From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([209.51.188.92]:56010)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <richard.henderson@linaro.org>) id 1gu9WL-00011c-20
	for qemu-devel@nongnu.org; Thu, 14 Feb 2019 00:25:13 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <richard.henderson@linaro.org>) id 1gu9WJ-0000k4-UG
	for qemu-devel@nongnu.org; Thu, 14 Feb 2019 00:25:13 -0500
Received: from mail-pf1-x444.google.com ([2607:f8b0:4864:20::444]:43668)
	by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16)
	(Exim 4.71) (envelope-from <richard.henderson@linaro.org>)
	id 1gu9WJ-0000fo-7m
	for qemu-devel@nongnu.org; Thu, 14 Feb 2019 00:25:11 -0500
Received: by mail-pf1-x444.google.com with SMTP id q17so2457771pfh.10
	for <qemu-devel@nongnu.org>; Wed, 13 Feb 2019 21:25:11 -0800 (PST)
References: <20190213143322.31371-1-david@redhat.com>
	<20190213143322.31371-13-david@redhat.com>
	<634cf76a-f1b9-138a-2ed4-e666c4be35f1@linaro.org>
	<99906aad-e22a-8cc3-8c49-4e2a2ce3d0e9@redhat.com>
From: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <0d90f059-bb8f-7979-6b41-feaea75953d5@linaro.org>
Date: Wed, 13 Feb 2019 21:25:06 -0800
MIME-Version: 1.0
In-Reply-To: <99906aad-e22a-8cc3-8c49-4e2a2ce3d0e9@redhat.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH v2 12/15] s390x/tcg: Implement XxC and
 checks for most FP instructions
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: David Hildenbrand <david@redhat.com>, qemu-devel@nongnu.org
Cc: qemu-s390x@nongnu.org, Thomas Huth <thuth@redhat.com>, Halil Pasic <pasic@linux.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Janosch Frank <frankja@linux.ibm.com>, Cornelia Huck <cohuck@redhat.com>

On 2/13/19 11:53 AM, David Hildenbrand wrote:
> On 13.02.19 20:31, Richard Henderson wrote:
>> On 2/13/19 6:33 AM, David Hildenbrand wrote:
>>> With the floating-point extension facility
>>> - CONVERT FROM LOGICAL
>>> - CONVERT TO LOGICAL
>>> - CONVERT TO FIXED
>>> - CONVERT FROM FIXED
>>> - LOAD FP INTEGER
>>> have both, a rounding mode specification and the inexact-exception control
>>> (XxC). Other instructions will be handled separatly.
>>>
>>> Check for valid rounding modes and forward also the XxC (via m4). To avoid
>>> a lot of boilerplate code and changes to the helpers, combine both, the
>>> m3 and m4 field in a combined 32 bit TCG variable. Perform checks at
>>> a central place, taking in account if the m3 or m4 field was ignore
>>> before the floating-point extension facility was introduced.
>>>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>
>> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>>
>>> +static inline bool xxc_from_m34(uint32_t m34)
>>> +{
>>> +    /* XxC is bit 1 of m4 */
>>> +    return (extract32(m34, 4, 4) & 0x4) != 0;
>>
>> Better as extract32(m32, 6, 1);
> 
> Is it "better as" that or "better written as" that?
> 
> I think "extract32(m34, 4, 4) & 0x4" is slightly easier to understand.
> (get m4 field and take the bit number 1)

I don't like not extracting the bit that you want.  Do you prefer to let the
compiler fold the constant?  E.g.  4 + 3 - 1?

I hate big-endian bit numbering...


r~