| // Copyright 2006 The RE2 Authors. All Rights Reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| #ifndef UTIL_SPARSE_ARRAY_H_ |
| #define UTIL_SPARSE_ARRAY_H_ |
| |
| // DESCRIPTION |
| // |
| // SparseArray<T>(m) is a map from integers in [0, m) to T values. |
| // It requires (sizeof(T)+sizeof(int))*m memory, but it provides |
| // fast iteration through the elements in the array and fast clearing |
| // of the array. The array has a concept of certain elements being |
| // uninitialized (having no value). |
| // |
| // Insertion and deletion are constant time operations. |
| // |
| // Allocating the array is a constant time operation |
| // when memory allocation is a constant time operation. |
| // |
| // Clearing the array is a constant time operation (unusual!). |
| // |
| // Iterating through the array is an O(n) operation, where n |
| // is the number of items in the array (not O(m)). |
| // |
| // The array iterator visits entries in the order they were first |
| // inserted into the array. It is safe to add items to the array while |
| // using an iterator: the iterator will visit indices added to the array |
| // during the iteration, but will not re-visit indices whose values |
| // change after visiting. Thus SparseArray can be a convenient |
| // implementation of a work queue. |
| // |
| // The SparseArray implementation is NOT thread-safe. It is up to the |
| // caller to make sure only one thread is accessing the array. (Typically |
| // these arrays are temporary values and used in situations where speed is |
| // important.) |
| // |
| // The SparseArray interface does not present all the usual STL bells and |
| // whistles. |
| // |
| // Implemented with reference to Briggs & Torczon, An Efficient |
| // Representation for Sparse Sets, ACM Letters on Programming Languages |
| // and Systems, Volume 2, Issue 1-4 (March-Dec. 1993), pp. 59-69. |
| // |
| // Briggs & Torczon popularized this technique, but it had been known |
| // long before their paper. They point out that Aho, Hopcroft, and |
| // Ullman's 1974 Design and Analysis of Computer Algorithms and Bentley's |
| // 1986 Programming Pearls both hint at the technique in exercises to the |
| // reader (in Aho & Hopcroft, exercise 2.12; in Bentley, column 1 |
| // exercise 8). |
| // |
| // Briggs & Torczon describe a sparse set implementation. I have |
| // trivially generalized it to create a sparse array (actually the original |
| // target of the AHU and Bentley exercises). |
| |
| // IMPLEMENTATION |
| // |
| // SparseArray is an array dense_ and an array sparse_, both of size max_size_. |
| // At any point, the number of elements in the sparse array is size_. |
| // |
| // The array dense_ contains the size_ elements in the sparse array (with |
| // their indices), |
| // in the order that the elements were first inserted. This array is dense: |
| // the size_ pairs are dense_[0] through dense_[size_-1]. |
| // |
| // The array sparse_ maps from indices in [0,m) to indices in [0,size_). |
| // For indices present in the array, dense_[sparse_[i]].index_ == i. |
| // For indices not present in the array, sparse_ can contain any value at all, |
| // perhaps outside the range [0, size_) but perhaps not. |
| // |
| // The lax requirement on sparse_ values makes clearing the array very easy: |
| // set size_ to 0. Lookups are slightly more complicated. |
| // An index i has a value in the array if and only if: |
| // sparse_[i] is in [0, size_) AND |
| // dense_[sparse_[i]].index_ == i. |
| // If both these properties hold, only then it is safe to refer to |
| // dense_[sparse_[i]].value_ |
| // as the value associated with index i. |
| // |
| // To insert a new entry, set sparse_[i] to size_, |
| // initialize dense_[size_], and then increment size_. |
| // |
| // Deletion of specific values from the array is implemented by |
| // swapping dense_[size_-1] and the dense_ being deleted and then |
| // updating the appropriate sparse_ entries. |
| // |
| // To make the sparse array as efficient as possible for non-primitive types, |
| // elements may or may not be destroyed when they are deleted from the sparse |
| // array through a call to erase(), erase_existing() or resize(). They |
| // immediately become inaccessible, but they are only guaranteed to be |
| // destroyed when the SparseArray destructor is called. |
| // |
| // A moved-from SparseArray will be empty. |
| |
| // Doing this simplifies the logic below. |
| #ifndef __has_feature |
| #define __has_feature(x) 0 |
| #endif |
| |
| #include <assert.h> |
| #include <stdint.h> |
| #include <string.h> |
| #if __has_feature(memory_sanitizer) |
| #include <sanitizer/msan_interface.h> |
| #endif |
| #include <algorithm> |
| #include <memory> |
| #include <type_traits> |
| #include <utility> |
| |
| namespace re2 { |
| |
| template<typename Value> |
| class SparseArray { |
| public: |
| SparseArray(); |
| explicit SparseArray(int max_size); |
| ~SparseArray(); |
| |
| // IndexValue pairs: exposed in SparseArray::iterator. |
| class IndexValue; |
| static_assert(std::is_trivially_destructible<IndexValue>::value, |
| "IndexValue must be trivially destructible"); |
| |
| typedef IndexValue value_type; |
| typedef IndexValue* iterator; |
| typedef const IndexValue* const_iterator; |
| |
| SparseArray(const SparseArray& src); |
| SparseArray(SparseArray&& src) /*noexcept*/; |
| |
| SparseArray& operator=(const SparseArray& src); |
| SparseArray& operator=(SparseArray&& src) /*noexcept*/; |
| |
| const IndexValue& iv(int i) const; |
| |
| // Return the number of entries in the array. |
| int size() const { |
| return size_; |
| } |
| |
| // Indicate whether the array is empty. |
| int empty() const { |
| return size_ == 0; |
| } |
| |
| // Iterate over the array. |
| iterator begin() { |
| return dense_.get(); |
| } |
| iterator end() { |
| return dense_.get() + size_; |
| } |
| |
| const_iterator begin() const { |
| return dense_.get(); |
| } |
| const_iterator end() const { |
| return dense_.get() + size_; |
| } |
| |
| // Change the maximum size of the array. |
| // Invalidates all iterators. |
| void resize(int max_size); |
| |
| // Return the maximum size of the array. |
| // Indices can be in the range [0, max_size). |
| int max_size() const { |
| return max_size_; |
| } |
| |
| // Clear the array. |
| void clear() { |
| size_ = 0; |
| } |
| |
| // Check whether index i is in the array. |
| bool has_index(int i) const; |
| |
| // Comparison function for sorting. |
| // Can sort the sparse array so that future iterations |
| // will visit indices in increasing order using |
| // std::sort(arr.begin(), arr.end(), arr.less); |
| static bool less(const IndexValue& a, const IndexValue& b); |
| |
| public: |
| // Set the value at index i to v. |
| iterator set(int i, const Value& v) { |
| return SetInternal(true, i, v); |
| } |
| iterator set(int i, Value&& v) { // NOLINT |
| return SetInternal(true, i, std::move(v)); |
| } |
| |
| std::pair<iterator, bool> insert(const value_type& v) { |
| return InsertInternal(v); |
| } |
| std::pair<iterator, bool> insert(value_type&& v) { // NOLINT |
| return InsertInternal(std::move(v)); |
| } |
| |
| template <typename... Args> |
| std::pair<iterator, bool> emplace(Args&&... args) { // NOLINT |
| return InsertInternal(value_type(std::forward<Args>(args)...)); |
| } |
| |
| iterator find(int i) { |
| if (has_index(i)) |
| return dense_.get() + sparse_[i]; |
| return end(); |
| } |
| |
| const_iterator find(int i) const { |
| if (has_index(i)) |
| return dense_.get() + sparse_[i]; |
| return end(); |
| } |
| |
| // Change the value at index i to v. |
| // Fast but unsafe: only use if has_index(i) is true. |
| iterator set_existing(int i, const Value& v) { |
| return SetExistingInternal(i, v); |
| } |
| iterator set_existing(int i, Value&& v) { // NOLINT |
| return SetExistingInternal(i, std::move(v)); |
| } |
| |
| // Set the value at the new index i to v. |
| // Fast but unsafe: only use if has_index(i) is false. |
| iterator set_new(int i, const Value& v) { |
| return SetInternal(false, i, v); |
| } |
| iterator set_new(int i, Value&& v) { // NOLINT |
| return SetInternal(false, i, std::move(v)); |
| } |
| |
| // Get the value at index i from the array.. |
| // Fast but unsafe: only use if has_index(i) is true. |
| const Value& get_existing(int i) const; |
| |
| // Erasing items from the array during iteration is in general |
| // NOT safe. There is one special case, which is that the current |
| // index-value pair can be erased as long as the iterator is then |
| // checked for being at the end before being incremented. |
| // For example: |
| // |
| // for (i = m.begin(); i != m.end(); ++i) { |
| // if (ShouldErase(i->index(), i->value())) { |
| // m.erase(i->index()); |
| // --i; |
| // } |
| // } |
| // |
| // Except in the specific case just described, elements must |
| // not be erased from the array (including clearing the array) |
| // while iterators are walking over the array. Otherwise, |
| // the iterators could walk past the end of the array. |
| |
| // Erases the element at index i from the array. |
| void erase(int i); |
| |
| // Erases the element at index i from the array. |
| // Fast but unsafe: only use if has_index(i) is true. |
| void erase_existing(int i); |
| |
| private: |
| template <typename U> |
| std::pair<iterator, bool> InsertInternal(U&& v) { |
| DebugCheckInvariants(); |
| std::pair<iterator, bool> p; |
| if (has_index(v.index_)) { |
| p = {dense_.get() + sparse_[v.index_], false}; |
| } else { |
| p = {set_new(std::forward<U>(v).index_, std::forward<U>(v).second), true}; |
| } |
| DebugCheckInvariants(); |
| return p; |
| } |
| |
| template <typename U> |
| iterator SetInternal(bool allow_overwrite, int i, U&& v) { // NOLINT |
| DebugCheckInvariants(); |
| if (static_cast<uint32_t>(i) >= static_cast<uint32_t>(max_size_)) { |
| assert(false && "illegal index"); |
| // Semantically, end() would be better here, but we already know |
| // the user did something stupid, so begin() insulates them from |
| // dereferencing an invalid pointer. |
| return begin(); |
| } |
| if (!allow_overwrite) { |
| assert(!has_index(i)); |
| create_index(i); |
| } else { |
| if (!has_index(i)) |
| create_index(i); |
| } |
| return set_existing(i, std::forward<U>(v)); // NOLINT |
| } |
| |
| template <typename U> |
| iterator SetExistingInternal(int i, U&& v) { // NOLINT |
| DebugCheckInvariants(); |
| assert(has_index(i)); |
| dense_[sparse_[i]].value() = std::forward<U>(v); |
| DebugCheckInvariants(); |
| return dense_.get() + sparse_[i]; |
| } |
| |
| // Add the index i to the array. |
| // Only use if has_index(i) is known to be false. |
| // Since it doesn't set the value associated with i, |
| // this function is private, only intended as a helper |
| // for other methods. |
| void create_index(int i); |
| |
| // In debug mode, verify that some invariant properties of the class |
| // are being maintained. This is called at the end of the constructor |
| // and at the beginning and end of all public non-const member functions. |
| void DebugCheckInvariants() const; |
| |
| // Initializes memory for elements [min, max). |
| void MaybeInitializeMemory(int min, int max) { |
| #if __has_feature(memory_sanitizer) |
| __msan_unpoison(sparse_.get() + min, (max - min) * sizeof sparse_[0]); |
| #elif defined(RE2_ON_VALGRIND) |
| for (int i = min; i < max; i++) { |
| sparse_[i] = 0xababababU; |
| } |
| #endif |
| } |
| |
| int size_ = 0; |
| int max_size_ = 0; |
| std::unique_ptr<int[]> sparse_; |
| std::unique_ptr<IndexValue[]> dense_; |
| }; |
| |
| template<typename Value> |
| SparseArray<Value>::SparseArray() = default; |
| |
| template<typename Value> |
| SparseArray<Value>::SparseArray(const SparseArray& src) |
| : size_(src.size_), |
| max_size_(src.max_size_), |
| sparse_(new int[max_size_]), |
| dense_(new IndexValue[max_size_]) { |
| std::copy_n(src.sparse_.get(), max_size_, sparse_.get()); |
| std::copy_n(src.dense_.get(), max_size_, dense_.get()); |
| } |
| |
| template<typename Value> |
| SparseArray<Value>::SparseArray(SparseArray&& src) /*noexcept*/ // NOLINT |
| : size_(src.size_), |
| max_size_(src.max_size_), |
| sparse_(std::move(src.sparse_)), |
| dense_(std::move(src.dense_)) { |
| src.size_ = 0; |
| src.max_size_ = 0; |
| } |
| |
| template<typename Value> |
| SparseArray<Value>& SparseArray<Value>::operator=(const SparseArray& src) { |
| size_ = src.size_; |
| max_size_ = src.max_size_; |
| std::unique_ptr<int[]> a(new int[max_size_]); |
| std::copy_n(src.sparse_.get(), src.max_size_, a.get()); |
| sparse_ = std::move(a); |
| std::unique_ptr<IndexValue[]> b(new IndexValue[max_size_]); |
| std::copy_n(src.dense_.get(), src.max_size_, b.get()); |
| dense_ = std::move(b); |
| return *this; |
| } |
| |
| template<typename Value> |
| SparseArray<Value>& SparseArray<Value>::operator=( |
| SparseArray&& src) /*noexcept*/ { // NOLINT |
| size_ = src.size_; |
| max_size_ = src.max_size_; |
| sparse_ = std::move(src.sparse_); |
| dense_ = std::move(src.dense_); |
| // clear out the source |
| src.size_ = 0; |
| src.max_size_ = 0; |
| return *this; |
| } |
| |
| // IndexValue pairs: exposed in SparseArray::iterator. |
| template<typename Value> |
| class SparseArray<Value>::IndexValue { |
| friend class SparseArray; |
| public: |
| typedef int first_type; |
| typedef Value second_type; |
| |
| IndexValue() {} |
| IndexValue(int i, const Value& v) : index_(i), second(v) {} |
| IndexValue(int i, Value&& v) : index_(i), second(std::move(v)) {} |
| |
| int index() const { return index_; } |
| |
| Value& value() /*&*/ { return second; } |
| const Value& value() const /*&*/ { return second; } |
| //Value&& value() /*&&*/ { return std::move(second); } // NOLINT |
| |
| private: |
| int index_; |
| |
| public: |
| // Provide the data in the 'second' member so that the utilities |
| // in map-util work. |
| // TODO(billydonahue): 'second' is public for short-term compatibility. |
| // Users will be transitioned to using value() accessor. |
| Value second; |
| }; |
| |
| template<typename Value> |
| const typename SparseArray<Value>::IndexValue& |
| SparseArray<Value>::iv(int i) const { |
| assert(i >= 0); |
| assert(i < size_); |
| return dense_[i]; |
| } |
| |
| // Change the maximum size of the array. |
| // Invalidates all iterators. |
| template<typename Value> |
| void SparseArray<Value>::resize(int max_size) { |
| DebugCheckInvariants(); |
| if (max_size > max_size_) { |
| std::unique_ptr<int[]> a(new int[max_size]); |
| if (sparse_) { |
| std::copy_n(sparse_.get(), max_size_, a.get()); |
| } |
| sparse_ = std::move(a); |
| |
| std::unique_ptr<IndexValue[]> b(new IndexValue[max_size]); |
| if (dense_) { |
| std::copy_n(dense_.get(), max_size_, b.get()); |
| } |
| dense_ = std::move(b); |
| |
| MaybeInitializeMemory(max_size_, max_size); |
| } |
| max_size_ = max_size; |
| if (size_ > max_size_) |
| size_ = max_size_; |
| DebugCheckInvariants(); |
| } |
| |
| // Check whether index i is in the array. |
| template<typename Value> |
| bool SparseArray<Value>::has_index(int i) const { |
| assert(i >= 0); |
| assert(i < max_size_); |
| if (static_cast<uint32_t>(i) >= static_cast<uint32_t>(max_size_)) { |
| return false; |
| } |
| // Unsigned comparison avoids checking sparse_[i] < 0. |
| return (uint32_t)sparse_[i] < (uint32_t)size_ && |
| dense_[sparse_[i]].index_ == i; |
| } |
| |
| template<typename Value> |
| const Value& SparseArray<Value>::get_existing(int i) const { |
| assert(has_index(i)); |
| return dense_[sparse_[i]].second; |
| } |
| |
| template<typename Value> |
| void SparseArray<Value>::erase(int i) { |
| DebugCheckInvariants(); |
| if (has_index(i)) |
| erase_existing(i); |
| DebugCheckInvariants(); |
| } |
| |
| template<typename Value> |
| void SparseArray<Value>::erase_existing(int i) { |
| DebugCheckInvariants(); |
| assert(has_index(i)); |
| int di = sparse_[i]; |
| if (di < size_ - 1) { |
| dense_[di] = std::move(dense_[size_ - 1]); |
| sparse_[dense_[di].index_] = di; |
| } |
| size_--; |
| DebugCheckInvariants(); |
| } |
| |
| template<typename Value> |
| void SparseArray<Value>::create_index(int i) { |
| assert(!has_index(i)); |
| assert(size_ < max_size_); |
| sparse_[i] = size_; |
| dense_[size_].index_ = i; |
| size_++; |
| } |
| |
| template<typename Value> SparseArray<Value>::SparseArray(int max_size) { |
| sparse_.reset(new int[max_size]); |
| dense_.reset(new IndexValue[max_size]); |
| size_ = 0; |
| MaybeInitializeMemory(size_, max_size); |
| max_size_ = max_size; |
| DebugCheckInvariants(); |
| } |
| |
| template<typename Value> SparseArray<Value>::~SparseArray() { |
| DebugCheckInvariants(); |
| } |
| |
| template<typename Value> void SparseArray<Value>::DebugCheckInvariants() const { |
| assert(0 <= size_); |
| assert(size_ <= max_size_); |
| assert(size_ == 0 || sparse_ != NULL); |
| } |
| |
| // Comparison function for sorting. |
| template<typename Value> bool SparseArray<Value>::less(const IndexValue& a, |
| const IndexValue& b) { |
| return a.index_ < b.index_; |
| } |
| |
| } // namespace re2 |
| |
| #endif // UTIL_SPARSE_ARRAY_H_ |