Add utility for flag bytes

v2/id3v2.go

@@ -297,12 +297,12 @@ func ParseHeader(reader io.Reader) *Header {
 
 	switch header.version {
 	case 2:
-		header.unsynchronization = (header.flags & 1 << 7) == 1
-		header.compression = (header.flags & 1 << 6) == 1
+		header.unsynchronization = isBitSet(header.flags, 7)
+		header.compression = isBitSet(header.flags, 6)
 	case 3:
-		header.unsynchronization = (header.flags & 1 << 7) == 1
-		header.extendedHeader = (header.flags & 1 << 6) == 1
-		header.experimental = (header.flags & 1 << 5) == 1
+		header.unsynchronization = isBitSet(header.flags, 7)
+		header.extendedHeader = isBitSet(header.flags, 6)
+		header.experimental = isBitSet(header.flags, 5)
 	}
 
 	return header

v2/util.go

@@ -0,0 +1,8 @@
+// Copyright 2013 Michael Yang. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+package v2
+
+func isBitSet(flag, index byte) bool {
+	return flag&(1<<index) == 1
+}