From 8d48c92b45aea91e2a2be90f2ed93677e85526f1 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Stefan=20Br=C3=83=C2=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Sat, 17 Dec 2016 03:55:10 +0100
Subject: [PATCH] fs/fat: simplify get_fatent for FAT12
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit
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.bruens@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);
--
2.39.5