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[Qemu-block] [PATCH v6 07/21] hbitmap: add hbitmap_merge
From: |
John Snow |
Subject: |
[Qemu-block] [PATCH v6 07/21] hbitmap: add hbitmap_merge |
Date: |
Fri, 17 Apr 2015 19:49:55 -0400 |
We add a bitmap merge operation to assist in error cases
where we wish to combine two bitmaps together.
This is algorithmically O(bits) provided HBITMAP_LEVELS remains
constant. For a full bitmap on a 64bit machine:
sum(bits/64^k, k, 0, HBITMAP_LEVELS) ~= 1.01587 * bits
We may be able to improve running speed for particularly sparse
bitmaps by using iterators, but the running time for dense maps
will be worse.
We present the simpler solution first, and we can refine it later
if needed.
Signed-off-by: John Snow <address@hidden>
---
include/qemu/hbitmap.h | 13 +++++++++++++
util/hbitmap.c | 33 +++++++++++++++++++++++++++++++++
2 files changed, 46 insertions(+)
diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
index 550d7ce..6cb2d0e 100644
--- a/include/qemu/hbitmap.h
+++ b/include/qemu/hbitmap.h
@@ -65,6 +65,19 @@ struct HBitmapIter {
HBitmap *hbitmap_alloc(uint64_t size, int granularity);
/**
+ * hbitmap_merge:
+ * @a: The bitmap to store the result in.
+ * @b: The bitmap to merge into @a.
+ * @return true if the merge was successful,
+ * false if it was not attempted.
+ *
+ * Merge two bitmaps together.
+ * A := A (BITOR) B.
+ * B is left unmodified.
+ */
+bool hbitmap_merge(HBitmap *a, const HBitmap *b);
+
+/**
* hbitmap_empty:
* @hb: HBitmap to operate on.
*
diff --git a/util/hbitmap.c b/util/hbitmap.c
index 5b78613..150d6e9 100644
--- a/util/hbitmap.c
+++ b/util/hbitmap.c
@@ -399,3 +399,36 @@ HBitmap *hbitmap_alloc(uint64_t size, int granularity)
hb->levels[0][0] |= 1UL << (BITS_PER_LONG - 1);
return hb;
}
+
+/**
+ * Given HBitmaps A and B, let A := A (BITOR) B.
+ * Bitmap B will not be modified.
+ *
+ * @return true if the merge was successful,
+ * false if it was not attempted.
+ */
+bool hbitmap_merge(HBitmap *a, const HBitmap *b)
+{
+ int i;
+ uint64_t j;
+
+ if ((a->size != b->size) || (a->granularity != b->granularity)) {
+ return false;
+ }
+
+ if (hbitmap_count(b) == 0) {
+ return true;
+ }
+
+ /* This merge is O(size), as BITS_PER_LONG and HBITMAP_LEVELS are constant.
+ * It may be possible to improve running times for sparsely populated maps
+ * by using hbitmap_iter_next, but this is suboptimal for dense maps.
+ */
+ for (i = HBITMAP_LEVELS - 1; i >= 0; i--) {
+ for (j = 0; j < a->sizes[i]; j++) {
+ a->levels[i][j] |= b->levels[i][j];
+ }
+ }
+
+ return true;
+}
--
2.1.0
- [Qemu-block] [PATCH v6 00/21] block: transactionless incremental backup series, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 01/21] docs: incremental backup documentation, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 03/21] qmp: Ensure consistent granularity type, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 02/21] qapi: Add optional field "name" to block dirty bitmap, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 05/21] block: Introduce bdrv_dirty_bitmap_granularity(), John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 06/21] hbitmap: cache array lengths, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 04/21] qmp: Add block-dirty-bitmap-add and block-dirty-bitmap-remove, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 07/21] hbitmap: add hbitmap_merge,
John Snow <=
- [Qemu-block] [PATCH v6 08/21] block: Add bitmap disabled status, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 09/21] block: Add bitmap successors, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 12/21] qmp: Add dirty bitmap status field in query-block, John Snow, 2015/04/17
- [Qemu-block] [PATCH v6 10/21] qmp: Add support of "dirty-bitmap" sync mode for drive-backup, John Snow, 2015/04/17