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Feature offset table backward search method

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Lev Dragunov 2015-02-27 10:48:29 +03:00 • committed by Alex Zolotarev
parent 47a9725c11
commit 07feabd910
3 changed files with 43 additions and 0 deletions
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25
indexer/features_offsets_table.cpp
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@ -90,4 +90,29 @@ namespace feature
ASSERT_LESS(index, size(), ("Index out of bounds", index, size()));
return m_table.select(index);
}
size_t FeaturesOffsetsTable::GetFeatureIndexbyOffset(uint64_t offset) const
{
ASSERT_LESS_OR_EQUAL(offset, m_table.select(size() - 1), ("Offset out of bounds", offset,
m_table.select(size() - 1)));
//Binary search in elias_fano list
size_t first = 0, last = size();
size_t count = last - first, step, current;
while (count > 0)
{
step = count / 2;
current = first + step;
if (m_table.select(current) < offset)
{
first = ++current;
count -= step + 1;
}
else
count = step;
}
return current;
}
} // namespace feature

4
indexer/features_offsets_table.hpp
View file

@ -84,6 +84,10 @@ namespace feature
/// \return offset a feature
uint64_t GetFeatureOffset(size_t index) const;
/// \param offset offset of a feature
/// \return index of a feature
size_t GetFeatureIndexbyOffset(uint64_t offset) const;
/// \return number of features offsets in a table.
inline uint64_t size() const
{

14
indexer/indexer_tests/features_offsets_table_test.cpp
View file

@ -45,6 +45,15 @@ namespace feature
TEST_EQUAL(static_cast<uint64_t>(510), table->GetFeatureOffset(5), ());
TEST_EQUAL(static_cast<uint64_t>(513), table->GetFeatureOffset(6), ());
TEST_EQUAL(static_cast<uint64_t>(1024), table->GetFeatureOffset(7), ());
TEST_EQUAL(static_cast<size_t>(0), table->GetFeatureIndexbyOffset(1), ());
TEST_EQUAL(static_cast<size_t>(1), table->GetFeatureIndexbyOffset(4), ());
TEST_EQUAL(static_cast<size_t>(2), table->GetFeatureIndexbyOffset(17), ());
TEST_EQUAL(static_cast<size_t>(3), table->GetFeatureIndexbyOffset(128), ());
TEST_EQUAL(static_cast<size_t>(4), table->GetFeatureIndexbyOffset(129), ());
TEST_EQUAL(static_cast<size_t>(5), table->GetFeatureIndexbyOffset(510), ());
TEST_EQUAL(static_cast<size_t>(6), table->GetFeatureIndexbyOffset(513), ());
TEST_EQUAL(static_cast<size_t>(7), table->GetFeatureIndexbyOffset(1024), ());
}
UNIT_TEST(FeaturesOffsetsTable_CreateIfNotExistsAndLoad)
@ -66,6 +75,11 @@ namespace feature
++builderSize;
});
TEST_EQUAL(builderSize, table->size(), ());
table = unique_ptr<FeaturesOffsetsTable>();
FilesMappingContainer newReadContainer(baseContainer.GetFileName());
table = unique_ptr<FeaturesOffsetsTable>(FeaturesOffsetsTable::Load(newReadContainer));
TEST_EQUAL(builderSize, table->size(), ());
}
UNIT_TEST(FeaturesOffsetsTable_ReadWrite)