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From: Rosario19 <Ros@invalid.invalid>
Newsgroups: comp.lang.c
Subject: Re: Can someone please verify the execution trace of this?
Date: Sun, 19 May 2024 06:25:21 +0200
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On Sat, 18 May 2024 16:40:45 -0500, olcott  wrote:

>People are saying that they have no idea what this code does
>because they do not believe it conforms to c11 or c17.
>
>typedef int (*ptr)();  // ptr is pointer to int function
>00 int H(ptr x, ptr y);
>01 int D(ptr x)
>02 {
>03   int Halt_Status = H(x, x);
>04   if (Halt_Status)
>05     HERE: goto HERE;
>06   return Halt_Status;
>07 }
>08
>09 int main()
>10 {
>11   H(D,D);

here you call H(D,D) D is just a pointer, but what is H? if it is a
ponter for me the program is not definited and has to stop here
im not one expert of C

>12   return 0;
>13 }
>
>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);
>
>*keeps repeating* (unless aborted)
>Line 01:
>Line 02:
>Line 03: simulated D(D) invokes simulated H(D,D) that simulates D(D)
>
>*Simulation invariant*
>D correctly simulated by H cannot possibly reach past its own line 03.
>
>The key thing to note is that no D correctly simulated by any H of every
>H/D pair specified by the above template ever reaches its own line 06
>and halts.