CVS: blob/src/lib crc32.c,NONE,1.1 Makefile.am,1.9,1.10

[Erik M. <er...@us...>]

Update of /cvsroot/blob/blob/src/lib
In directory usw-pr-cvs1:/tmp/cvs-serv335/src/lib

Modified Files:
	Makefile.am 
Added Files:
	crc32.c 
Log Message:
I've been playing with Russ' JFFS2 patch and had some problems with its
CRC32 implementation (both size and performance). Luckily Russell King
wrote a CRC32 implementation without the huge table, and after some tuning
it is both small and fast (on ARM).


--- NEW FILE: crc32.c ---
/*
 * crc32.c: calculate CRC32
 *
 * Copyright (C) 1995-2001 Russell King <rm...@ar...>
 *   based on linux/drivers/net/am79c961a.c
 * Copyright (C) 2002  Erik Mouw <J.A...@it...>
 *
 * $Id: crc32.c,v 1.1 2002/01/20 23:16:18 erikm Exp $
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */
/*
 * Note: this implementation doesn't use the usual lookup table
 * implementation by Gary S. Brown. The lookup table is quite large
 * (1kB) and it's quite slow because we run with d-cache enabled. The
 * i-cache is enabled, so computing the crc will be a lot faster. And
 * of course this implementation is a lot smaller :)
 * 
 */


#ident "$Id: crc32.c,v 1.1 2002/01/20 23:16:18 erikm Exp $"

#ifdef HAVE_CONFIG_H
# include <blob/config.h>
#endif

#include <blob/types.h>




#define POLYNOME	(0xedb88320)




static inline u32 update_crc(u32 crc, u8 byte)
{
        int i;
	u32 polynome = POLYNOME;
	/* the above might look stupid, but it is a cludge to get
	 * better code. with the -Os flag, the compiler moves the
	 * POLYNOME into the .rodata segment and reloads it on every
	 * run. this kinda defeats the purpose of doing CRC32 without
	 * a lookup table. by moving the polynome explicitly out of
	 * the loop, the compiler will allocate a register for it
	 * making the resulting code faster. -- Erik
	 */

        for (i = 8; i != 0; i--) {
                byte ^= crc & 1;
                crc >>= 1;

                if (byte & 1)
                        crc ^= polynome;

                byte >>= 1;
        }

        return crc;
}




u32 crc32(u32 val, const void *data, int len)
{
	u32 crc = val;
	u8 *tmp = (u8 *)data;

	while(len--)
		crc = update_crc(crc, *tmp++);

	return crc;
}

Index: Makefile.am
===================================================================
RCS file: /cvsroot/blob/blob/src/lib/Makefile.am,v
retrieving revision 1.9
retrieving revision 1.10
diff -u -d -r1.9 -r1.10
--- Makefile.am	2002/01/06 18:59:40	1.9
+++ Makefile.am	2002/01/20 23:16:18	1.10
@@ -27,6 +27,7 @@
 
 libblob_a_SOURCES	= \
 	command.c \
+	crc32.c \
 	error.c \
 	icache.c \
 	init.c \