From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from florence.buici.com ([206.124.142.26] ident=qmailr) by pentafluge.infradead.org with smtp (Exim 3.22 #1 (Red Hat Linux)) id 18AwZx-0007TP-00 for ; Sun, 10 Nov 2002 18:13:01 +0000 Date: Sun, 10 Nov 2002 10:43:21 -0800 From: Marc Singer To: Joakim Tjernlund Cc: linux-mtd@lists.infradead.org Subject: Re: crc32() optimization Message-ID: <20021110184321.GB16087@buici.com> References: <24987.1036797874@passion.cambridge.redhat.com> <002301c288cd$c11a6180$0200a8c0@telia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <002301c288cd$c11a6180$0200a8c0@telia.com> Sender: linux-mtd-admin@lists.infradead.org Errors-To: linux-mtd-admin@lists.infradead.org List-Help: List-Post: List-Subscribe: , List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: As it should. I wonder if you'd do better changing the loop slightly. Check for len == 0 and do a short-circuit return. Then do this for (++len; len & 0x7; len >>= 3) { ONCE(); // repeat eight times ... len >>= 3; } while (--len > 0) ONCE(); This is the implementation I've written for another project which we've found to be relatively optimal. Note that len *must* be an int even though contemporary convention is to use the size_t type. On Sun, Nov 10, 2002 at 04:28:00PM +0100, Joakim Tjernlund wrote: > Hi David > > This patch improves my scan time with 22%( from 2.39 to 1.86 seconds). > Maybe you want to include it in the 2.4 branch. > > I will put this in my next backport of the crc32 stuff from 2.5. > > Jocke > > Index: fs/jffs2/crc32.h > =================================================================== > RCS file: /home/cvs/mtd/fs/jffs2/crc32.h,v > retrieving revision 1.3 > diff -u -b -r1.3 crc32.h > --- fs/jffs2/crc32.h 26 Feb 2001 14:44:37 -0000 1.3 > +++ fs/jffs2/crc32.h 10 Nov 2002 15:25:11 -0000 > @@ -13,7 +13,16 @@ > crc32(__u32 val, const void *ss, int len) > { > const unsigned char *s = ss; > - while (--len >= 0) > + while (len >= 6){ > + val = crc32_table[(val ^ *s++) & 0xff] ^ (val >> 8); > + val = crc32_table[(val ^ *s++) & 0xff] ^ (val >> 8); > + val = crc32_table[(val ^ *s++) & 0xff] ^ (val >> 8); > + val = crc32_table[(val ^ *s++) & 0xff] ^ (val >> 8); > + val = crc32_table[(val ^ *s++) & 0xff] ^ (val >> 8); > + val = crc32_table[(val ^ *s++) & 0xff] ^ (val >> 8); > + len -= 6; > + } > + while (len--) > val = crc32_table[(val ^ *s++) & 0xff] ^ (val >> 8); > return val; > } > > > ______________________________________________________ > Linux MTD discussion mailing list > http://lists.infradead.org/mailman/listinfo/linux-mtd/