From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:56928)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <B07421@freescale.com>) id 1Qe866-0003kC-6N
	for qemu-devel@nongnu.org; Tue, 05 Jul 2011 12:03:39 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <B07421@freescale.com>) id 1Qe864-000489-Io
	for qemu-devel@nongnu.org; Tue, 05 Jul 2011 12:03:38 -0400
Received: from tx2ehsobe001.messaging.microsoft.com ([65.55.88.11]:23815
	helo=TX2EHSOBE002.bigfish.com) by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <B07421@freescale.com>) id 1Qe864-00047w-69
	for qemu-devel@nongnu.org; Tue, 05 Jul 2011 12:03:36 -0400
Date: Tue, 5 Jul 2011 11:02:22 -0500
From: Scott Wood <scottwood@freescale.com>
Message-ID: <20110705110222.1ef56c46@schlenkerla.am.freescale.net>
In-Reply-To: <4E11D70E.4070808@adacore.com>
References: <1309529621-27691-1-git-send-email-chouteau@adacore.com>
	<20110701152244.278e720b@schlenkerla.am.freescale.net>
	<4E11D70E.4070808@adacore.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH V2] [PowerPC][RFC] booke timers
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Fabien Chouteau <chouteau@adacore.com>
Cc: qemu-devel@nongnu.org

On Mon, 4 Jul 2011 17:06:54 +0200
Fabien Chouteau <chouteau@adacore.com> wrote:

> On 01/07/2011 22:22, Scott Wood wrote:
> > On Fri, 1 Jul 2011 16:13:41 +0200
> > Fabien Chouteau <chouteau@adacore.com> wrote:
> >> +static void booke_update_fixed_timer(CPUState         *env,
> >> +                                     uint8_t           target_bit,
> >> +                                     uint64_t          *next,
> >> +                                     struct QEMUTimer *timer)
> >> +{
> >> +    ppc_tb_t *tb_env = env->tb_env;
> >> +    uint64_t lapse;
> >> +    uint64_t tb;
> >> +    uint64_t period = 1 << (target_bit + 1);
> >> +    uint64_t now;
> >> +
> >> +    now = qemu_get_clock_ns(vm_clock);
> >> +    tb  = cpu_ppc_get_tb(tb_env, now, tb_env->tb_offset);
> >> +
> >> +    if (tb <= (1 << target_bit)) {
> >> +        lapse = (1 << target_bit) - tb;
> >> +    } else {
> >> +        lapse = period - ((tb - (1 << target_bit)) % period);
> > 
> > We know period is a power of two, so just do "& (period - 1)".
> > 
> > That should let you get rid of the special case for
> > "tb <= (1 << target_bit)" as well.
> > 
> 
> Do you mean "lapse = period - ((tb - (1 << target_bit)) & (period - 1));" ?

Yes.

Or more simply:

lapse = period - ((tb - period) & (period - 1));

> I don't see how this solves the "tb <= (1 << target_bit)" case.

Actually, since everything is unsigned the special case shouldn't be needed
regardless.

-Scott