add vendor data

vendor/github.com/dunglas/httpsfv/decimal.go

@@ -0,0 +1,64 @@
+package httpsfv
+
+import (
+	"errors"
+	"io"
+	"math"
+	"strconv"
+	"strings"
+)
+
+const maxDecDigit = 3
+
+// ErrInvalidDecimal is returned when a decimal is invalid.
+var ErrInvalidDecimal = errors.New("the integer portion is larger than 12 digits: invalid decimal")
+
+// marshalDecimal serializes as defined in
+// https://httpwg.org/specs/rfc9651.html#ser-decimal.
+//
+// TODO(dunglas): add support for decimal float type when one will be available
+// (https://github.com/golang/go/issues/19787)
+func marshalDecimal(b io.StringWriter, d float64) error {
+	const TH = 0.001
+
+	rounded := math.RoundToEven(d/TH) * TH
+	i, frac := math.Modf(rounded)
+
+	if i < -999999999999 || i > 999999999999 {
+		return ErrInvalidDecimal
+	}
+
+	if _, err := b.WriteString(strings.TrimRight(strconv.FormatFloat(rounded, 'f', 3, 64), "0")); err != nil {
+		return err
+	}
+
+	if frac == 0 {
+		_, err := b.WriteString("0")
+
+		return err
+	}
+
+	return nil
+}
+
+func parseDecimal(s *scanner, decSepOff int, str string, neg bool) (float64, error) {
+	if decSepOff == s.off-1 {
+		return 0, &UnmarshalError{s.off, ErrInvalidDecimalFormat}
+	}
+
+	if len(s.data[decSepOff+1:s.off]) > maxDecDigit {
+		return 0, &UnmarshalError{s.off, ErrNumberOutOfRange}
+	}
+
+	i, err := strconv.ParseFloat(str, 64)
+	if err != nil {
+		// Should never happen
+		return 0, &UnmarshalError{s.off, err}
+	}
+
+	if neg {
+		i = -i
+	}
+
+	return i, nil
+}