Message-ID: <50886B43.3080001@zytor.com>
Date: Wed, 24 Oct 2012 15:27:15 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Juri Lelli <juri.lelli@gmail.com>
CC: peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com,
        rostedt@goodmis.org, oleg@redhat.com, fweisbec@gmail.com,
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        harald.gustafsson@ericsson.com, vincent.guittot@linaro.org,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 02/16] math128, x86_64: Implement {mul,add}_u128 in 64bit
 asm
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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?

	-hpa

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