code: //==============================================================================
  //	
  //	Copyright (c) 2002-
  //	Authors:
  //	* Dave Parker <d.a.parker@cs.bham.ac.uk> (University of Birmingham/Oxford)
  //	* Joachim Klein <klein@tcs.inf.tu-dresden.de> (TU Dresden)
  //	
  //------------------------------------------------------------------------------
  //	
  //	This file is part of PRISM.
  //	
  //	PRISM is free software; you can redistribute it and/or modify
  //	it under the terms of the GNU General Public License as published by
  //	the Free Software Foundation; either version 2 of the License, or
  //	(at your option) any later version.
  //	
  //	PRISM 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 for more details.
  //	
  //	You should have received a copy of the GNU General Public License
  //	along with PRISM; if not, write to the Free Software Foundation,
  //	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  //	
  //==============================================================================
  
  package simulator.sampler;
  
  import simulator.*;
  import prism.*;
  import parser.*;
  import parser.ast.*;
  
  public class SamplerBoundedUntilDisc extends SamplerBoolean
  {
  	private Expression left;
  	private Expression right;
  	private int lb;
  	private int ub;
  	private boolean haveUpperBound;
  
  	/**
  	 * Construct a sampler for a (discrete-time) bounded until property.
  	 * Passed in ExpressionTemporal should be a property of this type.
  	 * All constants should have already been evaluated/replaced.
  	 */
  	public SamplerBoundedUntilDisc(ExpressionTemporal expr) throws PrismException
  	{
  		// Make sure expression is of the correct type
  		// Then extract other required info
  		if (expr.getOperator() != ExpressionTemporal.P_U)
  			throw new PrismException("Error creating Sampler");
  		left = expr.getOperand1();
  		right = expr.getOperand2();
  		// Lower bound
  		if (expr.getLowerBound() != null) {
  			lb = expr.getLowerBound().evaluateInt();
  			if (expr.lowerBoundIsStrict()) {
  				// Convert to non-strict bound:  >lb  <=>  >=lb+1
  				lb = lb + 1;
  			}
  		} else {
  			// No lower bound
  			lb = 0;
  		}
  		if (lb < 0) {
  			throw new PrismException("Invalid lower bound in "+expr);
  		}
  		// Upper bound
  		if (expr.getUpperBound() != null) {
  			haveUpperBound = true;
  			ub = expr.getUpperBound().evaluateInt();
  			if (expr.upperBoundIsStrict()) {
  				// Convert to non-strict bound:  <ub  <=>  <=ub-1
  				ub = ub - 1;
  			}
  
  			if (ub < 0) {
  				throw new PrismException("Invalid upper bound in "+expr);
  			}
  		} else {
  			// No upper bound
  			haveUpperBound = false;
  		}
  
  		// Initialise sampler info
  		reset();
  		resetStats();
  	}
  
  	@Override
  	public boolean update(Path path, TransitionList transList) throws PrismLangException
  	{
  		// If the answer is already known we should do nothing
  		if (valueKnown)
  			return true;
  		
  		long pathSize = path.size();
  		// Upper bound exceeded
  		if (haveUpperBound && pathSize > ub) {
  			valueKnown = true;
  			value = false;
  		}
  		// Lower bound not yet exceeded but LHS of until violated
  		// (no need to check RHS because too early)
  		else if (pathSize < lb) {
  			if (!left.evaluateBoolean(path.getCurrentState())) {
  				valueKnown = true;
  				value = false;
  			}
  		}
  		// Current time is between lower/upper bounds...
  		else {
  			State currentState = path.getCurrentState();
  			// Have we reached the target (i.e. RHS of until)?
  			if (right.evaluateBoolean(currentState)) {
  				valueKnown = true;
  				value = true;
  			}
  			// Or, if not, have we violated the LHS of the until?
  			else if (!left.evaluateBoolean(currentState)) {
  				valueKnown = true;
  				value = false;
  			}
  			// Or, if we are now at a deadlock
  			else if (transList != null && transList.isDeadlock()) {
  				valueKnown = true;
  				value = false;
  			}
  			// Otherwise, don't know
  		}
  		
  		return valueKnown;
  	}
  	
  	@Override
  	public boolean needsBoundedNumSteps()
  	{
  		// Bounded if there is an upper bound
  		return haveUpperBound;
  	}
  }
  