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From: Richard Heathfield <rjh@cpax.org.uk>
Newsgroups: comp.theory
Subject: Re: Every sufficiently competent C programmer knows
Date: Tue, 11 Mar 2025 18:23:24 +0000
Organization: Fix this later
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On 11/03/2025 17:42, Mike Terry wrote:
> Finally, if you really want to see the actual HHH code, its in 
> the halt7.c file (along with DDD) that PO provides links to from 
> time to time.  However it's not very illuminating due to 
> bugs/design errors/misunderstandings which only serve to 
> obfuscate PO's errors in thinking.

[I've now seen the code. Oh deary deary me.]

Thank you for a spirited attempt to be cogent - or at least as 
cogent as it is possible to be in the circumstances!

I think PO's first step must be to demonstrate that HHH() 
correctly diagnoses some easy functions, such as these:

int rha(unsigned int i)
{
   while(--i > 0)while(--i > 0);
   return 0;
}

int rhb(unsigned int i)
{
   if(i > 0)
   {
     rhb(i/10);
   }
   return putchar(i + '0');
}

int rhc(unsigned int i)
{
   typedef int(*pf)(unsigned int);
   pf arr[3] = {rha, rhb, rhc};
   return arr[i % 3];
}

and other such obvious tests.

HHH(), the procedure that decides whether a program halts, is 
required to work for all programs and all inputs. Does it work on 
those cited above? I'm guessing it doesn't.

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within