1 files changed, 82 insertions, 0 deletions
diff --git a/lib/tag.c b/lib/tag.c
new file mode 100644
index 000000000..8a4ee8925
--- /dev/null
+++ b/lib/tag.c
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2008, 2009 Nicira Networks.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <config.h>
+#include "tag.h"
+#include <limits.h>
+#include "random.h"
+#include "type-props.h"
+#include "util.h"
+
+#define N_TAG_BITS (CHAR_BIT * sizeof(tag_type))
+BUILD_ASSERT_DECL(IS_POW2(N_TAG_BITS));
+
+#define LOG2_N_TAG_BITS (N_TAG_BITS == 32 ? 5 : N_TAG_BITS == 64 ? 6 : 0)
+BUILD_ASSERT_DECL(LOG2_N_TAG_BITS > 0);
+
+/* Returns a randomly selected tag. */
+tag_type
+tag_create_random(void)
+{
+    int x, y;
+    do {
+        uint16_t r = random_uint16();
+        x = r & (N_TAG_BITS - 1);
+        y = r >> (16 - LOG2_N_TAG_BITS);
+    } while (x == y);
+    return (1u << x) | (1u << y);
+}
+
+/* Returns a tag deterministically generated from 'seed'.
+ *
+ * 'seed' should have data in all of its bits; if it has data only in its
+ * low-order bits then the resulting tags will be poorly distributed.  Use a
+ * hash function such as hash_bytes() to generate 'seed' if necessary. */
+tag_type
+tag_create_deterministic(uint32_t seed)
+{
+    int x = seed & (N_TAG_BITS - 1);
+    int y = (seed >> LOG2_N_TAG_BITS) % 31;
+    y += y >= x;
+    return (1u << x) | (1u << y);
+}
+
+/* Initializes 'set' as an empty tag set. */
+void
+tag_set_init(struct tag_set *set)
+{
+    memset(set, 0, sizeof *set);
+}
+
+/* Adds 'tag' to 'set'. */
+void
+tag_set_add(struct tag_set *set, tag_type tag)
+{
+    if (tag && (!tag_is_valid(tag) || !tag_set_intersects(set, tag))) {
+        /* XXX We could do better by finding the set member to which we would
+         * add the fewest number of 1-bits.  This would reduce the amount of
+         * ambiguity, since e.g. three 1-bits match 3 * 2 / 2 = 3 unique tags
+         * whereas four 1-bits match 4 * 3 / 2 = 6 unique tags. */
+        tag_type *t = &set->tags[set->n++ % TAG_SET_SIZE];
+        *t |= tag;
+        if (*t == TYPE_MAXIMUM(tag_type)) {
+            set->tags[0] = *t;
+        }
+
+        set->total |= tag;
+    }
+}
+