Subject: Re: [ub] Sized integer types and char bits
From: Gabriel Dos Reis (gdr_at_[hidden])
Date: 2013-10-25 13:44:41
A branch of this discussion, this started on th UB list, accidently went
off to being -ext only discussion after Mathias's reply. Forwarding
my reply here.
attached mail follows:
Matt Austern <austern_at_[hidden]> writes:
| On Fri, Oct 25, 2013 at 10:31 AM, Jeffrey Yasskin <jyasskin_at_[hidden]> wrote:
| Richard explicitly asked whether any such C++ users exist or are
| likely to exist in the future, and nobody's come up with any examples.
| So we appear to have a choice between helping some theoretical people
| or helping some actual people. (We help the actual people by telling
| them what to expect in the standard, while now they have to test and
| hope they find the right subset of undefined or implementation-defined
| behavior that's actually guaranteed to work.)
| It's actually a little worse than that. Testing can reveal what your
| implementation does today, with your particular input, with one set
| of compiler flags. No amount of testing can reveal what guarantees
| your implementation makes.
There are two separate issues here:
(1) whether we want C++ to continue to support non-two's complement
(2) what we want to say about overflowing shift arithmetic
Requiring two's complement does not necessarily solve (2). And solving
(2) does not necessarily imply "no" to (1).
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