src/theory/decision_strategy.h

   1 /*********************                                                        */
   2 /*! \file decision_strategy.h
   3  ** \verbatim
   4  ** Top contributors (to current version):
   5  **   Andrew Reynolds, Mathias Preiner
   6  ** This file is part of the CVC4 project.
   7  ** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS
   8  ** in the top-level source directory and their institutional affiliations.
   9  ** All rights reserved.  See the file COPYING in the top-level source
  10  ** directory for licensing information.\endverbatim
  11  **
  12  ** \brief Base classes for decision strategies used by theory solvers
  13  ** for use in the DecisionManager of TheoryEngine.
  14  **/
  15
  16 #include "cvc4_private.h"
  17
  18 #ifndef CVC4__THEORY__DECISION_STRATEGY__H
  19 #define CVC4__THEORY__DECISION_STRATEGY__H
  20
  21 #include <map>
  22 #include "context/cdo.h"
  23 #include "expr/node.h"
  24 #include "theory/valuation.h"
  25
  26 namespace CVC4 {
  27 namespace theory {
  28
  29 /**
  30  * Virtual base class for decision strategies.
  31  */
  32 class DecisionStrategy
  33 {
  34  public:
  35   DecisionStrategy() {}
  36   virtual ~DecisionStrategy() {}
  37   /**
  38    * Initalize this strategy, This is called once per satisfiability call by
  39    * the DecisionManager, prior to using this strategy.
  40    */
  41   virtual void initialize() = 0;
  42   /**
  43    * If this method returns a non-null node n, then n is the required next
  44    * decision of this strategy. It must be the case that n is a literal in
  45    * the current CNF stream.
  46    */
  47   virtual Node getNextDecisionRequest() = 0;
  48   /** identify this strategy (for debugging) */
  49   virtual std::string identify() const = 0;
  50 };
  51
  52 /**
  53  * Decision strategy finite model finding.
  54  *
  55  * This is a virtual base class for decision strategies that follow the
  56  * "finite model finding" pattern for decisions. Such strategies have the
  57  * distinguishing feature that they are interested in a stream of literals
  58  * L_1, L_2, L_3, ... and so on. At any given time, they request that L_i is
  59  * asserted true for a minimal i.
  60  *
  61  * To enforce this strategy, this class maintains a SAT-context dependent
  62  * index d_curr_literal, which corresponds to the minimal index of a literal
  63  * in the above list that is not asserted false. A call to
  64  * getNextDecisionRequest increments this value until we find a literal L_j
  65  * that is not assigned false. If L_j is unassigned, we return it as a decision,
  66  * otherwise we return no decisions.
  67  */
  68 class DecisionStrategyFmf : public DecisionStrategy
  69 {
  70  public:
  71   DecisionStrategyFmf(context::Context* satContext, Valuation valuation);
  72   virtual ~DecisionStrategyFmf() {}
  73   /** initialize */
  74   void initialize() override;
  75   /** get next decision request */
  76   Node getNextDecisionRequest() override;
  77   /** Make the n^th literal of this strategy */
  78   virtual Node mkLiteral(unsigned n) = 0;
  79   /**
  80    * This method returns true iff there exists a (minimal) i such that L_i
  81    * is a literal allocated by this class, and is asserted true in the current
  82    * context. If it returns true, the argument i is set to this i.
  83    */
  84   bool getAssertedLiteralIndex(unsigned& i) const;
  85   /**
  86    * This method returns the literal L_i allocated by this class that
  87    * has been asserted true in the current context and is such that i is
  88    * minimal. It returns null if no such literals exist.
  89    */
  90   Node getAssertedLiteral();
  91   /** Get the n^th literal of this strategy */
  92   Node getLiteral(unsigned lit);
  93
  94  protected:
  95   /**
  96    * The valuation of this class, used for knowing what literals are asserted,
  97    * and with what polarity.
  98    */
  99   Valuation d_valuation;
 100   /**
 101    * The (SAT-context-dependent) flag that is true if there exists a literal
 102    * of this class that is asserted true in the current context, according to
 103    * d_valuation.
 104    */
 105   context::CDO<bool> d_has_curr_literal;
 106   /**
 107    * The (SAT-context-dependent) index of the current literal of this strategy.
 108    * This corresponds to the first literal that is not asserted false in the
 109    * current context, according to d_valuation.
 110    */
 111   context::CDO<unsigned> d_curr_literal;
 112   /** the list of literals of this strategy */
 113   std::vector<Node> d_literals;
 114 };
 115
 116 /**
 117  * Special case of above where we only wish to allocate a single literal L_1.
 118  */
 119 class DecisionStrategySingleton : public DecisionStrategyFmf
 120 {
 121  public:
 122   DecisionStrategySingleton(const char* name,
 123                             Node lit,
 124                             context::Context* satContext,
 125                             Valuation valuation);
 126   /**
 127    * Make the n^th literal of this strategy. This method returns d_literal if
 128    * n=0, null otherwise.
 129    */
 130   Node mkLiteral(unsigned n) override;
 131   /** Get single literal */
 132   Node getSingleLiteral();
 133   /** identify */
 134   std::string identify() const override { return d_name; }
 135
 136  private:
 137   /** the name of this strategy */
 138   std::string d_name;
 139   /** the literal to decide on */
 140   Node d_literal;
 141 };
 142
 143 }  // namespace theory
 144 }  // namespace CVC4
 145
 146 #endif /* CVC4__THEORY__DECISION_STRATEGY__H */