From: Andi Kleen <andi@firstfloor.org>
To: Alexander van Heukelum <heukelum@fastmail.fm>
Cc: Andi Kleen <andi@firstfloor.org>,
Jeremy Fitzhardinge <jeremy@goop.org>,
Alexander van Heukelum <heukelum@mailshack.com>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: merge the simple bitops and move them to bitops.h
Date: Fri, 14 Mar 2008 23:18:45 +0100 [thread overview]
Message-ID: <20080314221845.GX2522@one.firstfloor.org> (raw)
In-Reply-To: <1205532078.32744.1242485965@webmail.messagingengine.com>
> #else
> static inline int fls64(__u64 x)
> {
> if (x == 0)
> return 0;
> return __fls(x) + 1;
That would require a polymorphic macro __fls that adapts to 32bit and 64bit
arguments. Not good C style.
> This is the only reason that this define exists. With another
> name it would be fine. HWEIGHT_USE_MULTIPLIER?
AFAIK it only exists because some ancient sparc chips had incredibly
slow multipliers.
> And my feeling is that this is exactly the reason why this is
> not a good version for a generic implementation in bitops.h. But
> I don't care much.
I bet most different approaches who might be slightly
faster for larger bit strings would make the one bit
case slower.
-Andi
next prev parent reply other threads:[~2008-03-14 22:16 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-12 20:01 [PATCH] x86: merge the simple bitops and move them to bitops.h Alexander van Heukelum
2008-03-14 18:07 ` Jeremy Fitzhardinge
2008-03-14 19:43 ` Alexander van Heukelum
2008-03-14 19:55 ` Andi Kleen
2008-03-14 21:33 ` Alexander van Heukelum
2008-03-14 21:42 ` Andi Kleen
2008-03-14 22:01 ` Alexander van Heukelum
2008-03-14 22:18 ` Andi Kleen [this message]
2008-03-15 17:54 ` Alexander van Heukelum
2008-03-15 19:19 ` K8, EFFICEON and CORE2 support the cmovxx instructions Alexander van Heukelum
2008-03-15 20:18 ` H. Peter Anvin
2008-03-15 21:06 ` Alexander van Heukelum
2008-03-15 21:11 ` Willy Tarreau
2008-03-16 13:16 ` [PATCH] x86: K8, GEODE_LX, CRUSOE, " Alexander van Heukelum
2008-03-21 12:38 ` Ingo Molnar
2008-03-14 20:35 ` [PATCH v2] x86: merge the simple bitops and move them to bitops.h Alexander van Heukelum
2008-03-14 23:30 ` Randy Dunlap
2008-03-15 12:04 ` [PATCH v3] " Alexander van Heukelum
2008-03-21 12:35 ` Ingo Molnar
2008-03-14 21:15 ` [PATCH] " Jeremy Fitzhardinge
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