Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Richard Heathfield <rjh@cpax.org.uk>
Newsgroups: comp.theory
Subject: Re: Formal systems that cannot possibly be incomplete except for
 unknowns and unknowable
Date: Thu, 8 May 2025 05:09:07 +0100
Organization: Fix this later
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On 08/05/2025 02:20, olcott wrote:

<snip>

> Does there exist an HHH such that DDD emulated by
> HHH according to the rules of the C programming language

Let's take a look.

The file is 1373 lines long, but don't worry, because I plan to 
stop at HHH's first departure from the rules of the C programming 
language (or at least the first departure I spot).

Turn in your songbook if you will to:

void CopyMachineCode(u8* source, u8** destination)
{
   u32 size;
   for (size = 0; source[size] != 0xcc; size++)
     ;
   *destination = (u8*) Allocate(size);
   for (u32 N = 0; N < size; N++)
   {
     Output("source[N]: ", source[N]);
     *destination[N] = source[N];
   }
   ((u32*)*destination)[-1] = size;
   Output("CopyMachineCode destination[-1]: ", 
((u32*)*destination)[-1]);
   Output("CopyMachineCode destination[-2]: ", 
((u32*)*destination)[-2]);
};

I'll ignore the syntax error (a null statement at file scope is a 
rookie error).

Instead, let's jump straight to this line:

   *destination = (u8*) Allocate(size);

On line 79 of my copy of the code, we find:

u32* Allocate(u32 size) { return 0; }

In C, 0 is a null pointer constant, so Allocate returns a null 
pointer constant... which is fine as long as you don't try to 
deref it. So now *destination is NULL.

We go on:

   for (u32 N = 0; N < size; N++)
   {
     Output("source[N]: ", source[N]);
     *destination[N] = source[N];
   }

*destination[N] is our first big problem (we're ignoring syntax 
errors, remember). destination is a null pointer, so 
destination[N] derefs a null pointer.

That's a fail. 0/10, D-, go away and write it again. And you 
/dare/ to impugn other people's C knowledge! Crack a book, for 
pity's sake.

-- 
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