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 <[email protected]>
Cc: Tejun Heo <[email protected]>
Reviewed-by: George Spelvin <[email protected]>
Cc: Yury Norov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions