| // 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. |
| |
| // 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 uses a vector dense_ and an array sparse_to_dense_, both of |
| // size max_size_. At any point, the number of elements in the sparse array is |
| // size_. |
| // |
| // The vector 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_to_dense_ maps from indices in [0,m) to indices in |
| // [0,size_). |
| // For indices present in the array, dense_[sparse_to_dense_[i]].index_ == i. |
| // For indices not present in the array, sparse_to_dense_ can contain |
| // any value at all, perhaps outside the range [0, size_) but perhaps not. |
| // |
| // The lax requirement on sparse_to_dense_ 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_to_dense_[i] is in [0, size_) AND |
| // dense_[sparse_to_dense_[i]].index_ == i. |
| // If both these properties hold, only then it is safe to refer to |
| // dense_[sparse_to_dense_[i]].value_ |
| // as the value associated with index i. |
| // |
| // To insert a new entry, set sparse_to_dense_[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_to_dense_ 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. |
| |
| #ifndef RE2_UTIL_SPARSE_ARRAY_H__ |
| #define RE2_UTIL_SPARSE_ARRAY_H__ |
| |
| #include "util/util.h" |
| |
| namespace re2 { |
| |
| template<typename Value> |
| class SparseArray { |
| public: |
| SparseArray(); |
| SparseArray(int max_size); |
| ~SparseArray(); |
| |
| // IndexValue pairs: exposed in SparseArray::iterator. |
| class IndexValue; |
| |
| typedef IndexValue value_type; |
| typedef typename vector<IndexValue>::iterator iterator; |
| typedef typename vector<IndexValue>::const_iterator const_iterator; |
| |
| inline const IndexValue& iv(int i) const; |
| |
| // Return the number of entries in the array. |
| int size() const { |
| return size_; |
| } |
| |
| // Iterate over the array. |
| iterator begin() { |
| return dense_.begin(); |
| } |
| iterator end() { |
| return dense_.begin() + size_; |
| } |
| |
| const_iterator begin() const { |
| return dense_.begin(); |
| } |
| const_iterator end() const { |
| return dense_.begin() + 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. |
| inline 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 |
| // 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. |
| inline iterator set(int i, Value v); |
| |
| pair<iterator, bool> insert(const value_type& new_value); |
| |
| // Returns the value at index i |
| // or defaultv if index i is not initialized in the array. |
| inline Value get(int i, Value defaultv) const; |
| |
| iterator find(int i); |
| |
| const_iterator find(int i) const; |
| |
| // Change the value at index i to v. |
| // Fast but unsafe: only use if has_index(i) is true. |
| inline iterator set_existing(int i, Value v); |
| |
| // Set the value at the new index i to v. |
| // Fast but unsafe: only use if has_index(i) is false. |
| inline iterator set_new(int i, Value v); |
| |
| // Get the value at index i from the array.. |
| // Fast but unsafe: only use if has_index(i) is true. |
| inline 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. |
| inline void erase(int i); |
| |
| // Erases the element at index i from the array. |
| // Fast but unsafe: only use if has_index(i) is true. |
| inline void erase_existing(int i); |
| |
| private: |
| // 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. |
| inline 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. |
| inline void DebugCheckInvariants() const; |
| |
| int size_; |
| int max_size_; |
| int* sparse_to_dense_; |
| vector<IndexValue> dense_; |
| bool valgrind_; |
| |
| DISALLOW_EVIL_CONSTRUCTORS(SparseArray); |
| }; |
| |
| template<typename Value> |
| SparseArray<Value>::SparseArray() |
| : size_(0), max_size_(0), sparse_to_dense_(NULL), dense_(), valgrind_(RunningOnValgrind()) {} |
| |
| // 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 index, const Value& value) : second(value), index_(index) {} |
| |
| int index() const { return index_; } |
| Value value() const { return second; } |
| |
| // Provide the data in the 'second' member so that the utilities |
| // in map-util work. |
| Value second; |
| |
| private: |
| int index_; |
| }; |
| |
| template<typename Value> |
| const typename SparseArray<Value>::IndexValue& |
| SparseArray<Value>::iv(int i) const { |
| DCHECK_GE(i, 0); |
| DCHECK_LT(i, size_); |
| return dense_[i]; |
| } |
| |
| // Change the maximum size of the array. |
| // Invalidates all iterators. |
| template<typename Value> |
| void SparseArray<Value>::resize(int new_max_size) { |
| DebugCheckInvariants(); |
| if (new_max_size > max_size_) { |
| int* a = new int[new_max_size]; |
| if (sparse_to_dense_) { |
| memmove(a, sparse_to_dense_, max_size_*sizeof a[0]); |
| // Don't need to zero the memory but appease Valgrind. |
| if (valgrind_) { |
| for (int i = max_size_; i < new_max_size; i++) |
| a[i] = 0xababababU; |
| } |
| delete[] sparse_to_dense_; |
| } |
| sparse_to_dense_ = a; |
| |
| dense_.resize(new_max_size); |
| } |
| max_size_ = new_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 { |
| DCHECK_GE(i, 0); |
| DCHECK_LT(i, max_size_); |
| if (static_cast<uint>(i) >= max_size_) { |
| return false; |
| } |
| // Unsigned comparison avoids checking sparse_to_dense_[i] < 0. |
| return (uint)sparse_to_dense_[i] < (uint)size_ && |
| dense_[sparse_to_dense_[i]].index_ == i; |
| } |
| |
| // Set the value at index i to v. |
| template<typename Value> |
| typename SparseArray<Value>::iterator SparseArray<Value>::set(int i, Value v) { |
| DebugCheckInvariants(); |
| if (static_cast<uint>(i) >= max_size_) { |
| // 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 (!has_index(i)) |
| create_index(i); |
| return set_existing(i, v); |
| } |
| |
| template<typename Value> |
| pair<typename SparseArray<Value>::iterator, bool> SparseArray<Value>::insert( |
| const value_type& new_value) { |
| DebugCheckInvariants(); |
| pair<typename SparseArray<Value>::iterator, bool> p; |
| if (has_index(new_value.index_)) { |
| p = make_pair(dense_.begin() + sparse_to_dense_[new_value.index_], false); |
| } else { |
| p = make_pair(set_new(new_value.index_, new_value.second), true); |
| } |
| DebugCheckInvariants(); |
| return p; |
| } |
| |
| template<typename Value> |
| Value SparseArray<Value>::get(int i, Value defaultv) const { |
| if (!has_index(i)) |
| return defaultv; |
| return get_existing(i); |
| } |
| |
| template<typename Value> |
| typename SparseArray<Value>::iterator SparseArray<Value>::find(int i) { |
| if (has_index(i)) |
| return dense_.begin() + sparse_to_dense_[i]; |
| return end(); |
| } |
| |
| template<typename Value> |
| typename SparseArray<Value>::const_iterator |
| SparseArray<Value>::find(int i) const { |
| if (has_index(i)) { |
| return dense_.begin() + sparse_to_dense_[i]; |
| } |
| return end(); |
| } |
| |
| template<typename Value> |
| typename SparseArray<Value>::iterator |
| SparseArray<Value>::set_existing(int i, Value v) { |
| DebugCheckInvariants(); |
| DCHECK(has_index(i)); |
| dense_[sparse_to_dense_[i]].second = v; |
| DebugCheckInvariants(); |
| return dense_.begin() + sparse_to_dense_[i]; |
| } |
| |
| template<typename Value> |
| typename SparseArray<Value>::iterator |
| SparseArray<Value>::set_new(int i, Value v) { |
| DebugCheckInvariants(); |
| if (static_cast<uint>(i) >= max_size_) { |
| // 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(); |
| } |
| DCHECK(!has_index(i)); |
| create_index(i); |
| return set_existing(i, v); |
| } |
| |
| template<typename Value> |
| Value SparseArray<Value>::get_existing(int i) const { |
| DCHECK(has_index(i)); |
| return dense_[sparse_to_dense_[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(); |
| DCHECK(has_index(i)); |
| int di = sparse_to_dense_[i]; |
| if (di < size_ - 1) { |
| dense_[di] = dense_[size_ - 1]; |
| sparse_to_dense_[dense_[di].index_] = di; |
| } |
| size_--; |
| DebugCheckInvariants(); |
| } |
| |
| template<typename Value> |
| void SparseArray<Value>::create_index(int i) { |
| DCHECK(!has_index(i)); |
| DCHECK_LT(size_, max_size_); |
| sparse_to_dense_[i] = size_; |
| dense_[size_].index_ = i; |
| size_++; |
| } |
| |
| template<typename Value> SparseArray<Value>::SparseArray(int max_size) { |
| max_size_ = max_size; |
| sparse_to_dense_ = new int[max_size]; |
| valgrind_ = RunningOnValgrind(); |
| dense_.resize(max_size); |
| // Don't need to zero the new memory, but appease Valgrind. |
| if (valgrind_) { |
| for (int i = 0; i < max_size; i++) { |
| sparse_to_dense_[i] = 0xababababU; |
| dense_[i].index_ = 0xababababU; |
| } |
| } |
| size_ = 0; |
| DebugCheckInvariants(); |
| } |
| |
| template<typename Value> SparseArray<Value>::~SparseArray() { |
| DebugCheckInvariants(); |
| delete[] sparse_to_dense_; |
| } |
| |
| template<typename Value> void SparseArray<Value>::DebugCheckInvariants() const { |
| DCHECK_LE(0, size_); |
| DCHECK_LE(size_, max_size_); |
| DCHECK(size_ == 0 || sparse_to_dense_ != 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 // RE2_UTIL_SPARSE_ARRAY_H__ |