001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.statistics.descriptive;
018
019import java.math.BigInteger;
020
021/**
022 * Returns the sum of the available values.
023 *
024 * <ul>
025 *   <li>The result is zero if no values are added.
026 * </ul>
027 *
028 * <p>This class uses an exact integer sum. The exact sum is
029 * returned using {@link #getAsBigInteger()}. Methods that return {@code int} or
030 * {@code long} primitives will raise an exception if the result overflows.
031 * The {@code long} value is safe up to the maximum array length for any input
032 * {@code int[]} data. The {@code long} value can overflow when instances are combined.
033 *
034 * <p>Note that the implementation does not use {@code BigInteger} arithmetic; for
035 * performance the sum is computed using primitives to create a signed 128-bit integer.
036 * Support is provided for at least 2<sup>63</sup> observations.
037 *
038 * <p>This class is designed to work with (though does not require)
039 * {@linkplain java.util.stream streams}.
040 *
041 * <p><strong>This implementation is not thread safe.</strong>
042 * If multiple threads access an instance of this class concurrently,
043 * and at least one of the threads invokes the {@link java.util.function.IntConsumer#accept(int) accept} or
044 * {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
045 *
046 * <p>However, it is safe to use {@link java.util.function.IntConsumer#accept(int) accept}
047 * and {@link StatisticAccumulator#combine(StatisticResult) combine}
048 * as {@code accumulator} and {@code combiner} functions of
049 * {@link java.util.stream.Collector Collector} on a parallel stream,
050 * because the parallel implementation of {@link java.util.stream.Stream#collect Stream.collect()}
051 * provides the necessary partitioning, isolation, and merging of results for
052 * safe and efficient parallel execution.
053 *
054 * @since 1.1
055 */
056public final class IntSum implements IntStatistic, StatisticAccumulator<IntSum> {
057    /** Sum of the values. */
058    private final Int128 sum;
059
060    /**
061     * Create an instance.
062     */
063    private IntSum() {
064        this(Int128.create());
065    }
066
067    /**
068     * Create an instance.
069     *
070     * @param sum Sum of the values.
071     */
072    private IntSum(Int128 sum) {
073        this.sum = sum;
074    }
075
076    /**
077     * Creates an instance.
078     *
079     * <p>The initial result is zero.
080     *
081     * @return {@code IntSum} instance.
082     */
083    public static IntSum create() {
084        return new IntSum();
085    }
086
087    /**
088     * Returns an instance populated using the input {@code values}.
089     *
090     * <p>When the input is an empty array, the result is zero.
091     *
092     * <p>The {@link #getAsLong()} result is valid for any input {@code int[]} length;
093     * the {@link #getAsInt()} result may overflow.
094     *
095     * @param values Values.
096     * @return {@code IntSum} instance.
097     */
098    public static IntSum of(int... values) {
099        // Sum of an array cannot exceed a 64-bit long
100        long s = 0;
101        for (final int x : values) {
102            s += x;
103        }
104        // Convert
105        return new IntSum(Int128.of(s));
106    }
107
108    /**
109     * Returns an instance populated using the specified range of {@code values}.
110     *
111     * <p>When the range is empty, the result is zero.
112     *
113     * <p>The {@link #getAsLong()} result is valid for any range length;
114     * the {@link #getAsInt()} result may overflow.
115     *
116     * @param values Values.
117     * @param from Inclusive start of the range.
118     * @param to Exclusive end of the range.
119     * @return {@code IntSum} instance.
120     * @throws IndexOutOfBoundsException if the sub-range is out of bounds
121     * @since 1.2
122     */
123    public static IntSum ofRange(int[] values, int from, int to) {
124        Statistics.checkFromToIndex(from, to, values.length);
125        return createFromRange(values, from, to);
126    }
127
128    /**
129     * Create an instance using the specified range of {@code values}.
130     *
131     * <p>Warning: No range checks are performed.
132     *
133     * @param values Values.
134     * @param from Inclusive start of the range.
135     * @param to Exclusive end of the range.
136     * @return {@code IntSum} instance.
137     */
138    static IntSum createFromRange(int[] values, int from, int to) {
139        // Sum of an array cannot exceed a 64-bit long
140        long s = 0;
141        for (int i = from; i < to; i++) {
142            s += values[i];
143        }
144        // Convert
145        return new IntSum(Int128.of(s));
146    }
147
148    /**
149     * Gets the sum.
150     *
151     * <p>This is package private for use in {@link IntStatistics}.
152     *
153     * @return the sum
154     */
155    Int128 getSum() {
156        return sum;
157    }
158
159    /**
160     * Updates the state of the statistic to reflect the addition of {@code value}.
161     *
162     * @param value Value.
163     */
164    @Override
165    public void accept(int value) {
166        sum.add(value);
167    }
168
169    /**
170     * Gets the sum of all input values.
171     *
172     * <p>When no values have been added, the result is zero.
173     *
174     * <p>Warning: This will raise an {@link ArithmeticException}
175     * if the result is not within the range {@code [-2^31, 2^31)}.
176     *
177     * @return sum of all values.
178     * @throws ArithmeticException if the {@code result} overflows an {@code int}
179     * @see #getAsBigInteger()
180     */
181    @Override
182    public int getAsInt() {
183        return sum.toIntExact();
184    }
185
186    /**
187     * Gets the sum of all input values.
188     *
189     * <p>When no values have been added, the result is zero.
190     *
191     * <p>Warning: This will raise an {@link ArithmeticException}
192     * if the result is not within the range {@code [-2^63, 2^63)}.
193     *
194     * @return sum of all values.
195     * @throws ArithmeticException if the {@code result} overflows a {@code long}
196     * @see #getAsBigInteger()
197     */
198    @Override
199    public long getAsLong() {
200        return sum.toLongExact();
201    }
202
203    /**
204     * Gets the sum of all input values.
205     *
206     * <p>When no values have been added, the result is zero.
207     *
208     * <p>Note that this conversion can lose information about the precision of the
209     * {@code BigInteger} value.
210     *
211     * @return sum of all values.
212     * @see #getAsBigInteger()
213     */
214    @Override
215    public double getAsDouble() {
216        return sum.toDouble();
217    }
218
219    /**
220     * Gets the sum of all input values.
221     *
222     * <p>When no values have been added, the result is zero.
223     *
224     * @return sum of all values.
225     */
226    @Override
227    public BigInteger getAsBigInteger() {
228        return sum.toBigInteger();
229    }
230
231    @Override
232    public IntSum combine(IntSum other) {
233        sum.add(other.sum);
234        return this;
235    }
236}