Convert ext4_count_free() to use memweight() instead of table lookup
based counting clear bits implementation. This change only affects
the code segments enabled by EXT4FS_DEBUG.
Note that this memweight() call can't be replaced with a single
bitmap_weight() call, although the pointer to the memory area is
aligned to long-word boundary. Because the size of the memory area
may not be a multiple of BITS_PER_LONG, then it returns wrong value on
big-endian architecture.
This also includes the following change.
- Remove unnecessary map == NULL check in ext4_count_free() which
always takes non-null pointer as the memory area.
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Cc: linux-ext4@xxxxxxxxxxxxxxx
---
v3: rewrite to keep ext4_count_free() as a wrapper for memweight()
v2: don't remove bitmap.c which now has other than ext4_count_free()
fs/ext4/bitmap.c | 11 +----------
1 files changed, 1 insertions(+), 10 deletions(-)
diff --git a/fs/ext4/bitmap.c b/fs/ext4/bitmap.c
index b319721..ff53d5d 100644
--- a/fs/ext4/bitmap.c
+++ b/fs/ext4/bitmap.c
@@ -13,18 +13,9 @@
#ifdef EXT4FS_DEBUG
-static const int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
-
unsigned int ext4_count_free(struct buffer_head *map, unsigned int numchars)
{
- unsigned int i, sum = 0;
-
- if (!map)
- return 0;
- for (i = 0; i < numchars; i++)
- sum += nibblemap[map->b_data[i] & 0xf] +
- nibblemap[(map->b_data[i] >> 4) & 0xf];
- return sum;
+ return numchars * BITS_PER_BYTE - memweight(map->b_data, numchars);
}
#endif /* EXT4FS_DEBUG */
--
1.7.7.6
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