codec/h264/h26dec/read.go: added fieldReader type to provide sticky error and specific methods for bool and int reading

codec/h264/h264dec/read.go

@@ -228,3 +228,43 @@ func readFlags(br *bits.BitReader, flags []flag) error {
 	}
 	return nil
 }
+
+// fieldReader provides methods for reading bool and int fields from a
+// bits.BitReader with a sticky error that may be checked after a series of
+// parsing read calls.
+type fieldReader struct {
+	e  error
+	br *bits.BitReader
+}
+
+// newFieldReader returns a new fieldReader.
+func newFieldReader(br *bits.BitReader) fieldReader {
+	return fieldReader{br: br}
+}
+
+// readBool returns a bool from reading one bit from br. If we have an error
+// already, we do not continue with the read.
+func (r fieldReader) readBool() bool {
+	if r.e != nil {
+		return false
+	}
+	var b uint64
+	b, r.e = r.br.ReadBits(1)
+	return b == 1
+}
+
+// readBitsInt returns an int from reading n bits from br. If we have an error
+// already, we do not continue with the read.
+func (r fieldReader) readBitsInt(n int) int {
+	if r.e != nil {
+		return 0
+	}
+	var b uint64
+	b, r.e = r.br.ReadBits(n)
+	return int(b)
+}
+
+// err returns the fieldReader's error e.
+func (r fieldReader) err() error {
+	return r.e
+}