:46 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-09-02 00:51 +0100
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-09-01 18:58 -0500
                Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-09-01 20:40 -0500
            Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-08-31 20:19 -0400
              Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2020-09-01 01:37 +0100
        Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-08-30 20:35 -0500
    Re: Transforming "C" into a Turing equivalent language 005 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-09-02 11:20 -0500
      Re: Transforming "C" into a Turing equivalent language 005 [Providing unlimited memory access to C] Kaz Kylheku <793-849-0957@kylheku.com> - 2020-09-02 17:22 +0000
        Re: Transforming "C" into a Turing equivalent language 005 [Providing unlimited memory access to C] olcott <NoOne@NoWhere.com> - 2020-09-02 12:27 -0500
  Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-08-31 11:18 -0700
    Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-08-31 21:34 +0000
      Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] Juha Nieminen <nospam@thanks.invalid> - 2020-09-01 09:13 +0000
        Re: Transforming "C" into a Turing equivalent language 001 [Providing unlimited memory access to C] boltar@nuttyella.co.uk - 2020-09-01 09:24 +0000

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