junrushao1994 commented on a change in pull request #5740:
URL: https://github.com/apache/incubator-tvm/pull/5740#discussion_r440670880
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File path: include/tvm/node/container.h
##########
@@ -43,51 +44,1188 @@ using runtime::Downcast;
using runtime::IterAdapter;
using runtime::make_object;
using runtime::Object;
+using runtime::ObjectEqual;
+using runtime::ObjectHash;
using runtime::ObjectPtr;
using runtime::ObjectPtrEqual;
using runtime::ObjectPtrHash;
using runtime::ObjectRef;
using runtime::String;
using runtime::StringObj;
-/*! \brief String-aware ObjectRef hash functor */
-struct ObjectHash {
- size_t operator()(const ObjectRef& a) const {
- if (const auto* str = a.as<StringObj>()) {
- return String::HashBytes(str->data, str->size);
- }
- return ObjectPtrHash()(a);
+#if (TVM_USE_STL_MAP != 0)
+
+/*! \brief Shared content of all specializations of hash map */
+class MapNode : public Object {
+ public:
+ /*! \brief Type of the keys in the hash map */
+ using key_type = ObjectRef;
+ /*! \brief Type of the values in the hash map */
+ using mapped_type = ObjectRef;
+ /*! \brief Type of the actual underlying container */
+ using ContainerType = std::unordered_map<ObjectRef, ObjectRef, ObjectHash,
ObjectEqual>;
+ /*! \brief Iterator class */
+ using iterator = ContainerType::iterator;
+ /*! \brief Iterator class */
+ using const_iterator = ContainerType::const_iterator;
+ /*! \brief Type of value stored in the hash map */
+ using KVType = ContainerType::value_type;
+
+ static_assert(std::is_standard_layout<KVType>::value, "KVType is not
standard layout");
+ static_assert(sizeof(KVType) == 16 || sizeof(KVType) == 8, "sizeof(KVType)
incorrect");
+
+ static constexpr const uint32_t _type_index =
runtime::TypeIndex::kRuntimeMap;
+ static constexpr const char* _type_key = "Map";
+ TVM_DECLARE_FINAL_OBJECT_INFO(MapNode, Object);
+
+ /*!
+ * \brief Number of elements in the SmallMapNode
+ * \return The result
+ */
+ size_t size() const { return data_.size(); }
+ /*!
+ * \brief Count the number of times a key exists in the hash map
+ * \param key The indexing key
+ * \return The result, 0 or 1
+ */
+ size_t count(const key_type& key) const { return data_.count(key); }
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The const reference to the value
+ */
+ const mapped_type& at(const key_type& key) const { return data_.at(key); }
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The mutable reference to the value
+ */
+ mapped_type& at(const key_type& key) { return data_.at(key); }
+ /*! \return begin iterator */
+ iterator begin() { return data_.begin(); }
+ /*! \return const begin iterator */
+ const_iterator begin() const { return data_.begin(); }
+ /*! \return end iterator */
+ iterator end() { return data_.end(); }
+ /*! \return end iterator */
+ const_iterator end() const { return data_.end(); }
+ /*!
+ * \brief Index value associated with a key
+ * \param key The indexing key
+ * \return The iterator of the entry associated with the key, end iterator
if not exists
+ */
+ const_iterator find(const key_type& key) const { return data_.find(key); }
+ /*!
+ * \brief Index value associated with a key
+ * \param key The indexing key
+ * \return The iterator of the entry associated with the key, end iterator
if not exists
+ */
+ iterator find(const key_type& key) { return data_.find(key); }
+ /*!
+ * \brief Erase the entry associated with the iterator
+ * \param position The iterator
+ */
+ void erase(const iterator& position) { data_.erase(position); }
+ /*!
+ * \brief Erase the entry associated with the key, do nothing if not exists
+ * \param key The indexing key
+ */
+ void erase(const key_type& key) { data_.erase(key); }
+
+ protected:
+ /*!
+ * \brief Create an empty container
+ * \return The object created
+ */
+ static ObjectPtr<MapNode> Empty() { return make_object<MapNode>(); }
+ /*!
+ * \brief Create the map using contents from the given iterators.
+ * \param first Begin of iterator
+ * \param last End of iterator
+ * \tparam IterType The type of iterator
+ * \return ObjectPtr to the map created
+ */
+ template <typename IterType>
+ static ObjectPtr<Object> CreateFromRange(IterType first, IterType last) {
+ ObjectPtr<MapNode> p = make_object<MapNode>();
+ p->data_ = std::unordered_map<ObjectRef, ObjectRef, ObjectHash,
ObjectEqual>(first, last);
+ return p;
+ }
+ /*!
+ * \brief InsertMaybeReHash an entry into the given hash map
+ * \param kv The entry to be inserted
+ * \param map The pointer to the map, can be changed if re-hashing happens
+ */
+ static void InsertMaybeReHash(const KVType& kv, ObjectPtr<Object>* map) {
+ MapNode* m = static_cast<MapNode*>(map->get());
+ m->data_[kv.first] = kv.second;
}
+ /*!
+ * \brief Create an empty container with elements copying from another
MapNode
+ * \param m The source container
+ * \return The object created
+ */
+ static ObjectPtr<MapNode> CopyFrom(MapNode* m) {
+ ObjectPtr<MapNode> p = make_object<MapNode>();
+ p->data_ = std::unordered_map<ObjectRef, ObjectRef, ObjectHash,
ObjectEqual>(m->data_.begin(),
+
m->data_.end());
+ return p;
+ }
+ /*! \brief The real container storing data */
+ ContainerType data_;
+ template <typename, typename, typename, typename>
+ friend class Map;
};
-/*! \brief String-aware ObjectRef equal functor */
-struct ObjectEqual {
- bool operator()(const ObjectRef& a, const ObjectRef& b) const {
- if (a.same_as(b)) {
- return true;
+#else
+
+/*! \brief Shared content of all specializations of hash map */
+class MapNode : public Object {
+ public:
+ /*! \brief Type of the keys in the hash map */
+ using key_type = ObjectRef;
+ /*! \brief Type of the values in the hash map */
+ using mapped_type = ObjectRef;
+ /*! \brief Type of value stored in the hash map */
+ using KVType = std::pair<ObjectRef, ObjectRef>;
+ /*! \brief Iterator class */
+ class iterator;
+
+ static_assert(std::is_standard_layout<KVType>::value, "KVType is not
standard layout");
+ static_assert(sizeof(KVType) == 16 || sizeof(KVType) == 8, "sizeof(KVType)
incorrect");
+
+ static constexpr const uint32_t _type_index =
runtime::TypeIndex::kRuntimeMap;
+ static constexpr const char* _type_key = "Map";
+ TVM_DECLARE_FINAL_OBJECT_INFO(MapNode, Object);
+
+ /*!
+ * \brief Number of elements in the SmallMapNode
+ * \return The result
+ */
+ size_t size() const { return size_; }
+ /*!
+ * \brief Count the number of times a key exists in the hash map
+ * \param key The indexing key
+ * \return The result, 0 or 1
+ */
+ size_t count(const key_type& key) const;
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The const reference to the value
+ */
+ const mapped_type& at(const key_type& key) const;
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The mutable reference to the value
+ */
+ mapped_type& at(const key_type& key);
+ /*! \return begin iterator */
+ iterator begin() const;
+ /*! \return end iterator */
+ iterator end() const;
+ /*!
+ * \brief Index value associated with a key
+ * \param key The indexing key
+ * \return The iterator of the entry associated with the key, end iterator
if not exists
+ */
+ iterator find(const key_type& key) const;
+ /*!
+ * \brief Erase the entry associated with the iterator
+ * \param position The iterator
+ */
+ void erase(const iterator& position);
+ /*!
+ * \brief Erase the entry associated with the key, do nothing if not exists
+ * \param key The indexing key
+ */
+ void erase(const key_type& key) { erase(find(key)); }
+
+ class iterator {
+ public:
+ using iterator_category = std::forward_iterator_tag;
+ using difference_type = int64_t;
+ using value_type = KVType;
+ using pointer = KVType*;
+ using reference = KVType&;
+ /*! \brief Default constructor */
+ iterator() : i(0), self(nullptr) {}
+ /*! \brief Compare iterators */
+ bool operator==(const iterator& other) const { return i == other.i && self
== other.self; }
+ /*! \brief Compare iterators */
+ bool operator!=(const iterator& other) const { return !(*this == other); }
+ /*! \brief De-reference iterators */
+ pointer operator->() const;
+ /*! \brief De-reference iterators */
+ reference operator*() const { return *((*this).operator->()); }
+ /*! \brief Prefix self increment, e.g. ++iter */
+ iterator& operator++();
+ /*! \brief Prefix self decrement, e.g. --iter */
+ iterator& operator--();
+ /*! \brief Suffix self increment */
+ iterator operator++(int) {
+ iterator copy = *this;
+ ++(*this);
+ return copy;
}
- if (const auto* str_a = a.as<StringObj>()) {
- if (const auto* str_b = b.as<StringObj>()) {
- return String::memncmp(str_a->data, str_b->data, str_a->size,
str_b->size) == 0;
+ /*! \brief Suffix self decrement */
+ iterator operator--(int) {
+ iterator copy = *this;
+ --(*this);
+ return copy;
+ }
+
+ protected:
+ /*! \brief Construct by value */
+ iterator(uint64_t i, const MapNode* self) : i(i), self(self) {}
+ /*! \brief The position on the array */
+ uint64_t i;
+ /*! \brief The container it points to */
+ const MapNode* self;
+
+ friend class DenseMapNode;
+ friend class SmallMapNode;
+ };
+
+ protected:
+ /*!
+ * \brief Create an empty container
+ * \return The object created
+ */
+ static ObjectPtr<MapNode> Empty();
+ /*!
+ * \brief Create the map using contents from the given iterators.
+ * \param first Begin of iterator
+ * \param last End of iterator
+ * \tparam IterType The type of iterator
+ * \return ObjectPtr to the map created
+ */
+ template <typename IterType>
+ static ObjectPtr<Object> CreateFromRange(IterType first, IterType last);
+ /*!
+ * \brief InsertMaybeReHash an entry into the given hash map
+ * \param kv The entry to be inserted
+ * \param map The pointer to the map, can be changed if re-hashing happens
+ */
+ static void InsertMaybeReHash(const KVType& kv, ObjectPtr<Object>* map);
+ /*!
+ * \brief Create an empty container with elements copying from another
SmallMapNode
+ * \param m The source container
+ * \return The object created
+ */
+ static ObjectPtr<MapNode> CopyFrom(MapNode* m);
+ /*! \brief number of slots minus 1 */
+ uint64_t slots_;
+ /*! \brief number of entries in the container */
+ uint64_t size_;
+ // Reference class
+ template <typename, typename, typename, typename>
+ friend class Map;
+};
+
+/*! \brief A specialization of small-sized hash map */
+class SmallMapNode : public MapNode,
+ public runtime::InplaceArrayBase<SmallMapNode,
MapNode::KVType> {
+ private:
+ static constexpr uint64_t kInitSize = 2;
+ static constexpr uint64_t kMaxSize = 4;
+
+ public:
+ using MapNode::iterator;
+ using MapNode::KVType;
+
+ /*! \brief Defaults to the destructor of InplaceArrayBase */
+ ~SmallMapNode() = default;
+ /*!
+ * \brief Count the number of times a key exists in the SmallMapNode
+ * \param key The indexing key
+ * \return The result, 0 or 1
+ */
+ size_t count(const key_type& key) const { return find(key).i < size_; }
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The const reference to the value
+ */
+ const mapped_type& at(const key_type& key) const {
+ iterator itr = find(key);
+ CHECK(itr.i < size_) << "IndexError: key is not in Map";
+ return itr->second;
+ }
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The mutable reference to the value
+ */
+ mapped_type& at(const key_type& key) {
+ iterator itr = find(key);
+ CHECK(itr.i < size_) << "IndexError: key is not in Map";
+ return itr->second;
+ }
+ /*! \return begin iterator */
+ iterator begin() const { return iterator(0, this); }
+ /*! \return end iterator */
+ iterator end() const { return iterator(size_, this); }
+ /*!
+ * \brief Index value associated with a key
+ * \param key The indexing key
+ * \return The iterator of the entry associated with the key, end iterator
if not exists
+ */
+ iterator find(const key_type& key) const {
+ KVType* ptr = static_cast<KVType*>(AddressOf(0));
+ for (uint64_t i = 0; i < size_; ++i, ++ptr) {
+ if (ObjectEqual()(ptr->first, key)) {
+ return iterator(i, this);
}
}
- return false;
+ return iterator(size_, this);
+ }
+ /*!
+ * \brief Erase the entry associated with the iterator
+ * \param position The iterator
+ */
+ void erase(const iterator& position) { Erase(position.i); }
+
+ private:
+ /*!
+ * \brief Remove a position in SmallMapNode
+ * \param i The position to be removed
+ */
+ void Erase(const uint64_t i) {
+ if (i >= size_) {
+ return;
+ }
+ KVType* begin = static_cast<KVType*>(AddressOf(0));
+ KVType* last = begin + (size_ - 1);
+ if (i + 1 == size_) {
+ last->first.ObjectRef::~ObjectRef();
+ last->second.ObjectRef::~ObjectRef();
+ } else {
+ *(begin + i) = std::move(*last);
+ }
+ size_ -= 1;
+ }
+ /*!
+ * \brief Create an empty container
+ * \param n Number of empty slots
+ * \return The object created
+ */
+ static ObjectPtr<SmallMapNode> Empty(uint64_t n = kInitSize) {
+ using ::tvm::runtime::make_inplace_array_object;
+ ObjectPtr<SmallMapNode> p = make_inplace_array_object<SmallMapNode,
KVType>(n);
+ p->size_ = 0;
+ p->slots_ = n;
+ return p;
+ }
+ /*!
+ * \brief Create an empty container initialized with a given range
+ * \param n Number of empty slots
+ * \param first begin of iterator
+ * \param last end of iterator
+ * \tparam IterType The type of iterator
+ * \return The object created
+ */
+ template <typename IterType>
+ static ObjectPtr<SmallMapNode> CreateFromRange(uint64_t n, IterType first,
IterType last) {
+ ObjectPtr<SmallMapNode> p = Empty(n);
+ KVType* ptr = static_cast<KVType*>(p->AddressOf(0));
+ for (; first != last; ++first, ++p->size_) {
+ new (ptr++) KVType(*first);
+ }
+ return p;
+ }
+ /*!
+ * \brief Create an empty container with elements copying from another
SmallMapNode
+ * \param m The source container
+ * \return The object created
+ */
+ static ObjectPtr<SmallMapNode> CopyFrom(SmallMapNode* m) {
+ KVType* first = static_cast<KVType*>(m->AddressOf(0));
+ KVType* last = first + m->size_;
+ return CreateFromRange(m->size_, first, last);
+ }
+ /*!
+ * \brief InsertMaybeReHash an entry into the given hash map
+ * \param kv The entry to be inserted
+ * \param map The pointer to the map, can be changed if re-hashing happens
+ */
+ static void InsertMaybeReHash(const KVType& kv, ObjectPtr<Object>* map) {
+ SmallMapNode* m = static_cast<SmallMapNode*>(map->get());
+ iterator itr = m->find(kv.first);
+ if (itr.i < m->size_) {
+ itr->second = kv.second;
+ return;
+ }
+ if (m->size_ < m->slots_) {
+ KVType* ptr = static_cast<KVType*>(m->AddressOf(m->size_));
+ new (ptr) KVType(kv);
+ ++m->size_;
+ return;
+ }
+ uint64_t next_size = std::max(m->slots_ * 2, uint64_t(kInitSize));
+ next_size = std::min(next_size, uint64_t(kMaxSize));
+ CHECK_GT(next_size, m->slots_);
+ ObjectPtr<Object> n = CreateFromRange(next_size, m->begin(), m->end());
+ InsertMaybeReHash(kv, &n);
+ *map = std::move(n);
}
+ /*!
+ * \brief Increment the pointer
+ * \param i The pointer to be incremented
+ * \return The increased pointer
+ */
+ uint64_t IncItr(uint64_t i) const { return i + 1 < size_ ? i + 1 : size_; }
+ /*!
+ * \brief Decrement the pointer
+ * \param i The pointer to be decremented
+ * \return The decreased pointer
+ */
+ uint64_t DecItr(uint64_t i) const { return i > 0 ? i - 1 : size_; }
+ /*!
+ * \brief De-reference the pointer
+ * \param i The pointer to be dereferenced
+ * \return The result
+ */
+ KVType* DeRefItr(uint64_t i) const { return
static_cast<KVType*>(AddressOf(i)); }
+ /*! \brief A size function used by InplaceArrayBase */
+ uint64_t GetSize() const { return size_; }
+
+ protected:
+ friend class MapNode;
+ friend class DenseMapNode;
+ friend ObjectPtr<MapNode> runtime::make_object<>();
+ friend class runtime::InplaceArrayBase<SmallMapNode, MapNode::KVType>;
};
-/*! \brief map node content */
-class MapNode : public Object {
+/*! \brief A specialization of hash map that implements the idea of
array-based hash map.
+ * Another reference implementation can be found [1].
+ *
+ * A. Overview
+ *
+ * DenseMapNode did several improvements over traditional separate chaining
hash,
+ * in terms of cache locality, memory footprints and data organization.
+ *
+ * A1. Implicit linked list. For better cache locality, instead of using
linked list
+ * explicitly for each bucket, we store list data into a single array that
spans contiguously
+ * in memory, and then carefully design access patterns to make sure most of
them fall into
+ * a single cache line.
+ *
+ * A2. 1-byte metadata. There is only 1 byte overhead for each slot in the
array to indexing and
+ * traversal. This can be divided in 3 parts.
+ * 1) Reserved code: (0b11111111)_2 indicates a slot is empty; (0b11111110)_2
indicates protected,
+ * which means the slot is empty but not allowed to be written.
+ * 2) If not empty or protected, the highest bit is used to indicate whether
data in the slot is
+ * head of a linked list.
+ * 3) The rest 7 bits are used as the "next pointer" (i.e. pointer to the next
element). On 64-bit
+ * architecture, an ordinary pointer can take up to 8 bytes, which is not
acceptable overhead when
+ * dealing with 16-byte ObjectRef pairs. Based on a commonly noticed fact that
the lists are
+ * relatively short (length <= 3) in hash maps, we follow [1]'s idea that only
allows the pointer to
+ * be one of the 126 possible values, i.e. if the next element of i-th slot is
(i + x)-th element,
+ * then x must be one of the 126 pre-defined values.
+ *
+ * A3. Data blocking. We organize the array in the way that every 16 elements
forms a data block.
+ * The 16-byte metadata of those 16 elements are stored together, followed by
the real data, i.e.
+ * 16 key-value pairs.
+ *
+ * B. Implementation details
+ *
+ * B1. Power-of-2 table size and Fibonacci Hashing. We use power-of-two as
table size to avoid
+ * modulo for more efficient arithmetics. To make the hash-to-slot mapping
distribute more evenly,
+ * we use the Fibonacci Hashing [2] trick.
+ *
+ * B2. Traverse a linked list in the array.
+ * 1) List head. Assume Fibonacci Hashing maps a given key to slot i, if
metadata at slot i
+ * indicates that it is list head, then we found the head; otherwise the list
is empty. No probing
+ * is done in this procedure. 2) Next element. To find the next element of a
non-empty slot i, we
+ * look at the last 7 bits of the metadata at slot i. If they are all zeros,
then it is the end of
+ * list; otherwise, we know that the next element is (i +
candidates[the-last-7-bits]).
+ *
+ * B3. InsertMaybeReHash an element. Following B2, we first traverse the
linked list to see if this
+ * element is in the linked list, and if not, we put it at the end by probing
the next empty
+ * position in one of the 126 candidate positions. If the linked list does not
even exist, but the
+ * slot for list head has been occupied by another linked list, we should find
this intruder another
+ * place.
+ *
+ * B4. Quadratic probing with triangle numbers. In open address hashing, it is
provable that probing
+ * with triangle numbers can traverse power-of-2-sized table [3]. In our
algorithm, we follow the
+ * suggestion in [1] that also use triangle numbers for "next pointer" as well
as sparing for list
+ * head.
+ *
+ * [1] https://github.com/skarupke/flat_hash_map
+ * [2] https://programmingpraxis.com/2018/06/19/fibonacci-hash/
+ * [3] https://fgiesen.wordpress.com/2015/02/22/triangular-numbers-mod-2n/
+ */
+class DenseMapNode : public MapNode {
+ private:
+ /*! \brief The number of elements in a memory block */
+ static constexpr int kBlockCap = 16;
+ /*! \brief Maximum load factor of the hash map */
+ static constexpr double kMaxLoadFactor = 0.99;
+ /*! \brief Binary representation of the metadata of an empty slot */
+ static constexpr uint8_t kEmptySlot = uint8_t(0b11111111);
+ /*! \brief Binary representation of the metadata of a protected slot */
+ static constexpr uint8_t kProtectedSlot = uint8_t(0b11111110);
+ /*! \brief Number of probing choices available */
+ static constexpr int kNumJumpDists = 126;
+ /*! \brief Head of the implicit linked list */
+ struct ListNode;
+ /*! \brief POD type of a block of memory */
+ struct Block {
+ uint8_t b[kBlockCap + kBlockCap * sizeof(KVType)];
+ };
+ static_assert(sizeof(Block) == kBlockCap * (sizeof(KVType) + 1),
"sizeof(Block) incorrect");
+ static_assert(std::is_standard_layout<Block>::value, "Block is not standard
layout");
+
public:
- /*! \brief The corresponding conatiner type */
- using ContainerType = std::unordered_map<ObjectRef, ObjectRef, ObjectHash,
ObjectEqual>;
+ using MapNode::iterator;
- /*! \brief the data content */
- ContainerType data;
+ /*!
+ * \brief Destroy the DenseMapNode
+ */
+ ~DenseMapNode() { this->Reset(); }
+ /*! \return The number of elements of the key */
+ size_t count(const key_type& key) const { return !Search(key).IsNone(); }
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The const reference to the value
+ */
+ const mapped_type& at(const key_type& key) const { return At(key); }
+ /*!
+ * \brief Index value associated with a key, throw exception if the key does
not exist
+ * \param key The indexing key
+ * \return The mutable reference to the value
+ */
+ mapped_type& at(const key_type& key) { return At(key); }
+ /*!
+ * \brief Index value associated with a key
+ * \param key The indexing key
+ * \return The iterator of the entry associated with the key, end iterator
if not exists
+ */
+ iterator find(const key_type& key) const {
+ ListNode n = Search(key);
+ return n.IsNone() ? end() : iterator(n.index, this);
+ }
+ /*!
+ * \brief Erase the entry associated with the iterator
+ * \param position The iterator
+ */
+ void erase(const iterator& position) {
+ uint64_t i = position.i;
+ if (position.self != nullptr && i <= this->slots_) {
+ Erase(ListNode(i, this));
+ }
+ }
+ /*! \return begin iterator */
+ iterator begin() const {
+ if (slots_ == 0) {
+ return iterator(0, this);
+ }
+ for (uint64_t i = 0; i <= slots_; ++i) {
+ if (!ListNode(i, this).IsEmpty()) {
+ return iterator(i, this);
+ }
+ }
+ return iterator(slots_ + 1, this);
+ }
+ /*! \return end iterator */
+ iterator end() const { return slots_ == 0 ? iterator(0, this) :
iterator(slots_ + 1, this); }
- static constexpr const char* _type_key = "Map";
- TVM_DECLARE_FINAL_OBJECT_INFO(MapNode, Object);
+ private:
+ /*!
+ * \brief Search for the given key
+ * \param key The key
+ * \return ListNode that associated with the key
+ */
+ ListNode Search(const key_type& key) const {
+ if (this->size_ == 0) {
+ return ListNode();
+ }
+ for (ListNode n = GetListHead(ObjectHash()(key)); !n.IsNone();
n.MoveToNext(this)) {
+ if (ObjectEqual()(key, n.Key())) {
+ return n;
+ }
+ }
+ return ListNode();
+ }
+ /*!
+ * \brief Search for the given key, throw exception if not exists
+ * \param key The key
+ * \return ListNode that associated with the key
+ */
+ mapped_type& At(const key_type& key) const {
+ ListNode n = Search(key);
+ CHECK(!n.IsNone()) << "IndexError: key is not in Map";
+ return n.Val();
+ }
+ /*!
+ * \brief Try to insert a key, or do nothing if already exists
+ * \param key The indexing key
+ * \param result The linked-list entry found or just constructed
+ * \return A boolean, indicating if actual insertion happens
+ */
+ bool TryInsert(const key_type& key, ListNode* result) {
+ if (slots_ == 0) {
+ return false;
+ }
+ // required that `m` to be the head of a linked list through which we can
iterator
+ ListNode m = IndexFromhash(ObjectHash()(key));
Review comment:
Using `iter` instead.
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