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fs/fat: simplify get_fatent for FAT12

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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>
This commit is contained in:
Stefan Brüns 2016-12-17 03:55:10 +01:00 committed by Tom Rini
parent b8948d2aef
commit 8d48c92b45
1 changed files with 5 additions and 29 deletions
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34
fs/fat/fat.c
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@ -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);