third_party/re2/util/sparse_set.h

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