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authorRasmus Villemoes <linux@rasmusvillemoes.dk>2015-04-15 16:17:42 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-04-15 16:35:24 -0700
commit89c1e79eb302349fcaf0697bc9116a4ff16bfeb0 (patch)
tree350e75e6960b31e2fb29c919a1522bcce166aa84 /include
parent8a72ed6fa7e89c5ecd68803cd1160c35b079ea3b (diff)
downloadlinux-89c1e79eb302349fcaf0697bc9116a4ff16bfeb0.tar.bz2
linux/bitmap.h: improve BITMAP_{LAST,FIRST}_WORD_MASK
The macro BITMAP_LAST_WORD_MASK can be implemented without a conditional, which will generally lead to slightly better generated code (221 bytes saved for allmodconfig-GCOV_KERNEL, ~2k with GCOV_KERNEL). As a small bonus, this also ensures that the nbits parameter is expanded exactly once. In BITMAP_FIRST_WORD_MASK, if start is signed gcc is technically allowed to assume it is positive (or divisible by BITS_PER_LONG), and hence just do the simple mask. It doesn't seem to use this, and even on an architecture like x86 where the shift only depends on the lower 5 or 6 bits, and these bits are not affected by the signedness of the expression, gcc still generates code to compute the C99 mandated value of start % BITS_PER_LONG. So just use a mask explicitly, also for consistency with BITMAP_LAST_WORD_MASK. Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Tejun Heo <tj@kernel.org> Reviewed-by: George Spelvin <linux@horizon.com> Cc: Yury Norov <yury.norov@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/bitmap.h8
1 files changed, 2 insertions, 6 deletions
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index dbfbf4990005..be4fa5ddf36c 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -172,12 +172,8 @@ extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned int
extern int bitmap_print_to_pagebuf(bool list, char *buf,
const unsigned long *maskp, int nmaskbits);
-#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) % BITS_PER_LONG))
-#define BITMAP_LAST_WORD_MASK(nbits) \
-( \
- ((nbits) % BITS_PER_LONG) ? \
- (1UL<<((nbits) % BITS_PER_LONG))-1 : ~0UL \
-)
+#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
+#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
#define small_const_nbits(nbits) \
(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)