[U-Boot] [PATCH] fs/fat: simplify get_fatent for FAT12

[Stefan Brüns]

From: Stefan Brüns <stefan.bru...@rwth-aachen.de>

Instead of shuffling bits from two adjacent 16 bit words, use one 16 bit
word with the appropriate byte offset in the buffer.

Signed-off-by: Stefan Brüns <stefan.bru...@rwth-aachen.de>
---
 fs/fat/fat.c | 34 +++++-----------------------------
 1 file changed, 5 insertions(+), 29 deletions(-)

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 73c3dd7f85..fe899d0442 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -181,7 +181,6 @@ static __u32 get_fatent(fsdata *mydata, __u32 entry)
        __u32 bufnum;
        __u32 off16, offset;
        __u32 ret = 0x00;
-       __u16 val1, val2;
 
        if (CHECK_CLUST(entry, mydata->fatsize)) {
                printf("Error: Invalid FAT entry: 0x%08x\n", entry);
@@ -243,35 +242,12 @@ static __u32 get_fatent(fsdata *mydata, __u32 entry)
                ret = FAT2CPU16(((__u16 *) mydata->fatbuf)[offset]);
                break;
        case 12:
-               off16 = (offset * 3) / 4;
+               off16 = (offset * 3) / 2;
+               ret = FAT2CPU16(*(__u16 *)(mydata->fatbuf + off16));
 
-               switch (offset & 0x3) {
-               case 0:
-                       ret = FAT2CPU16(((__u16 *) mydata->fatbuf)[off16]);
-                       ret &= 0xfff;
-                       break;
-               case 1:
-                       val1 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16]);
-                       val1 &= 0xf000;
-                       val2 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16 + 1]);
-                       val2 &= 0x00ff;
-                       ret = (val2 << 4) | (val1 >> 12);
-                       break;
-               case 2:
-                       val1 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16]);
-                       val1 &= 0xff00;
-                       val2 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16 + 1]);
-                       val2 &= 0x000f;
-                       ret = (val2 << 8) | (val1 >> 8);
-                       break;
-               case 3:
-                       ret = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16]);
-                       ret = (ret & 0xfff0) >> 4;
-                       break;
-               default:
-                       break;
-               }
-               break;
+               if (offset & 0x1)
+                       ret >>= 4;
+               ret &= 0xfff;
        }
        debug("FAT%d: ret: 0x%08x, entry: 0x%08x, offset: 0x%04x\n",
               mydata->fatsize, ret, entry, offset);
-- 
2.11.0

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