src/main/java/org/apache/sysds/runtime/compress/utils/IntArrayList.java

/*
 * 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.sysds.runtime.compress.utils;

import java.util.Arrays;

/**
 * This class provides a memory-efficient replacement for {@code ArrayList<Integer>} for restricted use cases.
 */
public class IntArrayList {
	private static final int INIT_CAPACITY = 4;
	private static final int RESIZE_FACTOR = 2;

	private int[] _data = null;
	private int _size;
	private int _val0;

	public IntArrayList() {
		_data = null;
		_size = 0;
	}

	public IntArrayList(int value) {
		this();
		appendValue(value);
	}

	public IntArrayList(int[] values){
		_data = values;
		_size = values.length;
	}

	public int size() {
		return _size;
	}

	public void appendValue(int value) {
		// embedded value (no array allocation)
		if(_size == 0) {
			_val0 = value;
			_size = 1;
			return;
		}

		// allocate or resize array if necessary
		if(_data == null) {
			_data = new int[INIT_CAPACITY];
			_data[0] = _val0;
		}
		else if(_size + 1 >= _data.length) {
			resize();
		}

		// append value
		_data[_size] = value;
		_size++;
	}

	/**
	 * Returns the underlying array of offsets. Note that this array might be physically larger than the actual length
	 * of the offset lists. Use size() to obtain the actual length.
	 * 
	 * @return integer array of offsets, the physical array length may be larger than the length of the offset list
	 */
	public int[] extractValues() {
		if(_size == 1)
			return new int[] {_val0};
		else
			return _data;
	}

	public int[] extractValues(boolean trim) {
		int[] ret = extractValues();
		return (trim && _size < ret.length) ? Arrays.copyOfRange(ret, 0, _size) : ret;
	}

	private void resize() {
		// check for integer overflow on resize
		if(_data.length > Integer.MAX_VALUE / RESIZE_FACTOR)
			throw new RuntimeException("IntArrayList resize leads to integer overflow: size=" + _size);

		// resize data array and copy existing contents
		_data = Arrays.copyOf(_data, _data.length * RESIZE_FACTOR);
	}

	@Override
	public String toString(){
		StringBuilder sb = new StringBuilder();
		
		if(_size == 1){
			sb.append(_val0);
		} else{
			sb.append("[");
			int i = 0;
			for(; i < _size-1; i++){
				sb.append(_data[i] + ",");
			}
			sb.append(_data[i]+"]");
		}
		return sb.toString();
	}
}