crc32() optimization

Joakim Tjernlund
2002-11-10T14:57:29Z

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;
}