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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c++
Subject: Re: counting_semaphore question
Date: Fri, 13 Sep 2024 16:46:31 +0200
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On 13/09/2024 15:21, Muttley@dastardlyhq.com wrote:
> On Fri, 13 Sep 2024 12:54:53 +0200
> David Brown <david.brown@hesbynett.no> boringly babbled:
>> On 13/09/2024 09:26, Muttley@dastardlyhq.com wrote:
>>> Clearly you've never done any low level networking where id fields are fixed
>>> sized and will eventually wrap. Eg, TCP sequence number. I'm sure there are
>>> a myriad of other examples.
>>
>> Clearly you can make up a complete load of drivel with no basis in reality.
> 
> Oh dear, someones been caught out and is throwing his toys out the pram.
> 
>> So let me be /clear/ here.  There is /no/ valid use of incrementing
>> something beyond its maximum value.  The whole concept makes no sense.
> 
> Bollocks.
> 
>> There /are/ lots of valid uses of wrapping types.  Sequence numbers in
>> low-level networking would be one example of that - one which I /have/
>> used countless times in my work.  But that is not incrementing beyond a
>> max value - it is using a modulo wrapping increment to give a result
>> /within/ the valid range, not beyond it.
> 
> Oh right, so for 32 bit TCP seq number instead of just doing:
> 
> ++tcp->seq_num;
> 
> which would autonatically wrap after 2^32, in your world we'd have do to:
> 
> tcp->seq_num = (uint32_t)(((uint_64_t)tcp->seq_num + 1) % 0x100000000L);
> 
> Really?
> 
> Don't be an ass.

What /are/ you talking about?  Do you even know how arithmetic works in 
C++ ?

If you have "uint32_t seq_num = 0xffffffff;", then write "seq_num++;", 
you are /not/ "incrementing beyond its maximum value".  You are 
incrementing modulo 2 ^ 32, because that's how the operation works in C++.

And if you have "int32_t seq_num;" and are using "++" to increment it 
and think you have wrapping, then you are writing crap code.


> 
>>> If you think thats clear I'd hate to see what you consider obtuse.
>>>
>>
>> Have you ever considered that /you/ might be the problem here?  Other
>> people seem to understand it fine.  Consider the common factor in all
>> your difficulties understanding the template parameter.
> 
> If it wasn't so vague I wouldn't have needed to ask the question.
> 

It is not vague.  Did you actually read the cppreference link, or the 
C++ standards?

>> But does all this mean that you now understand what the integer template
>> parameter is for, and what it does?  And do you understand how to use
>> the counting semaphore?  If so, that's great.
> 
> Aww bless, so kind.
> 

You really are a poor excuse for a human being.