linux-kernel - Re: [PATCH 10/10] udf: constify udf_bitmap

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Date:	Sat, 2 Feb 2008 22:37:07 +0100
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/10] udf: constify udf_bitmap_lookup array

On Thu, Jan 31, 2008 at 05:52:44PM +0100, Jan Kara wrote:
> On Wed 30-01-08 22:04:00, marcin.slusarz@...il.com wrote:
> > udf_bitmap_lookup never changes, so constify it
> > 
> > Signed-off-by: Marcin Slusarz <marcin.slusarz@...il.com>
> > Cc: Jan Kara <jack@...e.cz>
>   Hmm, rather than doing this, could you change the function to use
> standard functions for counting set bits? I guess bitmap_weight() in
> include/linux/bitmap.h should be what we need... Thanks.

---
udf: convert udf_count_free_bitmap to use bitmap_weight

replace handwritten bits counting with bitmap_weight

Signed-off-by: Marcin Slusarz <marcin.slusarz@...il.com>
Cc: Jan Kara <jack@...e.cz>
---
 fs/udf/super.c |   17 +++++------------
 1 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/fs/udf/super.c b/fs/udf/super.c
index 3afe764..0dcee12 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -53,6 +53,7 @@
 #include <linux/vfs.h>
 #include <linux/vmalloc.h>
 #include <linux/errno.h>
+#include <linux/bitmap.h>
 #include <asm/byteorder.h>
 
 #include <linux/udf_fs.h>
@@ -1969,10 +1970,6 @@ static int udf_statfs(struct dentry *dentry, struct kstatfs *buf)
 	return 0;
 }
 
-static unsigned char udf_bitmap_lookup[16] = {
-	0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4
-};
-
 static unsigned int udf_count_free_bitmap(struct super_block *sb,
 					  struct udf_bitmap *bitmap)
 {
@@ -1982,7 +1979,6 @@ static unsigned int udf_count_free_bitmap(struct super_block *sb,
 	int block = 0, newblock;
 	kernel_lb_addr loc;
 	uint32_t bytes;
-	uint8_t value;
 	uint8_t *ptr;
 	uint16_t ident;
 	struct spaceBitmapDesc *bm;
@@ -2008,13 +2004,10 @@ static unsigned int udf_count_free_bitmap(struct super_block *sb,
 	ptr = (uint8_t *)bh->b_data;
 
 	while (bytes > 0) {
-		while ((bytes > 0) && (index < sb->s_blocksize)) {
-			value = ptr[index];
-			accum += udf_bitmap_lookup[value & 0x0f];
-			accum += udf_bitmap_lookup[value >> 4];
-			index++;
-			bytes--;
-		}
+		u32 cur_bytes = min_t(u32, bytes, sb->s_blocksize - index);
+		accum += bitmap_weight((const unsigned long *)(ptr + index),
+					cur_bytes * 8);
+		bytes -= cur_bytes;
 		if (bytes) {
 			brelse(bh);
 			newblock = udf_get_lb_pblock(sb, loc, ++block);
-- 
1.5.3.7

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