1 files changed, 208 insertions, 1 deletions

diff --git a/src/utils.h b/src/utils.h
index 2885c520..d605891e 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -326,9 +326,9 @@ class Vector {
   // Returns a vector using the same backing storage as this one,
   // spanning from and including 'from', to but not including 'to'.
   Vector<T> SubVector(int from, int to) {
-    ASSERT(from < length_);
     ASSERT(to <= length_);
     ASSERT(from < to);
+    ASSERT(0 <= from);
     return Vector<T>(start() + from, to - from);
   }
 
@@ -476,6 +476,213 @@ inline Vector< Handle<Object> > HandleVector(v8::internal::Handle<T>* elms,
 }
 
 
+/*
+ * A class that collects values into a backing store.
+ * Specialized versions of the class can allow access to the backing store
+ * in different ways.
+ * There is no guarantee that the backing store is contiguous (and, as a
+ * consequence, no guarantees that consecutively added elements are adjacent
+ * in memory). The collector may move elements unless it has guaranteed not
+ * to.
+ */
+template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
+class Collector {
+ public:
+  explicit Collector(int initial_capacity = kMinCapacity)
+      : index_(0), size_(0) {
+    if (initial_capacity < kMinCapacity) {
+      initial_capacity = kMinCapacity;
+    }
+    current_chunk_ = Vector<T>::New(initial_capacity);
+  }
+
+  virtual ~Collector() {
+    // Free backing store (in reverse allocation order).
+    current_chunk_.Dispose();
+    for (int i = chunks_.length() - 1; i >= 0; i--) {
+      chunks_.at(i).Dispose();
+    }
+  }
+
+  // Add a single element.
+  inline void Add(T value) {
+    if (index_ >= current_chunk_.length()) {
+      Grow(1);
+    }
+    current_chunk_[index_] = value;
+    index_++;
+    size_++;
+  }
+
+  // Add a block of contiguous elements and return a Vector backed by the
+  // memory area.
+  // A basic Collector will keep this vector valid as long as the Collector
+  // is alive.
+  inline Vector<T> AddBlock(int size, T initial_value) {
+    ASSERT(size > 0);
+    if (size > current_chunk_.length() - index_) {
+      Grow(size);
+    }
+    T* position = current_chunk_.start() + index_;
+    index_ += size;
+    size_ += size;
+    for (int i = 0; i < size; i++) {
+      position[i] = initial_value;
+    }
+    return Vector<T>(position, size);
+  }
+
+
+  // Write the contents of the collector into the provided vector.
+  void WriteTo(Vector<T> destination) {
+    ASSERT(size_ <= destination.length());
+    int position = 0;
+    for (int i = 0; i < chunks_.length(); i++) {
+      Vector<T> chunk = chunks_.at(i);
+      for (int j = 0; j < chunk.length(); j++) {
+        destination[position] = chunk[j];
+        position++;
+      }
+    }
+    for (int i = 0; i < index_; i++) {
+      destination[position] = current_chunk_[i];
+      position++;
+    }
+  }
+
+  // Allocate a single contiguous vector, copy all the collected
+  // elements to the vector, and return it.
+  // The caller is responsible for freeing the memory of the returned
+  // vector (e.g., using Vector::Dispose).
+  Vector<T> ToVector() {
+    Vector<T> new_store = Vector<T>::New(size_);
+    WriteTo(new_store);
+    return new_store;
+  }
+
+  // Resets the collector to be empty.
+  virtual void Reset() {
+    for (int i = chunks_.length() - 1; i >= 0; i--) {
+      chunks_.at(i).Dispose();
+    }
+    chunks_.Rewind(0);
+    index_ = 0;
+    size_ = 0;
+  }
+
+  // Total number of elements added to collector so far.
+  inline int size() { return size_; }
+
+ protected:
+  static const int kMinCapacity = 16;
+  List<Vector<T> > chunks_;
+  Vector<T> current_chunk_;  // Block of memory currently being written into.
+  int index_;  // Current index in current chunk.
+  int size_;  // Total number of elements in collector.
+
+  // Creates a new current chunk, and stores the old chunk in the chunks_ list.
+  void Grow(int min_capacity) {
+    ASSERT(growth_factor > 1);
+    int growth = current_chunk_.length() * (growth_factor - 1);
+    if (growth > max_growth) {
+      growth = max_growth;
+    }
+    int new_capacity = current_chunk_.length() + growth;
+    if (new_capacity < min_capacity) {
+      new_capacity = min_capacity + growth;
+    }
+    Vector<T> new_chunk = Vector<T>::New(new_capacity);
+    int new_index = PrepareGrow(new_chunk);
+    if (index_ > 0) {
+      chunks_.Add(current_chunk_.SubVector(0, index_));
+    } else {
+      // Can happen if the call to PrepareGrow moves everything into
+      // the new chunk.
+      current_chunk_.Dispose();
+    }
+    current_chunk_ = new_chunk;
+    index_ = new_index;
+    ASSERT(index_ + min_capacity <= current_chunk_.length());
+  }
+
+  // Before replacing the current chunk, give a subclass the option to move
+  // some of the current data into the new chunk. The function may update
+  // the current index_ value to represent data no longer in the current chunk.
+  // Returns the initial index of the new chunk (after copied data).
+  virtual int PrepareGrow(Vector<T> new_chunk)  {
+    return 0;
+  }
+};
+
+
+/*
+ * A collector that allows sequences of values to be guaranteed to
+ * stay consecutive.
+ * If the backing store grows while a sequence is active, the current
+ * sequence might be moved, but after the sequence is ended, it will
+ * not move again.
+ * NOTICE: Blocks allocated using Collector::AddBlock(int) can move
+ * as well, if inside an active sequence where another element is added.
+ */
+template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
+class SequenceCollector : public Collector<T, growth_factor, max_growth> {
+ public:
+  explicit SequenceCollector(int initial_capacity)
+      : Collector<T, growth_factor, max_growth>(initial_capacity),
+        sequence_start_(kNoSequence) { }
+
+  virtual ~SequenceCollector() {}
+
+  void StartSequence() {
+    ASSERT(sequence_start_ == kNoSequence);
+    sequence_start_ = this->index_;
+  }
+
+  Vector<T> EndSequence() {
+    ASSERT(sequence_start_ != kNoSequence);
+    int sequence_start = sequence_start_;
+    sequence_start_ = kNoSequence;
+    if (sequence_start == this->index_) return Vector<T>();
+    return this->current_chunk_.SubVector(sequence_start, this->index_);
+  }
+
+  // Drops the currently added sequence, and all collected elements in it.
+  void DropSequence() {
+    ASSERT(sequence_start_ != kNoSequence);
+    int sequence_length = this->index_ - sequence_start_;
+    this->index_ = sequence_start_;
+    this->size_ -= sequence_length;
+    sequence_start_ = kNoSequence;
+  }
+
+  virtual void Reset() {
+    sequence_start_ = kNoSequence;
+    this->Collector<T, growth_factor, max_growth>::Reset();
+  }
+
+ private:
+  static const int kNoSequence = -1;
+  int sequence_start_;
+
+  // Move the currently active sequence to the new chunk.
+  virtual int PrepareGrow(Vector<T> new_chunk) {
+    if (sequence_start_ != kNoSequence) {
+      int sequence_length = this->index_ - sequence_start_;
+      // The new chunk is always larger than the current chunk, so there
+      // is room for the copy.
+      ASSERT(sequence_length < new_chunk.length());
+      for (int i = 0; i < sequence_length; i++) {
+        new_chunk[i] = this->current_chunk_[sequence_start_ + i];
+      }
+      this->index_ = sequence_start_;
+      sequence_start_ = 0;
+      return sequence_length;
+    }
+    return 0;
+  }
+};
+
+
 // Simple support to read a file into a 0-terminated C-string.
 // The returned buffer must be freed by the caller.
 // On return, *exits tells whether the file existed.