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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c
Subject: Re: transpiling to low level C
Date: Mon, 23 Dec 2024 13:18:46 +0100
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On 23/12/2024 12:35, bart wrote:
> On 23/12/2024 08:46, David Brown wrote:
> 
>> Tim ruled out &&, ||, ?:, goto, break, continue, if, for, while, 
>> switch, do, labels, setjmp and longjmp.
>>
>> He didn't rule out recursion, or the relational operators, or any 
>> other part of C.
>>
>>
>> int fact(int n);
>>
>> int fact_zero(int n) {
>>          return 1;
>> }
>>
>> int n_fact_n1(int n) {
>>          return n * fact(n - 1);
>> }
>>
>> int fact(int n) {
>>          return (int (*[])(int)){ fact_zero, n_fact_n1 }[(bool) n](n);
>> }
>>
>>
>> There are additional fun things that can be done using different 
>> operators.  For an unsigned integer "n" that is not big enough to 
>> wrap, "(n + 2) / (n + 1) - 1"  evaluates "(n == 0)".
> 
> Isn't this just !n ? I don't think "!" was ruled out. This would also 
> work for negative n.

Sure.  It was merely another example of something you could use, if you 
had ruled out simpler things (like the conversion to bool that I used, 
or the ! operator that you suggest).


> 
>> And Tim did not rule out using the standard library, which would 
>> surely open up new possibilities.
> 
> printf (not sprintf) would be reasonable here to show results. Anything 
> else could be considered cheating.
> 

No, I would not say so - as long as the standard library is not ruled 
out, it is part of C.  But I think you could reasonably argue that 
allowing the standard library makes this whole pointless exercise even 
more pointless!

> The original context was a small subset of C that can be used to 
> represent a larger subset.