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lib: bitmap: change bitmap_shift_right to take unsigned parameters

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I've previously changed the nbits parameter of most bitmap_* functions to
unsigned; now it is bitmap_shift_{left,right}'s turn.  This alone saves
some .text, but while at it I found that there were a few other things one
could do.  The end result of these seven patches is

  $ scripts/bloat-o-meter /tmp/bitmap.o.{old,new}
  add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-328 (-328)
  function                                     old     new   delta
  __bitmap_shift_right                         384     226    -158
  __bitmap_shift_left                          306     136    -170

and less importantly also a smaller stack footprint

  $ stack-o-meter.pl master bitmap
  file                 function                       old  new  delta
  lib/bitmap.o         __bitmap_shift_right             24    8  -16
  lib/bitmap.o         __bitmap_shift_left              24    0  -24

For each pair of 0 <= shift <= nbits <= 256 I've tested the end result
with a few randomly filled src buffers (including garbage beyond nbits),
in each case verifying that the shift {left,right}-most bits of dst are
zero and the remaining nbits-shift bits correspond to src, so I'm fairly
confident I didn't screw up.  That hasn't stopped me from being wrong
before, though.

This patch (of 7):

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.

The expressions involving "lim - 1" are still ok, since if lim is 0 the
loop is never executed.

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 14:36:02 -08:00 committed by Linus Torvalds
parent e8f2427832
commit 2fbad29917
2 changed files with 11 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/linux/bitmap.h
View File

@ -96,8 +96,8 @@ extern int __bitmap_equal(const unsigned long *bitmap1,
const unsigned long *bitmap2, unsigned int nbits);
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, int shift, int bits);
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 int __bitmap_and(unsigned long *dst, const unsigned long *bitmap1,
@ -313,13 +313,13 @@ static inline int bitmap_weight(const unsigned long *src, unsigned int nbits)
return __bitmap_weight(src, nbits);
}
static inline void bitmap_shift_right(unsigned long *dst,
const unsigned long *src, int n, int nbits)
static inline void bitmap_shift_right(unsigned long *dst, const unsigned long *src,
unsigned int shift, int nbits)
{
if (small_const_nbits(nbits))
*dst = (*src & BITMAP_LAST_WORD_MASK(nbits)) >> n;
*dst = (*src & BITMAP_LAST_WORD_MASK(nbits)) >> shift;
else
__bitmap_shift_right(dst, src, n, nbits);
__bitmap_shift_right(dst, src, shift, nbits);
}
static inline void bitmap_shift_left(unsigned long *dst,

10
lib/bitmap.c
View File

@ -104,17 +104,17 @@ EXPORT_SYMBOL(__bitmap_complement);
* @dst : destination bitmap
* @src : source bitmap
* @shift : shift by this many bits
* @bits : bitmap size, in bits
* @nbits : bitmap size, in bits
*
* Shifting right (dividing) means moving bits in the MS -> LS bit
* direction. Zeros are fed into the vacated MS positions and the
* LS bits shifted off the bottom are lost.
*/
void __bitmap_shift_right(unsigned long *dst,
const unsigned long *src, int shift, int bits)
void __bitmap_shift_right(unsigned long *dst, const unsigned long *src,
unsigned shift, unsigned nbits)
{
int k, lim = BITS_TO_LONGS(bits), left = bits % BITS_PER_LONG;
int off = shift/BITS_PER_LONG, rem = shift % BITS_PER_LONG;
unsigned k, lim = BITS_TO_LONGS(nbits), left = nbits % BITS_PER_LONG;
unsigned off = shift/BITS_PER_LONG, rem = shift % BITS_PER_LONG;
unsigned long mask = (1UL << left) - 1;
for (k = 0; off + k < lim; ++k) {
unsigned long upper, lower;