Re: Optimization techniques, C++ numeric representations

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From	David Brown <david.brown@hesbynett.no>
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Subject	Re: Optimization techniques, C++ numeric representations
Date	Mon, 29 Apr 2019 17:24:07 +0200
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On 27/04/2019 23:01, Hans Aberg wrote:
> On 2019-04-25 17:46, Martin Ward wrote:
>> If signed overflow was given a defined
>> behaviour (such as the two's complement result), then compilers for
>> CPUs which do not implement two's complement operations would have to
>> generate less efficient code (but does anyone still make such a CPU?).
>
> All C++ compilers use two's complement, and as of C++20, that is
> required, cf. [1], "Range of values". It is required for int32_t etc in
> C++11 [2] and C99 [3].
>
> 1. https://en.cppreference.com/w/cpp/language/types
> 2. https://en.cppreference.com/w/cpp/types/integer
> 3. https://en.cppreference.com/w/c/types/integer
> [I realize that if you look very hard, you can still find a few legacy
> machines that are not pure two's complement and do not have 8-bit byte
> addressing.  But these days, so what. -John]

Note, however, that this applies only to the representation of the
types.  C++20 will /not/ require two's complement wrapping on signed
integer overflow - this will remain undefined behaviour.  (And, as
always, compilers are free to define it if they want.)

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Thread

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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