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From: olcott <polcott333@gmail.com>
Newsgroups: comp.theory,comp.lang.c,comp.lang.c++
Subject: Every sufficiently competent C programmer knows --- original post
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Date: Sun, 16 Mar 2025 14:36:11 -0500
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On 3/16/2025 2:26 PM, Keith Thompson wrote:
> Richard Heathfield <rjh@cpax.org.uk> writes:
>> On 16/03/2025 10:31, Mikko wrote:
>>> False. You didn't say that HHH is a C function. In particular, the
>>> code
>>> shown above does not say so.
>>
>> It scarcely qualifies as C.
>>
>> For example, it begins by a goto this code:
>>
>> __asm__("lea eax, DATA1");
>>    __asm__("mov Aborted, eax");
>>    __asm__("lea eax, DATA2");
>>    __asm__("mov execution_trace, eax");
>>    __asm__("mov eax, END_OF_CODE");
>>    __asm__("mov End_Of_Code, eax");
>>
>> which any C compiler is free to reject.
>>
>> C99 introduced the asm keyword, but that's spelled asm, not __asm__,
>> and of course it's not a magic wand, so it can't make an inherently
>> unportable program work on every platform supported by C
>> compilers. C/370, for example, would have a fit.
> 
> No, C99 didn't introduce the asm keyword.  Both C90 and C99 (and all
> later editions) document the "asm" keyword as a common extension,
> but it's not in the list of keywords.  K&R1 (1978) mentions that
> some implementations reserve "fortran" and "asm".  A conforming C
> compiler must accept "asm" as an ordinary identifier.
> 
> I don't think Olcott intends HHH to be fully portable C (assuming
> he knows what that means).  In any case, his claims about "Every
> sufficiently competent C programmer" are ludicrous.
> 

*Every sufficiently competent C programmer knows*

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;
}

When HHH correctly emulates N steps of the
above functions none of them 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.


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