From: mita@miraclelinux•com (Akinobu Mita)
To: Gabriel Paubert <paubert@iram•es>
Cc: linux-mips@linux-mips•org, linux-m68k@vger•kernel.org,
linux-ia64@vger•kernel.org, Ian Molton <spyro@f2s•com>,
Balbir Singh <bsingharora@gmail•com>, Andi Kleen <ak@suse•de>,
David Howells <dhowells@redhat•com>,
linuxppc-dev@ozlabs•org, Greg Ungerer <gerg@uclinux•org>,
sparclinux@vger•kernel.org,
Miles Bader <uclinux-v850@lsi•nec.co.jp>,
Yoshinori Sato <ysato@users•sourceforge.jp>,
Hirokazu Takata <takata@linux-m32r•org>,
linuxsh-dev@lists•sourceforge.net,
Linus Torvalds <torvalds@osdl•org>,
Ivan Kokshaysky <ink@jurassic•park.msu.ru>,
linux@horizon•com, Richard Henderson <rth@twiddle•net>,
Chris Zankel <chris@zankel•net>,
dev-etrax@axis•com, ultralinux@vger•kernel.org,
linux-kernel@vger•kernel.org,
linuxsh-shmedia-dev@lists•sourceforge.net, linux390@de•ibm.com,
Russell King <rmk@arm•linux.org.uk>,
parisc-linux@parisc-linux•org
Subject: Re: [patch 14/44] generic hweight{64,32,16,8}()
Date: Mon, 6 Feb 2006 20:52:57 +0900 [thread overview]
Message-ID: <20060206115257.GB11836@miraclelinux.com> (raw)
In-Reply-To: <20060202012637.GA25093@iram.es>
On Thu, Feb 02, 2006 at 02:26:38AM +0100, Gabriel Paubert wrote:
>
> The first step can be implemented slightly better:
>
> unsigned int res = w-((w>>1)&0x55555555);
>
Yes. I've got many advices about hweight speedup.
static unsigned int hweight32(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x55555555);
res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
res = (res + (res >> 4)) & 0x0F0F0F0F;
res = res + (res >> 8);
return (res + (res >> 16)) & 0x000000FF;
}
static unsigned int hweight16(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x5555);
res = (res & 0x3333) + ((res >> 2) & 0x3333);
res = (res + (res >> 4)) & 0x0F0F;
return (res + (res >> 8)) & 0x00FF;
}
static unsigned int hweight8(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x55);
res = (res & 0x33) + ((res >> 2) & 0x33);
return (res + (res >> 4)) & 0x0F;
}
static unsigned long hweight64(__u64 w)
{
#if BITS_PER_LONG < 64
return hweight32((unsigned int)(w >> 32)) +
hweight32((unsigned int)w);
#else
__u64 res = w - ((w >> 1) & 0x5555555555555555ul);
res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
res = (res + (res >> 4)) & 0x0F0F0F0F0F0F0F0Ful;
res = res + (res >> 8);
res = res + (res >> 16);
return (res + (res >> 32)) & 0x00000000000000FFul;
#endif
}
next prev parent reply other threads:[~2006-02-06 11:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20060201090224.536581000@localhost.localdomain>
2006-02-01 9:02 ` [patch 06/44] generic __{, test_and_}{set, clear, change}_bit() and test_bit() Akinobu Mita
2006-02-01 9:02 ` [patch 10/44] generic fls64() Akinobu Mita
2006-02-01 9:02 ` [patch 12/44] generic sched_find_first_bit() Akinobu Mita
2006-02-03 3:58 ` [parisc-linux] " Grant Grundler
2006-02-01 9:02 ` [patch 14/44] generic hweight{64,32,16,8}() Akinobu Mita
2006-02-01 9:06 ` Andi Kleen
2006-02-01 9:26 ` Michael Tokarev
2006-02-01 10:24 ` Andi Kleen
2006-02-02 12:50 ` Akinobu Mita
2006-02-02 1:26 ` Gabriel Paubert
2006-02-06 11:52 ` Akinobu Mita [this message]
2006-02-03 8:31 ` Ulrich Eckhardt
2006-02-01 9:02 ` [patch 31/44] powerpc: use generic bitops Akinobu Mita
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