From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:49027)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kbastian@mail.uni-paderborn.de>) id 1c7Ptf-00068L-Sd
	for qemu-devel@nongnu.org; Thu, 17 Nov 2016 11:50:48 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <kbastian@mail.uni-paderborn.de>) id 1c7Ptb-0008Ro-0d
	for qemu-devel@nongnu.org; Thu, 17 Nov 2016 11:50:47 -0500
Received: from mail.uni-paderborn.de ([131.234.142.9]:42776)
	by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16)
	(Exim 4.71) (envelope-from <kbastian@mail.uni-paderborn.de>)
	id 1c7Pta-0008Rd-Jz
	for qemu-devel@nongnu.org; Thu, 17 Nov 2016 11:50:42 -0500
References: <1479324335-2074-1-git-send-email-rth@twiddle.net>
	<1479324335-2074-17-git-send-email-rth@twiddle.net>
From: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Message-ID: <1e2e6eab-921a-f30b-93d4-66bd62f68dd1@mail.uni-paderborn.de>
Date: Thu, 17 Nov 2016 17:50:40 +0100
MIME-Version: 1.0
In-Reply-To: <1479324335-2074-17-git-send-email-rth@twiddle.net>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Subject: Re: [Qemu-devel] [PATCH 16/25] tcg/i386: Handle ctz and clz opcodes
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: Richard Henderson <rth@twiddle.net>, qemu-devel@nongnu.org

On 11/16/2016 08:25 PM, Richard Henderson wrote:
> +
> +    OP_32_64(clz):
> +        if (const_args[2]) {
> +            tcg_debug_assert(have_bmi1);
> +            tcg_debug_assert(args[2] == (rexw ? 64 : 32));
> +            tcg_out_modrm(s, OPC_LZCNT + rexw, args[0], args[1]);
> +        } else {
> +            /* ??? See above.  */
> +            tcg_out_modrm(s, OPC_BSR + rexw, args[0], args[1]);

The Intel ISA manual states that it find the bit index of the most
significant bit, where the least significant bit is index 0. So for the
input 0x2 this should return 1. However this is not the number of
leading zeros.

Cheers,
    Bastian