1 files changed, 39 insertions, 0 deletions
diff --git a/cfa635/crc.go b/cfa635/crc.go
new file mode 100644
index 0000000..33a0757
--- /dev/null
+++ b/cfa635/crc.go
@@ -0,0 +1,39 @@
+// Copyright 2022 Benjamin Barenblat
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+package cfa635
+
+import (
+	"encoding/binary"
+
+	"github.com/sigurn/crc16"
+)
+
+var crcTable = crc16.MakeTable(crc16.CRC16_X_25)
+
+func pushCRC(b []byte) []byte {
+	end := len(b)
+	b = append(b, 0, 0)
+	binary.LittleEndian.PutUint16(b[end:len(b)], crc16.Checksum(b[:end], crcTable))
+	return b
+}
+
+func popCRC(b []byte) ([]byte, bool) {
+	if len(b) < 2 {
+		return b, false
+	}
+
+	end := len(b) - 2
+	return b[:end], crc16.Checksum(b[:end], crcTable) == binary.LittleEndian.Uint16(b[end:len(b)])
+}