From: Rutger Nijlunsing <rutger@nospam.com>
To: Balbir Singh <bsingharora@gmail.com>
Cc: Akinobu Mita <mita@miraclelinux.com>,
Grant Grundler <iod00d@hp.com>,
Linux Kernel Development <linux-kernel@vger.kernel.org>,
linux-ia64@vger.kernel.org
Subject: Re: [PATCH 8/12] generic hweight{32,16,8}()
Date: Thu, 26 Jan 2006 11:04:25 +0100 [thread overview]
Message-ID: <20060126100425.GA12345@nospam.com> (raw)
In-Reply-To: <661de9470601252312m1f9c9256peb79451e49fc8662@mail.gmail.com>
[snip]
> > /*
> > * hweightN: returns the hamming weight (i.e. the number
> > * of bits set) of a N-bit word
> > */
> >
> > -#define hweight32(x) generic_hweight32(x)
> > -#define hweight16(x) generic_hweight16(x)
> > -#define hweight8(x) generic_hweight8(x)
> > +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);
> > +}
> > +
>
> This can be replaced with
>
> register int res=w;
> res=res-((res>>1)&0x55555555);
> res=(res&0x33333333)+((res>>2)&0x33333333);
> res=(res+(res>>4))&0x0f0f0f0f;
> res=res+(res>>8);
> return (res+(res>>16)) & 0xff;
>
> Similar optimizations can be applied to the routines below. Please see
> http://www-cs-faculty.stanford.edu/~knuth/mmixware.html errata and the code
> in mmix-arith.w for the complete set of optimizations and credits.
>
> http://www.jjj.de/fxt/fxtbook.pdf is another inspirational source for
> such algorithms.
Ah, the joys of bit twiddling!
http://graphics.stanford.edu/~seander/bithacks.html
...has some more.
--
Rutger Nijlunsing ---------------------------------- eludias ed dse.nl
never attribute to a conspiracy which can be explained by incompetence
----------------------------------------------------------------------
next prev parent reply other threads:[~2006-01-26 10:04 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-25 11:26 [PATCH 0/6] RFC: use include/asm-generic/bitops.h Akinobu Mita
2006-01-25 11:28 ` [PATCH 1/6] {set,clear,test}_bit() related cleanup Akinobu Mita
2006-01-25 11:46 ` Andi Kleen
2006-01-26 16:14 ` Pavel Machek
2006-01-26 16:47 ` Russell King
2006-01-26 19:14 ` Paul Jackson
2006-01-25 11:30 ` [PATCH 2/6] use non atomic operations for minix_*_bit() and ext2_*_bit() Akinobu Mita
2006-01-25 11:32 ` [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h Akinobu Mita
2006-01-25 11:54 ` Keith Owens
2006-01-26 2:13 ` Akinobu Mita
2006-01-26 2:19 ` Akinobu Mita
2006-01-25 20:02 ` Russell King
2006-01-25 20:59 ` Grant Grundler
2006-01-26 3:27 ` Akinobu Mita
2006-01-26 3:29 ` [PATCH 1/12] generic *_bit() Akinobu Mita
2006-02-01 15:11 ` Chen, Kenneth W
2006-02-01 18:02 ` Christoph Hellwig
2006-02-01 18:07 ` Chen, Kenneth W
2006-02-01 19:19 ` Russell King
2006-02-01 19:25 ` Chen, Kenneth W
2006-02-01 19:35 ` Russell King
2006-02-03 10:24 ` Geert Uytterhoeven
2006-02-03 10:27 ` Russell King
2006-02-01 19:39 ` Grant Grundler
2006-02-01 21:41 ` Chen, Kenneth W
2006-02-01 22:09 ` Grant Grundler
2006-02-01 22:49 ` Anton Altaparmakov
2006-02-02 0:08 ` Grant Grundler
2006-02-02 8:52 ` Anton Altaparmakov
2006-02-02 10:13 ` Andreas Schwab
2006-02-02 22:43 ` Paul Mackerras
2006-01-26 3:30 ` [PATCH 2/12] generic __ffs() Akinobu Mita
2006-01-26 3:31 ` [PATCH 3/12] generic ffz() Akinobu Mita
2006-01-26 8:21 ` Michael Tokarev
2006-01-27 6:39 ` [PATCH] parisc: add ()-pair in __ffs() Akinobu Mita
2006-01-26 3:32 ` [PATCH 4/12] generic fls() and fls64() Akinobu Mita
2006-01-26 3:33 ` [PATCH 5/12] generic find_{next,first}{,_zero}_bit() Akinobu Mita
2006-01-26 3:34 ` [PATCH 6/12] generic sched_find_first_bit() Akinobu Mita
2006-01-26 3:35 ` [PATCH 7/12] generic ffs() Akinobu Mita
2006-01-26 3:36 ` [PATCH 8/12] generic hweight{32,16,8}() Akinobu Mita
2006-01-26 7:12 ` Balbir Singh
2006-01-26 10:04 ` Rutger Nijlunsing [this message]
2006-01-27 4:55 ` Akinobu Mita
2006-01-27 5:40 ` Balbir Singh
2006-01-27 6:40 ` Akinobu Mita
2006-01-31 11:14 ` Balbir Singh
2006-01-26 18:57 ` Bryan O'Sullivan
2006-01-27 4:43 ` Akinobu Mita
2006-01-27 5:23 ` Bryan O'Sullivan
2006-01-26 3:36 ` [PATCH 9/12] generic hweight64() Akinobu Mita
2006-01-26 7:05 ` Balbir Singh
2006-01-26 3:38 ` [PATCH 10/12] generic ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() Akinobu Mita
2006-01-26 3:38 ` [PATCH 11/12] generic ext2_{set,clear}_bit_atomic() Akinobu Mita
2006-01-26 3:39 ` [PATCH 12/12] generic minix_{test,set,test_and_clear,test,find_first_zero}_bit() Akinobu Mita
2006-01-25 23:25 ` [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h Ian Molton
2006-01-26 0:06 ` Richard Henderson
2006-01-26 4:34 ` Edgar Toernig
2006-01-26 17:30 ` Richard Henderson
2006-01-26 8:55 ` Russell King
2006-01-26 16:18 ` [parisc-linux] " Grant Grundler
2006-01-26 16:30 ` Nicolas Pitre
2006-01-26 16:40 ` Russell King
2006-01-26 23:04 ` Grant Grundler
2006-01-26 23:03 ` Russell King
2006-01-29 7:12 ` Stuart Brady
2006-01-30 4:03 ` David S. Miller
2006-01-30 17:06 ` Ralf Baechle
2006-01-30 19:50 ` Stuart Brady
2006-01-30 23:02 ` David S. Miller
2006-01-27 0:28 ` [parisc-linux] Re: [PATCH 3/6] C-language equivalents of John David Anglin
2006-01-27 12:51 ` [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h Hirokazu Takata
2006-01-30 3:29 ` Akinobu Mita
2006-01-25 11:34 ` [PATCH 5/6] fix warning on test_ti_thread_flag() Akinobu Mita
2006-01-25 12:28 ` Geert Uytterhoeven
2006-01-25 22:28 ` Paul Mackerras
2006-01-26 0:04 ` David S. Miller
2006-01-25 11:35 ` [PATCH 6/6] remove unused generic bitops in include/linux/bitops.h Akinobu Mita
[not found] ` <20060125113336.GE18584@miraclelinux.com>
2006-01-26 1:49 ` [PATCH 4/6] use include/asm-generic/bitops for each architecture Akinobu Mita
2006-01-26 2:37 ` Grant Grundler
2006-01-27 13:04 ` Hirokazu Takata
2006-01-30 3:15 ` Akinobu Mita
2006-01-31 16:49 [PATCH 8/12] generic hweight{32,16,8}() linux
2006-01-31 18:14 ` Grant Grundler
2006-02-02 9:34 ` Balbir Singh
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