1 files changed, 17 insertions, 0 deletions
diff --git a/src/org/traccar/helper/Crc.java b/src/org/traccar/helper/Crc.java
index 5a668f30a..213d1192a 100644
--- a/src/org/traccar/helper/Crc.java
+++ b/src/org/traccar/helper/Crc.java
@@ -154,4 +154,21 @@ public class Crc {
         return String.format("*%02x", checksum).toUpperCase();
     }
 
+    public static String luhnChecksum(String s) {
+        int sum = 0;
+        boolean evenPosition = true;
+        for (int i = s.length() - 1; i >= 0; i--) {
+            int n = Integer.parseInt(s.substring(i, i + 1));
+            if (evenPosition) {
+                n *= 2;
+                if (n > 9) {
+                    n = (n % 10) + 1;
+                }
+            }
+            sum += n;
+            evenPosition = !evenPosition;
+        }
+        return String.valueOf(10 - sum % 10);
+    }    
+    
 }