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+// 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.
+ */
+
+function alert(msg) {
+    print(msg);
+    assertEq(false, true);
+}
+
+/* --- 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();
+    assertEq(last.value, i);
+  }
+}
+
+/**
+ * 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);
+  assertEq(dst.value, 1170);
+  change(dst, 1050);
+  assertEq(src.value, 5);
+  change(scale, 5);
+  for (var i = 0; i < n - 1; i++) {
+    assertEq(dests.at(i).value, i * 5 + 1000);
+  }
+  change(offset, 2000);
+  for (var i = 0; i < n - 1; i++) {
+    assertEq(dests.at(i).value, i * 5 + 2000);
+  }
+}
+
+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);
+}
+
+deltaBlue();