From: Gabriel Paubert <paubert@iram.es>
To: Akinobu Mita <mita@miraclelinux.com>
Cc: linux-kernel@vger.kernel.org, linux-mips@linux-mips.org,
linux-ia64@vger.kernel.org, Ian Molton <spyro@f2s.com>,
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>,
Linus Torvalds <torvalds@osdl.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Hirokazu Takata <takata@linux-m32r.org>,
linuxsh-shmedia-dev@lists.sourceforge.net,
linux-m68k@vger.kernel.org,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Richard Henderson <rth@twiddle.net>,
Chris Zankel <chris@zankel.net>,
dev-etrax@axis.com, ultralinux@vger.kernel.org,
Andi Kleen <ak@suse.de>,
linuxsh-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: Thu, 2 Feb 2006 02:26:38 +0100 [thread overview]
Message-ID: <20060202012637.GA25093@iram.es> (raw)
In-Reply-To: <20060201090325.905071000@localhost.localdomain>
On Wed, Feb 01, 2006 at 06:02:38PM +0900, Akinobu Mita wrote:
>
> This patch introduces the C-language equivalents of the functions below:
>
> unsigned int hweight32(unsigned int w);
> unsigned int hweight16(unsigned int w);
> unsigned int hweight8(unsigned int w);
> unsigned long hweight64(__u64 w);
>
> In include/asm-generic/bitops/hweight.h
>
> This code largely copied from:
> include/linux/bitops.h
>
> Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
> include/asm-generic/bitops/hweight.h | 54 +++++++++++++++++++++++++++++++++++
> 1 files changed, 54 insertions(+)
>
> Index: 2.6-git/include/asm-generic/bitops/hweight.h
> ===================================================================
> --- /dev/null
> +++ 2.6-git/include/asm-generic/bitops/hweight.h
> @@ -0,0 +1,54 @@
> +#ifndef _ASM_GENERIC_BITOPS_HWEIGHT_H_
> +#define _ASM_GENERIC_BITOPS_HWEIGHT_H_
> +
> +#include <asm/types.h>
> +
> +/**
> + * hweightN - returns the hamming weight of a N-bit word
> + * @x: the word to weigh
> + *
> + * The Hamming Weight of a number is the total number of bits set in it.
> + */
> +
> +static inline unsigned int hweight32(unsigned int w)
> +{
> + unsigned int res = (w & 0x55555555) + ((w >> 1) & 0x55555555);
> + res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
> + res = (res & 0x0F0F0F0F) + ((res >> 4) & 0x0F0F0F0F);
> + res = (res & 0x00FF00FF) + ((res >> 8) & 0x00FF00FF);
> + return (res & 0x0000FFFF) + ((res >> 16) & 0x0000FFFF);
> +}
The first step can be implemented slightly better:
unsigned int res = w-((w>>1)&0x55555555);
as I found once on the web[1].
Several of the following steps can also be simplified
by omitting the masking when the result can't possibly
cause a carry to propagate too far.
This might also have a non negligible impact
on code size.
> +
> +static inline unsigned int hweight16(unsigned int w)
> +{
> + unsigned int res = (w & 0x5555) + ((w >> 1) & 0x5555);
> + res = (res & 0x3333) + ((res >> 2) & 0x3333);
> + res = (res & 0x0F0F) + ((res >> 4) & 0x0F0F);
> + return (res & 0x00FF) + ((res >> 8) & 0x00FF);
> +}
> +
> +static inline unsigned int hweight8(unsigned int w)
> +{
> + unsigned int res = (w & 0x55) + ((w >> 1) & 0x55);
> + res = (res & 0x33) + ((res >> 2) & 0x33);
> + return (res & 0x0F) + ((res >> 4) & 0x0F);
> +}
> +
> +static inline unsigned long hweight64(__u64 w)
> +{
> +#if BITS_PER_LONG == 32
> + return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w);
> +#elif BITS_PER_LONG == 64
> + u64 res;
> + res = (w & 0x5555555555555555ul) + ((w >> 1) & 0x5555555555555555ul);
> + res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
> + res = (res & 0x0F0F0F0F0F0F0F0Ful) + ((res >> 4) & 0x0F0F0F0F0F0F0F0Ful);
> + res = (res & 0x00FF00FF00FF00FFul) + ((res >> 8) & 0x00FF00FF00FF00FFul);
> + res = (res & 0x0000FFFF0000FFFFul) + ((res >> 16) & 0x0000FFFF0000FFFFul);
> + return (res & 0x00000000FFFFFFFFul) + ((res >> 32) & 0x00000000FFFFFFFFul);
> +#else
> +#error BITS_PER_LONG not defined
> +#endif
> +}
> +
> +#endif /* _ASM_GENERIC_BITOPS_HWEIGHT_H_ */
>
Regards,
Gabriel
[1] It might be better to write the first line
unsigned res = w - ((w&0xaaaaaaaa)>>1);
but I can never remember what the C standard guarantess about
right shifts values (very little IIRC). I believe that it will
work properly on all architectures that GCC supports, however,
and that it will help on many.
next prev parent reply other threads:[~2006-02-02 14:11 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-01 9:02 [patch 00/44] generic bitops Akinobu Mita
2006-02-01 9:02 ` [patch 01/44] ia64: use cpu_set() instead of __set_bit() Akinobu Mita
2006-02-01 9:02 ` [patch 02/44] parisc: add ()-pair in __ffz() macro Akinobu Mita
2006-02-01 9:02 ` [patch 03/44] cris: remove unnecessary local_irq_restore() Akinobu Mita
2006-02-01 9:02 ` [patch 04/44] use non atomic operations for minix_*_bit() and ext2_*_bit() Akinobu Mita
2006-02-01 9:02 ` [patch 05/44] generic {,test_and_}{set,clear,change}_bit() Akinobu Mita
2006-02-03 9:55 ` Martin Waitz
2006-02-06 23:07 ` Russell King
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 07/44] generic __ffs() Akinobu Mita
2006-02-01 9:02 ` [patch 08/44] generic ffz() Akinobu Mita
2006-02-01 9:02 ` [patch 09/44] generic fls() Akinobu Mita
2006-02-01 9:02 ` [patch 10/44] generic fls64() Akinobu Mita
2006-02-01 9:02 ` [patch 11/44] generic find_{next,first}{,_zero}_bit() 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 13/44] generic ffs() Akinobu Mita
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
2006-02-09 5:55 ` [PATCH] alpha: remove __alpha_cix__ and __alpha_fix__ Akinobu Mita
2006-02-09 19:12 ` Richard Henderson
2006-02-10 5:40 ` Akinobu Mita
2006-02-02 1:26 ` Gabriel Paubert [this message]
2006-02-06 11:52 ` [patch 14/44] generic hweight{64,32,16,8}() Akinobu Mita
2006-02-03 8:31 ` Ulrich Eckhardt
2006-02-01 9:02 ` [patch 15/44] generic ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() Akinobu Mita
2006-02-01 11:27 ` Roman Zippel
2006-02-06 11:47 ` Akinobu Mita
2006-02-08 10:41 ` Akinobu Mita
2006-02-01 9:02 ` [patch 16/44] generic ext2_{set,clear}_bit_atomic() Akinobu Mita
2006-02-01 9:02 ` [patch 17/44] generic minix_{test,set,test_and_clear,test,find_first_zero}_bit() Akinobu Mita
2006-02-01 9:02 ` [patch 18/44] alpha: use generic bitops Akinobu Mita
2006-02-01 9:02 ` [patch 19/44] arm: " Akinobu Mita
2006-02-01 9:02 ` [patch 20/44] arm26: " Akinobu Mita
2006-02-01 9:02 ` [patch 21/44] cris: " Akinobu Mita
2006-02-01 9:02 ` [patch 22/44] frv: " Akinobu Mita
2006-02-01 9:02 ` [patch 23/44] h8300: " Akinobu Mita
2006-02-01 9:02 ` [patch 24/44] i386: " Akinobu Mita
2006-02-01 9:02 ` [patch 25/44] ia64: " Akinobu Mita
2006-02-01 9:02 ` [patch 26/44] m32r: " Akinobu Mita
2006-02-01 9:02 ` [patch 27/44] m68k: " Akinobu Mita
2006-02-01 9:02 ` [patch 28/44] m68knommu: " Akinobu Mita
2006-02-01 9:02 ` [patch 29/44] mips: " Akinobu Mita
2006-02-01 9:02 ` [patch 30/44] parisc: " Akinobu Mita
2006-02-01 9:02 ` [patch 31/44] powerpc: " Akinobu Mita
2006-02-01 9:02 ` [patch 32/44] s390: " Akinobu Mita
2006-02-01 9:02 ` [patch 33/44] sh: " Akinobu Mita
2006-02-01 9:02 ` [patch 34/44] sh64: " Akinobu Mita
2006-02-01 9:02 ` [patch 35/44] sparc: " Akinobu Mita
2006-02-01 9:03 ` [patch 36/44] sparc64: " Akinobu Mita
2006-02-01 9:03 ` [patch 37/44] v850: " Akinobu Mita
2006-02-01 9:03 ` [patch 38/44] x86_64: " Akinobu Mita
2006-02-01 9:03 ` [patch 39/44] xtensa: " Akinobu Mita
2006-02-01 9:03 ` [patch 40/44] update include/asm-generic/bitops.h Akinobu Mita
2006-02-01 9:03 ` [patch 41/44] make thread_info.flags an unsigned long Akinobu Mita
2006-02-01 9:03 ` [patch 42/44] ia64: make partial_page.bitmap " Akinobu Mita
2006-02-01 9:03 ` [patch 43/44] ntfs: remove generic_ffs() Akinobu Mita
2006-02-01 9:03 ` [patch 44/44] remove unused generic bitops in include/linux/bitops.h Akinobu Mita
2006-02-06 10:26 ` [patch 11/44] generic find_{next,first}{,_zero}_bit() David Howells
2006-02-07 2:02 ` Akinobu Mita
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