linux-kernel - Re: [PATCH 02/16] math128, x86_64: Implement {mul,add}

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Date:	Wed, 24 Oct 2012 15:51:00 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Juri Lelli <juri.lelli@...il.com>
CC:	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
	rostedt@...dmis.org, oleg@...hat.com, fweisbec@...il.com,
	darren@...art.com, johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com,
	jkacur@...hat.com, harald.gustafsson@...csson.com,
	vincent.guittot@...aro.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 02/16] math128, x86_64: Implement {mul,add}_u128 in 64bit
 asm

On 10/24/2012 03:47 PM, Juri Lelli wrote:
>>
>> How could this work since u128 presumably has not yet been defined as a
>> structure?  After all, isn't it the absence of ARCH_HAS_INT128 which
>> makes that happen?
> 
> Sorry, you were not in the Cc list of the previous patch in the patchset,
> so you probably missed that. I should have triple checked git send-email
> Cc list. Sorry about that.
> 
> I'll add you there.
> 

Hmm... you realize that at least on some platform the u128 as a union is
going to perform worse than the plain __int128, right?  As such IMO it
would be better if the union was only defined if needed.

	-hpa

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