The Tor Browser: comparison js/src/v8/deltablue.js

comparison: js/src/v8/deltablue.js

js/src/v8/deltablue.js

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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', 66118, [
+new Benchmark('DeltaBlue', deltaBlue)
+]);
+/**
+* A JavaScript implementation of the DeltaBlue constraint-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 constraint 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.v2.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);
+}