Re: Optimization techniques

David Brown <david.brown@hesbynett.no>
Tue, 7 May 2019 16:43:42 +0200

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Related articles
[33 earlier articles]
Re: Optimization techniques david.brown@hesbynett.no (David Brown) (2019-05-01)
Re: Optimization techniques david.brown@hesbynett.no (David Brown) (2019-05-01)
Re: Optimization techniques martin@gkc.org.uk (Martin Ward) (2019-05-02)
Re: Optimization techniques 847-115-0292@kylheku.com (Kaz Kylheku) (2019-05-02)
Re: Optimization techniques 847-115-0292@kylheku.com (Kaz Kylheku) (2019-05-02)
Re: Optimization techniques robin51@dodo.com.au (Robin Vowels) (2019-05-07)
Re: Optimization techniques david.brown@hesbynett.no (David Brown) (2019-05-07)
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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.compilers
Date: Tue, 7 May 2019 16:43:42 +0200
Organization: A noiseless patient Spider
References: <72d208c9-169f-155c-5e73-9ca74f78e390@gkc.org.uk> 19-04-020 19-04-025
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Keywords: C, standards
Posted-Date: 07 May 2019 18:47:56 EDT
Content-Language: en-GB

On 26/04/2019 10:33, alexfrunews@gmail.com wrote:
> On Thursday, April 25, 2019 at 1:14:54 PM UTC-7, Martin Ward wrote:
> ...
>> With the current situation, anyone wanting to avoid
>> undefined behaviour (and don't we all?) has to write code like
>> this for any signed operation:
>>
>> signed int sum;
>> if (((si_b > 0) && (si_a > (INT_MAX - si_b))) ||
>> ((si_b < 0) && (si_a < (INT_MIN - si_b)))) {
>> /* Handle error */
>> } else {
>> sum = si_a + si_b;
>> }
>
> In this day and age it is a shame that the language that is still very
> much alive does not provide the programmer with easy-to-use (and
> implement!) tools to perform/handle:
>
> - overflow checks like the above for +, -, *, /,
> %, <<, both signed and unsigned
> - mathematically meaningful comparison of signed
> and unsigned integers
> - arithmetic right shift out of the box
> - ditto rotation
> - arbitrary precision arithmetic (for integers
> of compile-time-constant length)
> - endianness at last
> - (I probably forget many more)
>


One possible consideration here is that C, these days, regularly means
gcc and/or clang. These dominate the C compiler market to a very large
extent. And they both have support for overflow checks (and wrapping
signed arithmetic, if you want). Some other compilers I have used have
copied extensions from gcc.


Still, a major point of C is that it does not change much - it is
intentionally kept (relatively) small and as stable as possible.


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