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From: wij <wyniijj5@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: Can someone please verify the execution trace of this?
Date: Tue, 21 May 2024 02:23:23 +0800
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On Mon, 2024-05-20 at 12:23 -0500, olcott wrote:
> On 5/20/2024 11:21 AM, wij wrote:
> > On Mon, 2024-05-20 at 10:02 -0500, olcott wrote:
> > > On 5/20/2024 7:37 AM, wij wrote:
> > > > On Sun, 2024-05-19 at 21:43 -0500, olcott wrote:
> > > > > On 5/19/2024 8:52 PM, Bonita Montero wrote:
> > > > > > Am 19.05.2024 um 21:00 schrieb olcott:
> > > > > > > On 5/19/2024 1:08 PM, Bonita Montero wrote:
> > > > > > > > Am 18.05.2024 um 23:40 schrieb olcott:
> > > > > > > > > People are saying that they have no idea what this code d=
oes
> > > > > > > > > because they do not believe it conforms to c11 or c17.
> > > > > > > > >=20
> > > > > > > > > typedef int (*ptr)();=C2=A0 // ptr is pointer to int func=
tion
> > > > > > > > > 00 int H(ptr x, ptr y);
> > > > > > > > > 01 int D(ptr x)
> > > > > > > > > 02 {
> > > > > > > > > 03=C2=A0=C2=A0 int Halt_Status =3D H(x, x);
> > > > > > > > > 04=C2=A0=C2=A0 if (Halt_Status)
> > > > > > > > > 05=C2=A0=C2=A0=C2=A0=C2=A0 HERE: goto HERE;
> > > > > > > > > 06=C2=A0=C2=A0 return Halt_Status;
> > > > > > > > > 07 }
> > > > > > > > > 08
> > > > > > > > > 09 int main()
> > > > > > > > > 10 {
> > > > > > > > > 11=C2=A0=C2=A0 H(D,D);
> > > > > > > > > 12=C2=A0=C2=A0 return 0;
> > > > > > > > > 13 }
> > > > > > > > >=20
> > > > > > > > > In the above case a simulator is an x86 emulator that cor=
rectly
> > > > > > > > > emulates
> > > > > > > > > at least one of the x86 instructions of D in the order sp=
ecified by the
> > > > > > > > > x86 instructions of D.
> > > > > > > > >=20
> > > > > > > > > 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.
> > > > > > > > >=20
> > > > > > > > > *Execution Trace*
> > > > > > > > > Line 11: main() invokes H(D,D);
> > > > > > > > >=20
> > > > > > > > > *keeps repeating* (unless aborted)
> > > > > > > > > Line 01:
> > > > > > > > > Line 02:
> > > > > > > > > Line 03: simulated D(D) invokes simulated H(D,D) that sim=
ulates D(D)
> > > > > > > > >=20
> > > > > > > > > *Simulation invariant*
> > > > > > > > > D correctly simulated by H cannot possibly reach past its=
 own line 03.
> > > > > > > > >=20
> > > > > > > > > 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.
> > > > > > > > >=20
> > > > > > > >=20
> > > > > > > > Other people think 30s about this, you think years about th=
at.
> > > > > > > >=20
> > > > > > >=20
> > > > > > > It is the basis for my two decades long primary research into
> > > > > > > termination analysis. People on another forum have written
> > > > > > > hundreds of posts claiming that D correctly simulated by H
> > > > > > > reaches its own line 06 and halts.
> > > > > > >=20
> > > > > > > *I have only gotten truthful answers on this forum*
> > > > > > >=20
> > > > > >=20
> > > > > > That's not research, that's nonsense.
> > > > > >=20
> > > > >=20
> > > > > This is not the forum to show that it is not nonsense this is
> > > > > a simple C question that I should not even have to ask except
> > > > > for a few people in another forum that consistently lie about
> > > > > the answer.
> > > > >=20
> > > > > I have been a professional C++ developer since Y2K. So I already
> > > > > know the answer, I just need some competent people in this forum
> > > > > to attest to this answer. I met Bjarne Stroustrup back when he
> > > > > was going around the country promoting his new language.
> > > > >=20
> > > >=20
> > > > typedef int (*ptr)();=C2=A0 // ptr is pointer to int function
> > > > int H(ptr x, ptr y);
> > > > int D(ptr x)
> > > > {
> > > > =C2=A0=C2=A0=C2=A0 int Halt_Status =3D H(x, x);
> > > > =C2=A0=C2=A0=C2=A0 if (Halt_Status)
> > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 HERE: goto HERE;
> > > > =C2=A0=C2=A0=C2=A0 return Halt_Status;
> > > > }
> > > >=20
> > > > int main()
> > > > {
> > > > =C2=A0=C2=A0=C2=A0 H(D,D);
> > > > =C2=A0=C2=A0=C2=A0 return 0;
> > > > }
> > > >=20
> > > > The code above does not compile:
> > >=20
> > > *It does compile*
> > > *It does compile*
> > > *It does compile*
> > > *It does compile*
> > >=20
> > > typedef int (*ptr)();
> > > int H(ptr P, ptr I);
> > >=20
> > > int D(ptr x)
> > > {
> > > =C2=A0=C2=A0=C2=A0 int Halt_Status =3D H(x, x);
> > > =C2=A0=C2=A0=C2=A0 if (Halt_Status)
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 HERE: goto HERE;
> > > =C2=A0=C2=A0=C2=A0 return Halt_Status;
> > > }
> > >=20
> > > int main()
> > > {
> > > =C2=A0=C2=A0=C2=A0 H(D,D);
> > > =C2=A0=C2=A0=C2=A0 return 0;
> > > }
> > >=20
> > > cl=C2=A0 /GS- /std:c11 /c /arch:IA32 Test_Compile.c
> > > cl=C2=A0 /GS- /std:c17 /c /arch:IA32 Test_Compile.c
> > > if ERRORLEVEL 1 pause
> > >=20
> > >=20
> > > D:\__HP_Stream\__NLU_Notes\__Work_In_Progress\__Halt_Decider_X86\___x=
86utm_VS>echo
> > > off
> > >=20
> > > D:\__HP_Stream\__NLU_Notes\__Work_In_Progress\__Halt_Decider_X86\___x=
86utm_VS>REM
> > > 2022
> > >=20
> > > D:\__HP_Stream\__NLU_Notes\__Work_In_Progress\__Halt_Decider_X86\___x=
86utm_VS>call
> > > "C:\Program Files\Microsoft Visual
> > > Studio\2022\Community\Common7\Tools\VsDevCmd.BAT"
> > > *********************************************************************=
*
> > > ** Visual Studio 2022 Developer Command Prompt v17.6.4
> > > ** Copyright (c) 2022 Microsoft Corporation
> > > *********************************************************************=
*
> > > Microsoft (R) C/C++ Optimizing Compiler Version 19.36.32535 for x86
> > > Copyright (C) Microsoft Corporation.=C2=A0 All rights reserved.
> > >=20
> > > Test_Compile.c
> > > Microsoft (R) C/C++ Optimizing Compiler Version 19.36.32535 for x86
> > > Copyright (C) Microsoft Corporation.=C2=A0 All rights reserved.
> > >=20
> > > Test_Compile.c
> > > Press any key to continue . . .
> >=20
> > OK, My fault, gcc can compile (g++ can't. No idea why D's protocol does=
n't match
> > type ptr and get compiled in C).
> >=20
>=20
>=20
> 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.
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