Replace RE2 import with a dependency

third_party/re2/util/sparse_array.h

-// 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;
-
-  static bool InitMemory() {
-#ifdef MEMORY_SANITIZER
-    return true;
-#else
-    return RunningOnValgrind();
-#endif
-  }
-
-  int size_;
-  int max_size_;
-  int* sparse_to_dense_;
-  vector<IndexValue> dense_;
-
-  DISALLOW_COPY_AND_ASSIGN(SparseArray);
-};
-
-template<typename Value>
-SparseArray<Value>::SparseArray()
-    : size_(0), max_size_(0), sparse_to_dense_(NULL), dense_() {}
-
-// 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]);
-      delete[] sparse_to_dense_;
-    }
-    sparse_to_dense_ = a;
-
-    dense_.resize(new_max_size);
-
-    // These don't need to be initialized for correctness,
-    // but Valgrind will warn about use of uninitialized memory,
-    // so initialize the new memory when compiling debug binaries.
-    // Initialize it to garbage to detect bugs in the future.
-    if (InitMemory()) {
-      for (int i = max_size_; i < new_max_size; i++) {
-        sparse_to_dense_[i] = 0xababababU;
-        dense_[i].index_ = 0xababababU;
-      }
-    }
-  }
-  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) >= static_cast<uint>(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) >= static_cast<uint>(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) >= static_cast<uint>(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];
-  dense_.resize(max_size);
-  // Don't need to zero the new memory, but appease Valgrind.
-  if (InitMemory()) {
-    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__