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Skiplist::position_and_count fix

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Summary: Fixed bug for SkipList::position_and_count for an item lesser then all skiplist elements.

Reviewers: mislav.bradac

Reviewed By: mislav.bradac

Differential Revision: https://phabricator.memgraph.io/D629
This commit is contained in:
florijan 2017-08-03 14:41:51 +02:00
parent 31ee8a148f
commit bb5d06e276
2 changed files with 26 additions and 1 deletions
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6
src/data_structures/concurrent/skiplist.hpp
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@ -621,7 +621,7 @@ class SkipList : private Lockable<lock_t> {
// now we need to estimate the count of elements equal to item // now we need to estimate the count of elements equal to item
// we'll do that by looking for the first element that is greater // we'll do that by looking for the first element that is greater
// than item, and counting how far we have to look // than item, and counting how far we have to look
// first find the rightmost (highest) succ that has value == item // first find the rightmost (highest) succ that has value == item
int count_level = 0; int count_level = 0;
for (int i = position_level; i >= 0; i--) for (int i = position_level; i >= 0; i--)
@ -632,6 +632,10 @@ class SkipList : private Lockable<lock_t> {
count_level = std::min(count_level, count_max_level); count_level = std::min(count_level, count_max_level);
succ = succs[count_level]; succ = succs[count_level];
// it is possible that succ just became null (even though before
// it wasn't). that happens when item is lesser then all list elems
if (!succ) return std::make_pair(0, 0);
// now expand to the right as long as element value == item // now expand to the right as long as element value == item
// at the same time accumulate count // at the same time accumulate count
int count = 1 << count_level; int count = 1 << count_level;

21
tests/unit/skiplist_position_and_count.cpp
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@ -87,3 +87,24 @@ TEST(SkiplistPosAndCount, DefaultSpeedAndAccuracy) {
// estimations are always absolutely accurate // estimations are always absolutely accurate
EXPECT_POS_COUNT(5000, 5000, 0, 0, 0); EXPECT_POS_COUNT(5000, 5000, 0, 0, 0);
} }
#define EXPECT_FOR_OUT_OF_RANGE(skiplist_size, value) \
{ \
auto sl = SkiplistRange(skiplist_size); \
auto position_and_count = sl->access().position_and_count(value); \
EXPECT_EQ(position_and_count.first, value < 0 ? 0 : skiplist_size); \
EXPECT_EQ(position_and_count.second, 0); \
}
TEST(SkiplistPosAndCount, EdgeValues) {
// small list
EXPECT_FOR_OUT_OF_RANGE(100, -20);
EXPECT_FOR_OUT_OF_RANGE(100, -1);
EXPECT_FOR_OUT_OF_RANGE(100, 100);
EXPECT_FOR_OUT_OF_RANGE(100, 120);
// big list
EXPECT_FOR_OUT_OF_RANGE(100000, -20);
EXPECT_FOR_OUT_OF_RANGE(100000, -1);
EXPECT_FOR_OUT_OF_RANGE(100000, 100000);
EXPECT_FOR_OUT_OF_RANGE(100000, 100300);
}