From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=44695 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PftQ4-0004Xl-Oe for qemu-devel@nongnu.org; Thu, 20 Jan 2011 07:15:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PftQ3-0007Wg-Mk for qemu-devel@nongnu.org; Thu, 20 Jan 2011 07:15:16 -0500 Received: from mail-wy0-f173.google.com ([74.125.82.173]:44744) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PftQ3-0007WU-EZ for qemu-devel@nongnu.org; Thu, 20 Jan 2011 07:15:15 -0500 Received: by wyg36 with SMTP id 36so536019wyg.4 for ; Thu, 20 Jan 2011 04:15:14 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <4D382550.1080708@st.com> References: <4D370D0C.5040706@st.com> <4D382550.1080708@st.com> Date: Thu, 20 Jan 2011 12:15:14 +0000 Message-ID: Subject: Re: [Qemu-devel] [PATCH] Support saturation with shift=0. From: Peter Maydell Content-Type: text/plain; charset=UTF-8 List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christophe Lyon Cc: "qemu-devel@nongnu.org" On 20 January 2011 12:06, Christophe Lyon wrote: > On 19.01.2011 17:51, Peter Maydell wrote: >> On 19 January 2011 16:10, Christophe Lyon wrote: >>> >>> This patch fixes corner-case saturations, when the target range is >>> zero. It merely removes the guard against (sh == 0), and makes: >>> __ssat(0x87654321, 1) return 0xffffffff and set the saturation flag >> >> did you mean __ssat(0x87654321, 0) here? (they give the same >> result, of course, but it's the sh==0 case the patch is changing...) > > Well... the ARM ARM says that the position for saturation is in the > range 1 to 32, so I think the assembler encodes 1 less than what the > user actually wrote. Hence at user level we use '1', but '0' is encoded > and then parsed by qemu. Am I wrong? No, you're right, there's a "+1" in the SSAT decoding instructions which I hadn't noticed. -- PMM