Re: Optimization techniques

Hans Aberg <haberg-news@telia.com>
Sat, 27 Apr 2019 23:01:10 +0200

          From comp.compilers

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From: Hans Aberg <haberg-news@telia.com>
Newsgroups: comp.compilers
Date: Sat, 27 Apr 2019 23:01:10 +0200
Organization: A noiseless patient Spider
References: <72d208c9-169f-155c-5e73-9ca74f78e390@gkc.org.uk> 19-04-020
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Keywords: C, C++, arithmetic, comment
Posted-Date: 27 Apr 2019 17:13:19 EDT
Content-Language: en-US

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]


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