[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>

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 895049b2ac9cb65fd58af857e719bc7d8d03115e..204d8614406f9cd18efe2f660ebb1142e66d01f5 100644 (file)
--- 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 1c6f6b57ef1cfcd29f7931ef41a11f23632e41b7..467346b123d9ed8c4ca567e062255af7ba85741b 100644 (file)
--- 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 9a3d2725798439e2a745bca4f564f89228e77ae3..941da5c016a01e1434d3291fe1ec466c16adbb45 100644 (file)
--- 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