From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=48033 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Q2oYA-0007op-5g
	for qemu-devel@nongnu.org; Thu, 24 Mar 2011 13:42:24 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <rth@twiddle.net>) id 1Q2oY1-0003pu-Th
	for qemu-devel@nongnu.org; Thu, 24 Mar 2011 13:42:15 -0400
Received: from a.mail.sonic.net ([64.142.16.245]:55941)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth@twiddle.net>) id 1Q2oY1-0003pN-MH
	for qemu-devel@nongnu.org; Thu, 24 Mar 2011 13:42:13 -0400
Message-ID: <4D8B8264.7090605@twiddle.net>
Date: Thu, 24 Mar 2011 10:41:56 -0700
From: Richard Henderson <rth@twiddle.net>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH 14/17] s390x: Implement opcode helpers
References: <1300982333-12802-1-git-send-email-agraf@suse.de>	<1300982333-12802-15-git-send-email-agraf@suse.de>
	<AANLkTi=6dGucz1sjwWLxVqY2JsO=SWd=E4_z6R-T1krS@mail.gmail.com>
In-Reply-To: <AANLkTi=6dGucz1sjwWLxVqY2JsO=SWd=E4_z6R-T1krS@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
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.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: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Alexander Graf <agraf@suse.de>, Aurelien Jarno <aurelien@aurel32.net>, QEMU-devel Developers <qemu-devel@nongnu.org>

On 03/24/2011 10:29 AM, Peter Maydell wrote:
> On 24 March 2011 15:58, Alexander Graf <agraf@suse.de> wrote:
> 
> This is more random comments in passing than a thorough review; sorry.
> 
>> +#if HOST_LONG_BITS == 64 && defined(__GNUC__)
>> +        /* assuming 64-bit hosts have __uint128_t */
>> +        __uint128_t dividend = (((__uint128_t)env->regs[r1]) << 64) |
>> +                               (env->regs[r1+1]);
>> +        __uint128_t quotient = dividend / divisor;
>> +        env->regs[r1+1] = quotient;
>> +        __uint128_t remainder = dividend % divisor;
>> +        env->regs[r1] = remainder;
>> +#else
>> +        /* 32-bit hosts would need special wrapper functionality - just abort if
>> +           we encounter such a case; it's very unlikely anyways. */
>> +        cpu_abort(env, "128 -> 64/64 division not implemented\n");
>> +#endif
> 
> ...I'm still using a 32 bit system :-)

A couple of options:

(1) Steal code from gcc's __[u]divdi3 for implementing double-word division via
    single-word division.  In this case, your "single-word" will be long long.

(2) Implement a simple bit reduction loop.  This is probably easiest.

(3) Reuse some of the softfloat code that manipulates 128bit quantities.  This
    is probably the best option, particularly if the availability of __uint128
    is taught to softfloat so that it doesn't always open-code stuff that the
    compiler could take care of.


r~