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

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Date:	Wed, 24 Oct 2012 15:47:23 -0700
From:	Juri Lelli <juri.lelli@...il.com>
To:	"H. Peter Anvin" <hpa@...or.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 03:27 PM, H. Peter Anvin wrote:
> On 10/24/2012 02:53 PM, Juri Lelli wrote:
>> diff --git a/arch/x86/include/asm/math128.h b/arch/x86/include/asm/math128.h
>> new file mode 100644
>> index 0000000..c0e2a6c
>> --- /dev/null
>> +++ b/arch/x86/include/asm/math128.h
>> @@ -0,0 +1,39 @@
>> +#ifndef _ASM_MATH128_H
>> +#define _ASM_MATH128_H
>> +
>> +#ifdef CONFIG_X86_64
>> +
>> +#ifdef __SIZEOF_INT128__
>> +#define ARCH_HAS_INT128
>> +#endif
>> +
>> +#ifndef ARCH_HAS_INT128
>> +
>> +static inline u128 mul_u64_u64(u64 a, u64 b)
>> +{
>> +       u128 res;
>> +
>> +       asm("mulq %2"
>> +               : "=a" (res.lo), "=d" (res.hi)
>> +               :  "rm" (b), "0" (a));
>> +
>> +       return res;
>> +}
>> +#define mul_u64_u64 mul_u64_u64
>> +
>> +static inline u128 add_u128(u128 a, u128 b)
>> +{
>> +       u128 res;
>> +
>> +       asm("addq %2,%0;\n"
>> +           "adcq %3,%1;\n"
>> +               : "=rm" (res.lo), "=rm" (res.hi)
>> +               : "r" (b.lo), "r" (b.hi), "0" (a.lo), "1" (a.hi));
>> +
>> +       return res;
>> +}
>> +#define add_u128 add_u128
>> +
>
> 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.

Thanks and Regards,

- Juri
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