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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();