code: /**
   * Copyright (c) 2004-2005, 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:
   *
   * Redistributions of source code must retain the above copyright notice,
   * this list of conditions and the following disclaimer.
   *
   * 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.
   *
   * Neither the name of the University of California, Los Angeles nor the
   * names of its contributors may be used to endorse or promote products
   * derived from this software without specific prior written permission.
   *
   * 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
   * OWNER 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 avrora.sim.util;
  
  import avrora.sim.Simulator;
  import avrora.sim.State;
  
  /**
   * The <code>SequenceProbe</code> is a probe composer that allows a probe to be fired for every instruction
   * executed between a specified entrypoint and a specified exit point. For example, if the entrypoint is a
   * call instruction and the exit point is the instruction following the call instruction, then the probe will
   * fire for every instruction executed between the call and return, including both the call and the
   * instruction following the call. <br><br>
   * <p/>
   * This probe supports nested entries (e.g. recursive calls). It is best used on pieces of the program that
   * are single-entry/single-exit such as calls, interrupts, basic blocks, and SSE regions of control flow
   * graphs. It does not work well for loops because of the nesting behavior.
   *
   * @author Ben L. Titzer
   */
  public class SequenceProbe implements Simulator.Probe {
  
      /**
       * The immutable <code>entry_addr</code> field stores the address that enables the per-instruction calling
       * of the probe passed in the constructor.
       */
      public final int entry_addr;
  
      /**
       * The immutable <code>exit_addr</code> field stores the address that disables the per-instruction calling
       * of the probe passed when the nesting level reaches zero.
       */
      public final int exit_addr;
  
      /**
       * The immutable <code>probe</code> field stores a reference to the probe passed in the constructor.
       */
      public final Simulator.Probe probe;
  
      /**
       * The <code>nesting</code> field stores the current nesting level (i.e. the number of times
       * <code>entry_addr</code> has been reached without <code>exit_addr</code> intervening).
       */
      public int nesting;
  
      /**
       * The constructor for the <code>SequenceProbe</code> class simply stores its arguments into the
       * corresponding public final fields in this object, leaving the probe in a state where it is ready to be
       * inserted into a simulator.
       *
       * @param p     the probe to fire for each instruction when the sequence is entered
       * @param entry the byte address of the entrypoint to the sequence
       * @param exit  the byte address of the exitpoint of the sequence
       */
      public SequenceProbe(Simulator.Probe p, int entry, int exit) {
          entry_addr = entry;
          exit_addr = exit;
          probe = p;
      }
  
      /**
       * The <code>fireBefore()</code> method is called before the probed instruction executes. In the
       * implementation of the sequence probe, if the address is the entrypoint address, then the nesting level
       * is incremented. When the nesting level is greater than one, then the sequence probe will delegate the
       * <code>fireBefore()</code> call to the user probe.
       *
       * @param state   the state of the simulation
       * @param pc the address at which this instruction resides
       */
      public void fireBefore(State state, int pc) {
          if (pc == entry_addr) nesting++;
          if (nesting > 0) probe.fireBefore(state, pc);
      }
  
      /**
       * The <code>fireBefore()</code> method is called before the probed instruction executes. When the nesting
       * level is greater than one, then the sequence probe will delegate the <code>fireAfter()</code> call to
       * the user probe.  If the address is the exit point, then the nesting level is decremented after the call
       * to <code>fireAfter()</code> of the user probe.
       *
       * @param state   the state of the simulation
       * @param pc the address at which this instruction resides
       */
      public void fireAfter(State state, int pc) {
          if (nesting > 0) probe.fireAfter(state, pc);
          if (pc == exit_addr)
              nesting = (nesting - 1) <= 0 ? 0 : nesting - 1;
      }
  
      /**
       * The <code>reset()</code> method simply resets the nesting level of the sequence probe, as if it had
       * exited from all nested entries into the region.
       */
      public void reset() {
          nesting = 0;
      }
  }
  