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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c++
Subject: Re: two's complement idea
Date: Mon, 27 Jan 2020 01:17:45 -0800
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"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> writes:

> 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.

Or just size_t(-1)/2+1.