sat-solver/SolverTypes.h

/***********************************************************************************[SolverTypes.h]
MiniSat -- Copyright (c) 2003-2006, Niklas Een, Niklas Sorensson

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NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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**************************************************************************************************/


#ifndef SolverTypes_h
#define SolverTypes_h

#include <cassert>
#include <stdint.h>

namespace minisat
{

//=================================================================================================
// Variables, literals, lifted booleans, clauses:


// NOTE! Variables are just integers. No abstraction here. They should be chosen from 0..N,
// so that they can be used as array indices.

typedef int Var;
#define var_Undef (-1)


class Lit {
    int     x;
 public:
    Lit() : x(2*var_Undef)                                              { }   // (lit_Undef)
    explicit Lit(Var var, bool sign = false) : x((var+var) + (int)sign) { }

    // Don't use these for constructing/deconstructing literals. Use the normal constructors instead.
    friend int  toInt       (Lit p);  // Guarantees small, positive integers suitable for array indexing.
    friend Lit  toLit       (int i);  // Inverse of 'toInt()'
    friend Lit  operator   ~(Lit p);
    friend bool sign        (Lit p);
    friend int  var         (Lit p);
    friend Lit  unsign      (Lit p);
    friend Lit  id          (Lit p, bool sgn);

    bool operator == (Lit p) const { return x == p.x; }
    bool operator != (Lit p) const { return x != p.x; }
    bool operator <  (Lit p) const { return x < p.x;  } // '<' guarantees that p, ~p are adjacent in the ordering.
};

inline  int  toInt       (Lit p)           { return p.x; }
inline  Lit  toLit       (int i)           { Lit p; p.x = i; return p; }
inline  Lit  operator   ~(Lit p)           { Lit q; q.x = p.x ^ 1; return q; }
inline  bool sign        (Lit p)           { return p.x & 1; }
inline  int  var         (Lit p)           { return p.x >> 1; }
inline  Lit  unsign      (Lit p)           { Lit q; q.x = p.x & ~1; return q; }
inline  Lit  id          (Lit p, bool sgn) { Lit q; q.x = p.x ^ (int)sgn; return q; }

const Lit lit_Undef(var_Undef, false);  // }- Useful special constants.
const Lit lit_Error(var_Undef, true );  // }


//=================================================================================================
// Lifted booleans:


class lbool {
    char     value;
    explicit lbool(int v) : value(v) { }

public:
    lbool()       : value(0) { }
    lbool(bool x) : value((int)x*2-1) { }
    int toInt(void) const { return value; }

    bool  operator == (lbool b) const { return value == b.value; }
    bool  operator != (lbool b) const { return value != b.value; }
    lbool operator ^ (bool b) const { return b ? lbool(-value) : lbool(value); }

    friend int   toInt  (lbool l);
    friend lbool toLbool(int   v);
};
inline int   toInt  (lbool l) { return l.toInt(); }
inline lbool toLbool(int   v) { return lbool(v);  }

const lbool l_True  = toLbool( 1);
const lbool l_False = toLbool(-1);
const lbool l_Undef = toLbool( 0);

//=================================================================================================
// Clause -- a simple class for representing a clause:


class Clause {
public:
    uint32_t size_etc;
    union { float act; uint32_t abst; } extra;
    Lit     data[0];


    void calcAbstraction() {
        uint32_t abstraction = 0;
        for (int i = 0; i < size(); i++)
            abstraction |= 1 << (var(data[i]) & 31);
        extra.abst = abstraction;  }

    // NOTE: This constructor cannot be used directly (doesn't allocate enough memory).
    template<class V>
    Clause(const V& ps, bool learnt) {
        size_etc = (ps.size() << 3) | (uint32_t)learnt;
        for (int i = 0; i < ps.size(); i++) data[i] = ps[i];
        if (learnt) extra.act = 0; else calcAbstraction(); }

    // -- use this function instead:
    template<class V>
    friend Clause* Clause_new(const V& ps, bool learnt = false) {
        assert(sizeof(Lit)      == sizeof(uint32_t));
        assert(sizeof(float)    == sizeof(uint32_t));
        void* mem = malloc(sizeof(Clause) + sizeof(uint32_t)*(ps.size()));
        return new (mem) Clause(ps, learnt); }

    int          size        ()      const   { return size_etc >> 3; }
    void         shrink      (int i)         { assert(i <= size()); size_etc = (((size_etc >> 3) - i) << 3) | (size_etc & 7); }
    void         pop         ()              { shrink(1); }
    bool         learnt      ()      const   { return size_etc & 1; }
    uint32_t     mark        ()      const   { return (size_etc >> 1) & 3; }
    void         mark        (uint32_t m)    { size_etc = (size_etc & ~6) | ((m & 3) << 1); }
    const Lit&   last        ()      const   { return data[size()-1]; }

    // NOTE: somewhat unsafe to change the clause in-place! Must manually call 'calcAbstraction' afterwards for
    //       subsumption operations to behave correctly.
    Lit&         operator [] (int i)         { return data[i]; }
    Lit          operator [] (int i) const   { return data[i]; }
    operator const Lit* (void) const         { return data; }

    float&       activity    ()              { return extra.act; }
    uint32_t     abstraction () const { return extra.abst; }

    Lit          subsumes    (const Clause& other) const;
    void         strengthen  (Lit p);
};


/*_________________________________________________________________________________________________
|
|  subsumes : (other : const Clause&)  ->  Lit
|
|  Description:
|       Checks if clause subsumes 'other', and at the same time, if it can be used to simplify 'other'
|       by subsumption resolution.
|
|    Result:
|       lit_Error  - No subsumption or simplification
|       lit_Undef  - Clause subsumes 'other'
|       p          - The literal p can be deleted from 'other'
|________________________________________________________________________________________________@*/
inline Lit Clause::subsumes(const Clause& other) const
{
    if (other.size() < size() || (extra.abst & ~other.extra.abst) != 0)
        return lit_Error;

    Lit        ret = lit_Undef;
    const Lit* c  = (const Lit*)(*this);
    const Lit* d  = (const Lit*)other;

    for (int i = 0; i < size(); i++) {
        // search for c[i] or ~c[i]
        for (int j = 0; j < other.size(); j++)
            if (c[i] == d[j])
                goto ok;
            else if (ret == lit_Undef && c[i] == ~d[j]){
                ret = c[i];
                goto ok;
            }

        // did not find it
        return lit_Error;
    ok:;
    }

    return ret;
}


inline void Clause::strengthen(Lit p)
{
    remove(*this, p);
    calcAbstraction();
}
}

#endif