Path: csiph.com!xmission!news.snarked.org!news.linkpendium.com!news.linkpendium.com!panix!not-for-mail
From: cross@spitfire.i.gajendra.net (Dan Cross)
Newsgroups: comp.lang.c++
Subject: Re: two's complement idea
Date: Mon, 24 Feb 2020 03:12:22 +0000 (UTC)
Organization: PANIX Public Access Internet and UNIX, NYC
Lines: 21
Message-ID: <r2veum$8oa$1@reader2.panix.com>
References: <qppva0$cbj$1@news.albasani.net> <r08tpr$e3b$1@news.albasani.net> <r090qk$dv2$1@dont-email.me>
NNTP-Posting-Host: 166.84.136.80
X-Trace: reader2.panix.com 1582513942 8970 166.84.136.80 (24 Feb 2020 03:12:22 GMT)
X-Complaints-To: abuse@panix.com
NNTP-Posting-Date: Mon, 24 Feb 2020 03:12:22 +0000 (UTC)
X-Newsreader: trn 4.0-test77 (Sep 1, 2010)
Originator: cross@spitfire.i.gajendra.net (Dan Cross)
Xref: csiph.com comp.lang.c++:71988

In article <r090qk$dv2$1@dont-email.me>,
Alf P. Steinbach <alf.p.steinbach+usenet@gmail.com> wrote:
>On 22.01.2020 08:32, Bonita Montero wrote:
>> I recently had the problem that I wanted to have a constant which is
>> size_t wide and where the highest bit is set. I simply solved it that
>> way (I assume ptrdiff_t as wide as size_t, but this should be common
>> today on all platforms):
>> std::size_t const SIZE_T_MSB = std::numeric_limits<ptrdiff_t>::min();
>> A guarantee from the standard that signed values are 2's-complement
>> woud be nice for that.
>
>C++20 will give you that guarantee.
>
>But e.g. `size_t(-1) - size_t(-1)/2` does the job with just C++98 
>guarantees.

Hmm, can't one simply compute:

	~(size_t)0 ^ (~(size_t)0 >> 1)

?