PbSolver_convertBdd.cc

/**************************************************************************[PbSolver_convertBdd.cc]
Copyright (c) 2005-2010, Niklas Een, Niklas Sorensson

KP-MiniSat+ based on MiniSat+ -- Copyright (c) 2018-2020 Michał Karpiński, Marek Piotrów

UWrMaxSat based on KP-MiniSat+ -- Copyright (c) 2019-2020 Marek Piotrów

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#include "PbSolver.h"
#include "FEnv.h"
#include "Debug.h"


//=================================================================================================

#define lit2fml(p) id(var(var(p)),sign(p))

static
Formula convertOneToBdd(const vec<Lit>& ps, const vec<Int>& Cs, Int lo, int max_cost)
{
    FEnv::push();

    int size = Cs.size(), last;
    vec<Int>   material_left(size+1);
    vec<Pair<Interval<Int>, Formula> >     ttf(size+1);
    vec<std::map<Interval<Int>, Formula> > memo(size+1);
    Pair<Interval<Int>, Formula> tt, ff, result;
    const Int zero = 0; Int sum = 0;

    for (int i = 0; i < ttf.size(); i++) ttf[i].snd = _undef_;
    material_left[0] = 0;
    for (int i = 1; i < material_left.size(); i++)  material_left[i] = material_left[i-1] +  Cs[i-1];
    last = size;
    do {
        // lo - sum[last] <= (Cs[0]*ps[0] + ... + Cs[last-1]*ps[last-1])
        Int lower_limit = lo - sum;

        if (FEnv::topSize() > max_cost) {
            FEnv::pop();
            return _undef_;
        }
        if (lower_limit <= 0)
            result = Pair_new( Interval_new(Int_MIN,zero), _1_);
        else if (lower_limit > material_left[last])
            result = Pair_new( Interval_new(material_left[last] + 1, Int_MAX), _0_);
        else {
            assert(last > 0);
            auto search = memo[last].find(Interval_new(lower_limit,lower_limit));
    
            if (search == memo[last].end()) {
                sum += Cs[--last];
                continue;                                         // continue with computing the tt child node
             } else result = Pair_new(search->first, search->second);
        }
        do {
            if (ttf[last].snd == _undef_) {
               ttf[last] = result;
               sum -= Cs[last];
               break;                                             // continue with computing the ff child node
            }
            tt = ttf[last]; ff = result; ttf[last].snd = _undef_; // both children (tt and ff) are available with their intervals

            Int tt_beta = tt.fst.fst, tt_gamma = tt.fst.snd;      // [beta, gamma] is a corresponding interval
            Int ff_beta = ff.fst.fst, ff_gamma = ff.fst.snd;

            Interval<Int> interval = Interval_new(max(tt_beta.add(Cs[last]),ff_beta), min(tt_gamma.add(Cs[last]),ff_gamma));
            Formula fm = (tt.snd == ff.snd ? tt.snd : ITE(lit2fml(ps[last]), tt.snd, ff.snd));

            memo[++last][interval] = fm;                          // continue with the parent node
            result = Pair_new(interval, fm);
        } while (last < size);
    } while (last < size);
    if (opt_verbosity >= 1 && opt_minimization != 1 || opt_verbosity >= 2)
        if (FEnv::topSize() > 0)
            /**/ reportf("BDD-cost:%5d\n", FEnv::topSize());
        else if (!opt_maxsat) reportf("\n");

    FEnv::keep();
    return result.snd;
}

Formula convertToBdd(const Linear& c, int max_cost)
{
    vec<Lit> ls;
    vec<Int> Cs;
    Int csum = 0;
    Formula ret;

    for (int j = 0; j < c.size; j++)
        ls.push(c[j]), Cs.push(c(j)), csum += c(j);

    ret = convertOneToBdd(ls, Cs, c.lo, max_cost);    
    if(ret == _undef_ ) return ret;

    if(c.hi != Int_MAX) {
      ls.clear(); Cs.clear();
      for(int i=0; i<c.size; i++)
        ls.push(~c[i]), Cs.push(c(i));
      ret &= convertOneToBdd(ls, Cs, csum - c.hi, max_cost);
    }
    extern PbSolver *pb_solver;
    return ret == _undef_ || c.lit == lit_Undef || pb_solver->use_base_assump ? ret : ~lit2fml(c.lit) | ret ;
}