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From: Richard Harnden <richard.nospam@gmail.invalid>
Newsgroups: comp.lang.c++,comp.lang.c
Subject: Re: Can you see that D correctly simulated by H remains stuck in
 recursive simulation?
Date: Fri, 24 May 2024 13:10:52 +0100
Organization: A noiseless patient Spider
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On 23/05/2024 17:52, olcott wrote:
> typedef int (*ptr)();  // ptr is pointer to int function in C
> 00       int H(ptr p, ptr i);
> 01       int D(ptr p)
> 02       {
> 03         int Halt_Status = H(p, p);
> 04         if (Halt_Status)
> 05           HERE: goto HERE;
> 06         return Halt_Status;
> 07       }
> 08
> 09       int main()
> 10       {
> 11         H(D,D);
> 12         return 0;
> 13       }
> 
> The above template refers to an infinite set of H/D pairs where D is
> correctly simulated by pure function H. This was done because many
> reviewers used the shell game ploy to endlessly switch which H/D was
> being referred to.
> 
> *Correct Simulation Defined*
> This is provided because every reviewer had a different notion of
> correct simulation that diverges from this notion.
> 
> In the above case a simulator is an x86 emulator that correctly emulates
> at least one of the x86 instructions of D in the order specified by the
> x86 instructions of D.
> 
> This may include correctly emulating the x86 instructions of H in the
> order specified by the x86 instructions of H thus calling H(D,D) in
> recursive simulation.
> 
> *Execution Trace*
> Line 11: main() invokes H(D,D); H(D,D) simulates lines 01, 02, and 03 of
> D. This invokes H(D,D) again to repeat the process in endless recursive
> simulation.


So, you have: main -> H -> D -> H -> D -> ... -> H -> D until you run 
out of stack?

No return statement is ever reached.
Line 3 never completes.
Halt_Status at line 3 never gets a value.

</shrug>