From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-return-71205-listarch-gcc=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 19800 invoked by alias); 31 Mar 2003 05:17:13 -0000
Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Archive: <http://gcc.gnu.org/ml/gcc/>
List-Post: <mailto:gcc@gcc.gnu.org>
List-Help: <http://gcc.gnu.org/ml/>
Sender: gcc-owner@gcc.gnu.org
Received: (qmail 19793 invoked from network); 31 Mar 2003 05:17:12 -0000
Received: from unknown (HELO smtp1.euronet.nl) (194.134.35.133)
  by sources.redhat.com with SMTP; 31 Mar 2003 05:17:12 -0000
Received: from koffie.nl (rot2-p3309.dial.wanadoo.nl [62.234.207.237])
	by smtp1.euronet.nl (Postfix) with ESMTP
	id 7EF9067145; Mon, 31 Mar 2003 07:17:03 +0200 (MEST)
Message-ID: <3E87B155.3020408@koffie.nl>
Date: Mon, 31 Mar 2003 08:46:00 -0000
From: Segher Boessenkool <segher@koffie.nl>
User-Agent: Mozilla/5.0 (Macintosh; U; PPC; en-US; rv:1.2.1) Gecko/20021130
X-Accept-Language: en
MIME-Version: 1.0
To: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>
Cc: gcc@gcc.gnu.org
Subject: Re: long long bit-fields
References: <87of3taur5.fsf@student.uni-tuebingen.de>
In-Reply-To: <87of3taur5.fsf@student.uni-tuebingen.de>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-SW-Source: 2003-03/txt/msg01788.txt.bz2

Falk Hueffner wrote:
> Hi,
> 
> PR c/6346, middle-end/7018 and target/9620 deal with long long
> bit-fields. I guess part of the confusion comes from the fact that the
> C standard doesn't specify how they should behave (at least I couldn't
> find it). So what is the following program supposed to print?
> 
> #include <stdio.h>
> 
> int
> main(int argc, char *argv[]){
>     struct {
> 	unsigned long long ull31a: 31;
> 	unsigned long long ull31b: 31;
>     } x;
>     x.ull31a = -1;
>     x.ull31b = 1;
> 
>     printf("%016llx %016llx %016llx\n",
> 	   (x.ull31a << 48) >> 48,
> 	   (x.ull31a << 16),
> 	   (x.ull31b << 48));
> }
> 
> Candidates are:
> 
> ffffffffffffffff ffffffffffff0000 0000000000010000 (gcc)

Correct (the integer promotions promote an unsigned integer
bit-field to a signed integer, if it fits).

> ffffffffffffffff 00007fffffff0000 0001000000000000 (Compaq C)

Not correct.

> 000000000000ffff 00007fffffff0000 0001000000000000 (g++)
> 0000000000000000 ffffffffffff0000 0000000000000000 (Compaq C++)

Don't know about C++, sorry.


Segher