/*

 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * @test

 * @bug 8046516

 * @summary Segmentation fault in JVM (easily reproducible)

 * @run main/othervm -XX:-TieredCompilation -Xbatch TestLogSum

 * @author jackkamm@gmail.com

 */

import java.util.Arrays;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

public class TestLogSum {

  public static void main(String[] args) {

    double sum;

    for (int i = 0; i < 6; i++) {

        for (int n = 2; n < 30; n++) {

           for (int j = 1; j <= n; j++) {

              for (int k = 1; k <= j; k++) {

                // System.out.println(computeSum(k, j));

                sum = computeSum(k, j);

              }

           }

        }

      }

   }

   private static Map<List<Integer>, Double> cache = new HashMap<List<Integer>, Double>();

   public static double computeSum(int x, int y) {

      List<Integer> key = Arrays.asList(new Integer[] {x, y});

      if (!cache.containsKey(key)) {

        // explicitly creating/updating a double[] array, instead of using the LogSumArray wrapper object, will prevent the error

        LogSumArray toReturn = new LogSumArray(x);

        // changing loop indices will prevent the error

        // in particular, for(z=0; z<x-1; z++), and then using z+1 in place of z, will not produce error

        for (int z = 1; z < x+1; z++) {

           double logSummand = Math.log(z + x + y);

           toReturn.addLogSummand(logSummand);

        }

        // returning the value here without cacheing it will prevent the segfault

        cache.put(key, toReturn.retrieveLogSum());

      }

      return cache.get(key);

   }

   /*

    * Given a bunch of logarithms log(X),log(Y),log(Z),...

    * This class is used to compute the log of the sum, log(X+Y+Z+...)

    */

   private static class LogSumArray {

      private double[] logSummandArray;

      private int currSize;

      private double maxLogSummand;

      public LogSumArray(int maxEntries) {

        this.logSummandArray = new double[maxEntries];

        this.currSize = 0;

        this.maxLogSummand = Double.NEGATIVE_INFINITY;

      }

      public void addLogSummand(double logSummand) {

        logSummandArray[currSize] = logSummand;

        currSize++;

        // removing this line will prevent the error

        maxLogSummand = Math.max(maxLogSummand, logSummand);

      }

      public double retrieveLogSum() {

        if (maxLogSummand == Double.NEGATIVE_INFINITY) return Double.NEGATIVE_INFINITY;

        assert currSize <= logSummandArray.length;

        double factorSum = 0;

        for (int i = 0; i < currSize; i++) {

           factorSum += Math.exp(logSummandArray[i] - maxLogSummand);

        }

        return Math.log(factorSum) + maxLogSummand;

      }

   }

}