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1// Copyright 2008 the V8 project authors. All rights reserved.
2// Copyright 1996 John Maloney and Mario Wolczko.
3
4// This program is free software; you can redistribute it and/or modify
5// it under the terms of the GNU General Public License as published by
6// the Free Software Foundation; either version 2 of the License, or
7// (at your option) any later version.
8//
9// This program is distributed in the hope that it will be useful,
10// but WITHOUT ANY WARRANTY; without even the implied warranty of
11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12// GNU General Public License for more details.
13//
14// You should have received a copy of the GNU General Public License
15// along with this program; if not, write to the Free Software
16// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
17
18
19// This implementation of the DeltaBlue benchmark is derived
20// from the Smalltalk implementation by John Maloney and Mario
21// Wolczko. Some parts have been translated directly, whereas
22// others have been modified more aggresively to make it feel
23// more like a JavaScript program.
24
25/**
26 * A JavaScript implementation of the DeltaBlue constrain-solving
27 * algorithm, as described in:
28 *
29 * "The DeltaBlue Algorithm: An Incremental Constraint Hierarchy Solver"
30 *   Bjorn N. Freeman-Benson and John Maloney
31 *   January 1990 Communications of the ACM,
32 *   also available as University of Washington TR 89-08-06.
33 *
34 * Beware: this benchmark is written in a grotesque style where
35 * the constraint model is built by side-effects from constructors.
36 * I've kept it this way to avoid deviating too much from the original
37 * implementation.
38 */
39
40
41/* --- O b j e c t   M o d e l --- */
42
43Object.prototype.inheritsFrom = function (shuper) {
44  function Inheriter() { }
45  Inheriter.prototype = shuper.prototype;
46  this.prototype = new Inheriter();
47  this.superConstructor = shuper;
48}
49
50function OrderedCollection() {
51  this.elms = new Array();
52}
53
54OrderedCollection.prototype.add = function (elm) {
55  this.elms.push(elm);
56}
57
58OrderedCollection.prototype.at = function (index) {
59  return this.elms[index];
60}
61
62OrderedCollection.prototype.size = function () {
63  return this.elms.length;
64}
65
66OrderedCollection.prototype.removeFirst = function () {
67  return this.elms.pop();
68}
69
70OrderedCollection.prototype.remove = function (elm) {
71  var index = 0, skipped = 0;
72  for (var i = 0; i < this.elms.length; i++) {
73    var value = this.elms[i];
74    if (value != elm) {
75      this.elms[index] = value;
76      index++;
77    } else {
78      skipped++;
79    }
80  }
81  for (var i = 0; i < skipped; i++)
82    this.elms.pop();
83}
84
85/* --- *
86 * S t r e n g t h
87 * --- */
88
89/**
90 * Strengths are used to measure the relative importance of constraints.
91 * New strengths may be inserted in the strength hierarchy without
92 * disrupting current constraints.  Strengths cannot be created outside
93 * this class, so pointer comparison can be used for value comparison.
94 */
95function Strength(strengthValue, name) {
96  this.strengthValue = strengthValue;
97  this.name = name;
98}
99
100Strength.stronger = function (s1, s2) {
101  return s1.strengthValue < s2.strengthValue;
102}
103
104Strength.weaker = function (s1, s2) {
105  return s1.strengthValue > s2.strengthValue;
106}
107
108Strength.weakestOf = function (s1, s2) {
109  return this.weaker(s1, s2) ? s1 : s2;
110}
111
112Strength.strongest = function (s1, s2) {
113  return this.stronger(s1, s2) ? s1 : s2;
114}
115
116Strength.prototype.nextWeaker = function () {
117  switch (this.strengthValue) {
118    case 0: return Strength.WEAKEST;
119    case 1: return Strength.WEAK_DEFAULT;
120    case 2: return Strength.NORMAL;
121    case 3: return Strength.STRONG_DEFAULT;
122    case 4: return Strength.PREFERRED;
123    case 5: return Strength.REQUIRED;
124  }
125}
126
127// Strength constants.
128Strength.REQUIRED        = new Strength(0, "required");
129Strength.STONG_PREFERRED = new Strength(1, "strongPreferred");
130Strength.PREFERRED       = new Strength(2, "preferred");
131Strength.STRONG_DEFAULT  = new Strength(3, "strongDefault");
132Strength.NORMAL          = new Strength(4, "normal");
133Strength.WEAK_DEFAULT    = new Strength(5, "weakDefault");
134Strength.WEAKEST         = new Strength(6, "weakest");
135
136/* --- *
137 * C o n s t r a i n t
138 * --- */
139
140/**
141 * An abstract class representing a system-maintainable relationship
142 * (or "constraint") between a set of variables. A constraint supplies
143 * a strength instance variable; concrete subclasses provide a means
144 * of storing the constrained variables and other information required
145 * to represent a constraint.
146 */
147function Constraint(strength) {
148  this.strength = strength;
149}
150
151/**
152 * Activate this constraint and attempt to satisfy it.
153 */
154Constraint.prototype.addConstraint = function () {
155  this.addToGraph();
156  planner.incrementalAdd(this);
157}
158
159/**
160 * Attempt to find a way to enforce this constraint. If successful,
161 * record the solution, perhaps modifying the current dataflow
162 * graph. Answer the constraint that this constraint overrides, if
163 * there is one, or nil, if there isn't.
164 * Assume: I am not already satisfied.
165 */
166Constraint.prototype.satisfy = function (mark) {
167  this.chooseMethod(mark);
168  if (!this.isSatisfied()) {
169    if (this.strength == Strength.REQUIRED)
170      alert("Could not satisfy a required constraint!");
171    return null;
172  }
173  this.markInputs(mark);
174  var out = this.output();
175  var overridden = out.determinedBy;
176  if (overridden != null) overridden.markUnsatisfied();
177  out.determinedBy = this;
178  if (!planner.addPropagate(this, mark))
179    alert("Cycle encountered");
180  out.mark = mark;
181  return overridden;
182}
183
184Constraint.prototype.destroyConstraint = function () {
185  if (this.isSatisfied()) planner.incrementalRemove(this);
186  else this.removeFromGraph();
187}
188
189/**
190 * Normal constraints are not input constraints.  An input constraint
191 * is one that depends on external state, such as the mouse, the
192 * keybord, a clock, or some arbitraty piece of imperative code.
193 */
194Constraint.prototype.isInput = function () {
195  return false;
196}
197
198/* --- *
199 * U n a r y   C o n s t r a i n t
200 * --- */
201
202/**
203 * Abstract superclass for constraints having a single possible output
204 * variable.
205 */
206function UnaryConstraint(v, strength) {
207  UnaryConstraint.superConstructor.call(this, strength);
208  this.myOutput = v;
209  this.satisfied = false;
210  this.addConstraint();
211}
212
213UnaryConstraint.inheritsFrom(Constraint);
214
215/**
216 * Adds this constraint to the constraint graph
217 */
218UnaryConstraint.prototype.addToGraph = function () {
219  this.myOutput.addConstraint(this);
220  this.satisfied = false;
221}
222
223/**
224 * Decides if this constraint can be satisfied and records that
225 * decision.
226 */
227UnaryConstraint.prototype.chooseMethod = function (mark) {
228  this.satisfied = (this.myOutput.mark != mark)
229    && Strength.stronger(this.strength, this.myOutput.walkStrength);
230}
231
232/**
233 * Returns true if this constraint is satisfied in the current solution.
234 */
235UnaryConstraint.prototype.isSatisfied = function () {
236  return this.satisfied;
237}
238
239UnaryConstraint.prototype.markInputs = function (mark) {
240  // has no inputs
241}
242
243/**
244 * Returns the current output variable.
245 */
246UnaryConstraint.prototype.output = function () {
247  return this.myOutput;
248}
249
250/**
251 * Calculate the walkabout strength, the stay flag, and, if it is
252 * 'stay', the value for the current output of this constraint. Assume
253 * this constraint is satisfied.
254 */
255UnaryConstraint.prototype.recalculate = function () {
256  this.myOutput.walkStrength = this.strength;
257  this.myOutput.stay = !this.isInput();
258  if (this.myOutput.stay) this.execute(); // Stay optimization
259}
260
261/**
262 * Records that this constraint is unsatisfied
263 */
264UnaryConstraint.prototype.markUnsatisfied = function () {
265  this.satisfied = false;
266}
267
268UnaryConstraint.prototype.inputsKnown = function () {
269  return true;
270}
271
272UnaryConstraint.prototype.removeFromGraph = function () {
273  if (this.myOutput != null) this.myOutput.removeConstraint(this);
274  this.satisfied = false;
275}
276
277/* --- *
278 * S t a y   C o n s t r a i n t
279 * --- */
280
281/**
282 * Variables that should, with some level of preference, stay the same.
283 * Planners may exploit the fact that instances, if satisfied, will not
284 * change their output during plan execution.  This is called "stay
285 * optimization".
286 */
287function StayConstraint(v, str) {
288  StayConstraint.superConstructor.call(this, v, str);
289}
290
291StayConstraint.inheritsFrom(UnaryConstraint);
292
293StayConstraint.prototype.execute = function () {
294  // Stay constraints do nothing
295}
296
297/* --- *
298 * E d i t   C o n s t r a i n t
299 * --- */
300
301/**
302 * A unary input constraint used to mark a variable that the client
303 * wishes to change.
304 */
305function EditConstraint(v, str) {
306  EditConstraint.superConstructor.call(this, v, str);
307}
308
309EditConstraint.inheritsFrom(UnaryConstraint);
310
311/**
312 * Edits indicate that a variable is to be changed by imperative code.
313 */
314EditConstraint.prototype.isInput = function () {
315  return true;
316}
317
318EditConstraint.prototype.execute = function () {
319  // Edit constraints do nothing
320}
321
322/* --- *
323 * B i n a r y   C o n s t r a i n t
324 * --- */
325
326var Direction = new Object();
327Direction.NONE     = 0;
328Direction.FORWARD  = 1;
329Direction.BACKWARD = -1;
330
331/**
332 * Abstract superclass for constraints having two possible output
333 * variables.
334 */
335function BinaryConstraint(var1, var2, strength) {
336  BinaryConstraint.superConstructor.call(this, strength);
337  this.v1 = var1;
338  this.v2 = var2;
339  this.direction = Direction.NONE;
340  this.addConstraint();
341}
342
343BinaryConstraint.inheritsFrom(Constraint);
344
345/**
346 * Decides if this constratint can be satisfied and which way it
347 * should flow based on the relative strength of the variables related,
348 * and record that decision.
349 */
350BinaryConstraint.prototype.chooseMethod = function (mark) {
351  if (this.v1.mark == mark) {
352    this.direction = (this.v1.mark != mark && Strength.stronger(this.strength, this.v2.walkStrength))
353      ? Direction.FORWARD
354      : Direction.NONE;
355  }
356  if (this.v2.mark == mark) {
357    this.direction = (this.v1.mark != mark && Strength.stronger(this.strength, this.v1.walkStrength))
358      ? Direction.BACKWARD
359      : Direction.NONE;
360  }
361  if (Strength.weaker(this.v1.walkStrength, this.v2.walkStrength)) {
362    this.direction = Strength.stronger(this.strength, this.v1.walkStrength)
363      ? Direction.BACKWARD
364      : Direction.NONE;
365  } else {
366    this.direction = Strength.stronger(this.strength, this.v2.walkStrength)
367      ? Direction.FORWARD
368      : Direction.BACKWARD
369  }
370}
371
372/**
373 * Add this constraint to the constraint graph
374 */
375BinaryConstraint.prototype.addToGraph = function () {
376  this.v1.addConstraint(this);
377  this.v2.addConstraint(this);
378  this.direction = Direction.NONE;
379}
380
381/**
382 * Answer true if this constraint is satisfied in the current solution.
383 */
384BinaryConstraint.prototype.isSatisfied = function () {
385  return this.direction != Direction.NONE;
386}
387
388/**
389 * Mark the input variable with the given mark.
390 */
391BinaryConstraint.prototype.markInputs = function (mark) {
392  this.input().mark = mark;
393}
394
395/**
396 * Returns the current input variable
397 */
398BinaryConstraint.prototype.input = function () {
399  return (this.direction == Direction.FORWARD) ? this.v1 : this.v2;
400}
401
402/**
403 * Returns the current output variable
404 */
405BinaryConstraint.prototype.output = function () {
406  return (this.direction == Direction.FORWARD) ? this.v2 : this.v1;
407}
408
409/**
410 * Calculate the walkabout strength, the stay flag, and, if it is
411 * 'stay', the value for the current output of this
412 * constraint. Assume this constraint is satisfied.
413 */
414BinaryConstraint.prototype.recalculate = function () {
415  var ihn = this.input(), out = this.output();
416  out.walkStrength = Strength.weakestOf(this.strength, ihn.walkStrength);
417  out.stay = ihn.stay;
418  if (out.stay) this.execute();
419}
420
421/**
422 * Record the fact that this constraint is unsatisfied.
423 */
424BinaryConstraint.prototype.markUnsatisfied = function () {
425  this.direction = Direction.NONE;
426}
427
428BinaryConstraint.prototype.inputsKnown = function (mark) {
429  var i = this.input();
430  return i.mark == mark || i.stay || i.determinedBy == null;
431}
432
433BinaryConstraint.prototype.removeFromGraph = function () {
434  if (this.v1 != null) this.v1.removeConstraint(this);
435  if (this.v2 != null) this.v2.removeConstraint(this);
436  this.direction = Direction.NONE;
437}
438
439/* --- *
440 * S c a l e   C o n s t r a i n t
441 * --- */
442
443/**
444 * Relates two variables by the linear scaling relationship: "v2 =
445 * (v1 * scale) + offset". Either v1 or v2 may be changed to maintain
446 * this relationship but the scale factor and offset are considered
447 * read-only.
448 */
449function ScaleConstraint(src, scale, offset, dest, strength) {
450  this.direction = Direction.NONE;
451  this.scale = scale;
452  this.offset = offset;
453  ScaleConstraint.superConstructor.call(this, src, dest, strength);
454}
455
456ScaleConstraint.inheritsFrom(BinaryConstraint);
457
458/**
459 * Adds this constraint to the constraint graph.
460 */
461ScaleConstraint.prototype.addToGraph = function () {
462  ScaleConstraint.superConstructor.prototype.addToGraph.call(this);
463  this.scale.addConstraint(this);
464  this.offset.addConstraint(this);
465}
466
467ScaleConstraint.prototype.removeFromGraph = function () {
468  ScaleConstraint.superConstructor.prototype.removeFromGraph.call(this);
469  if (this.scale != null) this.scale.removeConstraint(this);
470  if (this.offset != null) this.offset.removeConstraint(this);
471}
472
473ScaleConstraint.prototype.markInputs = function (mark) {
474  ScaleConstraint.superConstructor.prototype.markInputs.call(this, mark);
475  this.scale.mark = this.offset.mark = mark;
476}
477
478/**
479 * Enforce this constraint. Assume that it is satisfied.
480 */
481ScaleConstraint.prototype.execute = function () {
482  if (this.direction == Direction.FORWARD) {
483    this.v2.value = this.v1.value * this.scale.value + this.offset.value;
484  } else {
485    this.v1.value = (this.v2.value - this.offset.value) / this.scale.value;
486  }
487}
488
489/**
490 * Calculate the walkabout strength, the stay flag, and, if it is
491 * 'stay', the value for the current output of this constraint. Assume
492 * this constraint is satisfied.
493 */
494ScaleConstraint.prototype.recalculate = function () {
495  var ihn = this.input(), out = this.output();
496  out.walkStrength = Strength.weakestOf(this.strength, ihn.walkStrength);
497  out.stay = ihn.stay && this.scale.stay && this.offset.stay;
498  if (out.stay) this.execute();
499}
500
501/* --- *
502 * E q u a l i t  y   C o n s t r a i n t
503 * --- */
504
505/**
506 * Constrains two variables to have the same value.
507 */
508function EqualityConstraint(var1, var2, strength) {
509  EqualityConstraint.superConstructor.call(this, var1, var2, strength);
510}
511
512EqualityConstraint.inheritsFrom(BinaryConstraint);
513
514/**
515 * Enforce this constraint. Assume that it is satisfied.
516 */
517EqualityConstraint.prototype.execute = function () {
518  this.output().value = this.input().value;
519}
520
521/* --- *
522 * V a r i a b l e
523 * --- */
524
525/**
526 * A constrained variable. In addition to its value, it maintain the
527 * structure of the constraint graph, the current dataflow graph, and
528 * various parameters of interest to the DeltaBlue incremental
529 * constraint solver.
530 **/
531function Variable(name, initialValue) {
532  this.value = initialValue || 0;
533  this.constraints = new OrderedCollection();
534  this.determinedBy = null;
535  this.mark = 0;
536  this.walkStrength = Strength.WEAKEST;
537  this.stay = true;
538  this.name = name;
539}
540
541/**
542 * Add the given constraint to the set of all constraints that refer
543 * this variable.
544 */
545Variable.prototype.addConstraint = function (c) {
546  this.constraints.add(c);
547}
548
549/**
550 * Removes all traces of c from this variable.
551 */
552Variable.prototype.removeConstraint = function (c) {
553  this.constraints.remove(c);
554  if (this.determinedBy == c) this.determinedBy = null;
555}
556
557/* --- *
558 * P l a n n e r
559 * --- */
560
561/**
562 * The DeltaBlue planner
563 */
564function Planner() {
565  this.currentMark = 0;
566}
567
568/**
569 * Attempt to satisfy the given constraint and, if successful,
570 * incrementally update the dataflow graph.  Details: If satifying
571 * the constraint is successful, it may override a weaker constraint
572 * on its output. The algorithm attempts to resatisfy that
573 * constraint using some other method. This process is repeated
574 * until either a) it reaches a variable that was not previously
575 * determined by any constraint or b) it reaches a constraint that
576 * is too weak to be satisfied using any of its methods. The
577 * variables of constraints that have been processed are marked with
578 * a unique mark value so that we know where we've been. This allows
579 * the algorithm to avoid getting into an infinite loop even if the
580 * constraint graph has an inadvertent cycle.
581 */
582Planner.prototype.incrementalAdd = function (c) {
583  var mark = this.newMark();
584  var overridden = c.satisfy(mark);
585  while (overridden != null)
586    overridden = overridden.satisfy(mark);
587}
588
589/**
590 * Entry point for retracting a constraint. Remove the given
591 * constraint and incrementally update the dataflow graph.
592 * Details: Retracting the given constraint may allow some currently
593 * unsatisfiable downstream constraint to be satisfied. We therefore collect
594 * a list of unsatisfied downstream constraints and attempt to
595 * satisfy each one in turn. This list is traversed by constraint
596 * strength, strongest first, as a heuristic for avoiding
597 * unnecessarily adding and then overriding weak constraints.
598 * Assume: c is satisfied.
599 */
600Planner.prototype.incrementalRemove = function (c) {
601  var out = c.output();
602  c.markUnsatisfied();
603  c.removeFromGraph();
604  var unsatisfied = this.removePropagateFrom(out);
605  var strength = Strength.REQUIRED;
606  do {
607    for (var i = 0; i < unsatisfied.size(); i++) {
608      var u = unsatisfied.at(i);
609      if (u.strength == strength)
610        this.incrementalAdd(u);
611    }
612    strength = strength.nextWeaker();
613  } while (strength != Strength.WEAKEST);
614}
615
616/**
617 * Select a previously unused mark value.
618 */
619Planner.prototype.newMark = function () {
620  return ++this.currentMark;
621}
622
623/**
624 * Extract a plan for resatisfaction starting from the given source
625 * constraints, usually a set of input constraints. This method
626 * assumes that stay optimization is desired; the plan will contain
627 * only constraints whose output variables are not stay. Constraints
628 * that do no computation, such as stay and edit constraints, are
629 * not included in the plan.
630 * Details: The outputs of a constraint are marked when it is added
631 * to the plan under construction. A constraint may be appended to
632 * the plan when all its input variables are known. A variable is
633 * known if either a) the variable is marked (indicating that has
634 * been computed by a constraint appearing earlier in the plan), b)
635 * the variable is 'stay' (i.e. it is a constant at plan execution
636 * time), or c) the variable is not determined by any
637 * constraint. The last provision is for past states of history
638 * variables, which are not stay but which are also not computed by
639 * any constraint.
640 * Assume: sources are all satisfied.
641 */
642Planner.prototype.makePlan = function (sources) {
643  var mark = this.newMark();
644  var plan = new Plan();
645  var todo = sources;
646  while (todo.size() > 0) {
647    var c = todo.removeFirst();
648    if (c.output().mark != mark && c.inputsKnown(mark)) {
649      plan.addConstraint(c);
650      c.output().mark = mark;
651      this.addConstraintsConsumingTo(c.output(), todo);
652    }
653  }
654  return plan;
655}
656
657/**
658 * Extract a plan for resatisfying starting from the output of the
659 * given constraints, usually a set of input constraints.
660 */
661Planner.prototype.extractPlanFromConstraints = function (constraints) {
662  var sources = new OrderedCollection();
663  for (var i = 0; i < constraints.size(); i++) {
664    var c = constraints.at(i);
665    if (c.isInput() && c.isSatisfied())
666      // not in plan already and eligible for inclusion
667      sources.add(c);
668  }
669  return this.makePlan(sources);
670}
671
672/**
673 * Recompute the walkabout strengths and stay flags of all variables
674 * downstream of the given constraint and recompute the actual
675 * values of all variables whose stay flag is true. If a cycle is
676 * detected, remove the given constraint and answer
677 * false. Otherwise, answer true.
678 * Details: Cycles are detected when a marked variable is
679 * encountered downstream of the given constraint. The sender is
680 * assumed to have marked the inputs of the given constraint with
681 * the given mark. Thus, encountering a marked node downstream of
682 * the output constraint means that there is a path from the
683 * constraint's output to one of its inputs.
684 */
685Planner.prototype.addPropagate = function (c, mark) {
686  var todo = new OrderedCollection();
687  todo.add(c);
688  while (todo.size() > 0) {
689    var d = todo.removeFirst();
690    if (d.output().mark == mark) {
691      this.incrementalRemove(c);
692      return false;
693    }
694    d.recalculate();
695    this.addConstraintsConsumingTo(d.output(), todo);
696  }
697  return true;
698}
699
700
701/**
702 * Update the walkabout strengths and stay flags of all variables
703 * downstream of the given constraint. Answer a collection of
704 * unsatisfied constraints sorted in order of decreasing strength.
705 */
706Planner.prototype.removePropagateFrom = function (out) {
707  out.determinedBy = null;
708  out.walkStrength = Strength.WEAKEST;
709  out.stay = true;
710  var unsatisfied = new OrderedCollection();
711  var todo = new OrderedCollection();
712  todo.add(out);
713  while (todo.size() > 0) {
714    var v = todo.removeFirst();
715    for (var i = 0; i < v.constraints.size(); i++) {
716      var c = v.constraints.at(i);
717      if (!c.isSatisfied())
718        unsatisfied.add(c);
719    }
720    var determining = v.determinedBy;
721    for (var i = 0; i < v.constraints.size(); i++) {
722      var next = v.constraints.at(i);
723      if (next != determining && next.isSatisfied()) {
724        next.recalculate();
725        todo.add(next.output());
726      }
727    }
728  }
729  return unsatisfied;
730}
731
732Planner.prototype.addConstraintsConsumingTo = function (v, coll) {
733  var determining = v.determinedBy;
734  var cc = v.constraints;
735  for (var i = 0; i < cc.size(); i++) {
736    var c = cc.at(i);
737    if (c != determining && c.isSatisfied())
738      coll.add(c);
739  }
740}
741
742/* --- *
743 * P l a n
744 * --- */
745
746/**
747 * A Plan is an ordered list of constraints to be executed in sequence
748 * to resatisfy all currently satisfiable constraints in the face of
749 * one or more changing inputs.
750 */
751function Plan() {
752  this.v = new OrderedCollection();
753}
754
755Plan.prototype.addConstraint = function (c) {
756  this.v.add(c);
757}
758
759Plan.prototype.size = function () {
760  return this.v.size();
761}
762
763Plan.prototype.constraintAt = function (index) {
764  return this.v.at(index);
765}
766
767Plan.prototype.execute = function () {
768  for (var i = 0; i < this.size(); i++) {
769    var c = this.constraintAt(i);
770    c.execute();
771  }
772}
773
774/* --- *
775 * M a i n
776 * --- */
777
778/**
779 * This is the standard DeltaBlue benchmark. A long chain of equality
780 * constraints is constructed with a stay constraint on one end. An
781 * edit constraint is then added to the opposite end and the time is
782 * measured for adding and removing this constraint, and extracting
783 * and executing a constraint satisfaction plan. There are two cases.
784 * In case 1, the added constraint is stronger than the stay
785 * constraint and values must propagate down the entire length of the
786 * chain. In case 2, the added constraint is weaker than the stay
787 * constraint so it cannot be accomodated. The cost in this case is,
788 * of course, very low. Typical situations lie somewhere between these
789 * two extremes.
790 */
791function chainTest(n) {
792  planner = new Planner();
793  var prev = null, first = null, last = null;
794
795  // Build chain of n equality constraints
796  for (var i = 0; i <= n; i++) {
797    var name = "v" + i;
798    var v = new Variable(name);
799    if (prev != null)
800      new EqualityConstraint(prev, v, Strength.REQUIRED);
801    if (i == 0) first = v;
802    if (i == n) last = v;
803    prev = v;
804  }
805
806  new StayConstraint(last, Strength.STRONG_DEFAULT);
807  var edit = new EditConstraint(first, Strength.PREFERRED);
808  var edits = new OrderedCollection();
809  edits.add(edit);
810  var plan = planner.extractPlanFromConstraints(edits);
811  for (var i = 0; i < 100; i++) {
812    first.value = i;
813    plan.execute();
814    if (last.value != i)
815      alert("Chain test failed.");
816  }
817}
818
819/**
820 * This test constructs a two sets of variables related to each
821 * other by a simple linear transformation (scale and offset). The
822 * time is measured to change a variable on either side of the
823 * mapping and to change the scale and offset factors.
824 */
825function projectionTest(n) {
826  planner = new Planner();
827  var scale = new Variable("scale", 10);
828  var offset = new Variable("offset", 1000);
829  var src = null, dst = null;
830
831  var dests = new OrderedCollection();
832  for (var i = 0; i < n; i++) {
833    src = new Variable("src" + i, i);
834    dst = new Variable("dst" + i, i);
835    dests.add(dst);
836    new StayConstraint(src, Strength.NORMAL);
837    new ScaleConstraint(src, scale, offset, dst, Strength.REQUIRED);
838  }
839
840  change(src, 17);
841  if (dst.value != 1170) alert("Projection 1 failed");
842  change(dst, 1050);
843  if (src.value != 5) alert("Projection 2 failed");
844  change(scale, 5);
845  for (var i = 0; i < n - 1; i++) {
846    if (dests.at(i).value != i * 5 + 1000)
847      alert("Projection 3 failed");
848  }
849  change(offset, 2000);
850  for (var i = 0; i < n - 1; i++) {
851    if (dests.at(i).value != i * 5 + 2000)
852      alert("Projection 4 failed");
853  }
854}
855
856function change(v, newValue) {
857  var edit = new EditConstraint(v, Strength.PREFERRED);
858  var edits = new OrderedCollection();
859  edits.add(edit);
860  var plan = planner.extractPlanFromConstraints(edits);
861  for (var i = 0; i < 10; i++) {
862    v.value = newValue;
863    plan.execute();
864  }
865  edit.destroyConstraint();
866}
867
868// Global variable holding the current planner.
869var planner = null;
870
871function deltaBlue() {
872  chainTest(100);
873  projectionTest(100);
874}
875
876for (var i = 0; i < 155; ++i)
877    deltaBlue();
878