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bitmap: bitmap_equal memcmp optimization 

The bitmap_equal function has optimized code for small bitmaps with less
than BITS_PER_LONG bits. For larger bitmaps the out-of-line function
__bitmap_equal is called.

For a constant number of bits divisible by BITS_PER_LONG the memcmp
function can be used. For s390 gcc knows how to optimize this function,
memcmp calls with up to 256 bytes / 2048 bits are translated into a
single instruction.

Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2016-05-25 09:32:20 +02:00
parent a9809407f6
commit 7dd968163f
1 changed files with 4 additions and 0 deletions
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4
include/linux/bitmap.h
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@ -267,6 +267,10 @@ static inline int bitmap_equal(const unsigned long *src1,
{
if (small_const_nbits(nbits))
return ! ((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits));
#ifdef CONFIG_S390
else if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0)
return !memcmp(src1, src2, nbits / 8);
#endif
else
return __bitmap_equal(src1, src2, nbits);
}