linux-kernel - Re: [0/3] Improve generic fls64 for 64-bit machines

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Date:	Thu, 03 Apr 2008 20:19:59 +0300
From:	Benny Halevy <bhalevy@...asas.com>
To:	Alexander van Heukelum <heukelum@...lshack.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [0/3] Improve generic fls64 for 64-bit machines

On Mar. 15, 2008, 19:29 +0200, Alexander van Heukelum <heukelum@...lshack.com> wrote:
> This series of patches:
> 
> [1/3] adds __fls.h to asm-generic
> [2/3] modifies asm-*/bitops.h for 64-bit archs to implement __fls
> [3/3] modifies asm-generic/fls64.h to make use of __fls

I strongly support this.

I wish we'd also have a consistent naming convention for all
the bitops functions so it will be clearer what data type the
function is working on and is the result 0 or 1 based.

It seems like what we currently have is:

name	type	first bit#
----	----	----------
ffs	int	1
fls	int	1
__ffs	ulong	0
__fls	ulong	0	# in your proposal
ffz	ulong	0
fls64	__u64	1

so it seems like
- ffz is misnamed and is rather confusing.
  Apprently is should be renamed to __ffz.

- (new) ffz(x) can be defined to ffs(~(x))

- It'd be nice to have ffs64, and maybe ffz64.

Benny

> 
> I have compiled i386 and x86_64, and they generate the same code as
> before the change. The changes to the other archs are a best effort.
> Please comment.
> 
> If this patch series is accepted, it will make one tiny bit of
> the x86-unification a tiny bit cleaner. The patches are against
> Linus' current tree.
> 
> Andrew, if no concensus can be reached that this is a bad patch
> series, would you be willing to add this to your tree?
> 
> Greetings,
> 	Alexander
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