[PATCH] fat: cleanup and optimization of checksum

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/fat/dir.c

@@ -263,7 +263,6 @@ parse_record:
 			unsigned char id;
 			unsigned char slot;
 			unsigned char slots;
-			unsigned char sum;
 			unsigned char alias_checksum;
 
 			if (!unicode) {
@@ -317,9 +316,7 @@ parse_long:
 				goto parse_long;
 			if (IS_FREE(de->name) || (de->attr & ATTR_VOLUME))
 				continue;
-			for (sum = 0, i = 0; i < 11; i++)
-				sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + de->name[i];
-			if (sum != alias_checksum)
+			if (fat_checksum(de->name) != alias_checksum)
 				nr_slots = 0;
 		}
 
@@ -479,7 +476,6 @@ GetNew:
 		unsigned char id;
 		unsigned char slot;
 		unsigned char slots;
-		unsigned char sum;
 		unsigned char alias_checksum;
 
 		if (!unicode) {
@@ -534,9 +530,7 @@ ParseLong:
 			goto ParseLong;
 		if (IS_FREE(de->name) || (de->attr & ATTR_VOLUME))
 			goto RecEnd;
-		for (sum = 0, i = 0; i < 11; i++)
-			sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + de->name[i];
-		if (sum != alias_checksum)
+		if (fat_checksum(de->name) != alias_checksum)
 			long_slots = 0;
 	}
 

fs/vfat/namei.c

@@ -621,8 +621,7 @@ static int vfat_build_slots(struct inode *dir, const unsigned char *name,
 	}
 
 	/* build the entry of long file name */
-	for (cksum = i = 0; i < 11; i++)
-		cksum = (((cksum&1)<<7)|((cksum&0xfe)>>1)) + msdos_name[i];
+	cksum = fat_checksum(msdos_name);
 
 	*nr_slots = usize / 13;
 	for (ps = slots, i = *nr_slots; i > 0; i--, ps++) {

include/linux/msdos_fs.h

@@ -282,6 +282,17 @@ static inline u8 fat_attr(struct inode *inode)
 		MSDOS_I(inode)->i_attrs;
 }
 
+static inline unsigned char fat_checksum(const __u8 *name)
+{
+	unsigned char s = name[0];
+	s = (s<<7) + (s>>1) + name[1];	s = (s<<7) + (s>>1) + name[2];
+	s = (s<<7) + (s>>1) + name[3];	s = (s<<7) + (s>>1) + name[4];
+	s = (s<<7) + (s>>1) + name[5];	s = (s<<7) + (s>>1) + name[6];
+	s = (s<<7) + (s>>1) + name[7];	s = (s<<7) + (s>>1) + name[8];
+	s = (s<<7) + (s>>1) + name[9];	s = (s<<7) + (s>>1) + name[10];
+	return s;
+}
+
 static inline sector_t fat_clus_to_blknr(struct msdos_sb_info *sbi, int clus)
 {
 	return ((sector_t)clus - FAT_START_ENT) * sbi->sec_per_clus