linux-kernel - Re: [RFC][PATCH 3/3] math128, x86_64: Implement {mult,add}

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Message-ID: <4F96E01E.6040109@zytor.com>
Date:	Tue, 24 Apr 2012 10:17:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juri Lelli <juri.lelli@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 3/3] math128, x86_64: Implement {mult,add}_u128 in
 64bit asm

On 04/24/2012 09:36 AM, Peter Zijlstra wrote:
> On Tue, 2012-04-24 at 09:34 -0700, H. Peter Anvin wrote:
>> On 04/24/2012 09:10 AM, Peter Zijlstra wrote:
>>
>> Are you sure that gcc won't simply generate this code already if given
>> "unsigned __int128"?
> 
> It might, but I've been told some GCC versions had issues, also lots of
> archs fall back to libgcc functions.
> 

Yes, but this is specific to x86-64.  If gcc can generate the code it
can also schedule the code, which it can't for assembly...

	-hpa


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