update vendor

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

@@ -0,0 +1,104 @@
+package explain
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// parseClause parses a line representing a clause in the DIMACS CNF syntax.
+func parseClause(fields []string) ([]int, error) {
+	clause := make([]int, 0, len(fields)-1)
+	for _, rawLit := range fields {
+		lit, err := strconv.Atoi(rawLit)
+		if err != nil {
+			return nil, fmt.Errorf("could not parse clause %v: %v", fields, err)
+		}
+		if lit != 0 {
+			clause = append(clause, lit)
+		}
+	}
+	return clause, nil
+}
+
+// ParseCNF parses a CNF and returns the associated problem.
+func ParseCNF(r io.Reader) (*Problem, error) {
+	sc := bufio.NewScanner(r)
+	var pb Problem
+	for sc.Scan() {
+		line := sc.Text()
+		fields := strings.Fields(line)
+		if len(fields) == 0 {
+			continue
+		}
+		switch fields[0] {
+		case "c":
+			continue
+		case "p":
+			if err := pb.parseHeader(fields); err != nil {
+				return nil, fmt.Errorf("could not parse header %q: %v", line, err)
+			}
+		default:
+			if err := pb.parseClause(fields); err != nil {
+				return nil, fmt.Errorf("could not parse clause %q: %v", line, err)
+			}
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, fmt.Errorf("could not parse problem: %v", err)
+	}
+	return &pb, nil
+}
+
+func (pb *Problem) parseHeader(fields []string) error {
+	if len(fields) != 4 {
+		return fmt.Errorf("expected 4 fields, got %d", len(fields))
+	}
+	strVars := fields[2]
+	strClauses := fields[3]
+	var err error
+	pb.NbVars, err = strconv.Atoi(fields[2])
+	if err != nil {
+		return fmt.Errorf("invalid number of vars %q: %v", strVars, err)
+	}
+	if pb.NbVars < 0 {
+		return fmt.Errorf("negative number of vars %d", pb.NbVars)
+	}
+	pb.units = make([]int, pb.NbVars)
+	pb.NbClauses, err = strconv.Atoi(fields[3])
+	if err != nil {
+		return fmt.Errorf("invalid number of clauses %s: %v", strClauses, err)
+	}
+	if pb.NbClauses < 0 {
+		return fmt.Errorf("negative number of clauses %d", pb.NbClauses)
+	}
+	pb.Clauses = make([][]int, 0, pb.NbClauses)
+	return nil
+}
+
+func (pb *Problem) parseClause(fields []string) error {
+	clause, err := parseClause(fields)
+	if err != nil {
+		return err
+	}
+	pb.Clauses = append(pb.Clauses, clause)
+	if len(clause) == 1 {
+		lit := clause[0]
+		v := lit
+		if lit < 0 {
+			v = -v
+		}
+		if v > pb.NbVars {
+			// There was an error in the header
+			return fmt.Errorf("found lit %d but problem was supposed to hold only %d vars", lit, pb.NbVars)
+		}
+		if lit > 0 {
+			pb.units[v-1] = 1
+		} else {
+			pb.units[v-1] = -1
+		}
+	}
+	return nil
+}