Re: Optimization techniques

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.compilers
Subject	Re: Optimization techniques
Date	2019-05-07 16:43 +0200
Organization	A noiseless patient Spider
Message-ID	<19-05-054@comp.compilers> (permalink)
References	<72d208c9-169f-155c-5e73-9ca74f78e390@gkc.org.uk> <19-04-020@comp.compilers> <19-04-025@comp.compilers>

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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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Re: Optimization techniques Martin Ward <martin@gkc.org.uk> - 2019-04-25 16:46 +0100
  Re: Optimization techniques Kaz Kylheku <847-115-0292@kylheku.com> - 2019-04-25 23:01 +0000
  Re: Optimization techniques alexfrunews@gmail.com - 2019-04-26 01:33 -0700
    Re: language design and Optimization techniques Martin Ward <martin@gkc.org.uk> - 2019-04-27 11:56 +0100
    Re: Optimization techniques 0xe2.0x9a.0x9b@gmail.com - 2019-04-27 04:56 -0700
      Re: C language andOptimization techniques alexfrunews@gmail.com - 2019-04-27 19:47 -0700
    Re: reliability features and Optimization techniques Bart <bc@freeuk.com> - 2019-04-28 11:58 +0100
      Re: reliability features and Optimization techniques Jan Ziak <0xe2.0x9a.0x9b@gmail.com> - 2019-04-29 04:33 -0700
    Re: Optimization techniques Gene Wirchenko <genew@telus.net> - 2019-04-30 18:11 -0700
    Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-05-07 16:43 +0200
  Re: Optimization techniques Hans Aberg <haberg-news@telia.com> - 2019-04-27 23:01 +0200
    Re: Optimization techniques, C++ numeric representations David Brown <david.brown@hesbynett.no> - 2019-04-29 17:24 +0200
      Re: Optimization techniques, C++ numeric representations Hans Aberg <haberg-news@telia.com> - 2019-04-30 15:01 +0200

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