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word-at-a-time: provide generic big-endian zero_bytemask implementation

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Whilst architectures may be able to do better than this (which they can,
by simply defining their own macro), this is a generic stab at a
zero_bytemask implementation for the asm-generic, big-endian
word-at-a-time implementation.

On arm64, a clz instruction is used to implement the fls efficiently.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Will Deacon 2013-12-12 17:40:22 +00:00 committed by Linus Torvalds
parent a5c21dcefa
commit 11ec50caed
1 changed files with 8 additions and 0 deletions
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8
include/asm-generic/word-at-a-time.h
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@ -49,4 +49,12 @@ static inline bool has_zero(unsigned long val, unsigned long *data, const struct
return (val + c->high_bits) & ~rhs;
}
#ifndef zero_bytemask
#ifdef CONFIG_64BIT
#define zero_bytemask(mask) (~0ul << fls64(mask))
#else
#define zero_bytemask(mask) (~0ul << fls(mask))
#endif /* CONFIG_64BIT */
#endif /* zero_bytemask */
#endif /* _ASM_WORD_AT_A_TIME_H */