1 // Copyright 2006 The RE2 Authors. All Rights Reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // DESCRIPTION 6 // 7 // SparseSet<T>(m) is a set of integers in [0, m). 8 // It requires sizeof(int)*m memory, but it provides 9 // fast iteration through the elements in the set and fast clearing 10 // of the set. 11 // 12 // Insertion and deletion are constant time operations. 13 // 14 // Allocating the set is a constant time operation 15 // when memory allocation is a constant time operation. 16 // 17 // Clearing the set is a constant time operation (unusual!). 18 // 19 // Iterating through the set is an O(n) operation, where n 20 // is the number of items in the set (not O(m)). 21 // 22 // The set iterator visits entries in the order they were first 23 // inserted into the array. It is safe to add items to the set while 24 // using an iterator: the iterator will visit indices added to the set 25 // during the iteration, but will not re-visit indices whose values 26 // change after visiting. Thus SparseSet can be a convenient 27 // implementation of a work queue. 28 // 29 // The SparseSet implementation is NOT thread-safe. It is up to the 30 // caller to make sure only one thread is accessing the set. (Typically 31 // these sets are temporary values and used in situations where speed is 32 // important.) 33 // 34 // The SparseSet interface does not present all the usual STL bells and 35 // whistles. 36 // 37 // Implemented with reference to Briggs & Torczon, An Efficient 38 // Representation for Sparse Sets, ACM Letters on Programming Languages 39 // and Systems, Volume 2, Issue 1-4 (March-Dec. 1993), pp. 59-69. 40 // 41 // For a generalization to sparse array, see sparse_array.h. 42 43 // IMPLEMENTATION 44 // 45 // See sparse_array.h for implementation details 46 47 #ifndef RE2_UTIL_SPARSE_SET_H__ 48 #define RE2_UTIL_SPARSE_SET_H__ 49 50 #include "util/util.h" 51 52 namespace re2 { 53 54 class SparseSet { 55 public: 56 SparseSet() 57 : size_(0), max_size_(0), sparse_to_dense_(NULL), dense_(NULL), valgrind_(RunningOnValgrind()) {} 58 59 SparseSet(int max_size) { 60 max_size_ = max_size; 61 sparse_to_dense_ = new int[max_size]; 62 dense_ = new int[max_size]; 63 valgrind_ = RunningOnValgrind(); 64 // Don't need to zero the memory, but do so anyway 65 // to appease Valgrind. 66 if (valgrind_) { 67 for (int i = 0; i < max_size; i++) { 68 dense_[i] = 0xababababU; 69 sparse_to_dense_[i] = 0xababababU; 70 } 71 } 72 size_ = 0; 73 } 74 75 ~SparseSet() { 76 delete[] sparse_to_dense_; 77 delete[] dense_; 78 } 79 80 typedef int* iterator; 81 typedef const int* const_iterator; 82 83 int size() const { return size_; } 84 iterator begin() { return dense_; } 85 iterator end() { return dense_ + size_; } 86 const_iterator begin() const { return dense_; } 87 const_iterator end() const { return dense_ + size_; } 88 89 // Change the maximum size of the array. 90 // Invalidates all iterators. 91 void resize(int new_max_size) { 92 if (size_ > new_max_size) 93 size_ = new_max_size; 94 if (new_max_size > max_size_) { 95 int* a = new int[new_max_size]; 96 if (sparse_to_dense_) { 97 memmove(a, sparse_to_dense_, max_size_*sizeof a[0]); 98 if (valgrind_) { 99 for (int i = max_size_; i < new_max_size; i++) 100 a[i] = 0xababababU; 101 } 102 delete[] sparse_to_dense_; 103 } 104 sparse_to_dense_ = a; 105 106 a = new int[new_max_size]; 107 if (dense_) { 108 memmove(a, dense_, size_*sizeof a[0]); 109 if (valgrind_) { 110 for (int i = size_; i < new_max_size; i++) 111 a[i] = 0xababababU; 112 } 113 delete[] dense_; 114 } 115 dense_ = a; 116 } 117 max_size_ = new_max_size; 118 } 119 120 // Return the maximum size of the array. 121 // Indices can be in the range [0, max_size). 122 int max_size() const { return max_size_; } 123 124 // Clear the array. 125 void clear() { size_ = 0; } 126 127 // Check whether i is in the array. 128 bool contains(int i) const { 129 DCHECK_GE(i, 0); 130 DCHECK_LT(i, max_size_); 131 if (static_cast<uint>(i) >= max_size_) { 132 return false; 133 } 134 // Unsigned comparison avoids checking sparse_to_dense_[i] < 0. 135 return (uint)sparse_to_dense_[i] < (uint)size_ && 136 dense_[sparse_to_dense_[i]] == i; 137 } 138 139 // Adds i to the set. 140 void insert(int i) { 141 if (!contains(i)) 142 insert_new(i); 143 } 144 145 // Set the value at the new index i to v. 146 // Fast but unsafe: only use if contains(i) is false. 147 void insert_new(int i) { 148 if (static_cast<uint>(i) >= max_size_) { 149 // Semantically, end() would be better here, but we already know 150 // the user did something stupid, so begin() insulates them from 151 // dereferencing an invalid pointer. 152 return; 153 } 154 DCHECK(!contains(i)); 155 DCHECK_LT(size_, max_size_); 156 sparse_to_dense_[i] = size_; 157 dense_[size_] = i; 158 size_++; 159 } 160 161 // Comparison function for sorting. 162 // Can sort the sparse array so that future iterations 163 // will visit indices in increasing order using 164 // sort(arr.begin(), arr.end(), arr.less); 165 static bool less(int a, int b) { return a < b; } 166 167 private: 168 int size_; 169 int max_size_; 170 int* sparse_to_dense_; 171 int* dense_; 172 bool valgrind_; 173 174 DISALLOW_EVIL_CONSTRUCTORS(SparseSet); 175 }; 176 177 } // namespace re2 178 179 #endif // RE2_UTIL_SPARSE_SET_H__ 180
