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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Recasting data as long ints and chars
Date: Wed, 29 Nov 2017 17:01:53 -0800
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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> Spiros Bousbouras <spibou@gmail.com> writes:
>> On Wed, 29 Nov 2017 01:07:28 +0000
>> Ben Bacarisse <ben.usenet@bsb.me.uk> wrote:
>>>   unsigned nb = 0;
>>>   unsigned U_ORDER = 0;
>>> 
>>> and loop setting
>>> 
>>>   (U_ORDER << CHAR_BIT) | nb++
>>
>> If  sizeof(unsigned) == 1    then   U_ORDER << CHAR_BIT
>> is undefined behaviour.
>
> Why?

Because CHAR_BIT (which would have to be at least 16) would be equal to
the width of the left operand.

N1570 6.5.7p3:
    The integer promotions are performed on each of the operands. The
    type of the result is that of the promoted left operand. If the
    value of the right operand is negative or is greater than or
    equal to the width of the promoted left operand, the behavior
    is undefined

> But that's a side issue.
[snip]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"