From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1JE4Dg-0003f5-3M
	for qemu-devel@nongnu.org; Sun, 13 Jan 2008 09:53:52 -0500
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1JE4De-0003eg-F8
	for qemu-devel@nongnu.org; Sun, 13 Jan 2008 09:53:51 -0500
Received: from [199.232.76.173] (helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1JE4De-0003ec-C3
	for qemu-devel@nongnu.org; Sun, 13 Jan 2008 09:53:50 -0500
Received: from mail.esmertec.com ([212.249.37.45] helo=postie.esmertec.com)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <ddenholm@esmertec.com>) id 1JE4Dd-0004SK-VE
	for qemu-devel@nongnu.org; Sun, 13 Jan 2008 09:53:50 -0500
Received: from mail.esmertec.com (unknown [10.10.10.10])
	by postie.esmertec.com (Postfix) with ESMTP id BE58C866E
	for <qemu-devel@nongnu.org>; Sun, 13 Jan 2008 15:53:46 +0100 (CET)
Received: from ddenholm by dalmore.esmertec.com with local (Exim 4.63)
	(envelope-from <ddenholm@esmertec.com>) id 1JE4Da-0000rF-By
	for qemu-devel@nongnu.org; Sun, 13 Jan 2008 14:53:46 +0000
References: <E1HnH2m-0003IA-3l@cvs>
From: Dave Denholm <ddenholm@esmertec.com>
Date: Sun, 13 Jan 2008 14:53:46 +0000
In-Reply-To: <E1HnH2m-0003IA-3l@cvs> (Thiemo Seufer's message of "Sun, 13
	May 2007 16:35:36 +0000")
Message-ID: <km1w8lvksl.fsf@dalmore.esmertec.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Subject: [Qemu-devel] BUG: qemu-sh4 - shar does logical not arithmetic right
	shift
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org

Thiemo Seufer <ths@networkno.de> writes:

(in May 2007)

> CVSROOT:	/sources/qemu
> Module name:	qemu
> Changes by:	Thiemo Seufer <ths>	07/05/13 16:35:36
>
> Modified files:
> 	target-sh4     : op.c 
>
> Log message:
> 	Remove unnecessary pointer magic in shift operations, by Magnus Damm.
>
> CVSWeb URLs:
> http://cvs.savannah.gnu.org/viewcvs/qemu/target-sh4/op.c?cvsroot=qemu&r1=1.4&r2=1.5
>

Hi,
   I'm just playing with qemu-sh4, and found that 'shar' seems to be doing
a logical right shift, rather than an arithmetic right shift.

I think that pointer magic was necessary after all.

In the current version of target-sh4/op.c, op_shar_Rn() and op_shlr_Rn() are identical,
which is surely wrong.

void OPPROTO op_shar_Rn(void)
{
    cond_t(env->gregs[PARAM1] & 1);
    env->gregs[PARAM1] >>= 1;
    RETURN();
}

void OPPROTO op_shlr_Rn(void)
{
    cond_t(env->gregs[PARAM1] & 1);
    env->gregs[PARAM1] >>= 1;
    RETURN();
}

The behaviour is consistent with  env->gregs[] being an array of unsigned ints,
(I'm not familiar with qemu details...) and so to get an arithmetic shift, some
kind of cast is necessary.

dd
-- 
Dave Denholm              <ddenholm@esmertec.com>       http://www.esmertec.com