improve util

util/rowcodec/decoder.go

@@ -464,28 +464,22 @@ func (decoder *BytesDecoder) DecodeToBytes(outputOffset map[int64]int, handle kv
 }
 
 func (decoder *BytesDecoder) encodeOldDatum(tp byte, val []byte) []byte {
+	buf := make([]byte, 0, 1+binary.MaxVarintLen64+len(val))
 	switch tp {
 	case BytesFlag:
-		buf := make([]byte, 0, 1+binary.MaxVarintLen64+len(val))
 		buf = append(buf, CompactBytesFlag)
 		buf = codec.EncodeCompactBytes(buf, val)
-		return buf
 	case IntFlag:
-		buf := make([]byte, 0, 1+binary.MaxVarintLen64)
 		buf = append(buf, VarintFlag)
 		buf = codec.EncodeVarint(buf, decodeInt(val))
-		return buf
 	case UintFlag:
-		buf := make([]byte, 0, 1+binary.MaxVarintLen64)
 		buf = append(buf, VaruintFlag)
 		buf = codec.EncodeUvarint(buf, decodeUint(val))
-		return buf
 	default:
-		buf := make([]byte, 0, 1+len(val))
 		buf = append(buf, tp)
 		buf = append(buf, val...)
-		return buf
 	}
+	return buf
 }
 
 // fieldType2Flag transforms field type into kv type flag.