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lib: bitmap: change bitmap_shift_left to take unsigned parameters 

gcc can generate slightly better code for stuff like "nbits %
BITS_PER_LONG" when it knows nbits is not negative.  Since negative size
bitmaps or shift amounts don't make sense, change these parameters of
bitmap_shift_right to unsigned.

If off >= lim (which requires shift >= nbits), k is initialized with a
large positive value, but since I've let k continue to be signed, the loop
will never run and dst will be zeroed as expected.  Inside the loop, k is
guaranteed to be non-negative, so the fact that it is promoted to unsigned
in the various expressions it appears in is harmless.

Also use "shift" and "nbits" consistently for the parameter names.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rasmus Villemoes 2015-02-13 14:36:13 -08:00 committed by Linus Torvalds
parent cfac1d080a
commit dba94c2553
2 changed files with 12 additions and 11 deletions
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12
include/linux/bitmap.h
View File

@ -98,8 +98,8 @@ extern void __bitmap_complement(unsigned long *dst, const unsigned long *src,
unsigned int nbits);
extern void __bitmap_shift_right(unsigned long *dst, const unsigned long *src,
unsigned int shift, unsigned int nbits);
extern void __bitmap_shift_left(unsigned long *dst,
const unsigned long *src, int shift, int bits);
extern void __bitmap_shift_left(unsigned long *dst, const unsigned long *src,
unsigned int shift, unsigned int nbits);
extern int __bitmap_and(unsigned long *dst, const unsigned long *bitmap1,
const unsigned long *bitmap2, unsigned int nbits);
extern void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1,
@ -322,13 +322,13 @@ static inline void bitmap_shift_right(unsigned long *dst, const unsigned long *s
__bitmap_shift_right(dst, src, shift, nbits);
}
static inline void bitmap_shift_left(unsigned long *dst,
const unsigned long *src, int n, int nbits)
static inline void bitmap_shift_left(unsigned long *dst, const unsigned long *src,
unsigned int shift, unsigned int nbits)
{
if (small_const_nbits(nbits))
*dst = (*src << n) & BITMAP_LAST_WORD_MASK(nbits);
*dst = (*src << shift) & BITMAP_LAST_WORD_MASK(nbits);
else
__bitmap_shift_left(dst, src, n, nbits);
__bitmap_shift_left(dst, src, shift, nbits);
}
static inline int bitmap_parse(const char *buf, unsigned int buflen,

11
lib/bitmap.c
View File

@ -148,18 +148,19 @@ EXPORT_SYMBOL(__bitmap_shift_right);
* @dst : destination bitmap
* @src : source bitmap
* @shift : shift by this many bits
* @bits : bitmap size, in bits
* @nbits : bitmap size, in bits
*
* Shifting left (multiplying) means moving bits in the LS -> MS
* direction. Zeros are fed into the vacated LS bit positions
* and those MS bits shifted off the top are lost.
*/
void __bitmap_shift_left(unsigned long *dst,
const unsigned long *src, int shift, int bits)
void __bitmap_shift_left(unsigned long *dst, const unsigned long *src,
unsigned int shift, unsigned int nbits)
{
int k, lim = BITS_TO_LONGS(bits), left = bits % BITS_PER_LONG;
int off = shift/BITS_PER_LONG, rem = shift % BITS_PER_LONG;
int k;
unsigned int lim = BITS_TO_LONGS(nbits), left = nbits % BITS_PER_LONG;
unsigned int off = shift/BITS_PER_LONG, rem = shift % BITS_PER_LONG;
for (k = lim - off - 1; k >= 0; --k) {
unsigned long upper, lower;