Add a vector class that can be referenced with both positive and negative indices. It is internally represented as two vectors, one for non-zero indices and one for negative indices. In this way, the vector can grow in both directions. If an index is not available in the vector, the default value is returned. If an object is put in the vector beyond its size, the empty spots in between are also filled with the default value.

I hope I'm not reinventing the wheel too much here. This might change anyway if this appears to be a performance bottleneck. 

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@32929 a592a061-630c-0410-9148-cb99ea01b6c8

src/Compare.cpp

@@ -183,6 +183,70 @@ static DocRangePair stepIntoInset(DocPair const & inset_location)
 }
 
 
+/**
+ *  This class is designed to hold a vector that has both positive as
+ *  negative indices. It is internally represented as two vectors, one
+ *  for non-zero indices and one for negative indices. In this way, the
+ *  vector can grow in both directions.
+ *    If an index is not available in the vector, the default value is
+ *  returned. If an object is put in the vector beyond its size, the
+ *  empty spots in between are also filled with the default value.
+ */
+template<class T>
+class compl_vector {
+public:
+	compl_vector() {}
+
+	void reset(T const & def)
+	{
+		default_ = def;
+		Vp_.clear();
+		Vn_.clear();
+	}
+
+
+	/// Gets the value at index. If it is not in the vector
+	/// the default value is returned.
+	T & get(int index) {
+		if (-index <= int(Vn_.size()) && index < int(Vp_.size()))
+			return index >= 0 ? Vp_[index] : Vn_[-index-1];
+		else
+			return default_;
+	}
+
+	/// Sets the value at index if it already
+	/// is in the vector. Otherwise it will be added to the
+	/// end padded with the default value.
+	void set(int index, T const & t) {
+		if (index >= -int(Vn_.size()) && index < int(Vp_.size())) {
+			if (index >= 0)
+				Vp_[index] = t;
+			else 
+				Vn_[-index-1] = t;
+		} else {
+			while (index > int(Vp_.size()))
+				Vp_.push_back(default_);
+			while (index < -int(Vn_.size()) - 1)
+				Vn_.push_back(default_);
+
+			if (index >= 0)
+				Vp_.push_back(t);
+			else
+				Vn_.push_back(t);
+		}
+	}
+
+private:
+	/// The vector for positive indices
+	vector<T> Vp_;
+	/// The vector for negative indices
+	vector<T> Vn_;
+	/// The default value that is inserted in the vector
+	/// if more space is needed
+	T default_;
+};
+
+
 /**
  * The implementation of the algorithm that does the comparison
  * between two documents.