text: // Copyright 2008 the V8 project authors. All rights reserved.
  // Copyright 1996 John Maloney and Mario Wolczko.
  
  // This program 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.
  //
  // This program 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 this program; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  
  
  // This implementation of the DeltaBlue benchmark is derived
  // from the Smalltalk implementation by John Maloney and Mario
  // Wolczko. Some parts have been translated directly, whereas
  // others have been modified more aggresively to make it feel
  // more like a JavaScript program.
  
  
  var DeltaBlue = new BenchmarkSuite('DeltaBlue', 71104, [
    new Benchmark('DeltaBlue', deltaBlue)
  ]);
  
  
  /**
   * A JavaScript implementation of the DeltaBlue constrain-solving
   * algorithm, as described in:
   *
   * "The DeltaBlue Algorithm: An Incremental Constraint Hierarchy Solver"
   *   Bjorn N. Freeman-Benson and John Maloney
   *   January 1990 Communications of the ACM,
   *   also available as University of Washington TR 89-08-06.
   *
   * Beware: this benchmark is written in a grotesque style where
   * the constraint model is built by side-effects from constructors.
   * I've kept it this way to avoid deviating too much from the original
   * implementation.
   */
  
  
  /* --- O b j e c t   M o d e l --- */
  
  Object.prototype.inheritsFrom = function (shuper) {
    function Inheriter() { }
    Inheriter.prototype = shuper.prototype;
    this.prototype = new Inheriter();
    this.superConstructor = shuper;
  }
  
  function OrderedCollection() {
    this.elms = new Array();
  }
  
  OrderedCollection.prototype.add = function (elm) {
    this.elms.push(elm);
  }
  
  OrderedCollection.prototype.at = function (index) {
    return this.elms[index];
  }
  
  OrderedCollection.prototype.size = function () {
    return this.elms.length;
  }
  
  OrderedCollection.prototype.removeFirst = function () {
    return this.elms.pop();
  }
  
  OrderedCollection.prototype.remove = function (elm) {
    var index = 0, skipped = 0;
    for (var i = 0; i < this.elms.length; i++) {
      var value = this.elms[i];
      if (value != elm) {
        this.elms[index] = value;
        index++;
      } else {
        skipped++;
      }
    }
    for (var i = 0; i < skipped; i++)
      this.elms.pop();
  }
  
  /* --- *
   * S t r e n g t h
   * --- */
  
  /**
   * Strengths are used to measure the relative importance of constraints.
   * New strengths may be inserted in the strength hierarchy without
   * disrupting current constraints.  Strengths cannot be created outside
   * this class, so pointer comparison can be used for value comparison.
   */
  function Strength(strengthValue, name) {
    this.strengthValue = strengthValue;
    this.name = name;
  }
  
  Strength.stronger = function (s1, s2) {
    return s1.strengthValue < s2.strengthValue;
  }
  
  Strength.weaker = function (s1, s2) {
    return s1.strengthValue > s2.strengthValue;
  }
  
  Strength.weakestOf = function (s1, s2) {
    return this.weaker(s1, s2) ? s1 : s2;
  }
  
  Strength.strongest = function (s1, s2) {
    return this.stronger(s1, s2) ? s1 : s2;
  }
  
  Strength.prototype.nextWeaker = function () {
    switch (this.strengthValue) {
      case 0: return Strength.WEAKEST;
      case 1: return Strength.WEAK_DEFAULT;
      case 2: return Strength.NORMAL;
      case 3: return Strength.STRONG_DEFAULT;
      case 4: return Strength.PREFERRED;
      case 5: return Strength.REQUIRED;
    }
  }
  
  // Strength constants.
  Strength.REQUIRED        = new Strength(0, "required");
  Strength.STONG_PREFERRED = new Strength(1, "strongPreferred");
  Strength.PREFERRED       = new Strength(2, "preferred");
  Strength.STRONG_DEFAULT  = new Strength(3, "strongDefault");
  Strength.NORMAL          = new Strength(4, "normal");
  Strength.WEAK_DEFAULT    = new Strength(5, "weakDefault");
  Strength.WEAKEST         = new Strength(6, "weakest");
  
  /* --- *
   * C o n s t r a i n t
   * --- */
  
  /**
   * An abstract class representing a system-maintainable relationship
   * (or "constraint") between a set of variables. A constraint supplies
   * a strength instance variable; concrete subclasses provide a means
   * of storing the constrained variables and other information required
   * to represent a constraint.
   */
  function Constraint(strength) {
    this.strength = strength;
  }
  
  /**
   * Activate this constraint and attempt to satisfy it.
   */
  Constraint.prototype.addConstraint = function () {
    this.addToGraph();
    planner.incrementalAdd(this);
  }
  
  /**
   * Attempt to find a way to enforce this constraint. If successful,
   * record the solution, perhaps modifying the current dataflow
   * graph. Answer the constraint that this constraint overrides, if
   * there is one, or nil, if there isn't.
   * Assume: I am not already satisfied.
   */
  Constraint.prototype.satisfy = function (mark) {
    this.chooseMethod(mark);
    if (!this.isSatisfied()) {
      if (this.strength == Strength.REQUIRED)
        alert("Could not satisfy a required constraint!");
      return null;
    }
    this.markInputs(mark);
    var out = this.output();
    var overridden = out.determinedBy;
    if (overridden != null) overridden.markUnsatisfied();
    out.determinedBy = this;
    if (!planner.addPropagate(this, mark))
      alert("Cycle encountered");
    out.mark = mark;
    return overridden;
  }
  
  Constraint.prototype.destroyConstraint = function () {
    if (this.isSatisfied()) planner.incrementalRemove(this);
    else this.removeFromGraph();
  }
  
  /**
   * Normal constraints are not input constraints.  An input constraint
   * is one that depends on external state, such as the mouse, the
   * keybord, a clock, or some arbitraty piece of imperative code.
   */
  Constraint.prototype.isInput = function () {
    return false;
  }
  
  /* --- *
   * U n a r y   C o n s t r a i n t
   * --- */
  
  /**
   * Abstract superclass for constraints having a single possible output
   * variable.
   */
  function UnaryConstraint(v, strength) {
    UnaryConstraint.superConstructor.call(this, strength);
    this.myOutput = v;
    this.satisfied = false;
    this.addConstraint();
  }
  
  UnaryConstraint.inheritsFrom(Constraint);
  
  /**
   * Adds this constraint to the constraint graph
   */
  UnaryConstraint.prototype.addToGraph = function () {
    this.myOutput.addConstraint(this);
    this.satisfied = false;
  }
  
  /**
   * Decides if this constraint can be satisfied and records that
   * decision.
   */
  UnaryConstraint.prototype.chooseMethod = function (mark) {
    this.satisfied = (this.myOutput.mark != mark)
      && Strength.stronger(this.strength, this.myOutput.walkStrength);
  }
  
  /**
   * Returns true if this constraint is satisfied in the current solution.
   */
  UnaryConstraint.prototype.isSatisfied = function () {
    return this.satisfied;
  }
  
  UnaryConstraint.prototype.markInputs = function (mark) {
    // has no inputs
  }
  
  /**
   * Returns the current output variable.
   */
  UnaryConstraint.prototype.output = function () {
    return this.myOutput;
  }
  
  /**
   * Calculate the walkabout strength, the stay flag, and, if it is
   * 'stay', the value for the current output of this constraint. Assume
   * this constraint is satisfied.
   */
  UnaryConstraint.prototype.recalculate = function () {
    this.myOutput.walkStrength = this.strength;
    this.myOutput.stay = !this.isInput();
    if (this.myOutput.stay) this.execute(); // Stay optimization
  }
  
  /**
   * Records that this constraint is unsatisfied
   */
  UnaryConstraint.prototype.markUnsatisfied = function () {
    this.satisfied = false;
  }
  
  UnaryConstraint.prototype.inputsKnown = function () {
    return true;
  }
  
  UnaryConstraint.prototype.removeFromGraph = function () {
    if (this.myOutput != null) this.myOutput.removeConstraint(this);
    this.satisfied = false;
  }
  
  /* --- *
   * S t a y   C o n s t r a i n t
   * --- */
  
  /**
   * Variables that should, with some level of preference, stay the same.
   * Planners may exploit the fact that instances, if satisfied, will not
   * change their output during plan execution.  This is called "stay
   * optimization".
   */
  function StayConstraint(v, str) {
    StayConstraint.superConstructor.call(this, v, str);
  }
  
  StayConstraint.inheritsFrom(UnaryConstraint);
  
  StayConstraint.prototype.execute = function () {
    // Stay constraints do nothing
  }
  
  /* --- *
   * E d i t   C o n s t r a i n t
   * --- */
  
  /**
   * A unary input constraint used to mark a variable that the client
   * wishes to change.
   */
  function EditConstraint(v, str) {
    EditConstraint.superConstructor.call(this, v, str);
  }
  
  EditConstraint.inheritsFrom(UnaryConstraint);
  
  /**
   * Edits indicate that a variable is to be changed by imperative code.
   */
  EditConstraint.prototype.isInput = function () {
    return true;
  }
  
  EditConstraint.prototype.execute = function () {
    // Edit constraints do nothing
  }
  
  /* --- *
   * B i n a r y   C o n s t r a i n t
   * --- */
  
  var Direction = new Object();
  Direction.NONE     = 0;
  Direction.FORWARD  = 1;
  Direction.BACKWARD = -1;
  
  /**
   * Abstract superclass for constraints having two possible output
   * variables.
   */
  function BinaryConstraint(var1, var2, strength) {
    BinaryConstraint.superConstructor.call(this, strength);
    this.v1 = var1;
    this.v2 = var2;
    this.direction = Direction.NONE;
    this.addConstraint();
  }
  
  BinaryConstraint.inheritsFrom(Constraint);
  
  /**
   * Decides if this constratint can be satisfied and which way it
   * should flow based on the relative strength of the variables related,
   * and record that decision.
   */
  BinaryConstraint.prototype.chooseMethod = function (mark) {
    if (this.v1.mark == mark) {
      this.direction = (this.v1.mark != mark && Strength.stronger(this.strength, this.v2.walkStrength))
        ? Direction.FORWARD
        : Direction.NONE;
    }
    if (this.v2.mark == mark) {
      this.direction = (this.v1.mark != mark && Strength.stronger(this.strength, this.v1.walkStrength))
        ? Direction.BACKWARD
        : Direction.NONE;
    }
    if (Strength.weaker(this.v1.walkStrength, this.v2.walkStrength)) {
      this.direction = Strength.stronger(this.strength, this.v1.walkStrength)
        ? Direction.BACKWARD
        : Direction.NONE;
    } else {
      this.direction = Strength.stronger(this.strength, this.v2.walkStrength)
        ? Direction.FORWARD
        : Direction.BACKWARD
    }
  }
  
  /**
   * Add this constraint to the constraint graph
   */
  BinaryConstraint.prototype.addToGraph = function () {
    this.v1.addConstraint(this);
    this.v2.addConstraint(this);
    this.direction = Direction.NONE;
  }
  
  /**
   * Answer true if this constraint is satisfied in the current solution.
   */
  BinaryConstraint.prototype.isSatisfied = function () {
    return this.direction != Direction.NONE;
  }
  
  /**
   * Mark the input variable with the given mark.
   */
  BinaryConstraint.prototype.markInputs = function (mark) {
    this.input().mark = mark;
  }
  
  /**
   * Returns the current input variable
   */
  BinaryConstraint.prototype.input = function () {
    return (this.direction == Direction.FORWARD) ? this.v1 : this.v2;
  }
  
  /**
   * Returns the current output variable
   */
  BinaryConstraint.prototype.output = function () {
    return (this.direction == Direction.FORWARD) ? this.v2 : this.v1;
  }
  
  /**
   * Calculate the walkabout strength, the stay flag, and, if it is
   * 'stay', the value for the current output of this
   * constraint. Assume this constraint is satisfied.
   */
  BinaryConstraint.prototype.recalculate = function () {
    var ihn = this.input(), out = this.output();
    out.walkStrength = Strength.weakestOf(this.strength, ihn.walkStrength);
    out.stay = ihn.stay;
    if (out.stay) this.execute();
  }
  
  /**
   * Record the fact that this constraint is unsatisfied.
   */
  BinaryConstraint.prototype.markUnsatisfied = function () {
    this.direction = Direction.NONE;
  }
  
  BinaryConstraint.prototype.inputsKnown = function (mark) {
    var i = this.input();
    return i.mark == mark || i.stay || i.determinedBy == null;
  }
  
  BinaryConstraint.prototype.removeFromGraph = function () {
    if (this.v1 != null) this.v1.removeConstraint(this);
    if (this.v2 != null) this.v2.removeConstraint(this);
    this.direction = Direction.NONE;
  }
  
  /* --- *
   * S c a l e   C o n s t r a i n t
   * --- */
  
  /**
   * Relates two variables by the linear scaling relationship: "v2 =
   * (v1 * scale) + offset". Either v1 or v2 may be changed to maintain
   * this relationship but the scale factor and offset are considered
   * read-only.
   */
  function ScaleConstraint(src, scale, offset, dest, strength) {
    this.direction = Direction.NONE;
    this.scale = scale;
    this.offset = offset;
    ScaleConstraint.superConstructor.call(this, src, dest, strength);
  }
  
  ScaleConstraint.inheritsFrom(BinaryConstraint);
  
  /**
   * Adds this constraint to the constraint graph.
   */
  ScaleConstraint.prototype.addToGraph = function () {
    ScaleConstraint.superConstructor.prototype.addToGraph.call(this);
    this.scale.addConstraint(this);
    this.offset.addConstraint(this);
  }
  
  ScaleConstraint.prototype.removeFromGraph = function () {
    ScaleConstraint.superConstructor.prototype.removeFromGraph.call(this);
    if (this.scale != null) this.scale.removeConstraint(this);
    if (this.offset != null) this.offset.removeConstraint(this);
  }
  
  ScaleConstraint.prototype.markInputs = function (mark) {
    ScaleConstraint.superConstructor.prototype.markInputs.call(this, mark);
    this.scale.mark = this.offset.mark = mark;
  }
  
  /**
   * Enforce this constraint. Assume that it is satisfied.
   */
  ScaleConstraint.prototype.execute = function () {
    if (this.direction == Direction.FORWARD) {
      this.v2.value = this.v1.value * this.scale.value + this.offset.value;
    } else {
      this.v1.value = (this.v2.value - this.offset.value) / this.scale.value;
    }
  }
  
  /**
   * Calculate the walkabout strength, the stay flag, and, if it is
   * 'stay', the value for the current output of this constraint. Assume
   * this constraint is satisfied.
   */
  ScaleConstraint.prototype.recalculate = function () {
    var ihn = this.input(), out = this.output();
    out.walkStrength = Strength.weakestOf(this.strength, ihn.walkStrength);
    out.stay = ihn.stay && this.scale.stay && this.offset.stay;
    if (out.stay) this.execute();
  }
  
  /* --- *
   * E q u a l i t  y   C o n s t r a i n t
   * --- */
  
  /**
   * Constrains two variables to have the same value.
   */
  function EqualityConstraint(var1, var2, strength) {
    EqualityConstraint.superConstructor.call(this, var1, var2, strength);
  }
  
  EqualityConstraint.inheritsFrom(BinaryConstraint);
  
  /**
   * Enforce this constraint. Assume that it is satisfied.
   */
  EqualityConstraint.prototype.execute = function () {
    this.output().value = this.input().value;
  }
  
  /* --- *
   * V a r i a b l e
   * --- */
  
  /**
   * A constrained variable. In addition to its value, it maintain the
   * structure of the constraint graph, the current dataflow graph, and
   * various parameters of interest to the DeltaBlue incremental
   * constraint solver.
   **/
  function Variable(name, initialValue) {
    this.value = initialValue || 0;
    this.constraints = new OrderedCollection();
    this.determinedBy = null;
    this.mark = 0;
    this.walkStrength = Strength.WEAKEST;
    this.stay = true;
    this.name = name;
  }
  
  /**
   * Add the given constraint to the set of all constraints that refer
   * this variable.
   */
  Variable.prototype.addConstraint = function (c) {
    this.constraints.add(c);
  }
  
  /**
   * Removes all traces of c from this variable.
   */
  Variable.prototype.removeConstraint = function (c) {
    this.constraints.remove(c);
    if (this.determinedBy == c) this.determinedBy = null;
  }
  
  /* --- *
   * P l a n n e r
   * --- */
  
  /**
   * The DeltaBlue planner
   */
  function Planner() {
    this.currentMark = 0;
  }
  
  /**
   * Attempt to satisfy the given constraint and, if successful,
   * incrementally update the dataflow graph.  Details: If satifying
   * the constraint is successful, it may override a weaker constraint
   * on its output. The algorithm attempts to resatisfy that
   * constraint using some other method. This process is repeated
   * until either a) it reaches a variable that was not previously
   * determined by any constraint or b) it reaches a constraint that
   * is too weak to be satisfied using any of its methods. The
   * variables of constraints that have been processed are marked with
   * a unique mark value so that we know where we've been. This allows
   * the algorithm to avoid getting into an infinite loop even if the
   * constraint graph has an inadvertent cycle.
   */
  Planner.prototype.incrementalAdd = function (c) {
    var mark = this.newMark();
    var overridden = c.satisfy(mark);
    while (overridden != null)
      overridden = overridden.satisfy(mark);
  }
  
  /**
   * Entry point for retracting a constraint. Remove the given
   * constraint and incrementally update the dataflow graph.
   * Details: Retracting the given constraint may allow some currently
   * unsatisfiable downstream constraint to be satisfied. We therefore collect
   * a list of unsatisfied downstream constraints and attempt to
   * satisfy each one in turn. This list is traversed by constraint
   * strength, strongest first, as a heuristic for avoiding
   * unnecessarily adding and then overriding weak constraints.
   * Assume: c is satisfied.
   */
  Planner.prototype.incrementalRemove = function (c) {
    var out = c.output();
    c.markUnsatisfied();
    c.removeFromGraph();
    var unsatisfied = this.removePropagateFrom(out);
    var strength = Strength.REQUIRED;
    do {
      for (var i = 0; i < unsatisfied.size(); i++) {
        var u = unsatisfied.at(i);
        if (u.strength == strength)
          this.incrementalAdd(u);
      }
      strength = strength.nextWeaker();
    } while (strength != Strength.WEAKEST);
  }
  
  /**
   * Select a previously unused mark value.
   */
  Planner.prototype.newMark = function () {
    return ++this.currentMark;
  }
  
  /**
   * Extract a plan for resatisfaction starting from the given source
   * constraints, usually a set of input constraints. This method
   * assumes that stay optimization is desired; the plan will contain
   * only constraints whose output variables are not stay. Constraints
   * that do no computation, such as stay and edit constraints, are
   * not included in the plan.
   * Details: The outputs of a constraint are marked when it is added
   * to the plan under construction. A constraint may be appended to
   * the plan when all its input variables are known. A variable is
   * known if either a) the variable is marked (indicating that has
   * been computed by a constraint appearing earlier in the plan), b)
   * the variable is 'stay' (i.e. it is a constant at plan execution
   * time), or c) the variable is not determined by any
   * constraint. The last provision is for past states of history
   * variables, which are not stay but which are also not computed by
   * any constraint.
   * Assume: sources are all satisfied.
   */
  Planner.prototype.makePlan = function (sources) {
    var mark = this.newMark();
    var plan = new Plan();
    var todo = sources;
    while (todo.size() > 0) {
      var c = todo.removeFirst();
      if (c.output().mark != mark && c.inputsKnown(mark)) {
        plan.addConstraint(c);
        c.output().mark = mark;
        this.addConstraintsConsumingTo(c.output(), todo);
      }
    }
    return plan;
  }
  
  /**
   * Extract a plan for resatisfying starting from the output of the
   * given constraints, usually a set of input constraints.
   */
  Planner.prototype.extractPlanFromConstraints = function (constraints) {
    var sources = new OrderedCollection();
    for (var i = 0; i < constraints.size(); i++) {
      var c = constraints.at(i);
      if (c.isInput() && c.isSatisfied())
        // not in plan already and eligible for inclusion
        sources.add(c);
    }
    return this.makePlan(sources);
  }
  
  /**
   * Recompute the walkabout strengths and stay flags of all variables
   * downstream of the given constraint and recompute the actual
   * values of all variables whose stay flag is true. If a cycle is
   * detected, remove the given constraint and answer
   * false. Otherwise, answer true.
   * Details: Cycles are detected when a marked variable is
   * encountered downstream of the given constraint. The sender is
   * assumed to have marked the inputs of the given constraint with
   * the given mark. Thus, encountering a marked node downstream of
   * the output constraint means that there is a path from the
   * constraint's output to one of its inputs.
   */
  Planner.prototype.addPropagate = function (c, mark) {
    var todo = new OrderedCollection();
    todo.add(c);
    while (todo.size() > 0) {
      var d = todo.removeFirst();
      if (d.output().mark == mark) {
        this.incrementalRemove(c);
        return false;
      }
      d.recalculate();
      this.addConstraintsConsumingTo(d.output(), todo);
    }
    return true;
  }
  
  
  /**
   * Update the walkabout strengths and stay flags of all variables
   * downstream of the given constraint. Answer a collection of
   * unsatisfied constraints sorted in order of decreasing strength.
   */
  Planner.prototype.removePropagateFrom = function (out) {
    out.determinedBy = null;
    out.walkStrength = Strength.WEAKEST;
    out.stay = true;
    var unsatisfied = new OrderedCollection();
    var todo = new OrderedCollection();
    todo.add(out);
    while (todo.size() > 0) {
      var v = todo.removeFirst();
      for (var i = 0; i < v.constraints.size(); i++) {
        var c = v.constraints.at(i);
        if (!c.isSatisfied())
          unsatisfied.add(c);
      }
      var determining = v.determinedBy;
      for (var i = 0; i < v.constraints.size(); i++) {
        var next = v.constraints.at(i);
        if (next != determining && next.isSatisfied()) {
          next.recalculate();
          todo.add(next.output());
        }
      }
    }
    return unsatisfied;
  }
  
  Planner.prototype.addConstraintsConsumingTo = function (v, coll) {
    var determining = v.determinedBy;
    var cc = v.constraints;
    for (var i = 0; i < cc.size(); i++) {
      var c = cc.at(i);
      if (c != determining && c.isSatisfied())
        coll.add(c);
    }
  }
  
  /* --- *
   * P l a n
   * --- */
  
  /**
   * A Plan is an ordered list of constraints to be executed in sequence
   * to resatisfy all currently satisfiable constraints in the face of
   * one or more changing inputs.
   */
  function Plan() {
    this.v = new OrderedCollection();
  }
  
  Plan.prototype.addConstraint = function (c) {
    this.v.add(c);
  }
  
  Plan.prototype.size = function () {
    return this.v.size();
  }
  
  Plan.prototype.constraintAt = function (index) {
    return this.v.at(index);
  }
  
  Plan.prototype.execute = function () {
    for (var i = 0; i < this.size(); i++) {
      var c = this.constraintAt(i);
      c.execute();
    }
  }
  
  /* --- *
   * M a i n
   * --- */
  
  /**
   * This is the standard DeltaBlue benchmark. A long chain of equality
   * constraints is constructed with a stay constraint on one end. An
   * edit constraint is then added to the opposite end and the time is
   * measured for adding and removing this constraint, and extracting
   * and executing a constraint satisfaction plan. There are two cases.
   * In case 1, the added constraint is stronger than the stay
   * constraint and values must propagate down the entire length of the
   * chain. In case 2, the added constraint is weaker than the stay
   * constraint so it cannot be accomodated. The cost in this case is,
   * of course, very low. Typical situations lie somewhere between these
   * two extremes.
   */
  function chainTest(n) {
    planner = new Planner();
    var prev = null, first = null, last = null;
  
    // Build chain of n equality constraints
    for (var i = 0; i <= n; i++) {
      var name = "v" + i;
      var v = new Variable(name);
      if (prev != null)
        new EqualityConstraint(prev, v, Strength.REQUIRED);
      if (i == 0) first = v;
      if (i == n) last = v;
      prev = v;
    }
  
    new StayConstraint(last, Strength.STRONG_DEFAULT);
    var edit = new EditConstraint(first, Strength.PREFERRED);
    var edits = new OrderedCollection();
    edits.add(edit);
    var plan = planner.extractPlanFromConstraints(edits);
    for (var i = 0; i < 100; i++) {
      first.value = i;
      plan.execute();
      if (last.value != i)
        alert("Chain test failed.");
    }
  }
  
  /**
   * This test constructs a two sets of variables related to each
   * other by a simple linear transformation (scale and offset). The
   * time is measured to change a variable on either side of the
   * mapping and to change the scale and offset factors.
   */
  function projectionTest(n) {
    planner = new Planner();
    var scale = new Variable("scale", 10);
    var offset = new Variable("offset", 1000);
    var src = null, dst = null;
  
    var dests = new OrderedCollection();
    for (var i = 0; i < n; i++) {
      src = new Variable("src" + i, i);
      dst = new Variable("dst" + i, i);
      dests.add(dst);
      new StayConstraint(src, Strength.NORMAL);
      new ScaleConstraint(src, scale, offset, dst, Strength.REQUIRED);
    }
  
    change(src, 17);
    if (dst.value != 1170) alert("Projection 1 failed");
    change(dst, 1050);
    if (src.value != 5) alert("Projection 2 failed");
    change(scale, 5);
    for (var i = 0; i < n - 1; i++) {
      if (dests.at(i).value != i * 5 + 1000)
        alert("Projection 3 failed");
    }
    change(offset, 2000);
    for (var i = 0; i < n - 1; i++) {
      if (dests.at(i).value != i * 5 + 2000)
        alert("Projection 4 failed");
    }
  }
  
  function change(v, newValue) {
    var edit = new EditConstraint(v, Strength.PREFERRED);
    var edits = new OrderedCollection();
    edits.add(edit);
    var plan = planner.extractPlanFromConstraints(edits);
    for (var i = 0; i < 10; i++) {
      v.value = newValue;
      plan.execute();
    }
    edit.destroyConstraint();
  }
  
  // Global variable holding the current planner.
  var planner = null;
  
  function deltaBlue() {
    chainTest(100);
    projectionTest(100);
  }
  