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), 58 valgrind_(RunningOnValgrindOrMemorySanitizer()) {} 59 60 SparseSet(int max_size) { 61 max_size_ = max_size; 62 sparse_to_dense_ = new int[max_size]; 63 dense_ = new int[max_size]; 64 valgrind_ = RunningOnValgrindOrMemorySanitizer(); 65 // Don't need to zero the memory, but do so anyway 66 // to appease Valgrind. 67 if (valgrind_) { 68 for (int i = 0; i < max_size; i++) { 69 dense_[i] = 0xababababU; 70 sparse_to_dense_[i] = 0xababababU; 71 } 72 } 73 size_ = 0; 74 } 75 76 ~SparseSet() { 77 delete[] sparse_to_dense_; 78 delete[] dense_; 79 } 80 81 typedef int* iterator; 82 typedef const int* const_iterator; 83 84 int size() const { return size_; } 85 iterator begin() { return dense_; } 86 iterator end() { return dense_ + size_; } 87 const_iterator begin() const { return dense_; } 88 const_iterator end() const { return dense_ + size_; } 89 90 // Change the maximum size of the array. 91 // Invalidates all iterators. 92 void resize(int new_max_size) { 93 if (size_ > new_max_size) 94 size_ = new_max_size; 95 if (new_max_size > max_size_) { 96 int* a = new int[new_max_size]; 97 if (sparse_to_dense_) { 98 memmove(a, sparse_to_dense_, max_size_*sizeof a[0]); 99 if (valgrind_) { 100 for (int i = max_size_; i < new_max_size; i++) 101 a[i] = 0xababababU; 102 } 103 delete[] sparse_to_dense_; 104 } 105 sparse_to_dense_ = a; 106 107 a = new int[new_max_size]; 108 if (dense_) { 109 memmove(a, dense_, size_*sizeof a[0]); 110 if (valgrind_) { 111 for (int i = size_; i < new_max_size; i++) 112 a[i] = 0xababababU; 113 } 114 delete[] dense_; 115 } 116 dense_ = a; 117 } 118 max_size_ = new_max_size; 119 } 120 121 // Return the maximum size of the array. 122 // Indices can be in the range [0, max_size). 123 int max_size() const { return max_size_; } 124 125 // Clear the array. 126 void clear() { size_ = 0; } 127 128 // Check whether i is in the array. 129 bool contains(int i) const { 130 DCHECK_GE(i, 0); 131 DCHECK_LT(i, max_size_); 132 if (static_cast<uint>(i) >= max_size_) { 133 return false; 134 } 135 // Unsigned comparison avoids checking sparse_to_dense_[i] < 0. 136 return (uint)sparse_to_dense_[i] < (uint)size_ && 137 dense_[sparse_to_dense_[i]] == i; 138 } 139 140 // Adds i to the set. 141 void insert(int i) { 142 if (!contains(i)) 143 insert_new(i); 144 } 145 146 // Set the value at the new index i to v. 147 // Fast but unsafe: only use if contains(i) is false. 148 void insert_new(int i) { 149 if (static_cast<uint>(i) >= max_size_) { 150 // Semantically, end() would be better here, but we already know 151 // the user did something stupid, so begin() insulates them from 152 // dereferencing an invalid pointer. 153 return; 154 } 155 DCHECK(!contains(i)); 156 DCHECK_LT(size_, max_size_); 157 sparse_to_dense_[i] = size_; 158 dense_[size_] = i; 159 size_++; 160 } 161 162 // Comparison function for sorting. 163 // Can sort the sparse array so that future iterations 164 // will visit indices in increasing order using 165 // sort(arr.begin(), arr.end(), arr.less); 166 static bool less(int a, int b) { return a < b; } 167 168 private: 169 int size_; 170 int max_size_; 171 int* sparse_to_dense_; 172 int* dense_; 173 bool valgrind_; 174 175 DISALLOW_EVIL_CONSTRUCTORS(SparseSet); 176 }; 177 178 } // namespace re2 179 180 #endif // RE2_UTIL_SPARSE_SET_H__ 181
