[SYSTEMML-2043] New abstraction for large dense row blocks

This patch introduces a new abstraction for dense row blocks, which is
the basis for supporting both small and large (>16GB) dense blocks,
while enabling memory-efficient linearized representations and efficient
operations for entire dense blocks.

src/main/java/org/apache/sysml/runtime/matrix/data/DenseBlock.java

@@ -0,0 +1,155 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ * 
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+
+package org.apache.sysml.runtime.matrix.data;
+
+import java.io.Serializable;
+
+/**
+ * This DenseBlock is an abstraction for different dense, row-major 
+ * matrix formats. For efficient dense operations, this API does not
+ * expose a row but a row-block abstraction, where a block can contain
+ * one or many contiguous rows.
+ * 
+ */
+public abstract class DenseBlock implements Serializable
+{
+	private static final long serialVersionUID = 7517220490270237832L;
+
+	public enum Type {
+		DRB, //dense row block
+		LDBR, //large dense row block
+	}
+
+	/**
+	 * Resets the dense block by deleting non-zero values. After this
+	 * call all countNonZeros() calls are guaranteed to return 0.
+	 */
+	public abstract void reset();
+
+	/**
+	 * Resets the dense block by deleting non-zero values. After this
+	 * call all countNonZeros() calls are guaranteed to return 0. If
+	 * the new dimensions exceed the current capacity, the underlying
+	 * storage is extended accordingly.
+	 * 
+	 * @param rlen number of rows
+	 * @param clen number of columns
+	 */
+	public abstract void reset(int rlen, int clen);
+
+	/**
+	 * Get the number of rows.
+	 * 
+	 * @return number of rows
+	 */
+	public abstract int numRows();
+
+	/**
+	 * Get the number of allocated blocks.
+	 * 
+	 * @return number of blocks
+	 */
+	public abstract int numBlocks();
+
+	/**
+	 * Get the length of the dense block as the product
+	 * of row and column dimensions.
+	 * 
+	 * @return length
+	 */
+	public abstract long size();
+
+	/**
+	 * Get the total length of allocated blocks.
+	 * 
+	 * @return capacity
+	 */
+	public abstract long capacity();
+
+	/**
+	 * Compute the number of non-zero values, which potentially 
+	 * makes a full pass over the underlying blocks.
+	 * 
+	 * @return number of non-zeros
+	 */
+	public abstract long countNonZeros();
+
+	/**
+	 * Get the allocated blocks.
+	 * 
+	 * @return blocks
+	 */
+	public abstract double[][] values();
+
+
+	/**
+	 * Get an allocated block.
+	 * 
+	 * @param bix block index
+	 * @return block
+	 */
+	public abstract double[] values(int bix);
+
+	/**
+	 * Get the block index for a given row.
+	 * 
+	 * @param r row index
+	 * @return block index
+	 */
+	public abstract int index(int r);
+
+	/**
+	 * Get the position for a given row within
+	 * its associated block.
+	 * 
+	 * @param r row index
+	 * @return block position
+	 */
+	public abstract int pos(int r);
+
+	/**
+	 * Get the position for a given row and column
+	 * within the associated block.
+	 * 
+	 * @param r row index
+	 * @param c column index
+	 * @return block position
+	 */
+	public abstract int pos(int r, int c);
+
+	/**
+	 * Set the given value for a given row and column.
+	 * 
+	 * @param r row index
+	 * @param c column index
+	 * @param v value
+	 */
+	public abstract void set(int r, int c, double v);
+
+	/**
+	 * Get the value for a given row and column.
+	 * 
+	 * @param r row index
+	 * @param c column index
+	 * @return value
+	 */
+	public abstract double get(int r, int c);
+}