[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>

3 files changed, 14 insertions, 10 deletions

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 895049b2ac9c..204d8614406f 100644
--- a/fs/fat/dir.c
+++ b/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;
         }
 
diff --git a/fs/vfat/namei.c b/fs/vfat/namei.c
index 1c6f6b57ef1c..467346b123d9 100644
--- a/fs/vfat/namei.c
+++ b/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++) {
diff --git a/include/linux/msdos_fs.h b/include/linux/msdos_fs.h
index 9a3d27257984..941da5c016a0 100644
--- a/include/linux/msdos_fs.h
+++ b/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