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336 lines
9.8 KiB
C++
336 lines
9.8 KiB
C++
#pragma once
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#include <Common/HashTable/HashTable.h>
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/** Two-level hash table.
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* Represents 256 (or 1ULL << BITS_FOR_BUCKET) small hash tables (buckets of the first level).
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* To determine which one to use, one of the bytes of the hash function is taken.
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*
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* Usually works a little slower than a simple hash table.
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* However, it has advantages in some cases:
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* - if you need to merge two hash tables together, then you can easily parallelize it by buckets;
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* - delay during resizes is amortized, since the small hash tables will be resized separately;
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* - in theory, resizes are cache-local in a larger range of sizes.
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*/
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template <size_t initial_size_degree = 8>
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struct TwoLevelHashTableGrower : public HashTableGrower<initial_size_degree>
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{
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/// Increase the size of the hash table.
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void increaseSize()
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{
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this->size_degree += this->size_degree >= 15 ? 1 : 2;
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}
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};
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template
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<
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typename Key,
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typename Cell,
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typename Hash,
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typename Grower,
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typename Allocator, /// TODO WithStackMemory
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typename ImplTable = HashTable<Key, Cell, Hash, Grower, Allocator>,
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size_t BITS_FOR_BUCKET = 8
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>
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class TwoLevelHashTable :
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private boost::noncopyable,
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protected Hash /// empty base optimization
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{
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protected:
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friend class const_iterator;
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friend class iterator;
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using HashValue = size_t;
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using Self = TwoLevelHashTable;
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public:
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using Impl = ImplTable;
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static constexpr size_t NUM_BUCKETS = 1ULL << BITS_FOR_BUCKET;
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static constexpr size_t MAX_BUCKET = NUM_BUCKETS - 1;
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size_t hash(const Key & x) const { return Hash::operator()(x); }
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/// NOTE Bad for hash tables with more than 2^32 cells.
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static size_t getBucketFromHash(size_t hash_value) { return (hash_value >> (32 - BITS_FOR_BUCKET)) & MAX_BUCKET; }
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protected:
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typename Impl::iterator beginOfNextNonEmptyBucket(size_t & bucket)
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{
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while (bucket != NUM_BUCKETS && impls[bucket].empty())
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++bucket;
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if (bucket != NUM_BUCKETS)
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return impls[bucket].begin();
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--bucket;
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return impls[MAX_BUCKET].end();
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}
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typename Impl::const_iterator beginOfNextNonEmptyBucket(size_t & bucket) const
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{
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while (bucket != NUM_BUCKETS && impls[bucket].empty())
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++bucket;
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if (bucket != NUM_BUCKETS)
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return impls[bucket].begin();
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--bucket;
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return impls[MAX_BUCKET].end();
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}
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public:
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using key_type = typename Impl::key_type;
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using mapped_type = typename Impl::mapped_type;
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using value_type = typename Impl::value_type;
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using cell_type = typename Impl::cell_type;
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using LookupResult = typename Impl::LookupResult;
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using ConstLookupResult = typename Impl::ConstLookupResult;
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Impl impls[NUM_BUCKETS];
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TwoLevelHashTable() {}
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/// Copy the data from another (normal) hash table. It should have the same hash function.
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template <typename Source>
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TwoLevelHashTable(const Source & src)
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{
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typename Source::const_iterator it = src.begin();
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/// It is assumed that the zero key (stored separately) is first in iteration order.
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if (it != src.end() && it.getPtr()->isZero(src))
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{
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insert(it->getValue());
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++it;
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}
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for (; it != src.end(); ++it)
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{
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const Cell * cell = it.getPtr();
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size_t hash_value = cell->getHash(src);
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size_t buck = getBucketFromHash(hash_value);
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impls[buck].insertUniqueNonZero(cell, hash_value);
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}
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}
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class iterator
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{
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Self * container;
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size_t bucket;
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typename Impl::iterator current_it;
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friend class TwoLevelHashTable;
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iterator(Self * container_, size_t bucket_, typename Impl::iterator current_it_)
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: container(container_), bucket(bucket_), current_it(current_it_) {}
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public:
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iterator() {}
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bool operator== (const iterator & rhs) const { return bucket == rhs.bucket && current_it == rhs.current_it; }
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bool operator!= (const iterator & rhs) const { return !(*this == rhs); }
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iterator & operator++()
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{
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++current_it;
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if (current_it == container->impls[bucket].end())
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{
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++bucket;
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current_it = container->beginOfNextNonEmptyBucket(bucket);
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}
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return *this;
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}
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Cell & operator* () const { return *current_it; }
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Cell * operator->() const { return current_it.getPtr(); }
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Cell * getPtr() const { return current_it.getPtr(); }
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size_t getHash() const { return current_it.getHash(); }
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};
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class const_iterator
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{
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Self * container;
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size_t bucket;
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typename Impl::const_iterator current_it;
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friend class TwoLevelHashTable;
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const_iterator(Self * container_, size_t bucket_, typename Impl::const_iterator current_it_)
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: container(container_), bucket(bucket_), current_it(current_it_) {}
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public:
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const_iterator() {}
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const_iterator(const iterator & rhs) : container(rhs.container), bucket(rhs.bucket), current_it(rhs.current_it) {}
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bool operator== (const const_iterator & rhs) const { return bucket == rhs.bucket && current_it == rhs.current_it; }
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bool operator!= (const const_iterator & rhs) const { return !(*this == rhs); }
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const_iterator & operator++()
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{
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++current_it;
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if (current_it == container->impls[bucket].end())
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{
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++bucket;
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current_it = container->beginOfNextNonEmptyBucket(bucket);
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}
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return *this;
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}
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const Cell & operator* () const { return *current_it; }
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const Cell * operator->() const { return current_it->getPtr(); }
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const Cell * getPtr() const { return current_it.getPtr(); }
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size_t getHash() const { return current_it.getHash(); }
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};
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const_iterator begin() const
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{
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size_t buck = 0;
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typename Impl::const_iterator impl_it = beginOfNextNonEmptyBucket(buck);
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return { this, buck, impl_it };
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}
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iterator begin()
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{
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size_t buck = 0;
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typename Impl::iterator impl_it = beginOfNextNonEmptyBucket(buck);
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return { this, buck, impl_it };
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}
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const_iterator end() const { return { this, MAX_BUCKET, impls[MAX_BUCKET].end() }; }
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iterator end() { return { this, MAX_BUCKET, impls[MAX_BUCKET].end() }; }
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/// Insert a value. In the case of any more complex values, it is better to use the `emplace` function.
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std::pair<LookupResult, bool> ALWAYS_INLINE insert(const value_type & x)
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{
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size_t hash_value = hash(Cell::getKey(x));
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std::pair<LookupResult, bool> res;
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emplace(Cell::getKey(x), res.first, res.second, hash_value);
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if (res.second)
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insertSetMapped(res.first->getMapped(), x);
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return res;
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}
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/** Insert the key,
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* return an iterator to a position that can be used for `placement new` of value,
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* as well as the flag - whether a new key was inserted.
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*
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* You have to make `placement new` values if you inserted a new key,
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* since when destroying a hash table, the destructor will be invoked for it!
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*
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* Example usage:
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*
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* Map::iterator it;
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* bool inserted;
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* map.emplace(key, it, inserted);
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* if (inserted)
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* new(&it->second) Mapped(value);
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*/
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template <typename KeyHolder>
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void ALWAYS_INLINE emplace(KeyHolder && key_holder, LookupResult & it, bool & inserted)
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{
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size_t hash_value = hash(keyHolderGetKey(key_holder));
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emplace(key_holder, it, inserted, hash_value);
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}
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/// Same, but with a precalculated values of hash function.
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template <typename KeyHolder>
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void ALWAYS_INLINE emplace(KeyHolder && key_holder, LookupResult & it,
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bool & inserted, size_t hash_value)
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{
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size_t buck = getBucketFromHash(hash_value);
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impls[buck].emplace(key_holder, it, inserted, hash_value);
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}
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LookupResult ALWAYS_INLINE find(Key x, size_t hash_value)
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{
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size_t buck = getBucketFromHash(hash_value);
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return impls[buck].find(x, hash_value);
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}
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ConstLookupResult ALWAYS_INLINE find(Key x, size_t hash_value) const
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{
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return const_cast<std::decay_t<decltype(*this)> *>(this)->find(x, hash_value);
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}
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LookupResult ALWAYS_INLINE find(Key x) { return find(x, hash(x)); }
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ConstLookupResult ALWAYS_INLINE find(Key x) const { return find(x, hash(x)); }
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void write(DB::WriteBuffer & wb) const
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{
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for (size_t i = 0; i < NUM_BUCKETS; ++i)
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impls[i].write(wb);
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}
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void writeText(DB::WriteBuffer & wb) const
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{
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for (size_t i = 0; i < NUM_BUCKETS; ++i)
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{
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if (i != 0)
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DB::writeChar(',', wb);
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impls[i].writeText(wb);
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}
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}
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void read(DB::ReadBuffer & rb)
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{
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for (size_t i = 0; i < NUM_BUCKETS; ++i)
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impls[i].read(rb);
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}
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void readText(DB::ReadBuffer & rb)
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{
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for (size_t i = 0; i < NUM_BUCKETS; ++i)
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{
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if (i != 0)
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DB::assertChar(',', rb);
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impls[i].readText(rb);
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}
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}
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size_t size() const
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{
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size_t res = 0;
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for (size_t i = 0; i < NUM_BUCKETS; ++i)
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res += impls[i].size();
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return res;
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}
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bool empty() const
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{
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for (size_t i = 0; i < NUM_BUCKETS; ++i)
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if (!impls[i].empty())
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return false;
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return true;
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}
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size_t getBufferSizeInBytes() const
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{
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size_t res = 0;
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for (size_t i = 0; i < NUM_BUCKETS; ++i)
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res += impls[i].getBufferSizeInBytes();
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return res;
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}
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};
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