FlapJackApps/libdc
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Cleanup: avoid undefined shift operation

Browse Source 
Shifting a 32bit value by 32 is undefined.

Instead of using shifts to create the mask, explicitly create it by
subtracting 1 from the signbit value (and using bitwise NOT to fill all
the higher bits).

This commit looks confusing because Jef wanted me to not have two places
where I use the bitwise not. So instead of creating an equivalent mask
variable and not having to change the return statements we end up with a
mask that is the bitwise invert of what was there before this commit and
therefore the return statements need to change as well.

Coverity CID 207769

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
This commit is contained in:
Dirk Hohndel 2017-12-28 09:59:11 -08:00
parent d7c0c62f8f
commit 3ce7230788
1 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
src/uwatec_smart_parser.c
View File

@ -886,15 +886,15 @@ uwatec_smart_fixsignbit (unsigned int x, unsigned int n)
return 0;
unsigned int signbit = (1 << (n - 1));
unsigned int mask = (0xFFFFFFFF << n);
unsigned int mask = (signbit - 1);
// When turning a two's-complement number with a certain number
// of bits into one with more bits, the sign bit must be repeated
// in all the extra bits.
if ((x & signbit) == signbit)
return x | mask;
return x | ~mask;
else
return x & ~mask;
return x & mask;
}