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From: olcott <polcott333@gmail.com>
Newsgroups: comp.theory
Subject: Re: Every sufficiently competent C programmer knows
Date: Tue, 11 Mar 2025 14:16:35 -0500
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On 3/11/2025 9:02 AM, Mikko wrote:
> On 2025-03-11 13:26:55 +0000, olcott said:
> 
>> On 3/11/2025 5:01 AM, Richard Heathfield wrote:
>>> On 11/03/2025 08:55, Fred. Zwarts wrote:
>>>> Op 11.mrt.2025 om 00:41 schreef olcott:
>>>>> typedef void (*ptr)();
>>>>> int HHH(ptr P);
>>>>>
>>>>> void Infinite_Loop()
>>>>> {
>>>>>    HERE: goto HERE;
>>>>>    return;
>>>>> }
>>>>>
>>>>> void Infinite_Recursion()
>>>>> {
>>>>>    Infinite_Recursion();
>>>>>    return;
>>>>> }
>>>>>
>>>>> void DDD()
>>>>> {
>>>>>    HHH(DDD);
>>>>>    return;
>>>>> }
>>>>>
>>>>> int DD()
>>>>> {
>>>>>    int Halt_Status = HHH(DD);
>>>>>    if (Halt_Status)
>>>>>      HERE: goto HERE;
>>>>>    return Halt_Status;
>>>>> }
>>>>>
>>>>> That when HHH correctly emulates N steps of the
>>>>> above functions that none of these functions can
>>>>> possibly reach their own "return" instruction
>>>>> and terminate normally.
>>>>>>
>>>>>
>>>>> Since HHH does see that same pattern that competent
>>>>> C programmers see it correctly aborts its emulation
>>>>> and rejects these inputs as non terminating.
>>>>
>>>> All competent C programmers see that HHH correctly reports that it 
>>>> cannot possibly reach the 'return' instruction.
>>>
>>> First, my credentials. I've been programming in C for over 35 years; 
>>> I'm told that my book on C has been used on two undergraduate Comp 
>>> Sci courses (one in the States and one in the UK); and I have my 
>>> Knuth cheque. I don't claim to be any kind of programming guru, but I 
>>> hope I do not overstate the case when I suggest that I can be 
>>> regarded as competent not just as a programmer but specifically in 
>>> the C language.
>>>
>>> And yet I can't even /see/ HHH, let alone judge what it does or does 
>>> not do correctly. All I see is a call to it.
>>
>> It is stipulated that HHH correctly emulates N
>> steps of the x86 machine code of its input functions.
>> This may or may not include HHH emulating itself
>> emulating an input.
> 
> The stipulation does not include the value of N (although a reasonable
> interpretation is that it is finite). Nor does the stipulation specify
> what HHH does after the emulation.
> 

It need not those are totally
irrelevant to the primary point:

When HHH correctly emulates N steps of the
above functions none of these functions can
possibly reach their own "return" instruction
and terminate normally.

For HHH(DDD) and HHH(DD) it is stipulated that
HHH does correctly emulate itself emulating
these inputs.

-- 
Copyright 2025 Olcott "Talent hits a target no one else can hit; Genius
hits a target no one else can see." Arthur Schopenhauer