linux-ext4 - [PATCH 4/6 -v2] libext2fs: optimize rb_get_bmap

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Message-Id: <1353947981-15219-5-git-send-email-tytso@mit.edu>
Date:	Mon, 26 Nov 2012 11:39:38 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>
Subject: [PATCH 4/6 -v2] libext2fs: optimize rb_get_bmap_range()

This simplifies the rb_get_bmap_range() function and speeds it up for
the case where most of the bitmap is zero.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Reviewed-by: Lukas Czerner <lczerner@...hat.com>
---
 lib/ext2fs/blkmap64_rb.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/lib/ext2fs/blkmap64_rb.c b/lib/ext2fs/blkmap64_rb.c
index 0fc7c57..eb56c85 100644
--- a/lib/ext2fs/blkmap64_rb.c
+++ b/lib/ext2fs/blkmap64_rb.c
@@ -741,32 +741,23 @@ static errcode_t rb_get_bmap_range(ext2fs_generic_bitmap bitmap,
 			break;
 	}
 
-	pos = start;
+	memset(out, 0, (num + 7) >> 3);
+
 	for (; parent != NULL; parent = next) {
 		next = ext2fs_rb_next(parent);
 		ext = ext2fs_rb_entry(parent, struct bmap_rb_extent, node);
 
-		while (((pos - start) < num) &&
-			(pos < ext->start)) {
-			ext2fs_fast_clear_bit64((pos - start), out);
-			pos++;
-		}
-
-		if ((pos - start) >= num)
-			return 0;
+		pos = ext->start;
+		if (pos < start)
+			pos = start;
 
-		while (((pos - start) < num) &&
-			(pos < (ext->start + ext->count))) {
+		while (pos < (ext->start + ext->count)) {
+			if ((pos - start) >= num)
+				return 0;
 			ext2fs_fast_set_bit64((pos - start), out);
 			pos++;
 		}
 	}
-
-	while ((pos - start) < num) {
-		ext2fs_fast_clear_bit64((pos - start), out);
-		pos++;
-	}
-
 	return 0;
 }
 
-- 
1.7.12.rc0.22.gcdd159b

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