update vendor

vendor/github.com/crillab/gophersat/explain/check.go

@@ -0,0 +1,149 @@
+// Package explain provides facilities to check and understand UNSAT instances.
+package explain
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+
+	"github.com/crillab/gophersat/solver"
+)
+
+// Options is a set of options that can be set to true during the checking process.
+type Options struct {
+	// If Verbose is true, information about resolution will be written on stdout.
+	Verbose bool
+}
+
+// Checks whether the clause satisfies the problem or not.
+// Will return true if the problem is UNSAT, false if it is SAT or indeterminate.
+func unsat(pb *Problem, clause []int) bool {
+	oldUnits := make([]int, len(pb.units))
+	copy(oldUnits, pb.units)
+	// lits is supposed to be implied by the problem.
+	// We add the negation of each lit as a unit clause to see if this is true.
+	for _, lit := range clause {
+		if lit > 0 {
+			pb.units[lit-1] = -1
+		} else {
+			pb.units[-lit-1] = 1
+		}
+	}
+	res := pb.unsat()
+	pb.units = oldUnits // We must restore the previous state
+	return res
+}
+
+// UnsatChan will wait RUP clauses from ch and use them as a certificate.
+// It will return true iff the certificate is valid, i.e iff it makes the problem UNSAT
+// through unit propagation.
+// If pb.Options.ExtractSubset is true, a subset will also be extracted for that problem.
+func (pb *Problem) UnsatChan(ch chan string) (valid bool, err error) {
+	defer pb.restore()
+	pb.initTagged()
+	for line := range ch {
+		fields := strings.Fields(line)
+		if len(fields) == 0 {
+			continue
+		}
+		if _, err := strconv.Atoi(fields[0]); err != nil {
+			// This is not a clause: ignore the line
+			continue
+		}
+		clause, err := parseClause(fields)
+		if err != nil {
+			return false, err
+		}
+		if !unsat(pb, clause) {
+			return false, nil
+		}
+		if len(clause) == 0 {
+			// This is the empty and unit propagation made the problem UNSAT: we're done.
+			return true, nil
+		}
+		// Since clause is a logical consequence, append it to the problem
+		pb.Clauses = append(pb.Clauses, clause)
+	}
+
+	// If we did not send any information through the channel
+	// It implies that the problem is trivially unsatisfiable
+	// Since we had only unit clauses inside the channel.
+	return true, nil
+}
+
+// Unsat will parse a certificate, and return true iff the certificate is valid, i.e iff it makes the problem UNSAT
+// through unit propagation.
+// If pb.Options.ExtractSubset is true, a subset will also be extracted for that problem.
+func (pb *Problem) Unsat(cert io.Reader) (valid bool, err error) {
+	defer pb.restore()
+	pb.initTagged()
+	sc := bufio.NewScanner(cert)
+	for sc.Scan() {
+		line := sc.Text()
+		fields := strings.Fields(line)
+		if len(fields) == 0 {
+			continue
+		}
+		if _, err := strconv.Atoi(fields[0]); err != nil {
+			// This is not a clause: ignore the line
+			continue
+		}
+		clause, err := parseClause(fields)
+		if err != nil {
+			return false, err
+		}
+		if !unsat(pb, clause) {
+			return false, nil
+		}
+		// Since clause is a logical consequence, append it to the problem
+		pb.Clauses = append(pb.Clauses, clause)
+	}
+	if err := sc.Err(); err != nil {
+		return false, fmt.Errorf("could not parse certificate: %v", err)
+	}
+	return true, nil
+}
+
+// ErrNotUnsat is the error returned when trying to get the MUS or UnsatSubset of a satisfiable problem.
+var ErrNotUnsat = fmt.Errorf("problem is not UNSAT")
+
+// UnsatSubset returns an unsatisfiable subset of the problem.
+// The subset is not guaranteed to be a MUS, meaning some clauses of the resulting
+// problem might be removed while still keeping the unsatisfiability of the problem.
+// However, this method is much more efficient than extracting a MUS, as it only calls
+// the SAT solver once.
+func (pb *Problem) UnsatSubset() (subset *Problem, err error) {
+	solverPb := solver.ParseSlice(pb.Clauses)
+	if solverPb.Status == solver.Unsat {
+		// Problem is trivially UNSAT
+		// Make a copy so that pb and pb2 are not the same value.
+		pb2 := *pb
+		return &pb2, nil
+	}
+	s := solver.New(solver.ParseSlice(pb.Clauses))
+	s.Certified = true
+	s.CertChan = make(chan string)
+	status := solver.Unsat
+	go func() {
+		status = s.Solve()
+		close(s.CertChan)
+	}()
+	if valid, err := pb.UnsatChan(s.CertChan); !valid || status == solver.Sat {
+		return nil, ErrNotUnsat
+	} else if err != nil {
+		return nil, fmt.Errorf("could not solve problem: %v", err)
+	}
+	subset = &Problem{
+		NbVars: pb.NbVars,
+	}
+	for i, clause := range pb.Clauses {
+		if pb.tagged[i] {
+			// clause was used to prove pb is UNSAT: it's part of the subset
+			subset.Clauses = append(subset.Clauses, clause)
+			subset.NbClauses++
+		}
+	}
+	return subset, nil
+}