xchaff_solver.cpp

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#include "xchaff_solver.h"
#include <algorithm>


CSolver::CSolver(void)    
{
    dlevel()=0;
    _params.time_limit          = 3600 * 48;            //2 days
    _params.decision_strategy   = 0;
    _params.preprocess_strategy = 0;
    _params.allow_clause_deletion               = true ;
    _params.clause_deletion_interval            = 5000;
    _params.max_unrelevance                     = 20;
    _params.min_num_clause_lits_for_delete      = 100;
    _params.max_conflict_clause_length          = 5000;
    _params.bubble_init_step    = 32;

    _params.randomness          = 0;
    _params.verbosity           = 0;

    _params.back_track_complete = true;
    _params.allow_multiple_conflict             = false;
    _params.allow_multiple_conflict_clause      = false;

    _params.allow_restart       = true; 
    _params.next_restart_time   = 50;           //this set the first restart time (in seconds)
    _params.restart_time_increment      = 0;
    _params.restart_time_incr_incr = 0;

    _params.next_restart_backtrack= 0;
    _params.restart_backtrack_incr= 40000;              
    _params.restart_backtrack_incr_incr = 100;

    _params.restart_randomness  = 0;    
    _params.base_randomness     = 0;
    _params.randomness          = 0;

    _stats.is_solver_started    = false;
    _stats.outcome              = UNKNOWN;
    _stats.is_mem_out           = false;
    _stats.start_cpu_time       = 0;            
    _stats.finish_cpu_time      = 0;
    _stats.last_cpu_time        = 0;            

    _stats.start_world_time     = 0;
    _stats.finish_world_time    = 0;

    _stats.num_decisions        = 0;
    _stats.num_backtracks       = 0;
    _stats.max_dlevel           = 0;
    _stats.num_implications     = 0;

    _num_marked                 = 0;
    _dlevel                     = 0;            
    _stats.total_bubble_move    = 0;

    _dlevel_hook = NULL;
    _decision_hook = NULL;
    _assignment_hook = NULL;
    _deduction_hook = NULL;
}

CSolver::~CSolver()
{
  if (_stats.is_solver_started) {
    for (unsigned i=0; i<variables().size(); ++i)
        delete _assignment_stack[i];
  }
}

void CSolver::run_periodic_functions(void)
{
    //a. clause deletion
    if ( _params.allow_clause_deletion &&
         _stats.num_backtracks % _params.clause_deletion_interval == 0)
            delete_unrelevant_clauses(); 
    //b. restart
    if (_params.allow_restart && _stats.num_backtracks > _params.next_restart_backtrack) {
        _params.next_restart_backtrack += _params.restart_backtrack_incr;
        _params.restart_backtrack_incr += _params.restart_backtrack_incr_incr;
        float current = current_cpu_time()/1000;
        if (current > _params.next_restart_time) {
            if (_params.verbosity > 1) cout << "restart..." << endl;
            _params.next_restart_time = current + _params.restart_time_increment;
            _params.restart_time_increment += _params.restart_time_incr_incr;
            _params.randomness = _params.restart_randomness;
            restart();
        }
    }    
    //c. update var stats for decision
    if ((_stats.num_decisions % 0xff)==0) 
            update_var_stats();
    //d. run hook functions
    for (unsigned i=0; i< _hooks.size(); ++i) {
        pair<int,pair<HookFunPtrT, int> > & hook = _hooks[i];
        if (_stats.num_decisions >= hook.first) {
            hook.first += hook.second.second;
            hook.second.first((void *) this);
        }
    }
} 


void CSolver::init(void)
{
    CDatabase::init();

    _stats.is_solver_started    = true;
    _stats.start_cpu_time       = current_cpu_time();
    _stats.start_world_time     = current_world_time();
    _stats.num_free_variables   = num_variables();
    for (unsigned i=0; i<variables().size(); ++i)
        _assignment_stack.push_back(new vector<int>);

    _var_order.resize( num_variables());
    _last_var_lits_count[0].resize(variables().size());
    _last_var_lits_count[1].resize(variables().size());
    CHECK(dump());
}


int CSolver::add_variables(int new_vars)
{
  int old_num_vars = variables().size();
  int num_vars = old_num_vars + new_vars;
  variables().resize(num_vars) ; 
  if (_stats.is_solver_started) {
    _stats.num_free_variables += new_vars;

    for (int i=old_num_vars; i<num_vars; ++i)
      _assignment_stack.push_back(new vector<int>);

    _var_order.resize(num_vars-1);
    _last_var_lits_count[0].resize(num_vars);
    _last_var_lits_count[1].resize(num_vars);
  }
  return old_num_vars;
}


ClauseIdx CSolver::add_clause(vector<int>& lits, bool addConflicts) {
    int new_cl;
    int n_lits = lits.size();
    //a. do we need to enlarge lits pool?
    while (lit_pool_free_space() <= n_lits + 1) { 
        if (enlarge_lit_pool()==false) 
            return -1; //mem out, can't enlarge lit pool, because 
                       //ClauseIdx can't be -1, so it shows error.
    }   
    //b. get a free cl index;
    if (_unused_clause_idx_queue.empty()) {
        new_cl = _clauses.size();
        _clauses.resize(new_cl + 1);
    }
    else {
        new_cl = _unused_clause_idx_queue.front();
        _unused_clause_idx_queue.pop();
    }
    //c. add the clause lits to lits pool
    clause(new_cl).init(lit_pool_end(), n_lits);

    //I want to verify added clauses are either all free or all 0
    bool satisfied = false, is_unit = false, is_conflict = false;
    int num_unknown = 0;
    for (int i=0; i< n_lits; ++i){
        int var_idx = lits[i]>>1;
        assert((unsigned)var_idx < variables().size());
        int var_sign = lits[i]&0x1;
        lit_pool_push_back( ((var_idx<<1) + var_sign) << 2);
        ++variable(var_idx).lits_count(var_sign);
        int lit_value = literal_value(clause(new_cl).literal(i));

        if (lit_value == 1) {
          satisfied = true;
        }
        else if (lit_value != 0) {
          ++num_unknown;
        }
    }
    is_conflict = !satisfied && (num_unknown == 0);
    is_unit = !satisfied && (num_unknown == 1);
    assert(_stats.is_solver_started || num_unknown == n_lits);
    lit_pool_push_back(-new_cl); //push in the clause idx in the end
    //d. set the head/tail pointers
    if (clause(new_cl).num_lits() > 1) {
        //add the ht. note: ht must be the last free var
        int max_idx = -1, max_dl = -1;
        CClause & cl = clause(new_cl);
        int i, sz = cl.num_lits();
        int other_ht_idx;
        for (i=0; i< sz; ++i) {
            int v_idx = cl.literals()[i].var_index();
            if (variable(v_idx).value()==UNKNOWN) {
                int v_sign = cl.literals()[i].var_sign();
                variable(v_idx).ht_ptr(v_sign).push_back( & cl.literals()[i]);
                cl.literals()[i].set_ht(1);
                other_ht_idx = i;
                break;
            }
            else {
                if (variable(v_idx).dlevel() > max_dl) {
                    max_dl = variable(v_idx).dlevel();
                    max_idx = i;
                }
            }
        }
        if (i >= sz) {
            //no unknown literals. so use the max dl literal
            int v_idx = cl.literals()[max_idx].var_index();
            int v_sign = cl.literals()[max_idx].var_sign();
            variable(v_idx).ht_ptr(v_sign).push_back( & cl.literals()[max_idx]);
            cl.literals()[max_idx].set_ht(1);
            other_ht_idx = max_idx;
        }
        max_idx = -1; max_dl = -1;
        for (i=sz-1; i>=0; --i) {
            if (i==other_ht_idx ) continue;
            int v_idx = cl.literals()[i].var_index();
            if (variable(v_idx).value()==UNKNOWN) {
                int v_sign = cl.literals()[i].var_sign();
                variable(v_idx).ht_ptr(v_sign).push_back( & cl.literals()[i]);
                cl.literals()[i].set_ht(-1);
                break;
            }
            else {
                if (variable(v_idx).dlevel() > max_dl) {
                    max_dl = variable(v_idx).dlevel();
                    max_idx = i;
                }
            }
        }
        if (i < 0) {
            int v_idx = cl.literals()[max_idx].var_index();
            int v_sign = cl.literals()[max_idx].var_sign();
            CLitPoolElement * lit_ptr = & cl.literals()[max_idx];
            variable(v_idx).ht_ptr(v_sign).push_back(lit_ptr);
            cl.literals()[max_idx].set_ht(-1);
        }
    }
    //update some statistics
    ++CDatabase::_stats.num_added_clauses; 
    CDatabase::_stats.num_added_literals += n_lits;
    if (is_unit && _stats.is_solver_started) {
      if (n_lits == 1) _addedUnitClauses.push_back(new_cl);
      int lit = find_unit_literal(new_cl);
      assert(lit);
      queue_implication(lit, new_cl);
    }
    else if (addConflicts && is_conflict) {
      _conflicts.push_back(new_cl);
    }
    return new_cl;
}


void CSolver::set_var_value(int v, int value, ClauseIdx ante, int dl)
{
    assert (value == 0 || value == 1);
    CHECK_FULL(dump());
    CHECK(verify_integrity());
    CHECK (cout << "Setting\t" << (value>0?"+":"-") << v 
           << " at " << dl << " because " << ante<< endl;);
    ++_stats.num_implications ;
    --num_free_variables();
    if (_assignment_hook) {
      (*_assignment_hook)(_assignment_hook_cookie, v, value);
    }
    CVariable & var = _variables[v];
    assert (var.value() == UNKNOWN);
    var.dlevel() = dl;
    var.value() = value;
    var.set_antecedence(ante);
    vector<CLitPoolElement *> & ht_ptrs = var.ht_ptr(value);
    if (dl == dlevel()) 
        set_var_value_with_current_dl(v, ht_ptrs);
    else 
        set_var_value_not_current_dl(v, ht_ptrs);
}


void CSolver::set_var_value_with_current_dl(int v, vector<CLitPoolElement *> & ht_ptrs)
{
    ClauseIdx cl_idx;
    CLitPoolElement * ht_ptr, * other_ht_ptr, * ptr;
    int dir;
    for (vector <CLitPoolElement *>::iterator itr = ht_ptrs.begin(); itr != ht_ptrs.end(); ++itr) {
        ht_ptr = *itr;
        dir = ht_ptr->direction();
        ptr = ht_ptr;
        while(1) {
            ptr += dir;
            if (ptr->val() <= 0) {
                if (dir == 1) 
                    cl_idx = - ptr->val();
                if (dir == ht_ptr->direction()) {
                    ptr = ht_ptr;
                    dir = -dir;
                    continue;
                }
                int the_value = literal_value (*other_ht_ptr);
                if (the_value == 0) //a conflict
                    _conflicts.push_back(cl_idx);
                else if ( the_value != 1) //e.g. unknown
                    queue_implication (other_ht_ptr->s_var(), cl_idx);
                break;
            }
            if (ptr->is_ht()) {
                other_ht_ptr = ptr;
                continue;
            }
            if (literal_value(*ptr) == 0) 
                continue;
            //now it's value is either 1 or unknown
            int v1 = ptr->var_index();
            int sign = ptr->var_sign();
            variable(v1).ht_ptr(sign).push_back(ptr);
            ht_ptr->unset_ht();
            ptr->set_ht(dir);

            *itr = ht_ptrs.back();
            ht_ptrs.pop_back();
            --itr;
            break;
        }
    }
}

void CSolver::set_var_value_not_current_dl(int v, vector<CLitPoolElement *> & ht_ptrs)
{
    ClauseIdx cl_idx;
    CLitPoolElement * ht_ptr, * other_ht_ptr, * ptr, * max_ptr = NULL;
    int dir,max_dl;

    for (vector <CLitPoolElement *>::iterator itr = ht_ptrs.begin(); 
         itr != ht_ptrs.end(); ++itr) {
        max_dl = -1;
        ht_ptr = *itr;
        dir = ht_ptr->direction();
        ptr = ht_ptr;
        while(1) {
            ptr += dir;
            if (ptr->val() <= 0) {
                if (dir == 1) 
                    cl_idx = - ptr->val();
                if (dir == ht_ptr->direction()) {
                    ptr = ht_ptr;
                    dir = -dir;
                    continue;
                }
                if (variable(ht_ptr->var_index()).dlevel() < max_dl) {
                    int v1 = max_ptr->var_index();
                    int sign = max_ptr->var_sign();
                    variable(v1).ht_ptr(sign).push_back(max_ptr);
                    ht_ptr->unset_ht();
                    max_ptr->set_ht(dir);
                    *itr = ht_ptrs.back();
                    ht_ptrs.pop_back();
                    --itr;
                }
                int the_value = literal_value (*other_ht_ptr);
                if (the_value == 0) //a conflict
                    _conflicts.push_back(cl_idx);
                else if ( the_value != 1) //e.g. unknown
                    queue_implication (other_ht_ptr->s_var(), cl_idx);
                break;
            }
            if (ptr->is_ht()) {
                other_ht_ptr = ptr;
                continue;
            }
            if (literal_value(*ptr) == 0) {
                if (variable(ptr->var_index()).dlevel() > max_dl) {
                    max_dl = variable(ptr->var_index()).dlevel();
                    max_ptr = ptr;
                }
                continue;
            }
            //now it's value is either 1 or unknown
            int v1 = ptr->var_index();
            int sign = ptr->var_sign();
            variable(v1).ht_ptr(sign).push_back(ptr);
            ht_ptr->unset_ht();
            ptr->set_ht(dir);

            *itr = ht_ptrs.back();
            ht_ptrs.pop_back();
            --itr;
            break;
        }
    }
}

void CSolver::unset_var_value(int v)
{
    CHECK(cout <<"Unset var " << (variable(v).value()?"+":"-") << v << endl;);
    CVariable & var = variable(v);
    if (var.var_score_pos() < _max_score_pos)
        _max_score_pos = var.var_score_pos();
    var.value() = UNKNOWN;
    var.set_antecedence(NULL_CLAUSE);
    var.dlevel() = -1;
    if (_assignment_hook) {
      (*_assignment_hook)(_assignment_hook_cookie, v, -1);
    }
}

int CSolver::find_max_clause_dlevel(ClauseIdx cl)
{
//if cl has single literal, then dlevel should be 0 
    int max_level = 0;
    if (cl == NULL_CLAUSE || cl == FLIPPED) 
        return dlevel();
    for (int i=0, sz= clause(cl).num_lits(); i<sz;  ++i) {
        int var_idx =((clause(cl).literals())[i]).var_index();
        if (_variables[var_idx].value() != UNKNOWN) {
            if (max_level < _variables[var_idx].dlevel())
                max_level =  _variables[var_idx].dlevel();
        }
    }
    return max_level; 
}

void CSolver::dump_assignment_stack(ostream & os) {
    cout << "Assignment Stack:  ";
    for (int i=0; i<= dlevel(); ++i) {
        if ((*_assignment_stack[i]).size() > 0)
        if (variable( (*_assignment_stack[i])[0]>>1).get_antecedence()==FLIPPED)
            cout << "*" ;
        cout << "(" <<i << ":";
        for (unsigned j=0; j<(*_assignment_stack[i]).size(); ++j )
            cout << ((*_assignment_stack[i])[j]&0x1?"-":"+")
                 << ((*_assignment_stack[i])[j] >> 1) << " ";
        cout << ") " << endl;
    }
    cout << endl;
}


bool CDatabase::is_conflict(ClauseIdx cl)
{
    CLitPoolElement * lits = clause(cl).literals();
    for (int i=0, sz= clause(cl).num_lits(); i<sz;  ++i)
        if (literal_value(lits[i]) != 0)
                return false;
    return true;
}

bool CDatabase::is_satisfied(ClauseIdx cl)
{
    CLitPoolElement * lits = clause(cl).literals();
    for (int i=0, sz= clause(cl).num_lits(); i<sz; ++i) 
        if (literal_value(lits[i]) == 1) 
            return true;
    return false;
}

int CDatabase::find_unit_literal(ClauseIdx cl) 
{
//if it's not unit, return 0.
    int unassigned = 0;
    for (int i=0, sz= clause(cl).num_lits(); i<sz;  ++i) {
        int var_idx =((clause(cl).literals())[i]).var_index();
        if (_variables[var_idx].value() == UNKNOWN) {
            if (unassigned == 0) 
                unassigned = clause(cl).literals()[i].s_var();
            else //more than one unassigned
                return 0;
        }
    }
    return unassigned;
}

void CSolver::delete_unrelevant_clauses(void) 
{
    CHECK_FULL (dump());
    int original_num_deleted = num_deleted_clauses();
    if (CDatabase::_stats.mem_used_up) {
        CDatabase::_stats.mem_used_up = false;
        if (++CDatabase::_stats.mem_used_up_counts < 5) {
            _params.max_unrelevance = (int) (_params.max_unrelevance * 0.8);
            if (_params.max_unrelevance < 4)
                _params.max_unrelevance = 4;
            _params.min_num_clause_lits_for_delete = (int) (_params.min_num_clause_lits_for_delete* 0.8);
            if (_params.min_num_clause_lits_for_delete < 10)
                _params.min_num_clause_lits_for_delete = 10;
            _params.max_conflict_clause_length = (int) (_params.max_conflict_clause_length*0.8);
            if (_params.max_conflict_clause_length < 50 )
                _params.max_conflict_clause_length = 50;
            CHECK(
            cout << "Forced to reduce unrelevance in clause deletion. " << endl;
            cout <<"MaxUnrel: " << _params.max_unrelevance 
                 << "  MinLenDel: " << _params.min_num_clause_lits_for_delete
                 << "  MaxLenCL : " << _params.max_conflict_clause_length << endl;
                );
        }
    }
    //first find out the clause to delete and mark them
    for (vector<CClause>::iterator itr = clauses().begin() + init_num_clauses(); 
         itr != clauses().end(); ++itr) {
        CClause & cl = * itr;
        if (!cl.in_use() || cl.num_lits() < _params.min_num_clause_lits_for_delete ) continue;
        int val_0_lits = 0, val_1_lits = 0, unknown_lits = 0;
        for (int i=0; i< cl.num_lits(); ++i) {
            int lit_value = literal_value (cl.literal(i));
            if (lit_value == 0 ) ++val_0_lits;
            else if (lit_value == 1) ++val_1_lits;
            else ++unknown_lits;
            if (unknown_lits + val_1_lits > _params.max_unrelevance) {
                mark_clause_deleted(cl);
                _unused_clause_idx_queue.push(itr - clauses().begin());
                CHECK (cout << "Deleting Unrelevant clause: " << cl << endl;);
                break;
            }
            if (cl.num_lits() > _params.max_conflict_clause_length && 
                (unknown_lits+val_1_lits > 1) ) { //to make sure it's not generating an implication
                                                  //and it's not an antecedence for other var assignment
                mark_clause_deleted(cl);
                CHECK (cout << "Deleting too large clause: " << cl << endl;);
                _unused_clause_idx_queue.push(itr - clauses().begin());
                break;
            }
        }
    }
    //now delete the index from variables
    if (original_num_deleted == num_deleted_clauses()) 
        return ; //didn't delete anything
    for (vector<CVariable>::iterator itr = variables().begin(); 
         itr != variables().end(); ++ itr) {
        for (int i=0; i<2; ++i) { //for each phase
            //delete the h_t index from the vars
            vector<CLitPoolElement *> & ht_ptr = (*itr).ht_ptr(i);
            for (vector<CLitPoolElement *>::iterator my_itr = ht_ptr.begin(); 
                 my_itr != ht_ptr.end(); ++my_itr) {
                if ( (*my_itr)->val() <= 0) {
                    *my_itr = ht_ptr.back();
                    ht_ptr.pop_back();
                    --my_itr;
                }
            }
        }
    }
    CHECK(cout << "Deleting " << num_deleted_clauses() - original_num_deleted << " Clause ";
      cout << " and " << num_deleted_literals() - original_del_lits << " Literals " << endl;);
    CHECK_FULL (dump());
}
//============================================================================================
bool CSolver::time_out(void) 
{
    if ( (current_cpu_time() - _stats.start_cpu_time)/1000.0 > _params.time_limit )
        return true;
    return false;
}

inline bool compare_var_stat(const pair<int, int> & v1, 
                            const pair<int, int> & v2) 
{
    if (v1.second > v2.second) return true;
    return false;
}

void CSolver::update_var_stats(void) 
{
    for(unsigned i=1; i< variables().size(); ++i) {
        CVariable & var = variable(i);
        var.score(0) = var.score(0)/2 + var.lits_count(0) - _last_var_lits_count[0][i];
        var.score(1) = var.score(1)/2 + var.lits_count(1) - _last_var_lits_count[1][i];
        _last_var_lits_count[0][i] = var.lits_count(0);
        _last_var_lits_count[1][i] = var.lits_count(1);
        _var_order[i-1] = pair<int, int>(i, var.score());
    }
    ::stable_sort(_var_order.begin(), _var_order.end(), compare_var_stat);
    for (unsigned i=0; i<_var_order.size(); ++i) 
        variable(_var_order[i].first).var_score_pos() = i;
    _max_score_pos = 0;
}

bool CSolver::decide_next_branch(void)
{
    ++_stats.num_decisions;
    if (!_implication_queue.empty()) {
        //some hook function did a decision, so skip my own decision making.
        //if the front of implication queue is 0, that means it's finished
        //because var index start from 1, so 2 *vid + sign won't be 0. 
        //else it's a valid decision.
        _max_score_pos = 0; //reset the max_score_position.
        return _implication_queue.front().first;
    }
        
    int s_var = 0;
    bool done = false;

    if (_decision_hook) {
      s_var = (*_decision_hook)(_decision_hook_cookie, &done);
    }
    if (!done && s_var < 2) {
      unsigned i, var_idx, sign;
      CVariable * ptr;

    for (i=_max_score_pos; i<_var_order.size(); ++i) {
        var_idx = _var_order[i].first;
        ptr = &(variables()[var_idx]);
        if (ptr->value()==UNKNOWN) {
            //move th max score position pointer
            _max_score_pos = i;
            //make some randomness happen
            if (--_params.randomness < _params.base_randomness)
                _params.randomness = _params.base_randomness;

            int randomness = _params.randomness;
            if (randomness >= num_free_variables())
                randomness = num_free_variables() - 1;
            int skip =random()%(1+randomness);
            int index = i;
            while (skip > 0) {
                ++index;
                var_idx = _var_order[index].first;
                ptr = &(variables()[var_idx]);
                if (ptr->value()==UNKNOWN)
                    --skip;
            }
            assert (ptr->value() == UNKNOWN);
            sign = ptr->score(0) > ptr->score(1) ? 0 : 1;
            s_var = var_idx + var_idx + sign;
            break;
        }
    }
    }

    if (s_var<2) //no more free vars, solution found,  quit
        return false;
    ++dlevel();
    if (_dlevel_hook) {
      (*_dlevel_hook)(_dlevel_hook_cookie, 1);
    }
    if (dlevel() > _stats.max_dlevel) _stats.max_dlevel = dlevel();
    CHECK (cout << "**Decision at Level " << dlevel() ;
           cout <<": " << s_var << "\te.g. " << (s_var&0x1?"-":" ") ;
           cout <<(s_var>>1)  << endl; );
    queue_implication(s_var, NULL_CLAUSE);
    return true;
}

int CSolver::preprocess(bool allowNewClauses) 
{
    //1. detect all the unused variables
  if (!allowNewClauses) {
    vector<int> un_used;
    for (int i=1, sz=variables().size(); i<sz; ++i) {
        CVariable & v = variable(i);
        if (v.lits_count(0) == 0 && v.lits_count(1) == 0) {
            un_used.push_back(i);
            v.value() = 1; 
            v.dlevel() = -1;
        }
    }
    num_free_variables() -= un_used.size();
    if (_params.verbosity>1 && un_used.size() > 0) {
        cout << un_used.size()<< " Variables are defined but not used " << endl;
        if (_params.verbosity > 2) {
            for (unsigned i=0; i< un_used.size(); ++i)
                cout << un_used[i] << " ";
            cout << endl;
        }
    }
    //2. detect all variables with only one phase occuring
    vector<int> uni_phased;
    for (int i=1, sz=variables().size(); i<sz; ++i) {
        CVariable & v = variable(i);
        if (v.value() != UNKNOWN)
            continue;
        if (v.lits_count(0) == 0){ //no positive phased lits.
            queue_implication( i+i+1, NULL_CLAUSE);
            uni_phased.push_back(-i);
        }
        else if (v.lits_count(1) == 0){ //no negative phased lits.
            queue_implication( i+i, NULL_CLAUSE);
            uni_phased.push_back(i);
        }
    }
    if (_params.verbosity>1 && uni_phased.size() > 0) {
        cout << uni_phased.size()<< " Variables only appear in one phase." << endl;
        if (_params.verbosity > 2) {
            for (unsigned i=0; i< uni_phased.size(); ++i)
                cout << uni_phased[i] << " ";
            cout <<endl;
        }
    }
  }
    //3. detect all the unit clauses
    for (ClauseIdx i=0, sz=clauses().size(); i<sz; ++i) {
        if (clause(i).num_lits() == 1){ //unit clause
            queue_implication(find_unit_literal(i), i);
        }
    }

    if(deduce()==CONFLICT) return CONFLICT;
    return NO_CONFLICT;    
}

void CSolver::real_solve(void)
{
    while(1) {
        run_periodic_functions();
        if (decide_next_branch() || !_implication_queue.empty() ||
            _conflicts.size() != 0) {
            while (deduce()==CONFLICT) { 
                int blevel = analyze_conflicts();
                if (blevel <= 0) {
                    _stats.outcome = UNSATISFIABLE;
                    return;
                }
                else if (_addedUnitClauses.size()) {
                  // reassert added unit clauses
                  unsigned idx = _addedUnitClauses.size()-1;
                  ClauseIdx cl = _addedUnitClauses.back();
                  int lit = find_unit_literal(cl);
                  while (lit != 0) {
                    queue_implication(lit, cl);
                    if (idx == 0) break;
                    cl = _addedUnitClauses[--idx];
                    lit = find_unit_literal(cl);
                  }
                }
            }
        }
        else {
          _stats.outcome = SATISFIABLE;
          return;
        }
        if (time_out()) { 
            _stats.outcome = TIME_OUT;
            return; 
        }
        if (_stats.is_mem_out) {
            _stats.outcome = MEM_OUT;
            return; 
        }
    }
}

int CSolver::solve(bool allowNewClauses)
{
    init();
    //preprocess 
    if(preprocess(allowNewClauses)==CONFLICT) {
        _stats.outcome = UNSATISFIABLE;
    }
    else { //the real search
      if (_dlevel_hook) {
        (*_dlevel_hook)(_dlevel_hook_cookie, 1);
      }
      real_solve();
    }
    _stats.finish_cpu_time = current_cpu_time();
    _stats.finish_world_time = current_world_time();
    return _stats.outcome;
}

int CSolver::continueCheck()
{
  real_solve();
  _stats.finish_cpu_time = current_cpu_time();
  _stats.finish_world_time = current_world_time();
  return _stats.outcome;
}

void CSolver::back_track(int blevel)
{
    CHECK (cout << "Back track to " << blevel <<" ,currently in "<< dlevel() << " level" << endl;);
    CHECK_FULL (dump());
    CHECK(verify_integrity());
    assert(blevel <= dlevel());
    for (int i=dlevel(); i>= blevel; --i) {
        vector<int> & assignments = *_assignment_stack[i];
        for (int j=assignments.size()-1 ; j>=0; --j) 
                unset_var_value(assignments[j]>>1);
        num_free_variables() += assignments.size();
        assignments.clear();
        if (_dlevel_hook) {
          (*_dlevel_hook)(_dlevel_hook_cookie, -1);
        }
    }
    dlevel() = blevel - 1;
    ++_stats.num_backtracks;
    CHECK_FULL (dump());
    CHECK(verify_integrity());
}

int CSolver::deduce(void) 
{
restart:
    while (!_implication_queue.empty() && _conflicts.size()==0) {
        int literal = _implication_queue.front().first;
        int variable_index = literal>>1;
        ClauseIdx cl = _implication_queue.front().second;
        _implication_queue.pop();
        CVariable * the_var = &(variables()[variable_index]);
        if ( the_var->value() == UNKNOWN) { // an implication
            int dl;
            if (_params.back_track_complete)
                dl = dlevel();
            else 
                dl = find_max_clause_dlevel(cl);
            set_var_value(variable_index, !(literal&0x1), cl, dl);
            the_var = &(variables()[variable_index]);
            _assignment_stack[dl]->push_back(literal);
            CHECK(verify_integrity());
        }
        else if (the_var->value() == (literal&0x1) ) { //a conflict
            //note: literal & 0x1 == 1 means the literal is in negative phase
            _conflicts.push_back(cl);
        }
    }
    if (!_conflicts.size() && _deduction_hook) {
      (*_deduction_hook)(_deduction_hook_cookie);
      if (!_implication_queue.empty()) goto restart;
    }
    while(!_implication_queue.empty()) _implication_queue.pop();
    return (_conflicts.size()?CONFLICT:NO_CONFLICT);
}


void CSolver::verify_integrity(void) 
{
}

void CSolver::mark_vars_at_level(ClauseIdx cl, int var_idx, int dl)
{
    for (CLitPoolElement * itr = clause(cl).literals(); (*itr).val() > 0 ; ++ itr) {
        int v = (*itr).var_index();
        if (v == var_idx) 
            continue;
        else if (variable(v).dlevel() == dl) {
            if (!variable(v).is_marked()) {
                variable(v).set_marked();
                ++ _num_marked;
            }
        }
        else {
            assert (variable(v).dlevel() < dl);
            if (variable(v).in_new_cl() == -1){ //it's not in the new cl
                variable(v).set_in_new_cl((*itr).var_sign());
                _conflict_lits.push_back((*itr).s_var());
            }
        }
    }
}

int CSolver::analyze_conflicts(void) {
    return conflict_analysis_zchaff();
}

int CSolver::conflict_analysis_zchaff (void) 
{
    assert (_conflicts.size());
    assert (_implication_queue.empty());
    assert (_num_marked == 0);
    static int entries = 0;
    ++ entries;
    int back_level = 0;
    ClauseIdx conflict_cl;
    vector<ClauseIdx> added_conflict_clauses;
    for (int i=0, sz=_conflicts.size(); i<sz; ++i) {
        ClauseIdx cl = _conflicts[i];

        if (!is_conflict(cl)) continue;

        back_level = 0; // reset it
        while (_conflict_lits.size()) {
            CVariable & var = variable(_conflict_lits.back() >> 1);
            _conflict_lits.pop_back();
            assert (var.in_new_cl() != -1);
            var.set_in_new_cl(-1);
        }
        int max_dlevel = find_max_clause_dlevel(cl); // find the max level, which is the back track level
        bool first_time = true; //its the beginning
        bool prev_is_uip = false;
        mark_vars_at_level (cl, -1 /*var*/, max_dlevel);

        vector <int> & assignments = *_assignment_stack[max_dlevel];
        for (int j = assignments.size() - 1; j >= 0; --j ) { //now add conflict lits, and unassign vars
            int assigned = assignments[j];
            if (variable(assigned>>1).is_marked()) {
                variable(assigned>>1).clear_marked();
                -- _num_marked; 
                ClauseIdx ante_cl = variables()[assigned>>1].get_antecedence();

                if ( (_num_marked == 0 && 
                      (!first_time) && 
                      (prev_is_uip == false))
                      || ante_cl==NULL_CLAUSE) { //conclude add clause
                    assert (variable(assigned>>1).in_new_cl()==-1);
                    _conflict_lits.push_back(assigned^0x1);  // add this assignment's reverse, e.g. UIP
                    int conflict_cl = add_clause(_conflict_lits, false);
                    if (conflict_cl < 0 ) {
                        _stats.is_mem_out = true;
                        _conflicts.clear();
                        assert (_implication_queue.empty());
                        return 1; 
                    }
                    _conflict_lits.pop_back();  // remove for continue use of _conflict_lits
                    added_conflict_clauses.push_back(conflict_cl);

                    CHECK(cout <<"Conflict clause: " << cl << " : " << clause(cl) << endl;
                          cout << "**Add Clause " <<conflict_cl<< " : "<<clause(conflict_cl) << endl; 
                        );

                    prev_is_uip = true;
                    break; //if do this, only one clause will be added.
                }
                else prev_is_uip = false;

                if ( ante_cl != NULL_CLAUSE ) 
                    mark_vars_at_level(ante_cl, assigned>>1/*var*/, max_dlevel);
                else 
                    assert (j == 0);
                first_time = false;
            }
        }
        back_level = max_dlevel;
        back_track(max_dlevel); 
    }
    assert (_num_marked == 0);
    if (back_level==0) //there are nothing to be done
            return back_level;

    if (_params.back_track_complete) {
        for (unsigned i=0; i< added_conflict_clauses.size(); ++i) {
            ClauseIdx cl = added_conflict_clauses[i];
            if (find_unit_literal(cl)) { //i.e. if it's a unit clause
                int dl = find_max_clause_dlevel(cl);
                if (dl < dlevel()) { //thus make sure implied vars are at current dl.
                    back_track(dl+1);
                }
            }
        }
    }
    int cnt = 0;
    for (int i=0, sz=added_conflict_clauses.size(); i<sz; ++i) {
        conflict_cl = added_conflict_clauses[i];
        int lit = find_unit_literal(conflict_cl);
        if (lit) {
            queue_implication(lit, conflict_cl);
            ++cnt;
        }
    }
    assert (cnt > 0);
    assert (!_params.back_track_complete || cnt == 1);

    _conflicts.clear();

    while (_conflict_lits.size()) {
        CVariable & var = variable(_conflict_lits.back() >> 1);
        _conflict_lits.pop_back();
        assert (var.in_new_cl() != -1);
        var.set_in_new_cl(-1);
    }
    CHECK( dump_assignment_stack(););
    CHECK(cout << "Conflict Analasis: conflict at level: " << back_level;
          cout << "  Assertion Clause is " << conflict_cl<< endl; );
    return back_level;
}               

---