diff options
author | Ben Pfaff <blp@nicira.com> | 2010-08-06 11:42:07 -0700 |
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committer | Ben Pfaff <blp@nicira.com> | 2010-08-06 12:59:48 -0700 |
commit | d12f7113b047455d410cb54862f339717d4c932f (patch) | |
tree | 710773a9a64773361f1c06413f9536c5086562b0 | |
parent | c393047875e2c9dc76b2f19092fff6bbf69ec4f9 (diff) |
tag: Be more precise about choosing tags to add, in tag_set_add().
It is not necessary to add a "tag" if all of the bits in it are already
present in some member of the set. This commit adds that optimization.
-rw-r--r-- | lib/tag.c | 27 |
1 files changed, 26 insertions, 1 deletions
@@ -61,11 +61,36 @@ tag_set_init(struct tag_set *set) memset(set, 0, sizeof *set); } +static bool +tag_is_worth_adding(const struct tag_set *set, tag_type tag) +{ + if (!tag) { + /* Nothing to add. */ + return false; + } else if ((set->total & tag) != tag) { + /* 'set' doesn't have all the bits in 'tag', so we need to add it. */ + return true; + } else { + /* We can drop it if some member of 'set' already includes all of the + * 1-bits in 'tag'. (tag_set_intersects() does a different test: + * whether some member of 'set' has at least two 1-bit in common with + * 'tag'.) */ + int i; + + for (i = 0; i < TAG_SET_SIZE; i++) { + if ((set->tags[i] & tag) == tag) { + return false; + } + } + return true; + } +} + /* 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))) { + if (tag_is_worth_adding(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 |