Package kodkod.engine.ucore

Source Code of kodkod.engine.ucore.StrategyUtils

/*
* Kodkod -- Copyright (c) 2005-2008, Emina Torlak
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package kodkod.engine.ucore;

import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

import kodkod.ast.Formula;
import kodkod.ast.Node;
import kodkod.ast.Variable;
import kodkod.engine.fol2sat.RecordFilter;
import kodkod.engine.fol2sat.TranslationLog;
import kodkod.engine.fol2sat.TranslationRecord;
import kodkod.engine.fol2sat.Translator;
import kodkod.engine.satlab.Clause;
import kodkod.engine.satlab.ResolutionTrace;
import kodkod.instance.TupleSet;
import kodkod.util.ints.IntBitSet;
import kodkod.util.ints.IntIterator;
import kodkod.util.ints.IntSet;
import kodkod.util.ints.IntTreeSet;
import kodkod.util.ints.Ints;
import kodkod.util.ints.SparseSequence;
import kodkod.util.ints.TreeSequence;

/**
* A collection of utility methods for implementing
* logic-level reduction strategies.
*
* @author Emina Torlak
*/
public final class StrategyUtils {
  private StrategyUtils() {}
 
 
  /**
   * Returns the variables that correspond to the roots of log.formula. 
   * @return
   * <pre>
   * { v: int | some r: log.records |
   *   r.node in log.roots() and
   *   r.env.isEmpty() and
   *   abs(r.literal) != Integer.MAX_VALUE and
   *   v = abs(r.literal) and
   *   no r': log.records | r'.node = r.node && log.replay.r' > log.replay.r }
   * </pre>
   */
  public static IntSet rootVars(TranslationLog log) {
    final IntSet rootVars = new IntTreeSet();
    final Set<Formula> roots = log.roots();
    final Map<Formula,int[]> maxRootVar = new LinkedHashMap<Formula,int[]>(roots.size());
    final RecordFilter filter = new RecordFilter() {
      public boolean accept(Node node, Formula translated, int literal, Map<Variable, TupleSet> env) {
        return roots.contains(translated) && env.isEmpty();
      }
    };
    for(Iterator<TranslationRecord> itr = log.replay(filter); itr.hasNext();) {
      TranslationRecord record = itr.next();
      int[] var = maxRootVar.get(record.translated());
      if (var==null) {
        var = new int[1];
        maxRootVar.put(record.translated(), var);
      }
      var[0] = StrictMath.abs(record.literal());
    }
   
    for(int[] var : maxRootVar.values()) {
      int topVar = var[0];
      if (topVar != Integer.MAX_VALUE) // formula simplified to TRUE
        rootVars.add(var[0]);
    }
   
//    for(Map.Entry<Formula,int[]> entry : maxRootVar.entrySet()) {
//      final int topVar = entry.getValue()[0];
//      if (topVar != Integer.MAX_VALUE) // formula simplified to TRUE
//        rootVars.add(topVar);
//      System.out.println(topVar + " ==>" + entry.getKey());
//    }
   
    return rootVars;
  }
  /**
   * Returns a map from  variables to the corresponding roots of log.formula.
   * @return
   * <pre>
   * { v: int, f: Formula | some r: log.records |
   *   r.translated in log.roots() and
   *   r.translated = f and
   *   r.env.isEmpty() and
   *   abs(r.literal) != Integer.MAX_VALUE and
   *   v = abs(r.literal) and
   *   no r': log.records | r'.node = r.node && log.replay.r' > log.replay.r }
   * </pre>
   */
  static SparseSequence<Formula> roots(TranslationLog log) {
    final SparseSequence<Formula> rootVars = new TreeSequence<Formula>();
    final Set<Formula> roots = log.roots();
    final Map<Formula,int[]> maxRootVar = new IdentityHashMap<Formula,int[]>(roots.size());
    final RecordFilter filter = new RecordFilter() {
      public boolean accept(Node node, Formula translated, int literal, Map<Variable, TupleSet> env) {
        return roots.contains(translated) && env.isEmpty();
      }
    };
    for(Iterator<TranslationRecord> itr = log.replay(filter); itr.hasNext();) {
      TranslationRecord record = itr.next();
      int[] var = maxRootVar.get(record.translated());
      if (var==null) {
        var = new int[1];
        maxRootVar.put(record.translated(), var);
      }
      var[0] = StrictMath.abs(record.literal());
    }
   
    for(Map.Entry<Formula,int[]> entry : maxRootVar.entrySet()) {
      final int topVar = entry.getValue()[0];
      if (topVar != Integer.MAX_VALUE) // formula simplified to TRUE
        rootVars.put(topVar, entry.getKey());
    }
    return rootVars;
  }
 
  /**
   * Returns the variables that correspond to the roots of log.formula, in the order
   * in which they were specified in log.formula. 
   * @return variables that correspond to the roots of log.formula, in the order
   * in which they were specified in log.formula.
   */
//  static IntVector orderedRootVars(TranslationLog log) {
//    final Set<Formula> roots = log.roots();
//    final Map<Formula,int[]> maxRootVar = new LinkedHashMap<Formula,int[]>(roots.size());
//    final RecordFilter filter = new RecordFilter() {
//      public boolean accept(Node node, int literal, Map<Variable, TupleSet> env) {
//        return roots.contains(node) && env.isEmpty();
//      }
//    };
//    for(Iterator<TranslationRecord> itr = log.replay(filter); itr.hasNext();) {
//      TranslationRecord record = itr.next();
//      int[] var = maxRootVar.get(record.node());
//      if (var==null) {
//        var = new int[1];
//        maxRootVar.put((Formula)record.node(), var);
//      }
//      var[0] = StrictMath.abs(record.literal());
//    }
//    final IntSet uniqueRoots = new IntTreeSet();
//    final IntVector orderedRoots = new ArrayIntVector(roots.size());
//    for(int[] var : maxRootVar.values()) {
//      int topVar = var[0];
//      if (topVar != Integer.MAX_VALUE) // formula simplified to TRUE
//        if (uniqueRoots.add(var[0])) {
//          orderedRoots.add(var[0]);
//        };
//    }
//    return orderedRoots;
//  }
 
  /**
   * Returns relevant  core variables; that is, all variables that occur both in the positive and
   * negative phase in trace.core.
   * @return { v: [1..) | (some p, n: trace.core | v in trace.elts[p].literals and -v in trace.elts[n].literals) }
   */
  public static IntSet coreVars(ResolutionTrace trace) {

    final IntSet posVars = new IntTreeSet(), negVars = new IntTreeSet();
   
    for(Iterator<Clause> iter = trace.iterator(trace.core()); iter.hasNext();) {
      Clause clause = iter.next();
      for(IntIterator lits = clause.literals(); lits.hasNext(); ) {
        int lit = lits.next();
        if (lit > 0) posVars.add(lit);
        else negVars.add(-lit);
      }
    }
   
    posVars.retainAll(negVars);
   
    assert !posVars.isEmpty();
    final IntSet ret = new IntBitSet(posVars.max()+1);
    ret.addAll(posVars);
   
    return ret;
  }
 
  /**
   * Returns the set of all variables in the core of the given trace
   * that form unit clauses.
   * @return { v: [1..) | some c: trace.core | c.size() = 1 and c.maxVariable() = v }
   */
  public static IntSet coreUnits(ResolutionTrace trace) {
    final IntSet units = new IntTreeSet();
   
    for(Iterator<Clause> itr = trace.reverseIterator(trace.core()); itr.hasNext(); ) {  
      Clause c = itr.next();
      if (c.size()==1) {
        units.add(c.maxVariable());
      }
    }
   
    if (units.isEmpty()) return Ints.EMPTY_SET;
   
    return Ints.asSet(units.toArray());
  }
 
  /**
   * Returns the consecutive variables at the tail of the core of the given trace
   * that form unit clauses. 
   * @return the consecutive variables at the tail of the core of the given trace
   * that form unit clauses
   */
  static IntSet coreTailUnits(ResolutionTrace trace) {
    final IntSet units = new IntTreeSet();
   
    for(Iterator<Clause> itr = trace.reverseIterator(trace.core()); itr.hasNext(); ) {  
      Clause c = itr.next();
      if (c.size()==1) {
        units.add(c.maxVariable());
      } else {
        break;
      }
    }
   
    return units;
  }
 
  /**
   * Returns the indices of all axioms
   * in the given trace that form the translations of the formulas
   * identified by the given variables.  This method assumes that
   * the axioms in the given trace were generated by the Kodkod
   * {@linkplain Translator}.
   * @return
   * let C = { c: trace.prover.clauses | c.maxVariable() in relevantVars },
   *     T = { c1, c2: C | c2.maxVariable() in abs(c1.literals) } |
   *     C.*T
   */
  static IntSet clausesFor(ResolutionTrace trace, IntSet relevantVars) {
//    System.out.println("relevant: " + relevantVars);
    final IntSet axioms = trace.axioms();

    final IntSet reachableVars = new IntBitSet(relevantVars.max()+1);
    reachableVars.addAll(relevantVars);

    final IntSet relevantAxioms = new IntBitSet(axioms.size());
   
    final Iterator<Clause> itr = trace.reverseIterator(axioms);
    for(int i = axioms.max(); i >= 0; i--) {
      Clause clause = itr.next();
      int maxVar = clause.maxVariable();
      if (reachableVars.contains(maxVar)) {
        for(IntIterator lits = clause.literals(); lits.hasNext(); ) {
          reachableVars.add(StrictMath.abs(lits.next()));
        }
        relevantAxioms.add(i);
      }
    }
   
    return  relevantAxioms;
  }
 
 
 
}
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