linux-kernel - Re: [PATCH] MPILIB: Provide count_leading/trailing

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Date:	Fri, 10 Aug 2012 14:08:24 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jengelh@...i.de
Cc:	dhowells@...hat.com, arnd@...db.de,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, dmitry.kasatkin@...el.com
Subject: Re: [PATCH] MPILIB: Provide count_leading/trailing_zeros() based
 on arch functions

From: Jan Engelhardt <jengelh@...i.de>
Date: Fri, 10 Aug 2012 14:51:49 +0200 (CEST)

> 
> On Saturday 2012-07-21 02:46, David Miller wrote:
>>> Arnd Bergmann <arnd@...db.de> wrote:
>>> 
>>>> I don't generally like to put stuff into asm-generic when it's unlikely
>>>> to be overridden by architectures. It would really belong into
>>>> include/linux, but then again we have all the other bitops in asm-generic
>>>> as well, so whatever...
>>> 
>>> Some arches (such as Sparc, I think) have count-leading-zero instructions.
>>
>>Yes, newer sparc64 chips have leading-zero-detect, and I was pretty
>>sure that powerpc had something similar.  It's called count-leading-
>>zeros or something like that.
> 
> And gcc has a __builtin_clz.

Which I can't use.  I have to patch the code at run time based upon
whether the cpu has the 'lzd' instruction or not.
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