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author | Rasmus Villemoes <linux@rasmusvillemoes.dk> | 2015-04-15 16:17:42 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-04-15 16:35:24 -0700 |
commit | 89c1e79eb302349fcaf0697bc9116a4ff16bfeb0 (patch) | |
tree | 350e75e6960b31e2fb29c919a1522bcce166aa84 /arch | |
parent | 8a72ed6fa7e89c5ecd68803cd1160c35b079ea3b (diff) | |
download | linux-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 'arch')
0 files changed, 0 insertions, 0 deletions