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lib/bitmap: fix off-by-one in bitmap_to_arr64()

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GENMASK*() family takes the first and the last bits of the mask
*including* them. So, with the current code bitmap_to_arr64()
doesn't clear the tail properly:

nbits %  exp             mask                must be
1        GENMASK(1, 0)   0x3                 0x1
...
63       GENMASK(63, 0)  0xffffffffffffffff  0x7fffffffffffffff

This was found by making the function always available instead of
32-bit BE systems only (for reusing in some new functionality).
Turn the number of bits into the last bit set by subtracting 1.
@nbits is already checked to be positive beforehand.

Fixes: 0a97953fd2 ("lib: add bitmap_{from,to}_arr64")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
This commit is contained in:
Alexander Lobakin 2022-07-11 20:09:29 +02:00 committed by Yury Norov
parent dc34d50366
commit 428bc09863
1 changed files with 1 additions and 1 deletions
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2
lib/bitmap.c
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@ -1564,7 +1564,7 @@ void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits)
/* Clear tail bits in the last element of array beyond nbits. */
if (nbits % 64)
buf[-1] &= GENMASK_ULL(nbits % 64, 0);
buf[-1] &= GENMASK_ULL((nbits - 1) % 64, 0);
}
EXPORT_SYMBOL(bitmap_to_arr64);
#endif