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Subject[PATCH] bitmap: Cleanup find_last_bit
Date
Fix cut & paste error in header comment.
Simplify implementation a bit.

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
---

Rusty, we're using a similar mechanism for finding the highest slot ID
in use in the nfsv4.1 slot table and I'm going to moev it over to
using find_last_bit in our 2.6.29 patchset.
While going over your implementation I noticed a tiny cut & paste error in
bitops.h and I'd also like to propose a couple simplifications to make
the implementation a bit more readable (at least to me :).

Benny

include/linux/bitops.h | 2 +-
lib/find_last_bit.c | 15 ++++++++-------
2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 6182913..886ebf0 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -142,7 +142,7 @@ extern unsigned long find_first_zero_bit(const unsigned long *addr,
* @addr: The address to start the search at
* @size: The maximum size to search
*
- * Returns the bit number of the first set bit, or size.
+ * Returns the bit number of the last set bit, or size.
*/
extern unsigned long find_last_bit(const unsigned long *addr,
unsigned long size);
diff --git a/lib/find_last_bit.c b/lib/find_last_bit.c
index 5d202e3..e9d9cdc 100644
--- a/lib/find_last_bit.c
+++ b/lib/find_last_bit.c
@@ -24,22 +24,23 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
words = size / BITS_PER_LONG;

/* Partial final word? */
- if (size & (BITS_PER_LONG-1)) {
- tmp = (addr[words] & (~0UL >> (BITS_PER_LONG
- - (size & (BITS_PER_LONG-1)))));
+ tmp = size & (BITS_PER_LONG-1);
+ if (tmp) {
+ tmp = addr[words] & (~0UL >> (BITS_PER_LONG - tmp));
if (tmp)
goto found;
}

while (words) {
tmp = addr[--words];
- if (tmp) {
-found:
- return words * BITS_PER_LONG + __fls(tmp);
- }
+ if (tmp)
+ goto found;
}

/* Not found */
return size;
+
+found:
+ return words * BITS_PER_LONG + __fls(tmp);
}
EXPORT_SYMBOL(find_last_bit);
--
1.6.1.3


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