1 files changed, 177 insertions, 0 deletions
diff --git a/util/sparse_set.h b/util/sparse_set.h
new file mode 100644
index 0000000..9cb5753
--- /dev/null
+++ b/util/sparse_set.h
@@ -0,0 +1,177 @@
+// 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
+// 
+// SparseSet<T>(m) is a set of integers in [0, m).
+// It requires sizeof(int)*m memory, but it provides
+// fast iteration through the elements in the set and fast clearing
+// of the set.
+// 
+// Insertion and deletion are constant time operations.
+// 
+// Allocating the set is a constant time operation 
+// when memory allocation is a constant time operation.
+// 
+// Clearing the set is a constant time operation (unusual!).
+// 
+// Iterating through the set is an O(n) operation, where n
+// is the number of items in the set (not O(m)).
+//
+// The set iterator visits entries in the order they were first 
+// inserted into the array.  It is safe to add items to the set while
+// using an iterator: the iterator will visit indices added to the set
+// during the iteration, but will not re-visit indices whose values
+// change after visiting.  Thus SparseSet can be a convenient
+// implementation of a work queue.
+// 
+// The SparseSet implementation is NOT thread-safe.  It is up to the
+// caller to make sure only one thread is accessing the set.  (Typically
+// these sets are temporary values and used in situations where speed is
+// important.)
+// 
+// The SparseSet 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.
+// 
+// For a generalization to sparse array, see sparse_array.h.
+
+// IMPLEMENTATION
+//
+// See sparse_array.h for implementation details
+
+#ifndef RE2_UTIL_SPARSE_SET_H__
+#define RE2_UTIL_SPARSE_SET_H__
+
+#include "util/util.h"
+
+namespace re2 {
+
+class SparseSet {
+ public:
+  SparseSet()
+    : size_(0), max_size_(0), sparse_to_dense_(NULL), dense_(NULL) {}
+
+  SparseSet(int max_size) {
+    max_size_ = max_size;
+    sparse_to_dense_ = new int[max_size];
+    dense_ = new int[max_size];
+    // Don't need to zero the memory, but do so anyway
+    // to appease Valgrind.
+    if (RunningOnValgrind()) {
+      for (int i = 0; i < max_size; i++) {
+        dense_[i] = 0xababababU;
+        sparse_to_dense_[i] = 0xababababU;
+      }
+    }
+    size_ = 0;
+  }
+
+  ~SparseSet() {
+    delete[] sparse_to_dense_;
+    delete[] dense_;
+  }
+
+  typedef int* iterator;
+  typedef const int* const_iterator;
+
+  int size() const { return size_; }
+  iterator begin() { return dense_; }
+  iterator end() { return dense_ + size_; }
+  const_iterator begin() const { return dense_; }
+  const_iterator end() const { return dense_ + size_; }
+
+  // Change the maximum size of the array.
+  // Invalidates all iterators.
+  void resize(int new_max_size) {
+    if (size_ > new_max_size)
+      size_ = new_max_size;
+    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]);
+        if (RunningOnValgrind()) {
+          for (int i = max_size_; i < new_max_size; i++)
+            a[i] = 0xababababU;
+        }
+        delete[] sparse_to_dense_;
+      }
+      sparse_to_dense_ = a;
+
+      a = new int[new_max_size];
+      if (dense_) {
+        memmove(a, dense_, size_*sizeof a[0]);
+        if (RunningOnValgrind()) {
+          for (int i = size_; i < new_max_size; i++)
+            a[i] = 0xababababU;
+        }
+        delete[] dense_;
+      }
+      dense_ = a;
+    }
+    max_size_ = new_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 i is in the array.
+  bool contains(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]] == i;
+  }
+
+  // Adds i to the set.
+  void insert(int i) {
+    if (!contains(i))
+      insert_new(i);
+  }
+
+  // Set the value at the new index i to v.
+  // Fast but unsafe: only use if contains(i) is false.
+  void insert_new(int i) {
+    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;
+    }
+    DCHECK(!contains(i));
+    DCHECK_LT(size_, max_size_);
+    sparse_to_dense_[i] = size_;
+    dense_[size_] = i;
+    size_++;
+  }
+
+  // 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(int a, int b) { return a < b; }
+
+ private:
+  int size_;
+  int max_size_;
+  int* sparse_to_dense_;
+  int* dense_;
+
+  DISALLOW_EVIL_CONSTRUCTORS(SparseSet);
+};
+
+}  // namespace re2
+
+#endif  // RE2_UTIL_SPARSE_SET_H__