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authorJohn Snow <jsnow@redhat.com>2015-04-17 19:49:55 -0400
committerKevin Wolf <kwolf@redhat.com>2015-04-28 15:36:10 +0200
commitbe58721dbf882fa8830f3669f499b0a5b501e90f (patch)
tree32499b1555c9e8130a1990392d7ba58eeafb8a84 /util/hbitmap.c
parent8515efbef1759b9143f06e9722c8f4e145032181 (diff)
hbitmap: add hbitmap_merge
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 <jsnow@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Message-id: 1429314609-29776-8-git-send-email-jsnow@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'util/hbitmap.c')
-rw-r--r--util/hbitmap.c33
1 files changed, 33 insertions, 0 deletions
diff --git a/util/hbitmap.c b/util/hbitmap.c
index 5b78613400..150d6e98b7 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;
+}