code: /*
   * Copyright (c) 2017-2018 The Regents of the University of California
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   *
   * 1. Redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   * notice, this list of conditions and the following disclaimer in the
   * documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  package edu.berkeley.cs.jqf.fuzz.ei;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  
  import edu.berkeley.cs.jqf.fuzz.util.Counter;
  import edu.berkeley.cs.jqf.fuzz.util.NonZeroCachingCounter;
  import edu.berkeley.cs.jqf.instrument.tracing.events.CallEvent;
  import edu.berkeley.cs.jqf.instrument.tracing.events.ReturnEvent;
  import edu.berkeley.cs.jqf.instrument.tracing.events.TraceEvent;
  import edu.berkeley.cs.jqf.instrument.tracing.events.TraceEventVisitor;
  
  /**
   * A mutable state representing the current call stack with prefix counts,
   * used to compute light-weight execution indexes.
   *
   * @see ExecutionIndex
   *
   * @author Rohan Padhye
   */
  public class ExecutionIndexingState implements TraceEventVisitor {
      private final int COUNTER_SIZE = 6151;
      private final int MAX_SUPPORTED_DEPTH = 1024; // Nothing deeper than this
  
      private int depth = 0;
      private ArrayList<Counter> stackOfCounters = new ArrayList<>();
      private int[] rollingIndex = new int[2*MAX_SUPPORTED_DEPTH];
  
      public ExecutionIndexingState() {
          // Create a counter for depth = 0
          stackOfCounters.add(new NonZeroCachingCounter(COUNTER_SIZE));
      }
  
      public void pushCall(CallEvent e) {
          // Increment counter for call-site (note: this is subject to hash collisions)
          int count = stackOfCounters.get(depth).increment(e.getIid());
  
          // Add to rolling execution index
          rollingIndex[2*depth] = e.getIid();
          rollingIndex[2*depth + 1] = count;
  
          // Increment depth
          depth++;
  
          // Ensure that we do not go very deep
          if (depth >= MAX_SUPPORTED_DEPTH) {
              throw new StackOverflowError("Very deep stack; cannot compute execution index");
          }
  
          // Push a new counter if it does not exist
          if (depth >= stackOfCounters.size()) {
              stackOfCounters.add(new NonZeroCachingCounter(COUNTER_SIZE));
          }
  
      }
  
      public void popReturn(ReturnEvent e) {
          // Clear the top-of-stack
          stackOfCounters.get(depth).clear();
  
          // Decrement depth
          depth--;
  
          assert (depth >= 0);
      }
  
      public ExecutionIndex getExecutionIndex(TraceEvent e) {
          // Increment counter for event (note: this is subject to hash collisions)
          int count = stackOfCounters.get(depth).increment(e.getIid());
  
          // Add to rolling execution index
          rollingIndex[2*depth] = e.getIid();
          rollingIndex[2*depth + 1] = count;
  
          // Snapshot the rolling index
          int size = 2*(depth+1); // 2 integers for each depth value
          int[] ei = Arrays.copyOf(rollingIndex, size);
  
          // Create an execution index
          return new ExecutionIndex(ei);
      }
  
      @Override
      public void visitCallEvent(CallEvent c) {
          this.pushCall(c);
      }
  
      @Override
      public void visitReturnEvent(ReturnEvent r) {
          this.popReturn(r);
      }
  }
  