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RE: crc32() optimization



I wonder how this plays out with the 2.4.19 changes that move all crc32
function to linux/lib.  Has anybody heard if the new crc32 stuff is faster
than the support that was in fs/jffs2/crc32.h?

-Paul


-----Original Message-----
From: Joakim Tjernlund [mailto:Joakim.Tjernlund@xxxxxxx.se]
Sent: Sunday, November 10, 2002 7:28 AM
To: David Woodhouse
Cc: jffs-dev@xxxxxxx.org
Subject: crc32() optimization


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;
 }


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