| // Copyright 2018 The Abseil Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // A btree implementation of the STL set and map interfaces. A btree is smaller |
| // and generally also faster than STL set/map (refer to the benchmarks below). |
| // The red-black tree implementation of STL set/map has an overhead of 3 |
| // pointers (left, right and parent) plus the node color information for each |
| // stored value. So a set<int32_t> consumes 40 bytes for each value stored in |
| // 64-bit mode. This btree implementation stores multiple values on fixed |
| // size nodes (usually 256 bytes) and doesn't store child pointers for leaf |
| // nodes. The result is that a btree_set<int32_t> may use much less memory per |
| // stored value. For the random insertion benchmark in btree_bench.cc, a |
| // btree_set<int32_t> with node-size of 256 uses 5.1 bytes per stored value. |
| // |
| // The packing of multiple values on to each node of a btree has another effect |
| // besides better space utilization: better cache locality due to fewer cache |
| // lines being accessed. Better cache locality translates into faster |
| // operations. |
| // |
| // CAVEATS |
| // |
| // Insertions and deletions on a btree can cause splitting, merging or |
| // rebalancing of btree nodes. And even without these operations, insertions |
| // and deletions on a btree will move values around within a node. In both |
| // cases, the result is that insertions and deletions can invalidate iterators |
| // pointing to values other than the one being inserted/deleted. Therefore, this |
| // container does not provide pointer stability. This is notably different from |
| // STL set/map which takes care to not invalidate iterators on insert/erase |
| // except, of course, for iterators pointing to the value being erased. A |
| // partial workaround when erasing is available: erase() returns an iterator |
| // pointing to the item just after the one that was erased (or end() if none |
| // exists). |
| |
| #ifndef ABSL_CONTAINER_INTERNAL_BTREE_H_ |
| #define ABSL_CONTAINER_INTERNAL_BTREE_H_ |
| |
| #include <algorithm> |
| #include <cassert> |
| #include <cstddef> |
| #include <cstdint> |
| #include <cstring> |
| #include <functional> |
| #include <iterator> |
| #include <limits> |
| #include <string> |
| #include <type_traits> |
| #include <utility> |
| |
| #include "absl/base/config.h" |
| #include "absl/base/internal/raw_logging.h" |
| #include "absl/base/macros.h" |
| #include "absl/container/internal/common.h" |
| #include "absl/container/internal/common_policy_traits.h" |
| #include "absl/container/internal/compressed_tuple.h" |
| #include "absl/container/internal/container_memory.h" |
| #include "absl/container/internal/layout.h" |
| #include "absl/memory/memory.h" |
| #include "absl/meta/type_traits.h" |
| #include "absl/strings/cord.h" |
| #include "absl/strings/string_view.h" |
| #include "absl/types/compare.h" |
| |
| namespace absl { |
| ABSL_NAMESPACE_BEGIN |
| namespace container_internal { |
| |
| #ifdef ABSL_BTREE_ENABLE_GENERATIONS |
| #error ABSL_BTREE_ENABLE_GENERATIONS cannot be directly set |
| #elif (defined(ABSL_HAVE_ADDRESS_SANITIZER) || \ |
| defined(ABSL_HAVE_HWADDRESS_SANITIZER) || \ |
| defined(ABSL_HAVE_MEMORY_SANITIZER)) && \ |
| !defined(NDEBUG_SANITIZER) // If defined, performance is important. |
| // When compiled in sanitizer mode, we add generation integers to the nodes and |
| // iterators. When iterators are used, we validate that the container has not |
| // been mutated since the iterator was constructed. |
| #define ABSL_BTREE_ENABLE_GENERATIONS |
| #endif |
| |
| #ifdef ABSL_BTREE_ENABLE_GENERATIONS |
| constexpr bool BtreeGenerationsEnabled() { return true; } |
| #else |
| constexpr bool BtreeGenerationsEnabled() { return false; } |
| #endif |
| |
| template <typename Compare, typename T, typename U> |
| using compare_result_t = absl::result_of_t<const Compare(const T &, const U &)>; |
| |
| // A helper class that indicates if the Compare parameter is a key-compare-to |
| // comparator. |
| template <typename Compare, typename T> |
| using btree_is_key_compare_to = |
| std::is_convertible<compare_result_t<Compare, T, T>, absl::weak_ordering>; |
| |
| struct StringBtreeDefaultLess { |
| using is_transparent = void; |
| |
| StringBtreeDefaultLess() = default; |
| |
| // Compatibility constructor. |
| StringBtreeDefaultLess(std::less<std::string>) {} // NOLINT |
| StringBtreeDefaultLess(std::less<absl::string_view>) {} // NOLINT |
| |
| // Allow converting to std::less for use in key_comp()/value_comp(). |
| explicit operator std::less<std::string>() const { return {}; } |
| explicit operator std::less<absl::string_view>() const { return {}; } |
| explicit operator std::less<absl::Cord>() const { return {}; } |
| |
| absl::weak_ordering operator()(absl::string_view lhs, |
| absl::string_view rhs) const { |
| return compare_internal::compare_result_as_ordering(lhs.compare(rhs)); |
| } |
| StringBtreeDefaultLess(std::less<absl::Cord>) {} // NOLINT |
| absl::weak_ordering operator()(const absl::Cord &lhs, |
| const absl::Cord &rhs) const { |
| return compare_internal::compare_result_as_ordering(lhs.Compare(rhs)); |
| } |
| absl::weak_ordering operator()(const absl::Cord &lhs, |
| absl::string_view rhs) const { |
| return compare_internal::compare_result_as_ordering(lhs.Compare(rhs)); |
| } |
| absl::weak_ordering operator()(absl::string_view lhs, |
| const absl::Cord &rhs) const { |
| return compare_internal::compare_result_as_ordering(-rhs.Compare(lhs)); |
| } |
| }; |
| |
| struct StringBtreeDefaultGreater { |
| using is_transparent = void; |
| |
| StringBtreeDefaultGreater() = default; |
| |
| StringBtreeDefaultGreater(std::greater<std::string>) {} // NOLINT |
| StringBtreeDefaultGreater(std::greater<absl::string_view>) {} // NOLINT |
| |
| // Allow converting to std::greater for use in key_comp()/value_comp(). |
| explicit operator std::greater<std::string>() const { return {}; } |
| explicit operator std::greater<absl::string_view>() const { return {}; } |
| explicit operator std::greater<absl::Cord>() const { return {}; } |
| |
| absl::weak_ordering operator()(absl::string_view lhs, |
| absl::string_view rhs) const { |
| return compare_internal::compare_result_as_ordering(rhs.compare(lhs)); |
| } |
| StringBtreeDefaultGreater(std::greater<absl::Cord>) {} // NOLINT |
| absl::weak_ordering operator()(const absl::Cord &lhs, |
| const absl::Cord &rhs) const { |
| return compare_internal::compare_result_as_ordering(rhs.Compare(lhs)); |
| } |
| absl::weak_ordering operator()(const absl::Cord &lhs, |
| absl::string_view rhs) const { |
| return compare_internal::compare_result_as_ordering(-lhs.Compare(rhs)); |
| } |
| absl::weak_ordering operator()(absl::string_view lhs, |
| const absl::Cord &rhs) const { |
| return compare_internal::compare_result_as_ordering(rhs.Compare(lhs)); |
| } |
| }; |
| |
| // See below comments for checked_compare. |
| template <typename Compare, bool is_class = std::is_class<Compare>::value> |
| struct checked_compare_base : Compare { |
| using Compare::Compare; |
| explicit checked_compare_base(Compare c) : Compare(std::move(c)) {} |
| const Compare &comp() const { return *this; } |
| }; |
| template <typename Compare> |
| struct checked_compare_base<Compare, false> { |
| explicit checked_compare_base(Compare c) : compare(std::move(c)) {} |
| const Compare &comp() const { return compare; } |
| Compare compare; |
| }; |
| |
| // A mechanism for opting out of checked_compare for use only in btree_test.cc. |
| struct BtreeTestOnlyCheckedCompareOptOutBase {}; |
| |
| // A helper class to adapt the specified comparator for two use cases: |
| // (1) When using common Abseil string types with common comparison functors, |
| // convert a boolean comparison into a three-way comparison that returns an |
| // `absl::weak_ordering`. This helper class is specialized for |
| // less<std::string>, greater<std::string>, less<string_view>, |
| // greater<string_view>, less<absl::Cord>, and greater<absl::Cord>. |
| // (2) Adapt the comparator to diagnose cases of non-strict-weak-ordering (see |
| // https://en.cppreference.com/w/cpp/named_req/Compare) in debug mode. Whenever |
| // a comparison is made, we will make assertions to verify that the comparator |
| // is valid. |
| template <typename Compare, typename Key> |
| struct key_compare_adapter { |
| // Inherit from checked_compare_base to support function pointers and also |
| // keep empty-base-optimization (EBO) support for classes. |
| // Note: we can't use CompressedTuple here because that would interfere |
| // with the EBO for `btree::rightmost_`. `btree::rightmost_` is itself a |
| // CompressedTuple and nested `CompressedTuple`s don't support EBO. |
| // TODO(b/214288561): use CompressedTuple instead once it supports EBO for |
| // nested `CompressedTuple`s. |
| struct checked_compare : checked_compare_base<Compare> { |
| private: |
| using Base = typename checked_compare::checked_compare_base; |
| using Base::comp; |
| |
| // If possible, returns whether `t` is equivalent to itself. We can only do |
| // this for `Key`s because we can't be sure that it's safe to call |
| // `comp()(k, k)` otherwise. Even if SFINAE allows it, there could be a |
| // compilation failure inside the implementation of the comparison operator. |
| bool is_self_equivalent(const Key &k) const { |
| // Note: this works for both boolean and three-way comparators. |
| return comp()(k, k) == 0; |
| } |
| // If we can't compare `t` with itself, returns true unconditionally. |
| template <typename T> |
| bool is_self_equivalent(const T &) const { |
| return true; |
| } |
| |
| public: |
| using Base::Base; |
| checked_compare(Compare comp) : Base(std::move(comp)) {} // NOLINT |
| |
| // Allow converting to Compare for use in key_comp()/value_comp(). |
| explicit operator Compare() const { return comp(); } |
| |
| template <typename T, typename U, |
| absl::enable_if_t< |
| std::is_same<bool, compare_result_t<Compare, T, U>>::value, |
| int> = 0> |
| bool operator()(const T &lhs, const U &rhs) const { |
| // NOTE: if any of these assertions fail, then the comparator does not |
| // establish a strict-weak-ordering (see |
| // https://en.cppreference.com/w/cpp/named_req/Compare). |
| assert(is_self_equivalent(lhs)); |
| assert(is_self_equivalent(rhs)); |
| const bool lhs_comp_rhs = comp()(lhs, rhs); |
| assert(!lhs_comp_rhs || !comp()(rhs, lhs)); |
| return lhs_comp_rhs; |
| } |
| |
| template < |
| typename T, typename U, |
| absl::enable_if_t<std::is_convertible<compare_result_t<Compare, T, U>, |
| absl::weak_ordering>::value, |
| int> = 0> |
| absl::weak_ordering operator()(const T &lhs, const U &rhs) const { |
| // NOTE: if any of these assertions fail, then the comparator does not |
| // establish a strict-weak-ordering (see |
| // https://en.cppreference.com/w/cpp/named_req/Compare). |
| assert(is_self_equivalent(lhs)); |
| assert(is_self_equivalent(rhs)); |
| const absl::weak_ordering lhs_comp_rhs = comp()(lhs, rhs); |
| #ifndef NDEBUG |
| const absl::weak_ordering rhs_comp_lhs = comp()(rhs, lhs); |
| if (lhs_comp_rhs > 0) { |
| assert(rhs_comp_lhs < 0 && "lhs_comp_rhs > 0 -> rhs_comp_lhs < 0"); |
| } else if (lhs_comp_rhs == 0) { |
| assert(rhs_comp_lhs == 0 && "lhs_comp_rhs == 0 -> rhs_comp_lhs == 0"); |
| } else { |
| assert(rhs_comp_lhs > 0 && "lhs_comp_rhs < 0 -> rhs_comp_lhs > 0"); |
| } |
| #endif |
| return lhs_comp_rhs; |
| } |
| }; |
| using type = absl::conditional_t< |
| std::is_base_of<BtreeTestOnlyCheckedCompareOptOutBase, Compare>::value, |
| Compare, checked_compare>; |
| }; |
| |
| template <> |
| struct key_compare_adapter<std::less<std::string>, std::string> { |
| using type = StringBtreeDefaultLess; |
| }; |
| |
| template <> |
| struct key_compare_adapter<std::greater<std::string>, std::string> { |
| using type = StringBtreeDefaultGreater; |
| }; |
| |
| template <> |
| struct key_compare_adapter<std::less<absl::string_view>, absl::string_view> { |
| using type = StringBtreeDefaultLess; |
| }; |
| |
| template <> |
| struct key_compare_adapter<std::greater<absl::string_view>, absl::string_view> { |
| using type = StringBtreeDefaultGreater; |
| }; |
| |
| template <> |
| struct key_compare_adapter<std::less<absl::Cord>, absl::Cord> { |
| using type = StringBtreeDefaultLess; |
| }; |
| |
| template <> |
| struct key_compare_adapter<std::greater<absl::Cord>, absl::Cord> { |
| using type = StringBtreeDefaultGreater; |
| }; |
| |
| // Detects an 'absl_btree_prefer_linear_node_search' member. This is |
| // a protocol used as an opt-in or opt-out of linear search. |
| // |
| // For example, this would be useful for key types that wrap an integer |
| // and define their own cheap operator<(). For example: |
| // |
| // class K { |
| // public: |
| // using absl_btree_prefer_linear_node_search = std::true_type; |
| // ... |
| // private: |
| // friend bool operator<(K a, K b) { return a.k_ < b.k_; } |
| // int k_; |
| // }; |
| // |
| // btree_map<K, V> m; // Uses linear search |
| // |
| // If T has the preference tag, then it has a preference. |
| // Btree will use the tag's truth value. |
| template <typename T, typename = void> |
| struct has_linear_node_search_preference : std::false_type {}; |
| template <typename T, typename = void> |
| struct prefers_linear_node_search : std::false_type {}; |
| template <typename T> |
| struct has_linear_node_search_preference< |
| T, absl::void_t<typename T::absl_btree_prefer_linear_node_search>> |
| : std::true_type {}; |
| template <typename T> |
| struct prefers_linear_node_search< |
| T, absl::void_t<typename T::absl_btree_prefer_linear_node_search>> |
| : T::absl_btree_prefer_linear_node_search {}; |
| |
| template <typename Compare, typename Key> |
| constexpr bool compare_has_valid_result_type() { |
| using compare_result_type = compare_result_t<Compare, Key, Key>; |
| return std::is_same<compare_result_type, bool>::value || |
| std::is_convertible<compare_result_type, absl::weak_ordering>::value; |
| } |
| |
| template <typename original_key_compare, typename value_type> |
| class map_value_compare { |
| template <typename Params> |
| friend class btree; |
| |
| // Note: this `protected` is part of the API of std::map::value_compare. See |
| // https://en.cppreference.com/w/cpp/container/map/value_compare. |
| protected: |
| explicit map_value_compare(original_key_compare c) : comp(std::move(c)) {} |
| |
| original_key_compare comp; // NOLINT |
| |
| public: |
| auto operator()(const value_type &lhs, const value_type &rhs) const |
| -> decltype(comp(lhs.first, rhs.first)) { |
| return comp(lhs.first, rhs.first); |
| } |
| }; |
| |
| template <typename Key, typename Compare, typename Alloc, int TargetNodeSize, |
| bool IsMulti, bool IsMap, typename SlotPolicy> |
| struct common_params : common_policy_traits<SlotPolicy> { |
| using original_key_compare = Compare; |
| |
| // If Compare is a common comparator for a string-like type, then we adapt it |
| // to use heterogeneous lookup and to be a key-compare-to comparator. |
| // We also adapt the comparator to diagnose invalid comparators in debug mode. |
| // We disable this when `Compare` is invalid in a way that will cause |
| // adaptation to fail (having invalid return type) so that we can give a |
| // better compilation failure in static_assert_validation. If we don't do |
| // this, then there will be cascading compilation failures that are confusing |
| // for users. |
| using key_compare = |
| absl::conditional_t<!compare_has_valid_result_type<Compare, Key>(), |
| Compare, |
| typename key_compare_adapter<Compare, Key>::type>; |
| |
| static constexpr bool kIsKeyCompareStringAdapted = |
| std::is_same<key_compare, StringBtreeDefaultLess>::value || |
| std::is_same<key_compare, StringBtreeDefaultGreater>::value; |
| static constexpr bool kIsKeyCompareTransparent = |
| IsTransparent<original_key_compare>::value || kIsKeyCompareStringAdapted; |
| |
| // A type which indicates if we have a key-compare-to functor or a plain old |
| // key-compare functor. |
| using is_key_compare_to = btree_is_key_compare_to<key_compare, Key>; |
| |
| using allocator_type = Alloc; |
| using key_type = Key; |
| using size_type = size_t; |
| using difference_type = ptrdiff_t; |
| |
| using slot_policy = SlotPolicy; |
| using slot_type = typename slot_policy::slot_type; |
| using value_type = typename slot_policy::value_type; |
| using init_type = typename slot_policy::mutable_value_type; |
| using pointer = value_type *; |
| using const_pointer = const value_type *; |
| using reference = value_type &; |
| using const_reference = const value_type &; |
| |
| using value_compare = |
| absl::conditional_t<IsMap, |
| map_value_compare<original_key_compare, value_type>, |
| original_key_compare>; |
| using is_map_container = std::integral_constant<bool, IsMap>; |
| |
| // For the given lookup key type, returns whether we can have multiple |
| // equivalent keys in the btree. If this is a multi-container, then we can. |
| // Otherwise, we can have multiple equivalent keys only if all of the |
| // following conditions are met: |
| // - The comparator is transparent. |
| // - The lookup key type is not the same as key_type. |
| // - The comparator is not a StringBtreeDefault{Less,Greater} comparator |
| // that we know has the same equivalence classes for all lookup types. |
| template <typename LookupKey> |
| constexpr static bool can_have_multiple_equivalent_keys() { |
| return IsMulti || (IsTransparent<key_compare>::value && |
| !std::is_same<LookupKey, Key>::value && |
| !kIsKeyCompareStringAdapted); |
| } |
| |
| enum { |
| kTargetNodeSize = TargetNodeSize, |
| |
| // Upper bound for the available space for slots. This is largest for leaf |
| // nodes, which have overhead of at least a pointer + 4 bytes (for storing |
| // 3 field_types and an enum). |
| kNodeSlotSpace = TargetNodeSize - /*minimum overhead=*/(sizeof(void *) + 4), |
| }; |
| |
| // This is an integral type large enough to hold as many slots as will fit a |
| // node of TargetNodeSize bytes. |
| using node_count_type = |
| absl::conditional_t<(kNodeSlotSpace / sizeof(slot_type) > |
| (std::numeric_limits<uint8_t>::max)()), |
| uint16_t, uint8_t>; // NOLINT |
| }; |
| |
| // An adapter class that converts a lower-bound compare into an upper-bound |
| // compare. Note: there is no need to make a version of this adapter specialized |
| // for key-compare-to functors because the upper-bound (the first value greater |
| // than the input) is never an exact match. |
| template <typename Compare> |
| struct upper_bound_adapter { |
| explicit upper_bound_adapter(const Compare &c) : comp(c) {} |
| template <typename K1, typename K2> |
| bool operator()(const K1 &a, const K2 &b) const { |
| // Returns true when a is not greater than b. |
| return !compare_internal::compare_result_as_less_than(comp(b, a)); |
| } |
| |
| private: |
| Compare comp; |
| }; |
| |
| enum class MatchKind : uint8_t { kEq, kNe }; |
| |
| template <typename V, bool IsCompareTo> |
| struct SearchResult { |
| V value; |
| MatchKind match; |
| |
| static constexpr bool HasMatch() { return true; } |
| bool IsEq() const { return match == MatchKind::kEq; } |
| }; |
| |
| // When we don't use CompareTo, `match` is not present. |
| // This ensures that callers can't use it accidentally when it provides no |
| // useful information. |
| template <typename V> |
| struct SearchResult<V, false> { |
| SearchResult() = default; |
| explicit SearchResult(V v) : value(v) {} |
| SearchResult(V v, MatchKind /*match*/) : value(v) {} |
| |
| V value; |
| |
| static constexpr bool HasMatch() { return false; } |
| static constexpr bool IsEq() { return false; } |
| }; |
| |
| // A node in the btree holding. The same node type is used for both internal |
| // and leaf nodes in the btree, though the nodes are allocated in such a way |
| // that the children array is only valid in internal nodes. |
| template <typename Params> |
| class btree_node { |
| using is_key_compare_to = typename Params::is_key_compare_to; |
| using field_type = typename Params::node_count_type; |
| using allocator_type = typename Params::allocator_type; |
| using slot_type = typename Params::slot_type; |
| using original_key_compare = typename Params::original_key_compare; |
| |
| public: |
| using params_type = Params; |
| using key_type = typename Params::key_type; |
| using value_type = typename Params::value_type; |
| using pointer = typename Params::pointer; |
| using const_pointer = typename Params::const_pointer; |
| using reference = typename Params::reference; |
| using const_reference = typename Params::const_reference; |
| using key_compare = typename Params::key_compare; |
| using size_type = typename Params::size_type; |
| using difference_type = typename Params::difference_type; |
| |
| // Btree decides whether to use linear node search as follows: |
| // - If the comparator expresses a preference, use that. |
| // - If the key expresses a preference, use that. |
| // - If the key is arithmetic and the comparator is std::less or |
| // std::greater, choose linear. |
| // - Otherwise, choose binary. |
| // TODO(ezb): Might make sense to add condition(s) based on node-size. |
| using use_linear_search = std::integral_constant< |
| bool, has_linear_node_search_preference<original_key_compare>::value |
| ? prefers_linear_node_search<original_key_compare>::value |
| : has_linear_node_search_preference<key_type>::value |
| ? prefers_linear_node_search<key_type>::value |
| : std::is_arithmetic<key_type>::value && |
| (std::is_same<std::less<key_type>, |
| original_key_compare>::value || |
| std::is_same<std::greater<key_type>, |
| original_key_compare>::value)>; |
| |
| // This class is organized by absl::container_internal::Layout as if it had |
| // the following structure: |
| // // A pointer to the node's parent. |
| // btree_node *parent; |
| // |
| // // When ABSL_BTREE_ENABLE_GENERATIONS is defined, we also have a |
| // // generation integer in order to check that when iterators are |
| // // used, they haven't been invalidated already. Only the generation on |
| // // the root is used, but we have one on each node because whether a node |
| // // is root or not can change. |
| // uint32_t generation; |
| // |
| // // The position of the node in the node's parent. |
| // field_type position; |
| // // The index of the first populated value in `values`. |
| // // TODO(ezb): right now, `start` is always 0. Update insertion/merge |
| // // logic to allow for floating storage within nodes. |
| // field_type start; |
| // // The index after the last populated value in `values`. Currently, this |
| // // is the same as the count of values. |
| // field_type finish; |
| // // The maximum number of values the node can hold. This is an integer in |
| // // [1, kNodeSlots] for root leaf nodes, kNodeSlots for non-root leaf |
| // // nodes, and kInternalNodeMaxCount (as a sentinel value) for internal |
| // // nodes (even though there are still kNodeSlots values in the node). |
| // // TODO(ezb): make max_count use only 4 bits and record log2(capacity) |
| // // to free extra bits for is_root, etc. |
| // field_type max_count; |
| // |
| // // The array of values. The capacity is `max_count` for leaf nodes and |
| // // kNodeSlots for internal nodes. Only the values in |
| // // [start, finish) have been initialized and are valid. |
| // slot_type values[max_count]; |
| // |
| // // The array of child pointers. The keys in children[i] are all less |
| // // than key(i). The keys in children[i + 1] are all greater than key(i). |
| // // There are 0 children for leaf nodes and kNodeSlots + 1 children for |
| // // internal nodes. |
| // btree_node *children[kNodeSlots + 1]; |
| // |
| // This class is only constructed by EmptyNodeType. Normally, pointers to the |
| // layout above are allocated, cast to btree_node*, and de-allocated within |
| // the btree implementation. |
| ~btree_node() = default; |
| btree_node(btree_node const &) = delete; |
| btree_node &operator=(btree_node const &) = delete; |
| |
| protected: |
| btree_node() = default; |
| |
| private: |
| using layout_type = |
| absl::container_internal::Layout<btree_node *, uint32_t, field_type, |
| slot_type, btree_node *>; |
| using leaf_layout_type = typename layout_type::template WithStaticSizes< |
| /*parent*/ 1, |
| /*generation*/ BtreeGenerationsEnabled() ? 1 : 0, |
| /*position, start, finish, max_count*/ 4>; |
| constexpr static size_type SizeWithNSlots(size_type n) { |
| return leaf_layout_type(/*slots*/ n, /*children*/ 0).AllocSize(); |
| } |
| // A lower bound for the overhead of fields other than slots in a leaf node. |
| constexpr static size_type MinimumOverhead() { |
| return SizeWithNSlots(1) - sizeof(slot_type); |
| } |
| |
| // Compute how many values we can fit onto a leaf node taking into account |
| // padding. |
| constexpr static size_type NodeTargetSlots(const size_type begin, |
| const size_type end) { |
| return begin == end ? begin |
| : SizeWithNSlots((begin + end) / 2 + 1) > |
| params_type::kTargetNodeSize |
| ? NodeTargetSlots(begin, (begin + end) / 2) |
| : NodeTargetSlots((begin + end) / 2 + 1, end); |
| } |
| |
| constexpr static size_type kTargetNodeSize = params_type::kTargetNodeSize; |
| constexpr static size_type kNodeTargetSlots = |
| NodeTargetSlots(0, kTargetNodeSize); |
| |
| // We need a minimum of 3 slots per internal node in order to perform |
| // splitting (1 value for the two nodes involved in the split and 1 value |
| // propagated to the parent as the delimiter for the split). For performance |
| // reasons, we don't allow 3 slots-per-node due to bad worst case occupancy of |
| // 1/3 (for a node, not a b-tree). |
| constexpr static size_type kMinNodeSlots = 4; |
| |
| constexpr static size_type kNodeSlots = |
| kNodeTargetSlots >= kMinNodeSlots ? kNodeTargetSlots : kMinNodeSlots; |
| |
| using internal_layout_type = typename layout_type::template WithStaticSizes< |
| /*parent*/ 1, |
| /*generation*/ BtreeGenerationsEnabled() ? 1 : 0, |
| /*position, start, finish, max_count*/ 4, /*slots*/ kNodeSlots, |
| /*children*/ kNodeSlots + 1>; |
| |
| // The node is internal (i.e. is not a leaf node) if and only if `max_count` |
| // has this value. |
| constexpr static field_type kInternalNodeMaxCount = 0; |
| |
| // Leaves can have less than kNodeSlots values. |
| constexpr static leaf_layout_type LeafLayout( |
| const size_type slot_count = kNodeSlots) { |
| return leaf_layout_type(slot_count, 0); |
| } |
| constexpr static auto InternalLayout() { return internal_layout_type(); } |
| constexpr static size_type LeafSize(const size_type slot_count = kNodeSlots) { |
| return LeafLayout(slot_count).AllocSize(); |
| } |
| constexpr static size_type InternalSize() { |
| return InternalLayout().AllocSize(); |
| } |
| |
| constexpr static size_type Alignment() { |
| static_assert(LeafLayout(1).Alignment() == InternalLayout().Alignment(), |
| "Alignment of all nodes must be equal."); |
| return InternalLayout().Alignment(); |
| } |
| |
| // N is the index of the type in the Layout definition. |
| // ElementType<N> is the Nth type in the Layout definition. |
| template <size_type N> |
| inline typename layout_type::template ElementType<N> *GetField() { |
| // We assert that we don't read from values that aren't there. |
| assert(N < 4 || is_internal()); |
| return InternalLayout().template Pointer<N>(reinterpret_cast<char *>(this)); |
| } |
| template <size_type N> |
| inline const typename layout_type::template ElementType<N> *GetField() const { |
| assert(N < 4 || is_internal()); |
| return InternalLayout().template Pointer<N>( |
| reinterpret_cast<const char *>(this)); |
| } |
| void set_parent(btree_node *p) { *GetField<0>() = p; } |
| field_type &mutable_finish() { return GetField<2>()[2]; } |
| slot_type *slot(size_type i) { return &GetField<3>()[i]; } |
| slot_type *start_slot() { return slot(start()); } |
| slot_type *finish_slot() { return slot(finish()); } |
| const slot_type *slot(size_type i) const { return &GetField<3>()[i]; } |
| void set_position(field_type v) { GetField<2>()[0] = v; } |
| void set_start(field_type v) { GetField<2>()[1] = v; } |
| void set_finish(field_type v) { GetField<2>()[2] = v; } |
| // This method is only called by the node init methods. |
| void set_max_count(field_type v) { GetField<2>()[3] = v; } |
| |
| public: |
| // Whether this is a leaf node or not. This value doesn't change after the |
| // node is created. |
| bool is_leaf() const { return GetField<2>()[3] != kInternalNodeMaxCount; } |
| // Whether this is an internal node or not. This value doesn't change after |
| // the node is created. |
| bool is_internal() const { return !is_leaf(); } |
| |
| // Getter for the position of this node in its parent. |
| field_type position() const { return GetField<2>()[0]; } |
| |
| // Getter for the offset of the first value in the `values` array. |
| field_type start() const { |
| // TODO(ezb): when floating storage is implemented, return GetField<2>()[1]; |
| assert(GetField<2>()[1] == 0); |
| return 0; |
| } |
| |
| // Getter for the offset after the last value in the `values` array. |
| field_type finish() const { return GetField<2>()[2]; } |
| |
| // Getters for the number of values stored in this node. |
| field_type count() const { |
| assert(finish() >= start()); |
| return finish() - start(); |
| } |
| field_type max_count() const { |
| // Internal nodes have max_count==kInternalNodeMaxCount. |
| // Leaf nodes have max_count in [1, kNodeSlots]. |
| const field_type max_count = GetField<2>()[3]; |
| return max_count == field_type{kInternalNodeMaxCount} |
| ? field_type{kNodeSlots} |
| : max_count; |
| } |
| |
| // Getter for the parent of this node. |
| btree_node *parent() const { return *GetField<0>(); } |
| // Getter for whether the node is the root of the tree. The parent of the |
| // root of the tree is the leftmost node in the tree which is guaranteed to |
| // be a leaf. |
| bool is_root() const { return parent()->is_leaf(); } |
| void make_root() { |
| assert(parent()->is_root()); |
| set_generation(parent()->generation()); |
| set_parent(parent()->parent()); |
| } |
| |
| // Gets the root node's generation integer, which is the one used by the tree. |
| uint32_t *get_root_generation() const { |
| assert(BtreeGenerationsEnabled()); |
| const btree_node *curr = this; |
| for (; !curr->is_root(); curr = curr->parent()) continue; |
| return const_cast<uint32_t *>(&curr->GetField<1>()[0]); |
| } |
| |
| // Returns the generation for iterator validation. |
| uint32_t generation() const { |
| return BtreeGenerationsEnabled() ? *get_root_generation() : 0; |
| } |
| // Updates generation. Should only be called on a root node or during node |
| // initialization. |
| void set_generation(uint32_t generation) { |
| if (BtreeGenerationsEnabled()) GetField<1>()[0] = generation; |
| } |
| // Updates the generation. We do this whenever the node is mutated. |
| void next_generation() { |
| if (BtreeGenerationsEnabled()) ++*get_root_generation(); |
| } |
| |
| // Getters for the key/value at position i in the node. |
| const key_type &key(size_type i) const { return params_type::key(slot(i)); } |
| reference value(size_type i) { return params_type::element(slot(i)); } |
| const_reference value(size_type i) const { |
| return params_type::element(slot(i)); |
| } |
| |
| // Getters/setter for the child at position i in the node. |
| btree_node *child(field_type i) const { return GetField<4>()[i]; } |
| btree_node *start_child() const { return child(start()); } |
| btree_node *&mutable_child(field_type i) { return GetField<4>()[i]; } |
| void clear_child(field_type i) { |
| absl::container_internal::SanitizerPoisonObject(&mutable_child(i)); |
| } |
| void set_child_noupdate_position(field_type i, btree_node *c) { |
| absl::container_internal::SanitizerUnpoisonObject(&mutable_child(i)); |
| mutable_child(i) = c; |
| } |
| void set_child(field_type i, btree_node *c) { |
| set_child_noupdate_position(i, c); |
| c->set_position(i); |
| } |
| void init_child(field_type i, btree_node *c) { |
| set_child(i, c); |
| c->set_parent(this); |
| } |
| |
| // Returns the position of the first value whose key is not less than k. |
| template <typename K> |
| SearchResult<size_type, is_key_compare_to::value> lower_bound( |
| const K &k, const key_compare &comp) const { |
| return use_linear_search::value ? linear_search(k, comp) |
| : binary_search(k, comp); |
| } |
| // Returns the position of the first value whose key is greater than k. |
| template <typename K> |
| size_type upper_bound(const K &k, const key_compare &comp) const { |
| auto upper_compare = upper_bound_adapter<key_compare>(comp); |
| return use_linear_search::value ? linear_search(k, upper_compare).value |
| : binary_search(k, upper_compare).value; |
| } |
| |
| template <typename K, typename Compare> |
| SearchResult<size_type, btree_is_key_compare_to<Compare, key_type>::value> |
| linear_search(const K &k, const Compare &comp) const { |
| return linear_search_impl(k, start(), finish(), comp, |
| btree_is_key_compare_to<Compare, key_type>()); |
| } |
| |
| template <typename K, typename Compare> |
| SearchResult<size_type, btree_is_key_compare_to<Compare, key_type>::value> |
| binary_search(const K &k, const Compare &comp) const { |
| return binary_search_impl(k, start(), finish(), comp, |
| btree_is_key_compare_to<Compare, key_type>()); |
| } |
| |
| // Returns the position of the first value whose key is not less than k using |
| // linear search performed using plain compare. |
| template <typename K, typename Compare> |
| SearchResult<size_type, false> linear_search_impl( |
| const K &k, size_type s, const size_type e, const Compare &comp, |
| std::false_type /* IsCompareTo */) const { |
| while (s < e) { |
| if (!comp(key(s), k)) { |
| break; |
| } |
| ++s; |
| } |
| return SearchResult<size_type, false>{s}; |
| } |
| |
| // Returns the position of the first value whose key is not less than k using |
| // linear search performed using compare-to. |
| template <typename K, typename Compare> |
| SearchResult<size_type, true> linear_search_impl( |
| const K &k, size_type s, const size_type e, const Compare &comp, |
| std::true_type /* IsCompareTo */) const { |
| while (s < e) { |
| const absl::weak_ordering c = comp(key(s), k); |
| if (c == 0) { |
| return {s, MatchKind::kEq}; |
| } else if (c > 0) { |
| break; |
| } |
| ++s; |
| } |
| return {s, MatchKind::kNe}; |
| } |
| |
| // Returns the position of the first value whose key is not less than k using |
| // binary search performed using plain compare. |
| template <typename K, typename Compare> |
| SearchResult<size_type, false> binary_search_impl( |
| const K &k, size_type s, size_type e, const Compare &comp, |
| std::false_type /* IsCompareTo */) const { |
| while (s != e) { |
| const size_type mid = (s + e) >> 1; |
| if (comp(key(mid), k)) { |
| s = mid + 1; |
| } else { |
| e = mid; |
| } |
| } |
| return SearchResult<size_type, false>{s}; |
| } |
| |
| // Returns the position of the first value whose key is not less than k using |
| // binary search performed using compare-to. |
| template <typename K, typename CompareTo> |
| SearchResult<size_type, true> binary_search_impl( |
| const K &k, size_type s, size_type e, const CompareTo &comp, |
| std::true_type /* IsCompareTo */) const { |
| if (params_type::template can_have_multiple_equivalent_keys<K>()) { |
| MatchKind exact_match = MatchKind::kNe; |
| while (s != e) { |
| const size_type mid = (s + e) >> 1; |
| const absl::weak_ordering c = comp(key(mid), k); |
| if (c < 0) { |
| s = mid + 1; |
| } else { |
| e = mid; |
| if (c == 0) { |
| // Need to return the first value whose key is not less than k, |
| // which requires continuing the binary search if there could be |
| // multiple equivalent keys. |
| exact_match = MatchKind::kEq; |
| } |
| } |
| } |
| return {s, exact_match}; |
| } else { // Can't have multiple equivalent keys. |
| while (s != e) { |
| const size_type mid = (s + e) >> 1; |
| const absl::weak_ordering c = comp(key(mid), k); |
| if (c < 0) { |
| s = mid + 1; |
| } else if (c > 0) { |
| e = mid; |
| } else { |
| return {mid, MatchKind::kEq}; |
| } |
| } |
| return {s, MatchKind::kNe}; |
| } |
| } |
| |
| // Returns whether key i is ordered correctly with respect to the other keys |
| // in the node. The motivation here is to detect comparators that violate |
| // transitivity. Note: we only do comparisons of keys on this node rather than |
| // the whole tree so that this is constant time. |
| template <typename Compare> |
| bool is_ordered_correctly(field_type i, const Compare &comp) const { |
| if (std::is_base_of<BtreeTestOnlyCheckedCompareOptOutBase, |
| Compare>::value || |
| params_type::kIsKeyCompareStringAdapted) { |
| return true; |
| } |
| |
| const auto compare = [&](field_type a, field_type b) { |
| const absl::weak_ordering cmp = |
| compare_internal::do_three_way_comparison(comp, key(a), key(b)); |
| return cmp < 0 ? -1 : cmp > 0 ? 1 : 0; |
| }; |
| int cmp = -1; |
| constexpr bool kCanHaveEquivKeys = |
| params_type::template can_have_multiple_equivalent_keys<key_type>(); |
| for (field_type j = start(); j < finish(); ++j) { |
| if (j == i) { |
| if (cmp > 0) return false; |
| continue; |
| } |
| int new_cmp = compare(j, i); |
| if (new_cmp < cmp || (!kCanHaveEquivKeys && new_cmp == 0)) return false; |
| cmp = new_cmp; |
| } |
| return true; |
| } |
| |
| // Emplaces a value at position i, shifting all existing values and |
| // children at positions >= i to the right by 1. |
| template <typename... Args> |
| void emplace_value(field_type i, allocator_type *alloc, Args &&...args); |
| |
| // Removes the values at positions [i, i + to_erase), shifting all existing |
| // values and children after that range to the left by to_erase. Clears all |
| // children between [i, i + to_erase). |
| void remove_values(field_type i, field_type to_erase, allocator_type *alloc); |
| |
| // Rebalances a node with its right sibling. |
| void rebalance_right_to_left(field_type to_move, btree_node *right, |
| allocator_type *alloc); |
| void rebalance_left_to_right(field_type to_move, btree_node *right, |
| allocator_type *alloc); |
| |
| // Splits a node, moving a portion of the node's values to its right sibling. |
| void split(int insert_position, btree_node *dest, allocator_type *alloc); |
| |
| // Merges a node with its right sibling, moving all of the values and the |
| // delimiting key in the parent node onto itself, and deleting the src node. |
| void merge(btree_node *src, allocator_type *alloc); |
| |
| // Node allocation/deletion routines. |
| void init_leaf(field_type position, field_type max_count, |
| btree_node *parent) { |
| set_generation(0); |
| set_parent(parent); |
| set_position(position); |
| set_start(0); |
| set_finish(0); |
| set_max_count(max_count); |
| absl::container_internal::SanitizerPoisonMemoryRegion( |
| start_slot(), max_count * sizeof(slot_type)); |
| } |
| void init_internal(field_type position, btree_node *parent) { |
| init_leaf(position, kNodeSlots, parent); |
| // Set `max_count` to a sentinel value to indicate that this node is |
| // internal. |
| set_max_count(kInternalNodeMaxCount); |
| absl::container_internal::SanitizerPoisonMemoryRegion( |
| &mutable_child(start()), (kNodeSlots + 1) * sizeof(btree_node *)); |
| } |
| |
| static void deallocate(const size_type size, btree_node *node, |
| allocator_type *alloc) { |
| absl::container_internal::SanitizerUnpoisonMemoryRegion(node, size); |
| absl::container_internal::Deallocate<Alignment()>(alloc, node, size); |
| } |
| |
| // Deletes a node and all of its children. |
| static void clear_and_delete(btree_node *node, allocator_type *alloc); |
| |
| private: |
| template <typename... Args> |
| void value_init(const field_type i, allocator_type *alloc, Args &&...args) { |
| next_generation(); |
| absl::container_internal::SanitizerUnpoisonObject(slot(i)); |
| params_type::construct(alloc, slot(i), std::forward<Args>(args)...); |
| } |
| void value_destroy(const field_type i, allocator_type *alloc) { |
| next_generation(); |
| params_type::destroy(alloc, slot(i)); |
| absl::container_internal::SanitizerPoisonObject(slot(i)); |
| } |
| void value_destroy_n(const field_type i, const field_type n, |
| allocator_type *alloc) { |
| next_generation(); |
| for (slot_type *s = slot(i), *end = slot(i + n); s != end; ++s) { |
| params_type::destroy(alloc, s); |
| absl::container_internal::SanitizerPoisonObject(s); |
| } |
| } |
| |
| static void transfer(slot_type *dest, slot_type *src, allocator_type *alloc) { |
| absl::container_internal::SanitizerUnpoisonObject(dest); |
| params_type::transfer(alloc, dest, src); |
| absl::container_internal::SanitizerPoisonObject(src); |
| } |
| |
| // Transfers value from slot `src_i` in `src_node` to slot `dest_i` in `this`. |
| void transfer(const size_type dest_i, const size_type src_i, |
| btree_node *src_node, allocator_type *alloc) { |
| next_generation(); |
| transfer(slot(dest_i), src_node->slot(src_i), alloc); |
| } |
| |
| // Transfers `n` values starting at value `src_i` in `src_node` into the |
| // values starting at value `dest_i` in `this`. |
| void transfer_n(const size_type n, const size_type dest_i, |
| const size_type src_i, btree_node *src_node, |
| allocator_type *alloc) { |
| next_generation(); |
| for (slot_type *src = src_node->slot(src_i), *end = src + n, |
| *dest = slot(dest_i); |
| src != end; ++src, ++dest) { |
| transfer(dest, src, alloc); |
| } |
| } |
| |
| // Same as above, except that we start at the end and work our way to the |
| // beginning. |
| void transfer_n_backward(const size_type n, const size_type dest_i, |
| const size_type src_i, btree_node *src_node, |
| allocator_type *alloc) { |
| next_generation(); |
| for (slot_type *src = src_node->slot(src_i + n), *end = src - n, |
| *dest = slot(dest_i + n); |
| src != end; --src, --dest) { |
| // If we modified the loop index calculations above to avoid the -1s here, |
| // it would result in UB in the computation of `end` (and possibly `src` |
| // as well, if n == 0), since slot() is effectively an array index and it |
| // is UB to compute the address of any out-of-bounds array element except |
| // for one-past-the-end. |
| transfer(dest - 1, src - 1, alloc); |
| } |
| } |
| |
| template <typename P> |
| friend class btree; |
| template <typename N, typename R, typename P> |
| friend class btree_iterator; |
| friend class BtreeNodePeer; |
| friend struct btree_access; |
| }; |
| |
| template <typename Node> |
| bool AreNodesFromSameContainer(const Node *node_a, const Node *node_b) { |
| // If either node is null, then give up on checking whether they're from the |
| // same container. (If exactly one is null, then we'll trigger the |
| // default-constructed assert in Equals.) |
| if (node_a == nullptr || node_b == nullptr) return true; |
| while (!node_a->is_root()) node_a = node_a->parent(); |
| while (!node_b->is_root()) node_b = node_b->parent(); |
| return node_a == node_b; |
| } |
| |
| class btree_iterator_generation_info_enabled { |
| public: |
| explicit btree_iterator_generation_info_enabled(uint32_t g) |
| : generation_(g) {} |
| |
| // Updates the generation. For use internally right before we return an |
| // iterator to the user. |
| template <typename Node> |
| void update_generation(const Node *node) { |
| if (node != nullptr) generation_ = node->generation(); |
| } |
| uint32_t generation() const { return generation_; } |
| |
| template <typename Node> |
| void assert_valid_generation(const Node *node) const { |
| if (node != nullptr && node->generation() != generation_) { |
| ABSL_INTERNAL_LOG( |
| FATAL, |
| "Attempting to use an invalidated iterator. The corresponding b-tree " |
| "container has been mutated since this iterator was constructed."); |
| } |
| } |
| |
| private: |
| // Used to check that the iterator hasn't been invalidated. |
| uint32_t generation_; |
| }; |
| |
| class btree_iterator_generation_info_disabled { |
| public: |
| explicit btree_iterator_generation_info_disabled(uint32_t) {} |
| static void update_generation(const void *) {} |
| static uint32_t generation() { return 0; } |
| static void assert_valid_generation(const void *) {} |
| }; |
| |
| #ifdef ABSL_BTREE_ENABLE_GENERATIONS |
| using btree_iterator_generation_info = btree_iterator_generation_info_enabled; |
| #else |
| using btree_iterator_generation_info = btree_iterator_generation_info_disabled; |
| #endif |
| |
| template <typename Node, typename Reference, typename Pointer> |
| class btree_iterator : private btree_iterator_generation_info { |
| using field_type = typename Node::field_type; |
| using key_type = typename Node::key_type; |
| using size_type = typename Node::size_type; |
| using params_type = typename Node::params_type; |
| using is_map_container = typename params_type::is_map_container; |
| |
| using node_type = Node; |
| using normal_node = typename std::remove_const<Node>::type; |
| using const_node = const Node; |
| using normal_pointer = typename params_type::pointer; |
| using normal_reference = typename params_type::reference; |
| using const_pointer = typename params_type::const_pointer; |
| using const_reference = typename params_type::const_reference; |
| using slot_type = typename params_type::slot_type; |
| |
| // In sets, all iterators are const. |
| using iterator = absl::conditional_t< |
| is_map_container::value, |
| btree_iterator<normal_node, normal_reference, normal_pointer>, |
| btree_iterator<normal_node, const_reference, const_pointer>>; |
| using const_iterator = |
| btree_iterator<const_node, const_reference, const_pointer>; |
| |
| public: |
| // These aliases are public for std::iterator_traits. |
| using difference_type = typename Node::difference_type; |
| using value_type = typename params_type::value_type; |
| using pointer = Pointer; |
| using reference = Reference; |
| using iterator_category = std::bidirectional_iterator_tag; |
| |
| btree_iterator() : btree_iterator(nullptr, -1) {} |
| explicit btree_iterator(Node *n) : btree_iterator(n, n->start()) {} |
| btree_iterator(Node *n, int p) |
| : btree_iterator_generation_info(n != nullptr ? n->generation() |
| : ~uint32_t{}), |
| node_(n), |
| position_(p) {} |
| |
| // NOTE: this SFINAE allows for implicit conversions from iterator to |
| // const_iterator, but it specifically avoids hiding the copy constructor so |
| // that the trivial one will be used when possible. |
| template <typename N, typename R, typename P, |
| absl::enable_if_t< |
| std::is_same<btree_iterator<N, R, P>, iterator>::value && |
| std::is_same<btree_iterator, const_iterator>::value, |
| int> = 0> |
| btree_iterator(const btree_iterator<N, R, P> other) // NOLINT |
| : btree_iterator_generation_info(other), |
| node_(other.node_), |
| position_(other.position_) {} |
| |
| bool operator==(const iterator &other) const { |
| return Equals(other); |
| } |
| bool operator==(const const_iterator &other) const { |
| return Equals(other); |
| } |
| bool operator!=(const iterator &other) const { |
| return !Equals(other); |
| } |
| bool operator!=(const const_iterator &other) const { |
| return !Equals(other); |
| } |
| |
| // Returns n such that n calls to ++other yields *this. |
| // Precondition: n exists. |
| difference_type operator-(const_iterator other) const { |
| if (node_ == other.node_) { |
| if (node_->is_leaf()) return position_ - other.position_; |
| if (position_ == other.position_) return 0; |
| } |
| return distance_slow(other); |
| } |
| |
| // Accessors for the key/value the iterator is pointing at. |
| reference operator*() const { |
| ABSL_HARDENING_ASSERT(node_ != nullptr); |
| assert_valid_generation(node_); |
| ABSL_HARDENING_ASSERT(position_ >= node_->start()); |
| if (position_ >= node_->finish()) { |
| ABSL_HARDENING_ASSERT(!IsEndIterator() && "Dereferencing end() iterator"); |
| ABSL_HARDENING_ASSERT(position_ < node_->finish()); |
| } |
| return node_->value(static_cast<field_type>(position_)); |
| } |
| pointer operator->() const { return &operator*(); } |
| |
| btree_iterator &operator++() { |
| increment(); |
| return *this; |
| } |
| btree_iterator &operator--() { |
| decrement(); |
| return *this; |
| } |
| btree_iterator operator++(int) { |
| btree_iterator tmp = *this; |
| ++*this; |
| return tmp; |
| } |
| btree_iterator operator--(int) { |
| btree_iterator tmp = *this; |
| --*this; |
| return tmp; |
| } |
| |
| private: |
| friend iterator; |
| friend const_iterator; |
| template <typename Params> |
| friend class btree; |
| template <typename Tree> |
| friend class btree_container; |
| template <typename Tree> |
| friend class btree_set_container; |
| template <typename Tree> |
| friend class btree_map_container; |
| template <typename Tree> |
| friend class btree_multiset_container; |
| template <typename TreeType, typename CheckerType> |
| friend class base_checker; |
| friend struct btree_access; |
| |
| // This SFINAE allows explicit conversions from const_iterator to |
| // iterator, but also avoids hiding the copy constructor. |
| // NOTE: the const_cast is safe because this constructor is only called by |
| // non-const methods and the container owns the nodes. |
| template <typename N, typename R, typename P, |
| absl::enable_if_t< |
| std::is_same<btree_iterator<N, R, P>, const_iterator>::value && |
| std::is_same<btree_iterator, iterator>::value, |
| int> = 0> |
| explicit btree_iterator(const btree_iterator<N, R, P> other) |
| : btree_iterator_generation_info(other.generation()), |
| node_(const_cast<node_type *>(other.node_)), |
| position_(other.position_) {} |
| |
| bool Equals(const const_iterator other) const { |
| ABSL_HARDENING_ASSERT(((node_ == nullptr && other.node_ == nullptr) || |
| (node_ != nullptr && other.node_ != nullptr)) && |
| "Comparing default-constructed iterator with " |
| "non-default-constructed iterator."); |
| // Note: we use assert instead of ABSL_HARDENING_ASSERT here because this |
| // changes the complexity of Equals from O(1) to O(log(N) + log(M)) where |
| // N/M are sizes of the containers containing node_/other.node_. |
| assert(AreNodesFromSameContainer(node_, other.node_) && |
| "Comparing iterators from different containers."); |
| assert_valid_generation(node_); |
| other.assert_valid_generation(other.node_); |
| return node_ == other.node_ && position_ == other.position_; |
| } |
| |
| bool IsEndIterator() const { |
| if (position_ != node_->finish()) return false; |
| node_type *node = node_; |
| while (!node->is_root()) { |
| if (node->position() != node->parent()->finish()) return false; |
| node = node->parent(); |
| } |
| return true; |
| } |
| |
| // Returns n such that n calls to ++other yields *this. |
| // Precondition: n exists && (this->node_ != other.node_ || |
| // !this->node_->is_leaf() || this->position_ != other.position_). |
| difference_type distance_slow(const_iterator other) const; |
| |
| // Increment/decrement the iterator. |
| void increment() { |
| assert_valid_generation(node_); |
| if (node_->is_leaf() && ++position_ < node_->finish()) { |
| return; |
| } |
| increment_slow(); |
| } |
| void increment_slow(); |
| |
| void decrement() { |
| assert_valid_generation(node_); |
| if (node_->is_leaf() && --position_ >= node_->start()) { |
| return; |
| } |
| decrement_slow(); |
| } |
| void decrement_slow(); |
| |
| const key_type &key() const { |
| return node_->key(static_cast<size_type>(position_)); |
| } |
| decltype(std::declval<Node *>()->slot(0)) slot() { |
| return node_->slot(static_cast<size_type>(position_)); |
| } |
| |
| void update_generation() { |
| btree_iterator_generation_info::update_generation(node_); |
| } |
| |
| // The node in the tree the iterator is pointing at. |
| Node *node_; |
| // The position within the node of the tree the iterator is pointing at. |
| // NOTE: this is an int rather than a field_type because iterators can point |
| // to invalid positions (such as -1) in certain circumstances. |
| int position_; |
| }; |
| |
| template <typename Params> |
| class btree { |
| using node_type = btree_node<Params>; |
| using is_key_compare_to = typename Params::is_key_compare_to; |
| using field_type = typename node_type::field_type; |
| |
| // We use a static empty node for the root/leftmost/rightmost of empty btrees |
| // in order to avoid branching in begin()/end(). |
| struct EmptyNodeType : node_type { |
| using field_type = typename node_type::field_type; |
| node_type *parent; |
| #ifdef ABSL_BTREE_ENABLE_GENERATIONS |
| uint32_t generation = 0; |
| #endif |
| field_type position = 0; |
| field_type start = 0; |
| field_type finish = 0; |
| // max_count must be != kInternalNodeMaxCount (so that this node is regarded |
| // as a leaf node). max_count() is never called when the tree is empty. |
| field_type max_count = node_type::kInternalNodeMaxCount + 1; |
| |
| constexpr EmptyNodeType() : parent(this) {} |
| }; |
| |
| static node_type *EmptyNode() { |
| alignas(node_type::Alignment()) static constexpr EmptyNodeType empty_node; |
| return const_cast<EmptyNodeType *>(&empty_node); |
| } |
| |
| enum : uint32_t { |
| kNodeSlots = node_type::kNodeSlots, |
| kMinNodeValues = kNodeSlots / 2, |
| }; |
| |
| struct node_stats { |
| using size_type = typename Params::size_type; |
| |
| node_stats(size_type l, size_type i) : leaf_nodes(l), internal_nodes(i) {} |
| |
| node_stats &operator+=(const node_stats &other) { |
| leaf_nodes += other.leaf_nodes; |
| internal_nodes += other.internal_nodes; |
| return *this; |
| } |
| |
| size_type leaf_nodes; |
| size_type internal_nodes; |
| }; |
| |
| public: |
| using key_type = typename Params::key_type; |
| using value_type = typename Params::value_type; |
| using size_type = typename Params::size_type; |
| using difference_type = typename Params::difference_type; |
| using key_compare = typename Params::key_compare; |
| using original_key_compare = typename Params::original_key_compare; |
| using value_compare = typename Params::value_compare; |
| using allocator_type = typename Params::allocator_type; |
| using reference = typename Params::reference; |
| using const_reference = typename Params::const_reference; |
| using pointer = typename Params::pointer; |
| using const_pointer = typename Params::const_pointer; |
| using iterator = |
| typename btree_iterator<node_type, reference, pointer>::iterator; |
| using const_iterator = typename iterator::const_iterator; |
| using reverse_iterator = std::reverse_iterator<iterator>; |
| using const_reverse_iterator = std::reverse_iterator<const_iterator>; |
| using node_handle_type = node_handle<Params, Params, allocator_type>; |
| |
| // Internal types made public for use by btree_container types. |
| using params_type = Params; |
| using slot_type = typename Params::slot_type; |
| |
| private: |
| // Copies or moves (depending on the template parameter) the values in |
| // other into this btree in their order in other. This btree must be empty |
| // before this method is called. This method is used in copy construction, |
| // copy assignment, and move assignment. |
| template <typename Btree> |
| void copy_or_move_values_in_order(Btree &other); |
| |
| // Validates that various assumptions/requirements are true at compile time. |
| constexpr static bool static_assert_validation(); |
| |
| public: |
| btree(const key_compare &comp, const allocator_type &alloc) |
| : root_(EmptyNode()), rightmost_(comp, alloc, EmptyNode()), size_(0) {} |
| |
| btree(const btree &other) : btree(other, other.allocator()) {} |
| btree(const btree &other, const allocator_type &alloc) |
| : btree(other.key_comp(), alloc) { |
| copy_or_move_values_in_order(other); |
| } |
| btree(btree &&other) noexcept |
| : root_(std::exchange(other.root_, EmptyNode())), |
| rightmost_(std::move(other.rightmost_)), |
| size_(std::exchange(other.size_, 0u)) { |
| other.mutable_rightmost() = EmptyNode(); |
| } |
| btree(btree &&other, const allocator_type &alloc) |
| : btree(other.key_comp(), alloc) { |
| if (alloc == other.allocator()) { |
| swap(other); |
| } else { |
| // Move values from `other` one at a time when allocators are different. |
| copy_or_move_values_in_order(other); |
| } |
| } |
| |
| ~btree() { |
| // Put static_asserts in destructor to avoid triggering them before the type |
| // is complete. |
| static_assert(static_assert_validation(), "This call must be elided."); |
| clear(); |
| } |
| |
| // Assign the contents of other to *this. |
| btree &operator=(const btree &other); |
| btree &operator=(btree &&other) noexcept; |
| |
| iterator begin() { return iterator(leftmost()); } |
| const_iterator begin() const { return const_iterator(leftmost()); } |
| iterator end() { return iterator(rightmost(), rightmost()->finish()); } |
| const_iterator end() const { |
| return const_iterator(rightmost(), rightmost()->finish()); |
| } |
| reverse_iterator rbegin() { return reverse_iterator(end()); } |
| const_reverse_iterator rbegin() const { |
| return const_reverse_iterator(end()); |
| } |
| reverse_iterator rend() { return reverse_iterator(begin()); } |
| const_reverse_iterator rend() const { |
| return const_reverse_iterator(begin()); |
| } |
| |
| // Finds the first element whose key is not less than `key`. |
| template <typename K> |
| iterator lower_bound(const K &key) { |
| return internal_end(internal_lower_bound(key).value); |
| } |
| template <typename K> |
| const_iterator lower_bound(const K &key) const { |
| return internal_end(internal_lower_bound(key).value); |
| } |
| |
| // Finds the first element whose key is not less than `key` and also returns |
| // whether that element is equal to `key`. |
| template <typename K> |
| std::pair<iterator, bool> lower_bound_equal(const K &key) const; |
| |
| // Finds the first element whose key is greater than `key`. |
| template <typename K> |
| iterator upper_bound(const K &key) { |
| return internal_end(internal_upper_bound(key)); |
| } |
| template <typename K> |
| const_iterator upper_bound(const K &key) const { |
| return internal_end(internal_upper_bound(key)); |
| } |
| |
| // Finds the range of values which compare equal to key. The first member of |
| // the returned pair is equal to lower_bound(key). The second member of the |
| // pair is equal to upper_bound(key). |
| template <typename K> |
| std::pair<iterator, iterator> equal_range(const K &key); |
| template <typename K> |
| std::pair<const_iterator, const_iterator> equal_range(const K &key) const { |
| return const_cast<btree *>(this)->equal_range(key); |
| } |
| |
| // Inserts a value into the btree only if it does not already exist. The |
| // boolean return value indicates whether insertion succeeded or failed. |
| // Requirement: if `key` already exists in the btree, does not consume `args`. |
| // Requirement: `key` is never referenced after consuming `args`. |
| template <typename K, typename... Args> |
| std::pair<iterator, bool> insert_unique(const K &key, Args &&...args); |
| |
| // Inserts with hint. Checks to see if the value should be placed immediately |
| // before `position` in the tree. If so, then the insertion will take |
| // amortized constant time. If not, the insertion will take amortized |
| // logarithmic time as if a call to insert_unique() were made. |
| // Requirement: if `key` already exists in the btree, does not consume `args`. |
| // Requirement: `key` is never referenced after consuming `args`. |
| template <typename K, typename... Args> |
| std::pair<iterator, bool> insert_hint_unique(iterator position, const K &key, |
| Args &&...args); |
| |
| // Insert a range of values into the btree. |
| // Note: the first overload avoids constructing a value_type if the key |
| // already exists in the btree. |
| template <typename InputIterator, |
| typename = decltype(std::declval<const key_compare &>()( |
| params_type::key(*std::declval<InputIterator>()), |
| std::declval<const key_type &>()))> |
| void insert_iterator_unique(InputIterator b, InputIterator e, int); |
| // We need the second overload for cases in which we need to construct a |
| // value_type in order to compare it with the keys already in the btree. |
| template <typename InputIterator> |
| void insert_iterator_unique(InputIterator b, InputIterator e, char); |
| |
| // Inserts a value into the btree. |
| template <typename ValueType> |
| iterator insert_multi(const key_type &key, ValueType &&v); |
| |
| // Inserts a value into the btree. |
| template <typename ValueType> |
| iterator insert_multi(ValueType &&v) { |
| return insert_multi(params_type::key(v), std::forward<ValueType>(v)); |
| } |
| |
| // Insert with hint. Check to see if the value should be placed immediately |
| // before position in the tree. If it does, then the insertion will take |
| // amortized constant time. If not, the insertion will take amortized |
| // logarithmic time as if a call to insert_multi(v) were made. |
| template <typename ValueType> |
| iterator insert_hint_multi(iterator position, ValueType &&v); |
| |
| // Insert a range of values into the btree. |
| template <typename InputIterator> |
| void insert_iterator_multi(InputIterator b, |
| InputIterator e); |
| |
| // Erase the specified iterator from the btree. The iterator must be valid |
| // (i.e. not equal to end()). Return an iterator pointing to the node after |
| // the one that was erased (or end() if none exists). |
| // Requirement: does not read the value at `*iter`. |
| iterator erase(iterator iter); |
| |
| // Erases range. Returns the number of keys erased and an iterator pointing |
| // to the element after the last erased element. |
| std::pair<size_type, iterator> erase_range(iterator begin, iterator end); |
| |
| // Finds an element with key equivalent to `key` or returns `end()` if `key` |
| // is not present. |
| template <typename K> |
| iterator find(const K &key) { |
| return internal_end(internal_find(key)); |
| } |
| template <typename K> |
| const_iterator find(const K &key) const { |
| return internal_end(internal_find(key)); |
| } |
| |
| // Clear the btree, deleting all of the values it contains. |
| void clear(); |
| |
| // Swaps the contents of `this` and `other`. |
| void swap(btree &other); |
| |
| const key_compare &key_comp() const noexcept { |
| return rightmost_.template get<0>(); |
| } |
| template <typename K1, typename K2> |
| bool compare_keys(const K1 &a, const K2 &b) const { |
| return compare_internal::compare_result_as_less_than(key_comp()(a, b)); |
| } |
| |
| value_compare value_comp() const { |
| return value_compare(original_key_compare(key_comp())); |
| } |
| |
| // Verifies the structure of the btree. |
| void verify() const; |
| |
| // Size routines. |
| size_type size() const { return size_; } |
| size_type max_size() const { return (std::numeric_limits<size_type>::max)(); } |
| bool empty() const { return size_ == 0; } |
| |
| // The height of the btree. An empty tree will have height 0. |
| size_type height() const { |
| size_type h = 0; |
| if (!empty()) { |
| // Count the length of the chain from the leftmost node up to the |
| // root. We actually count from the root back around to the level below |
| // the root, but the calculation is the same because of the circularity |
| // of that traversal. |
| const node_type *n = root(); |
| do { |
| ++h; |
| n = n->parent(); |
| } while (n != root()); |
| } |
| return h; |
| } |
| |
| // The number of internal, leaf and total nodes used by the btree. |
| size_type leaf_nodes() const { return internal_stats(root()).leaf_nodes; } |
| size_type internal_nodes() const { |
| return internal_stats(root()).internal_nodes; |
| } |
| size_type nodes() const { |
| node_stats stats = internal_stats(root()); |
| return stats.leaf_nodes + stats.internal_nodes; |
| } |
| |
| // The total number of bytes used by the btree. |
| // TODO(b/169338300): update to support node_btree_*. |
| size_type bytes_used() const { |
| node_stats stats = internal_stats(root()); |
| if (stats.leaf_nodes == 1 && stats.internal_nodes == 0) { |
| return sizeof(*this) + node_type::LeafSize(root()->max_count()); |
| } else { |
| return sizeof(*this) + stats.leaf_nodes * node_type::LeafSize() + |
| stats.internal_nodes * node_type::InternalSize(); |
| } |
| } |
| |
| // The average number of bytes used per value stored in the btree assuming |
| // random insertion order. |
| static double average_bytes_per_value() { |
| // The expected number of values per node with random insertion order is the |
| // average of the maximum and minimum numbers of values per node. |
| const double expected_values_per_node = (kNodeSlots + kMinNodeValues) / 2.0; |
| return node_type::LeafSize() / expected_values_per_node; |
| } |
| |
| // The fullness of the btree. Computed as the number of elements in the btree |
| // divided by the maximum number of elements a tree with the current number |
| // of nodes could hold. A value of 1 indicates perfect space |
| // utilization. Smaller values indicate space wastage. |
| // Returns 0 for empty trees. |
| double fullness() const { |
| if (empty()) return 0.0; |
| return static_cast<double>(size()) / (nodes() * kNodeSlots); |
| } |
| // The overhead of the btree structure in bytes per node. Computed as the |
| // total number of bytes used by the btree minus the number of bytes used for |
| // storing elements divided by the number of elements. |
| // Returns 0 for empty trees. |
| double overhead() const { |
| if (empty()) return 0.0; |
| return (bytes_used() - size() * sizeof(value_type)) / |
| static_cast<double>(size()); |
| } |
| |
| // The allocator used by the btree. |
| allocator_type get_allocator() const { return allocator(); } |
| |
| private: |
| friend struct btree_access; |
| |
| // Internal accessor routines. |
| node_type *root() { return root_; } |
| const node_type *root() const { return root_; } |
| node_type *&mutable_root() noexcept { return root_; } |
| node_type *rightmost() { return rightmost_.template get<2>(); } |
| const node_type *rightmost() const { return rightmost_.template get<2>(); } |
| node_type *&mutable_rightmost() noexcept { |
| return rightmost_.template get<2>(); |
| } |
| key_compare *mutable_key_comp() noexcept { |
| return &rightmost_.template get<0>(); |
| } |
| |
| // The leftmost node is stored as the parent of the root node. |
| node_type *leftmost() { return root()->parent(); } |
| const node_type *leftmost() const { return root()->parent(); } |
| |
| // Allocator routines. |
| allocator_type *mutable_allocator() noexcept { |
| return &rightmost_.template get<1>(); |
| } |
| const allocator_type &allocator() const noexcept { |
| return rightmost_.template get<1>(); |
| } |
| |
| // Allocates a correctly aligned node of at least size bytes using the |
| // allocator. |
| node_type *allocate(size_type size) { |
| return reinterpret_cast<node_type *>( |
| absl::container_internal::Allocate<node_type::Alignment()>( |
| mutable_allocator(), size)); |
| } |
| |
| // Node creation/deletion routines. |
| node_type *new_internal_node(field_type position, node_type *parent) { |
| node_type *n = allocate(node_type::InternalSize()); |
| n->init_internal(position, parent); |
| return n; |
| } |
| node_type *new_leaf_node(field_type position, node_type *parent) { |
| node_type *n = allocate(node_type::LeafSize()); |
| n->init_leaf(position, kNodeSlots, parent); |
| return n; |
| } |
| node_type *new_leaf_root_node(field_type max_count) { |
| node_type *n = allocate(node_type::LeafSize(max_count)); |
| n->init_leaf(/*position=*/0, max_count, /*parent=*/n); |
| return n; |
| } |
| |
| // Deletion helper routines. |
| iterator rebalance_after_delete(iterator iter); |
| |
| // Rebalances or splits the node iter points to. |
| void rebalance_or_split(iterator *iter); |
| |
| // Merges the values of left, right and the delimiting key on their parent |
| // onto left, removing the delimiting key and deleting right. |
| void merge_nodes(node_type *left, node_type *right); |
| |
| // Tries to merge node with its left or right sibling, and failing that, |
| // rebalance with its left or right sibling. Returns true if a merge |
| // occurred, at which point it is no longer valid to access node. Returns |
| // false if no merging took place. |
| bool try_merge_or_rebalance(iterator *iter); |
| |
| // Tries to shrink the height of the tree by 1. |
| void try_shrink(); |
| |
| iterator internal_end(iterator iter) { |
| return iter.node_ != nullptr ? iter : end(); |
| } |
| const_iterator internal_end(const_iterator iter) const { |
| return iter.node_ != nullptr ? iter : end(); |
| } |
| |
| // Emplaces a value into the btree immediately before iter. Requires that |
| // key(v) <= iter.key() and (--iter).key() <= key(v). |
| template <typename... Args> |
| iterator internal_emplace(iterator iter, Args &&...args); |
| |
| // Returns an iterator pointing to the first value >= the value "iter" is |
| // pointing at. Note that "iter" might be pointing to an invalid location such |
| // as iter.position_ == iter.node_->finish(). This routine simply moves iter |
| // up in the tree to a valid location. Requires: iter.node_ is non-null. |
| template <typename IterType> |
| static IterType internal_last(IterType iter); |
| |
| // Returns an iterator pointing to the leaf position at which key would |
| // reside in the tree, unless there is an exact match - in which case, the |
| // result may not be on a leaf. When there's a three-way comparator, we can |
| // return whether there was an exact match. This allows the caller to avoid a |
| // subsequent comparison to determine if an exact match was made, which is |
| // important for keys with expensive comparison, such as strings. |
| template <typename K> |
| SearchResult<iterator, is_key_compare_to::value> internal_locate( |
| const K &key) const; |
| |
| // Internal routine which implements lower_bound(). |
| template <typename K> |
| SearchResult<iterator, is_key_compare_to::value> internal_lower_bound( |
| const K &key) const; |
| |
| // Internal routine which implements upper_bound(). |
| template <typename K> |
| iterator internal_upper_bound(const K &key) const; |
| |
| // Internal routine which implements find(). |
| template <typename K> |
| iterator internal_find(const K &key) const; |
| |
| // Verifies the tree structure of node. |
| size_type internal_verify(const node_type *node, const key_type *lo, |
| const key_type *hi) const; |
| |
| node_stats internal_stats(const node_type *node) const { |
| // The root can be a static empty node. |
| if (node == nullptr || (node == root() && empty())) { |
| return node_stats(0, 0); |
| } |
| if (node->is_leaf()) { |
| return node_stats(1, 0); |
| } |
| node_stats res(0, 1); |
| for (int i = node->start(); i <= node->finish(); ++i) { |
| res += internal_stats(node->child(i)); |
| } |
| return res; |
| } |
| |
| node_type *root_; |
| |
| // A pointer to the rightmost node. Note that the leftmost node is stored as |
| // the root's parent. We use compressed tuple in order to save space because |
| // key_compare and allocator_type are usually empty. |
| absl::container_internal::CompressedTuple<key_compare, allocator_type, |
| node_type *> |
| rightmost_; |
| |
| // Number of values. |
| size_type size_; |
| }; |
| |
| //// |
| // btree_node methods |
| template <typename P> |
| template <typename... Args> |
| inline void btree_node<P>::emplace_value(const field_type i, |
| allocator_type *alloc, |
| Args &&...args) { |
| assert(i >= start()); |
| assert(i <= finish()); |
| // Shift old values to create space for new value and then construct it in |
| // place. |
| if (i < finish()) { |
| transfer_n_backward(finish() - i, /*dest_i=*/i + 1, /*src_i=*/i, this, |
| alloc); |
| } |
| value_init(static_cast<field_type>(i), alloc, std::forward<Args>(args)...); |
| set_finish(finish() + 1); |
| |
| if (is_internal() && finish() > i + 1) { |
| for (field_type j = finish(); j > i + 1; --j) { |
| set_child(j, child(j - 1)); |
| } |
| clear_child(i + 1); |
| } |
| } |
| |
| template <typename P> |
| inline void btree_node<P>::remove_values(const field_type i, |
| const field_type to_erase, |
| allocator_type *alloc) { |
| // Transfer values after the removed range into their new places. |
| value_destroy_n(i, to_erase, alloc); |
| const field_type orig_finish = finish(); |
| const field_type src_i = i + to_erase; |
| transfer_n(orig_finish - src_i, i, src_i, this, alloc); |
| |
| if (is_internal()) { |
| // Delete all children between begin and end. |
| for (field_type j = 0; j < to_erase; ++j) { |
| clear_and_delete(child(i + j + 1), alloc); |
| } |
| // Rotate children after end into new positions. |
| for (field_type j = i + to_erase + 1; j <= orig_finish; ++j) { |
| set_child(j - to_erase, child(j)); |
| clear_child(j); |
| } |
| } |
| set_finish(orig_finish - to_erase); |
| } |
| |
| template <typename P> |
| void btree_node<P>::rebalance_right_to_left(field_type to_move, |
| btree_node *right, |
| allocator_type *alloc) { |
| assert(parent() == right->parent()); |
| assert(position() + 1 == right->position()); |
| assert(right->count() >= count()); |
| assert(to_move >= 1); |
| assert(to_move <= right->count()); |
| |
| // 1) Move the delimiting value in the parent to the left node. |
| transfer(finish(), position(), parent(), alloc); |
| |
| // 2) Move the (to_move - 1) values from the right node to the left node. |
| transfer_n(to_move - 1, finish() + 1, right->start(), right, alloc); |
| |
| // 3) Move the new delimiting value to the parent from the right node. |
| parent()->transfer(position(), right->start() + to_move - 1, right, alloc); |
| |
| // 4) Shift the values in the right node to their correct positions. |
| right->transfer_n(right->count() - to_move, right->start(), |
| right->start() + to_move, right, alloc); |
| |
| if (is_internal()) { |
| // Move the child pointers from the right to the left node. |
| for (field_type i = 0; i < to_move; ++i) { |
| init_child(finish() + i + 1, right->child(i)); |
| } |
| for (field_type i = right->start(); i <= right->finish() - to_move; ++i) { |
| assert(i + to_move <= right->max_count()); |
| right->init_child(i, right->child(i + to_move)); |
| right->clear_child(i + to_move); |
| } |
| } |
| |
| // Fixup `finish` on the left and right nodes. |
| set_finish(finish() + to_move); |
| right->set_finish(right->finish() - to_move); |
| } |
| |
| template <typename P> |
| void btree_node<P>::rebalance_left_to_right(field_type to_move, |
| btree_node *right, |
| allocator_type *alloc) { |
| assert(parent() == right->parent()); |
| assert(position() + 1 == right->position()); |
| assert(count() >= right->count()); |
| assert(to_move >= 1); |
| assert(to_move <= count()); |
| |
| // Values in the right node are shifted to the right to make room for the |
| // new to_move values. Then, the delimiting value in the parent and the |
| // other (to_move - 1) values in the left node are moved into the right node. |
| // Lastly, a new delimiting value is moved from the left node into the |
| // parent, and the remaining empty left node entries are destroyed. |
| |
| // 1) Shift existing values in the right node to their correct positions. |
| right->transfer_n_backward(right->count(), right->start() + to_move, |
| right->start(), right, alloc); |
| |
| // 2) Move the delimiting value in the parent to the right node. |
| right->transfer(right->start() + to_move - 1, position(), parent(), alloc); |
| |
| // 3) Move the (to_move - 1) values from the left node to the right node. |
| right->transfer_n(to_move - 1, right->start(), finish() - (to_move - 1), this, |
| alloc); |
| |
| // 4) Move the new delimiting value to the parent from the left node. |
| parent()->transfer(position(), finish() - to_move, this, alloc); |
| |
| if (is_internal()) { |
| // Move the child pointers from the left to the right node. |
| for (field_type i = right->finish() + 1; i > right->start(); --i) { |
| right->init_child(i - 1 + to_move, right->child(i - 1)); |
| right->clear_child(i - 1); |
| } |
| for (field_type i = 1; i <= to_move; ++i) { |
| right->init_child(i - 1, child(finish() - to_move + i)); |
| clear_child(finish() - to_move + i); |
| } |
| } |
| |
| // Fixup the counts on the left and right nodes. |
| set_finish(finish() - to_move); |
| right->set_finish(right->finish() + to_move); |
| } |
| |
| template <typename P> |
| void btree_node<P>::split(const int insert_position, btree_node *dest, |
| allocator_type *alloc) { |
| assert(dest->count() == 0); |
| assert(max_count() == kNodeSlots); |
| assert(position() + 1 == dest->position()); |
| assert(parent() == dest->parent()); |
| |
| // We bias the split based on the position being inserted. If we're |
| // inserting at the beginning of the left node then bias the split to put |
| // more values on the right node. If we're inserting at the end of the |
| // right node then bias the split to put more values on the left node. |
| if (insert_position == start()) { |
| dest->set_finish(dest->start() + finish() - 1); |
| } else if (insert_position == kNodeSlots) { |
| dest->set_finish(dest->start()); |
| } else { |
| dest->set_finish(dest->start() + count() / 2); |
| } |
| set_finish(finish() - dest->count()); |
| assert(count() >= 1); |
| |
| // Move values from the left sibling to the right sibling. |
| dest->transfer_n(dest->count(), dest->start(), finish(), this, alloc); |
| |
| // The split key is the largest value in the left sibling. |
| --mutable_finish(); |
| parent()->emplace_value(position(), alloc, finish_slot()); |
| value_destroy(finish(), alloc); |
| parent()->set_child_noupdate_position(position() + 1, dest); |
| |
| if (is_internal()) { |
| for (field_type i = dest->start(), j = finish() + 1; i <= dest->finish(); |
| ++i, ++j) { |
| assert(child(j) != nullptr); |
| dest->init_child(i, child(j)); |
| clear_child(j); |
| } |
| } |
| } |
| |
| template <typename P> |
| void btree_node<P>::merge(btree_node *src, allocator_type *alloc) { |
| assert(parent() == src->parent()); |
| assert(position() + 1 == src->position()); |
| |
| // Move the delimiting value to the left node. |
| value_init(finish(), alloc, parent()->slot(position())); |
| |
| // Move the values from the right to the left node. |
| transfer_n(src->count(), finish() + 1, src->start(), src, alloc); |
| |
| if (is_internal()) { |
| // Move the child pointers from the right to the left node. |
| for (field_type i = src->start(), j = finish() + 1; i <= src->finish(); |
| ++i, ++j) { |
| init_child(j, src->child(i)); |
| src->clear_child(i); |
| } |
| } |
| |
| // Fixup `finish` on the src and dest nodes. |
| set_finish(start() + 1 + count() + src->count()); |
| src->set_finish(src->start()); |
| |
| // Remove the value on the parent node and delete the src node. |
| parent()->remove_values(position(), /*to_erase=*/1, alloc); |
| } |
| |
| template <typename P> |
| void btree_node<P>::clear_and_delete(btree_node *node, allocator_type *alloc) { |
| if (node->is_leaf()) { |
| node->value_destroy_n(node->start(), node->count(), alloc); |
| deallocate(LeafSize(node->max_count()), node, alloc); |
| return; |
| } |
| if (node->count() == 0) { |
| deallocate(InternalSize(), node, alloc); |
| return; |
| } |
| |
| // The parent of the root of the subtree we are deleting. |
| btree_node *delete_root_parent = node->parent(); |
| |
| // Navigate to the leftmost leaf under node, and then delete upwards. |
| while (node->is_internal()) node = node->start_child(); |
| #ifdef ABSL_BTREE_ENABLE_GENERATIONS |
| // When generations are enabled, we delete the leftmost leaf last in case it's |
| // the parent of the root and we need to check whether it's a leaf before we |
| // can update the root's generation. |
| // TODO(ezb): if we change btree_node::is_root to check a bool inside the node |
| // instead of checking whether the parent is a leaf, we can remove this logic. |
| btree_node *leftmost_leaf = node; |
| #endif |
| // Use `size_type` because `pos` needs to be able to hold `kNodeSlots+1`, |
| // which isn't guaranteed to be a valid `field_type`. |
| size_type pos = node->position(); |
| btree_node *parent = node->parent(); |
| for (;;) { |
| // In each iteration of the next loop, we delete one leaf node and go right. |
| assert(pos <= parent->finish()); |
| do { |
| node = parent->child(static_cast<field_type>(pos)); |
| if (node->is_internal()) { |
| // Navigate to the leftmost leaf under node. |
| while (node->is_internal()) node = node->start_child(); |
| pos = node->position(); |
| parent = node->parent(); |
| } |
| node->value_destroy_n(node->start(), node->count(), alloc); |
| #ifdef ABSL_BTREE_ENABLE_GENERATIONS |
| if (leftmost_leaf != node) |
| #endif |
| deallocate(LeafSize(node->max_count()), node, alloc); |
| ++pos; |
| } while (pos <= parent->finish()); |
| |
| // Once we've deleted all children of parent, delete parent and go up/right. |
| assert(pos > parent->finish()); |
| do { |
| node = parent; |
| pos = node->position(); |
| parent = node->parent(); |
| node->value_destroy_n(node->start(), node->count(), alloc); |
| deallocate(InternalSize(), node, alloc); |
| if (parent == delete_root_parent) { |
| #ifdef ABSL_BTREE_ENABLE_GENERATIONS |
| deallocate(LeafSize(leftmost_leaf->max_count()), leftmost_leaf, alloc); |
| #endif |
| return; |
| } |
| ++pos; |
| } while (pos > parent->finish()); |
| } |
| } |
| |
| //// |
| // btree_iterator methods |
| |
| // Note: the implementation here is based on btree_node::clear_and_delete. |
| template <typename N, typename R, typename P> |
| auto btree_iterator<N, R, P>::distance_slow(const_iterator other) const |
| -> difference_type { |
| const_iterator begin = other; |
| const_iterator end = *this; |
| assert(begin.node_ != end.node_ || !begin.node_->is_leaf() || |
| begin.position_ != end.position_); |
| |
| const node_type *node = begin.node_; |
| // We need to compensate for double counting if begin.node_ is a leaf node. |
| difference_type count = node->is_leaf() ? -begin.position_ : 0; |
| |
| // First navigate to the leftmost leaf node past begin. |
| if (node->is_internal()) { |
| ++count; |
| node = node->child(begin.position_ + 1); |
| } |
| while (node->is_internal()) node = node->start_child(); |
| |
| // Use `size_type` because `pos` needs to be able to hold `kNodeSlots+1`, |
| // which isn't guaranteed to be a valid `field_type`. |
| size_type pos = node->position(); |
| const node_type *parent = node->parent(); |
| for (;;) { |
| // In each iteration of the next loop, we count one leaf node and go right. |
| assert(pos <= parent->finish()); |
| do { |
| node = parent->child(static_cast<field_type>(pos)); |
| if (node->is_internal()) { |
| // Navigate to the leftmost leaf under node. |
| while (node->is_internal()) node = node->start_child(); |
| pos = node->position(); |
| parent = node->parent(); |
| } |
| if (node == end.node_) return count + end.position_; |
| if (parent == end.node_ && pos == static_cast<size_type>(end.position_)) |
| return count + node->count(); |
| // +1 is for the next internal node value. |
| count += node->count() + 1; |
| ++pos; |
| } while (pos <= parent->finish()); |
| |
| // Once we've counted all children of parent, go up/right. |
| assert(pos > parent->finish()); |
| do { |
| node = parent; |
| pos = node->position(); |
| parent = node->parent(); |
| // -1 because we counted the value at end and shouldn't. |
| if (parent == end.node_ && pos == static_cast<size_type>(end.position_)) |
| return count - 1; |
| ++pos; |
| } while (pos > parent->finish()); |
| } |
| } |
| |
| template <typename N, typename R, typename P> |
| void btree_iterator<N, R, P>::increment_slow() { |
| if (node_->is_leaf()) { |
| assert(position_ >= node_->finish()); |
| btree_iterator save(*this); |
| while (position_ == node_->finish() && !node_->is_root()) { |
| assert(node_->parent()->child(node_->position()) == node_); |
| position_ = node_->position(); |
| node_ = node_->parent(); |
| } |
| // TODO(ezb): assert we aren't incrementing end() instead of handling. |
| if (position_ == node_->finish()) { |
| *this = save; |
| } |
| } else { |
| assert(position_ < node_->finish()); |
| node_ = node_->child(static_cast<field_type>(position_ + 1)); |
| while (node_->is_internal()) { |
| node_ = node_->start_child(); |
| } |
| position_ = node_->start(); |
| } |
| } |
| |
| template <typename N, typename R, typename P> |
| void btree_iterator<N, R, P>::decrement_slow() { |
| if (node_->is_leaf()) { |
| assert(position_ <= -1); |
| btree_iterator save(*this); |
| while (position_ < node_->start() && !node_->is_root()) { |
| assert(node_->parent()->child(node_->position()) == node_); |
| position_ = node_->position() - 1; |
| node_ = node_->parent(); |
| } |
| // TODO(ezb): assert we aren't decrementing begin() instead of handling. |
| if (position_ < node_->start()) { |
| *this = save; |
| } |
| } else { |
| assert(position_ >= node_->start()); |
| node_ = node_->child(static_cast<field_type>(position_)); |
| while (node_->is_internal()) { |
| node_ = node_->child(node_->finish()); |
| } |
| position_ = node_->finish() - 1; |
| } |
| } |
| |
| //// |
| // btree methods |
| template <typename P> |
| template <typename Btree> |
| void btree<P>::copy_or_move_values_in_order(Btree &other) { |
| static_assert(std::is_same<btree, Btree>::value || |
| std::is_same<const btree, Btree>::value, |
| "Btree type must be same or const."); |
| assert(empty()); |
| |
| // We can avoid key comparisons because we know the order of the |
| // values is the same order we'll store them in. |
| auto iter = other.begin(); |
| if (iter == other.end()) return; |
| insert_multi(iter.slot()); |
| ++iter; |
| for (; iter != other.end(); ++iter) { |
| // If the btree is not empty, we can just insert the new value at the end |
| // of the tree. |
| internal_emplace(end(), iter.slot()); |
| } |
| } |
| |
| template <typename P> |
| constexpr bool btree<P>::static_assert_validation() { |
| static_assert(std::is_nothrow_copy_constructible<key_compare>::value, |
| "Key comparison must be nothrow copy constructible"); |
| static_assert(std::is_nothrow_copy_constructible<allocator_type>::value, |
| "Allocator must be nothrow copy constructible"); |
| static_assert(std::is_trivially_copyable<iterator>::value, |
| "iterator not trivially copyable."); |
| |
| // Note: We assert that kTargetValues, which is computed from |
| // Params::kTargetNodeSize, must fit the node_type::field_type. |
| static_assert( |
| kNodeSlots < (1 << (8 * sizeof(typename node_type::field_type))), |
| "target node size too large"); |
| |
| // Verify that key_compare returns an absl::{weak,strong}_ordering or bool. |
| static_assert( |
| compare_has_valid_result_type<key_compare, key_type>(), |
| "key comparison function must return absl::{weak,strong}_ordering or " |
| "bool."); |
| |
| // Test the assumption made in setting kNodeSlotSpace. |
| static_assert(node_type::MinimumOverhead() >= sizeof(void *) + 4, |
| "node space assumption incorrect"); |
| |
| return true; |
| } |
| |
| template <typename P> |
| template <typename K> |
| auto btree<P>::lower_bound_equal(const K &key) const |
| -> std::pair<iterator, bool> { |
| const SearchResult<iterator, is_key_compare_to::value> res = |
| internal_lower_bound(key); |
| const iterator lower = iterator(internal_end(res.value)); |
| const bool equal = res.HasMatch() |
| ? res.IsEq() |
| : lower != end() && !compare_keys(key, lower.key()); |
| return {lower, equal}; |
| } |
| |
| template <typename P> |
| template <typename K> |
| auto btree<P>::equal_range(const K &key) -> std::pair<iterator, iterator> { |
| const std::pair<iterator, bool> lower_and_equal = lower_bound_equal(key); |
| const iterator lower = lower_and_equal.first; |
| if (!lower_and_equal.second) { |
| return {lower, lower}; |
| } |
| |
| const iterator next = std::next(lower); |
| if (!params_type::template can_have_multiple_equivalent_keys<K>()) { |
| // The next iterator after lower must point to a key greater than `key`. |
| // Note: if this assert fails, then it may indicate that the comparator does |
| // not meet the equivalence requirements for Compare |
| // (see https://en.cppreference.com/w/cpp/named_req/Compare). |
| assert(next == end() || compare_keys(key, next.key())); |
| return {lower, next}; |
| } |
| // Try once more to avoid the call to upper_bound() if there's only one |
| // equivalent key. This should prevent all calls to upper_bound() in cases of |
| // unique-containers with heterogeneous comparators in which all comparison |
| // operators have the same equivalence classes. |
| if (next == end() || compare_keys(key, next.key())) return {lower, next}; |
| |
| // In this case, we need to call upper_bound() to avoid worst case O(N) |
| // behavior if we were to iterate over equal keys. |
| return {lower, upper_bound(key)}; |
| } |
| |
| template <typename P> |
| template <typename K, typename... Args> |
| auto btree<P>::insert_unique(const K &key, Args &&...args) |
| -> std::pair<iterator, bool> { |
| if (empty()) { |
| mutable_root() = mutable_rightmost() = new_leaf_root_node(1); |
| } |
| |
| SearchResult<iterator, is_key_compare_to::value> res = internal_locate(key); |
| iterator iter = res.value; |
| |
| if (res.HasMatch()) { |
| if (res.IsEq()) { |
| // The key already exists in the tree, do nothing. |
| return {iter, false}; |
| } |
| } else { |
| iterator last = internal_last(iter); |
| if (last.node_ && !compare_keys(key, last.key())) { |
| // The key already exists in the tree, do nothing. |
| return {last, false}; |
| } |
| } |
| return {internal_emplace(iter, std::forward<Args>(args)...), true}; |
| } |
| |
| template <typename P> |
| template <typename K, typename... Args> |
| inline auto btree<P>::insert_hint_unique(iterator position, const K &key, |
| Args &&...args) |
| -> std::pair<iterator, bool> { |
| if (!empty()) { |
| if (position == end() || compare_keys(key, position.key())) { |
| if (position == begin() || compare_keys(std::prev(position).key(), key)) { |
| // prev.key() < key < position.key() |
| return {internal_emplace(position, std::forward<Args>(args)...), true}; |
| } |
| } else if (compare_keys(position.key(), key)) { |
| ++position; |
| if (position == end() || compare_keys(key, position.key())) { |
| // {original `position`}.key() < key < {current `position`}.key() |
| return {internal_emplace(position, std::forward<Args>(args)...), true}; |
| } |
| } else { |
| // position.key() == key |
| return {position, false}; |
| } |
| } |
| return insert_unique(key, std::forward<Args>(args)...); |
| } |
| |
| template <typename P> |
| template <typename InputIterator, typename> |
| void btree<P>::insert_iterator_unique(InputIterator b, InputIterator e, int) { |
| for (; b != e; ++b) { |
| insert_hint_unique(end(), params_type::key(*b), *b); |
| } |
| } |
| |
| template <typename P> |
| template <typename InputIterator> |
| void btree<P>::insert_iterator_unique(InputIterator b, InputIterator e, char) { |
| for (; b != e; ++b) { |
| // Use a node handle to manage a temp slot. |
| auto node_handle = |
| CommonAccess::Construct<node_handle_type>(get_allocator(), *b); |
| slot_type *slot = CommonAccess::GetSlot(node_handle); |
| insert_hint_unique(end(), params_type::key(slot), slot); |
| } |
| } |
| |
| template <typename P> |
| template <typename ValueType> |
| auto btree<P>::insert_multi(const key_type &key, ValueType &&v) -> iterator { |
| if (empty()) { |
| mutable_root() = mutable_rightmost() = new_leaf_root_node(1); |
| } |
| |
| iterator iter = internal_upper_bound(key); |
| if (iter.node_ == nullptr) { |
| iter = end(); |
| } |
| return internal_emplace(iter, std::forward<ValueType>(v)); |
| } |
| |
| template <typename P> |
| template <typename ValueType> |
| auto btree<P>::insert_hint_multi(iterator position, ValueType &&v) -> iterator { |
| if (!empty()) { |
| const key_type &key = params_type::key(v); |
| if (position == end() || !compare_keys(position.key(), key)) { |
| if (position == begin() || |
| !compare_keys(key, std::prev(position).key())) { |
| // prev.key() <= key <= position.key() |
| return internal_emplace(position, std::forward<ValueType>(v)); |
| } |
| } else { |
| ++position; |
| if (position == end() || !compare_keys(position.key(), key)) { |
| // {original `position`}.key() < key < {current `position`}.key() |
| return internal_emplace(position, std::forward<ValueType>(v)); |
| } |
| } |
| } |
| return insert_multi(std::forward<ValueType>(v)); |
| } |
| |
| template <typename P> |
| template <typename InputIterator> |
| void btree<P>::insert_iterator_multi(InputIterator b, InputIterator e) { |
| for (; b != e; ++b) { |
| insert_hint_multi(end(), *b); |
| } |
| } |
| |
| template <typename P> |
| auto btree<P>::operator=(const btree &other) -> btree & { |
| if (this != &other) { |
| clear(); |
| |
| *mutable_key_comp() = other.key_comp(); |
| if (absl::allocator_traits< |
| allocator_type>::propagate_on_container_copy_assignment::value) { |
| *mutable_allocator() = other.allocator(); |
| } |
| |
| copy_or_move_values_in_order(other); |
| } |
| return *this; |
| } |
| |
| template <typename P> |
| auto btree<P>::operator=(btree &&other) noexcept -> btree & { |
| if (this != &other) { |
| clear(); |
| |
| using std::swap; |
| if (absl::allocator_traits< |
| allocator_type>::propagate_on_container_move_assignment::value) { |
| swap(root_, other.root_); |
| // Note: `rightmost_` also contains the allocator and the key comparator. |
| swap(rightmost_, other.rightmost_); |
| swap(size_, other.size_); |
| } else { |
| if (allocator() == other.allocator()) { |
| swap(mutable_root(), other.mutable_root()); |
| swap(*mutable_key_comp(), *other.mutable_key_comp()); |
| swap(mutable_rightmost(), other.mutable_rightmost()); |
| swap(size_, other.size_); |
| } else { |
| // We aren't allowed to propagate the allocator and the allocator is |
| // different so we can't take over its memory. We must move each element |
| // individually. We need both `other` and `this` to have `other`s key |
| // comparator while moving the values so we can't swap the key |
| // comparators. |
| *mutable_key_comp() = other.key_comp(); |
| copy_or_move_values_in_order(other); |
| } |
| } |
| } |
| return *this; |
| } |
| |
| template <typename P> |
| auto btree<P>::erase(iterator iter) -> iterator { |
| iter.node_->value_destroy(static_cast<field_type>(iter.position_), |
| mutable_allocator()); |
| iter.update_generation(); |
| |
| const bool internal_delete = iter.node_->is_internal(); |
| if (internal_delete) { |
| // Deletion of a value on an internal node. First, transfer the largest |
| // value from our left child here, then erase/rebalance from that position. |
| // We can get to the largest value from our left child by decrementing iter. |
| iterator internal_iter(iter); |
| --iter; |
| assert(iter.node_->is_leaf()); |
| internal_iter.node_->transfer( |
| static_cast<size_type>(internal_iter.position_), |
| static_cast<size_type>(iter.position_), iter.node_, |
| mutable_allocator()); |
| } else { |
| // Shift values after erased position in leaf. In the internal case, we |
| // don't need to do this because the leaf position is the end of the node. |
| const field_type transfer_from = |
| static_cast<field_type>(iter.position_ + 1); |
| const field_type num_to_transfer = iter.node_->finish() - transfer_from; |
| iter.node_->transfer_n(num_to_transfer, |
| static_cast<size_type>(iter.position_), |
| transfer_from, iter.node_, mutable_allocator()); |
| } |
| // Update node finish and container size. |
| iter.node_->set_finish(iter.node_->finish() - 1); |
| --size_; |
| |
| // We want to return the next value after the one we just erased. If we |
| // erased from an internal node (internal_delete == true), then the next |
| // value is ++(++iter). If we erased from a leaf node (internal_delete == |
| // false) then the next value is ++iter. Note that ++iter may point to an |
| // internal node and the value in the internal node may move to a leaf node |
| // (iter.node_) when rebalancing is performed at the leaf level. |
| |
| iterator res = rebalance_after_delete(iter); |
| |
| // If we erased from an internal node, advance the iterator. |
| if (internal_delete) { |
| ++res; |
| } |
| return res; |
| } |
| |
| template <typename P> |
| auto btree<P>::rebalance_after_delete(iterator iter) -> iterator { |
| // Merge/rebalance as we walk back up the tree. |
| iterator res(iter); |
| bool first_iteration = true; |
| for (;;) { |
| if (iter.node_ == root()) { |
| try_shrink(); |
| if (empty()) { |
| return end(); |
| } |
| break; |
| } |
| if (iter.node_->count() >= kMinNodeValues) { |
| break; |
| } |
| bool merged = try_merge_or_rebalance(&iter); |
| // On the first iteration, we should update `res` with `iter` because `res` |
| // may have been invalidated. |
| if (first_iteration) { |
| res = iter; |
| first_iteration = false; |
| } |
| if (!merged) { |
| break; |
| } |
| iter.position_ = iter.node_->position(); |
| iter.node_ = iter.node_->parent(); |
| } |
| res.update_generation(); |
| |
| // Adjust our return value. If we're pointing at the end of a node, advance |
| // the iterator. |
| if (res.position_ == res.node_->finish()) { |
| res.position_ = res.node_->finish() - 1; |
| ++res; |
| } |
| |
| return res; |
| } |
| |
| // Note: we tried implementing this more efficiently by erasing all of the |
| // elements in [begin, end) at once and then doing rebalancing once at the end |
| // (rather than interleaving deletion and rebalancing), but that adds a lot of |
| // complexity, which seems to outweigh the performance win. |
| template <typename P> |
| auto btree<P>::erase_range(iterator begin, iterator end) |
| -> std::pair<size_type, iterator> { |
| size_type count = static_cast<size_type>(end - begin); |
| assert(count >= 0); |
| |
| if (count == 0) { |
| return {0, begin}; |
| } |
| |
| if (static_cast<size_type>(count) == size_) { |
| clear(); |
| return {count, this->end()}; |
| } |
| |
| if (begin.node_ == end.node_) { |
| assert(end.position_ > begin.position_); |
| begin.node_->remove_values( |
| static_cast<field_type>(begin.position_), |
| static_cast<field_type>(end.position_ - begin.position_), |
| mutable_allocator()); |
| size_ -= count; |
| return {count, rebalance_after_delete(begin)}; |
| } |
| |
| const size_type target_size = size_ - count; |
| while (size_ > target_size) { |
| if (begin.node_->is_leaf()) { |
| const size_type remaining_to_erase = size_ - target_size; |
| const size_type remaining_in_node = |
| static_cast<size_type>(begin.node_->finish() - begin.position_); |
| const field_type to_erase = static_cast<field_type>( |
| (std::min)(remaining_to_erase, remaining_in_node)); |
| begin.node_->remove_values(static_cast<field_type>(begin.position_), |
| to_erase, mutable_allocator()); |
| size_ -= to_erase; |
| begin = rebalance_after_delete(begin); |
| } else { |
| begin = erase(begin); |
| } |
| } |
| begin.update_generation(); |
| return {count, begin}; |
| } |
| |
| template <typename P> |
| void btree<P>::clear() { |
| if (!empty()) { |
| node_type::clear_and_delete(root(), mutable_allocator()); |
| } |
| mutable_root() = mutable_rightmost() = EmptyNode(); |
| size_ = 0; |
| } |
| |
| template <typename P> |
| void btree<P>::swap(btree &other) { |
| using std::swap; |
| if (absl::allocator_traits< |
| allocator_type>::propagate_on_container_swap::value) { |
| // Note: `rightmost_` also contains the allocator and the key comparator. |
| swap(rightmost_, other.rightmost_); |
| } else { |
| // It's undefined behavior if the allocators are unequal here. |
| assert(allocator() == other.allocator()); |
| swap(mutable_rightmost(), other.mutable_rightmost()); |
| swap(*mutable_key_comp(), *other.mutable_key_comp()); |
| } |
| swap(mutable_root(), other.mutable_root()); |
| swap(size_, other.size_); |
| } |
| |
| template <typename P> |
| void btree<P>::verify() const { |
| assert(root() != nullptr); |
| assert(leftmost() != nullptr); |
| assert(rightmost() != nullptr); |
| assert(empty() || size() == internal_verify(root(), nullptr, nullptr)); |
| assert(leftmost() == (++const_iterator(root(), -1)).node_); |
| assert(rightmost() == (--const_iterator(root(), root()->finish())).node_); |
| assert(leftmost()->is_leaf()); |
| assert(rightmost()->is_leaf()); |
| } |
| |
| template <typename P> |
| void btree<P>::rebalance_or_split(iterator *iter) { |
| node_type *&node = iter->node_; |
| int &insert_position = iter->position_; |
| assert(node->count() == node->max_count()); |
| assert(kNodeSlots == node->max_count()); |
| |
| // First try to make room on the node by rebalancing. |
| node_type *parent = node->parent(); |
| if (node != root()) { |
| if (node->position() > parent->start()) { |
| // Try rebalancing with our left sibling. |
| node_type *left = parent->child(node->position() - 1); |
| assert(left->max_count() == kNodeSlots); |
| if (left->count() < kNodeSlots) { |
| // We bias rebalancing based on the position being inserted. If we're |
| // inserting at the end of the right node then we bias rebalancing to |
| // fill up the left node. |
| field_type to_move = |
| (kNodeSlots - left->count()) / |
| (1 + (static_cast<field_type>(insert_position) < kNodeSlots)); |
| to_move = (std::max)(field_type{1}, to_move); |
| |
| if (static_cast<field_type>(insert_position) - to_move >= |
| node->start() || |
| left->count() + to_move < kNodeSlots) { |
| left->rebalance_right_to_left(to_move, node, mutable_allocator()); |
| |
| assert(node->max_count() - node->count() == to_move); |
| insert_position = static_cast<int>( |
| static_cast<field_type>(insert_position) - to_move); |
| if (insert_position < node->start()) { |
| insert_position = insert_position + left->count() + 1; |
| node = left; |
| } |
| |
| assert(node->count() < node->max_count()); |
| return; |
| } |
| } |
| } |
| |
| if (node->position() < parent->finish()) { |
| // Try rebalancing with our right sibling. |
| node_type *right = parent->child(node->position() + 1); |
| assert(right->max_count() == kNodeSlots); |
| if (right->count() < kNodeSlots) { |
| // We bias rebalancing based on the position being inserted. If we're |
| // inserting at the beginning of the left node then we bias rebalancing |
| // to fill up the right node. |
| field_type to_move = (kNodeSlots - right->count()) / |
| (1 + (insert_position > node->start())); |
| to_move = (std::max)(field_type{1}, to_move); |
| |
| if (static_cast<field_type>(insert_position) <= |
| node->finish() - to_move || |
| right->count() + to_move < kNodeSlots) { |
| node->rebalance_left_to_right(to_move, right, mutable_allocator()); |
| |
| if (insert_position > node->finish()) { |
| insert_position = insert_position - node->count() - 1; |
| node = right; |
| } |
| |
| assert(node->count() < node->max_count()); |
| return; |
| } |
| } |
| } |
| |
| // Rebalancing failed, make sure there is room on the parent node for a new |
| // value. |
| assert(parent->max_count() == kNodeSlots); |
| if (parent->count() == kNodeSlots) { |
| iterator parent_iter(parent, node->position()); |
| rebalance_or_split(&parent_iter); |
| parent = node->parent(); |
| } |
| } else { |
| // Rebalancing not possible because this is the root node. |
| // Create a new root node and set the current root node as the child of the |
| // new root. |
| parent = new_internal_node(/*position=*/0, parent); |
| parent->set_generation(root()->generation()); |
| parent->init_child(parent->start(), node); |
| mutable_root() = parent; |
| // If the former root was a leaf node, then it's now the rightmost node. |
| assert(parent->start_child()->is_internal() || |
| parent->start_child() == rightmost()); |
| } |
| |
| // Split the node. |
| node_type *split_node; |
| if (node->is_leaf()) { |
| split_node = new_leaf_node(node->position() + 1, parent); |
| node->split(insert_position, split_node, mutable_allocator()); |
| if (rightmost() == node) mutable_rightmost() = split_node; |
| } else { |
| split_node = new_internal_node(node->position() + 1, parent); |
| node->split(insert_position, split_node, mutable_allocator()); |
| } |
| |
| if (insert_position > node->finish()) { |
| insert_position = insert_position - node->count() - 1; |
| node = split_node; |
| } |
| } |
| |
| template <typename P> |
| void btree<P>::merge_nodes(node_type *left, node_type *right) { |
| left->merge(right, mutable_allocator()); |
| if (rightmost() == right) mutable_rightmost() = left; |
| } |
| |
| template <typename P> |
| bool btree<P>::try_merge_or_rebalance(iterator *iter) { |
| node_type *parent = iter->node_->parent(); |
| if (iter->node_->position() > parent->start()) { |
| // Try merging with our left sibling. |
|