EasySAT.cpp

/************************************************************************************
EasySAT: A CDCL SAT Solver
================================================================================
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************************************************************************************/
#include "EasySAT.hpp"
#include <fstream>

#define value(lit) (lit > 0 ? value[lit] : -value[-lit])    // Get the value of a literal
#define watch(id) (watches[vars + id])                      // Remapping a literal [-maxvar, +maxvar] to its watcher.

char *read_whitespace(char *p) {                            // Aid function for parser
    while ((*p >= 9 && *p <= 13) || *p == 32) ++p;
    return p;
}

char *read_until_new_line(char *p) {                        // Aid function for parser
    while (*p != '\n') {
        if (*p++ == '\0') exit(1);
    }
    return ++p;
}

char *read_int(char *p, int *i) {                           // Aid function for parser
    bool sym = true; *i = 0;
    p = read_whitespace(p);
    if (*p == '-') sym = false, ++p;
    while (*p >= '0' && *p <= '9') {
        if (*p == '\0') return p;
        *i = *i * 10 + *p - '0', ++p;
    }
    if (!sym) *i = -(*i);
    return p;
}

int Solver::add_clause(std::vector<int> &c) {                   
    clause_DB.push_back(Clause(c.size()));                          // Add a clause c into database.
    int id = clause_DB.size() - 1;                                  // Getting clause index.
    for (int i = 0; i < (int)c.size(); i++) clause_DB[id][i] = c[i];     // Copy literals
    watch(-c[0]).push_back(Watcher(id, c[1]));                      // Watch this clause by literal -c[0]
    watch(-c[1]).push_back(Watcher(id, c[0]));                      // Watch this clause by literal -c[1]
    return id;                                                      
}

int Solver::parse(char *filename) {
    std::ifstream fin(filename);                                    // Fast load begin                                 
    fin.seekg(0, fin.end);
    size_t file_len = fin.tellg();
	fin.seekg(0, fin.beg);
	char *data = new char[file_len + 1], *p = data;
	fin.read(data, file_len);
	fin.close();                                                    // Fast load end
	data[file_len] = '\0';
    std::vector<int> buffer;                                        // Save the clause that waiting to push
    while (*p != '\0') {
        p = read_whitespace(p);
        if (*p == '\0') break;
        if (*p == 'c') p = read_until_new_line(p);
        else if (*p == 'p') {                                                               // Deal with 'p cnf' line.
            if (*(p + 1) == ' ' && *(p + 2) == 'c' && *(p + 3) == 'n' && *(p + 4) == 'f') {
                p += 5, p = read_int(p, &vars), p = read_int(p, &clauses);
                alloc_memory();
            } 
            else printf("PARSE ERROR! Unexpected char\n"), exit(2);                        // Wrong 'p ' line.
        }
        else {                                                                             
            int32_t dimacs_lit;
            p = read_int(p, &dimacs_lit);
            if (*p == '\0' && dimacs_lit != 0)                                              // Unexpected EOF
                printf("c PARSE ERROR! Unexpected EOF\n"), exit(1);
            if (dimacs_lit == 0) {                                                          // Finish read a clause.
                if (buffer.size() == 0) return 20;                                          // Read an empty clause.
                if (buffer.size() == 1 && value(buffer[0]) == -1) return 20;                // Found confliction in origin clauses
                if (buffer.size() == 1 && !value(buffer[0])) assign(buffer[0], 0, -1);      // Found an unit clause.
                else if (buffer.size() > 1) add_clause(buffer);                             // Found a clause who has more than 1 literals.
                buffer.clear();                                                             // For the next clause.
            }       
            else buffer.push_back(dimacs_lit);                                              // read a literal
        }
    }
    origin_clauses = clause_DB.size();
    return (propagate() == -1 ? 0 : 20);                                                    // Simplify by BCP.
}

void Solver::alloc_memory() {
    value       = new int[vars + 1];
    reason      = new int[vars + 1];
    level       = new int[vars + 1];
    mark        = new int[vars + 1];
    local_best  = new int[vars + 1];
    saved       = new int[vars + 1];
    activity    = new double[vars + 1];
    watches     = new std::vector<Watcher>[vars * 2 + 1];
    conflicts = time_stamp = propagated = restarts = rephases = reduces = threshold = 0;
    fast_lbd_sum = lbd_queue_size = lbd_queue_pos = slow_lbd_sum = 0;
    var_inc = 1, rephase_limit = 1024, reduce_limit = 8192;
    vsids.setComp(GreaterActivity(activity));
    for (int i = 1; i <= vars; i++) 
        value[i] = reason[i] = level[i] = mark[i] = local_best[i] = activity[i] = saved[i] = 0, vsids.insert(i);
}

void Solver::bump_var(int var, double coeff) {
    if ((activity[var] += var_inc * coeff) > 1e100) {           // Update score and prevent float overflow
        for (int i = 1; i <= vars; i++) activity[i] *= 1e-100;
        var_inc *= 1e-100;}
    if (vsids.inHeap(var)) vsids.update(var);                 // update heap
}

void Solver::assign(int lit, int l, int cref) {
    int var = abs(lit);
    value[var]  = lit > 0 ? 1 : -1;
    level[var]  = l, reason[var] = cref;                                         
    trail.push_back(lit);
}

int Solver::propagate() {
    while (propagated < (int)trail.size()) { 
        int p = trail[propagated++];                    // Pick an unpropagated literal in trail.
        std::vector<Watcher> &ws = watch(p);            // Fetch the watcher for this literal.
        int i, j, size = ws.size();                     
        for (i = j = 0; i < size; ) {               
            int blocker = ws[i].blocker;                       
            if (value(blocker) == 1) {                  // Pre-judge whether the clause is already SAT
                ws[j++] = ws[i++]; continue;
            }
            int cref = ws[i].idx_clause, k, sz;
            Clause& c = clause_DB[cref];                // Fetch a clause from watcher
            if (c[0] == -p) c[0] = c[1], c[1] = -p;     // Make sure c[1] is the false literal (-p).
            Watcher w = Watcher(cref, c[0]);            // Prepare a new watcher for c[1]
            i++;
            if (value(c[0]) == 1) {                     // Check whether another lit is SAT.
                ws[j++] = w; continue;
            }
            for (k = 2, sz = c.lit.size(); k < sz && value(c[k]) == -1; k++);    // Find a new watch literal.
            if (k < sz) {                               // Move the watch literal to the second place
                c[1] = c[k], c[k] = -p;
                watch(-c[1]).push_back(w);
            }
            else {                                      // Can not find a new watch literl
                ws[j++] = w;
                if (value(c[0]) == -1) {                // There is a confliction
                    while (i < size) ws[j++] = ws[i++];
                    ws.resize(j);
                    return cref;
                }
                else assign(c[0], level[abs(p)], cref);// Find a new unit clause and assign it.
            }
        }
        ws.resize(j);
    }
    return -1;                                          // Meet a convergence
}

int Solver::analyze(int conflict, int &backtrackLevel, int &lbd) {
    ++time_stamp;
    learnt.clear();
    Clause &c = clause_DB[conflict]; 
    int highestLevel = level[abs(c[0])];
    if (highestLevel == 0) return 20;
    learnt.push_back(0);        // leave a place to save the First-UIP
    std::vector<int> bump;      // The variables to bump
    int should_visit_ct = 0,    // The number of literals that have not been visited in the higest level of the implication graph.
        resolve_lit = 0,        // The literal to do resolution.
        index = trail.size() - 1;
    do {
        Clause &c = clause_DB[conflict];
        for (int i = (resolve_lit == 0 ? 0 : 1); i < (int)c.lit.size(); i++) {
            int var = abs(c[i]);
            if (mark[var] != time_stamp && level[var] > 0) {
                bump_var(var, 0.5);
                bump.push_back(var);
                mark[var] = time_stamp;
                if (level[var] >= highestLevel) should_visit_ct++;
                else learnt.push_back(c[i]);
            }
        }
        do {                                         // Find the last marked literal in the trail to do resolution.
            while (mark[abs(trail[index--])] != time_stamp);
            resolve_lit = trail[index + 1];
        } while (level[abs(resolve_lit)] < highestLevel);
        conflict = reason[abs(resolve_lit)], mark[abs(resolve_lit)] = 0, should_visit_ct--;
    } while (should_visit_ct > 0);                   // Have find the convergence node in the highest level (First UIP)
    learnt[0] = -resolve_lit;
    ++time_stamp, lbd = 0;
    for (int i = 0; i < (int)learnt.size(); i++) {   // Calculate the LBD.
        int l = level[abs(learnt[i])];
        if (l && mark[l] != time_stamp) 
            mark[l] = time_stamp, ++lbd;
    }
    if (lbd_queue_size < 50) lbd_queue_size++;       // update fast-slow.
    else fast_lbd_sum -= lbd_queue[lbd_queue_pos];
    fast_lbd_sum += lbd, lbd_queue[lbd_queue_pos++] = lbd;
    if (lbd_queue_pos == 50) lbd_queue_pos = 0;
    slow_lbd_sum += (lbd > 50 ? 50 : lbd);
    if (learnt.size() == 1) backtrackLevel = 0;
    else {                                           // find the second highest level for backtracking.
        int max_id = 1;
        for (int i = 2; i < (int)learnt.size(); i++)
            if (level[abs(learnt[i])] > level[abs(learnt[max_id])]) max_id = i;
        int p = learnt[max_id];
        learnt[max_id] = learnt[1], learnt[1] = p, backtrackLevel = level[abs(p)];
    }
    for (int i = 0; i < (int)bump.size(); i++)       // heuristically bump some variables.
        if (level[bump[i]] >= backtrackLevel - 1) bump_var(bump[i], 1);
    return 0;
}

void Solver::backtrack(int backtrackLevel) {
    if ((int)pos_in_trail.size() <= backtrackLevel) return;
    for (int i = trail.size() - 1; i >= pos_in_trail[backtrackLevel]; i--) {
        int v = abs(trail[i]);
        value[v] = 0, saved[v] = trail[i] > 0 ? 1 : -1; // phase saving 
        if (!vsids.inHeap(v)) vsids.insert(v);          // update heap
    }
    propagated = pos_in_trail[backtrackLevel];
    trail.resize(propagated);
    pos_in_trail.resize(backtrackLevel);
}

int Solver::decide() {      
    int next = -1;
    while (next == -1 || value(next) != 0) {    // Picking a variable according to VSIDS
        if (vsids.empty()) return 10;
        else next = vsids.pop();
    }
    pos_in_trail.push_back(trail.size());
    if (saved[next]) next *= saved[next];       // Pick the polarity of the varible
    assign(next, pos_in_trail.size(), -1);
    return 0;
}

void Solver::restart() {
    fast_lbd_sum = lbd_queue_size = lbd_queue_pos = 0;
    backtrack(0);
    int phase_rand = rand() % 100;              // probabilistic rephasing
    if ((phase_rand -= 60) < 0)     for (int i = 1; i <= vars; i++) saved[i] = local_best[i];
    else if ((phase_rand -= 5) < 0) for (int i = 1; i <= vars; i++) saved[i] = -local_best[i];
    else if ((phase_rand -= 20) < 0)for (int i = 1; i <= vars; i++) saved[i] = rand() % 2 ? 1 : -1;
}

void Solver::rephase() {
    rephases = 0, threshold *= 0.9, rephase_limit += 8192;
}

void Solver::reduce() {
    backtrack(0);
    reduces = 0, reduce_limit += 512;
    int new_size = origin_clauses, old_size = clause_DB.size();
    reduce_map.resize(old_size);
    for (int i = origin_clauses; i < old_size; i++) {    // random delete 50% bad clauses (LBD>=5)
        if (clause_DB[i].lbd >= 5 && rand() % 2 == 0) reduce_map[i] = -1;  // remove clause
        else {
            if (new_size != i) clause_DB[new_size] = clause_DB[i];
            reduce_map[i] = new_size++;
        }
    }
    clause_DB.resize(new_size, Clause(0));
    for (int v = -vars; v <= vars; v++) {   // Update the watches.
        if (v == 0) continue;
        int old_sz = watch(v).size(), new_sz = 0;
        for (int i = 0; i < old_sz; i++) {
            int old_idx = watch(v)[i].idx_clause;
            int new_idx = old_idx < origin_clauses ? old_idx : reduce_map[old_idx];
            if (new_idx != -1) {
                watch(v)[i].idx_clause = new_idx;
                if (new_sz != i) watch(v)[new_sz] = watch(v)[i];
                new_sz++;
            }
        }
        watch(v).resize(new_sz);
    }
}

int Solver::solve() {
    int res = 0;
    while (!res) {
        int cref = propagate();                         // Boolean Constraint Propagation (BCP)
        if (cref != -1) {                               // Find a conflict
            int backtrackLevel = 0, lbd = 0;
            res = analyze(cref, backtrackLevel, lbd);   // Conflict analyze
            if (res == 20) break;                       // Find a conflict in 0-level
            backtrack(backtrackLevel);                  // backtracking         
            if (learnt.size() == 1) assign(learnt[0], 0, -1);   // Learnt a unit clause.
            else {                     
                int cref = add_clause(learnt);                  // Add a clause to data base.
                clause_DB[cref].lbd = lbd;              
                assign(learnt[0], backtrackLevel, cref);        // The learnt clause implies the assignment of the UIP variable.
            }
            var_inc *= (1 / 0.8);                               // var_decay for locality
            ++restarts, ++conflicts, ++rephases, ++reduces;     
            if ((int)trail.size() > threshold) {                // update the local-best phase
                threshold = trail.size();                       
                for (int i = 1; i <= vars; i++) local_best[i] = value[i];
            }
        }
        else if (reduces >= reduce_limit) reduce();            
        else if (lbd_queue_size == 50 && 0.8 * fast_lbd_sum / lbd_queue_size > slow_lbd_sum / conflicts) restart(); 
        else if (rephases >= rephase_limit) rephase();
        else res = decide();
    }
    return res;
}

void Solver::printModel() {
    printf("v ");
    for (int i = 1; i <= vars; i++) printf("%d ", value[i] * i);
    puts("0");
}

int main(int argc, char **argv) {
    Solver S;
    int res = S.parse(argv[1]);
    if (res == 20) printf("s UNSATISFIABLE\n");
    else {
        res = S.solve();
        if (res == 10) {
            printf("s SATISFIABLE\n");
            S.printModel();
        }
        else if (res == 20) printf("s UNSATISFIABLE\n");
    }
    return 0;
}