From d12f7113b047455d410cb54862f339717d4c932f Mon Sep 17 00:00:00 2001 From: Ben Pfaff Date: Fri, 6 Aug 2010 11:42:07 -0700 Subject: [PATCH] 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. --- lib/tag.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-) diff --git a/lib/tag.c b/lib/tag.c index 0430224c..0fd0de12 100644 --- a/lib/tag.c +++ b/lib/tag.c @@ -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 -- 2.30.2