handle negative values, fix 1

src/smq/snmp/snmp.go

@@ -56,6 +56,9 @@ func calculateDifference(key string, newValue string) (string, error) {
       Timestamp: currentTime,
       Value: newValue,
     }
+    if diffValuePerSecond < 0 {
+      return "", fmt.Errorf("negative difference value: %d", diffValuePerSecond)
+    }
     return strconv.Itoa(diffValuePerSecond), nil
   } else {
     log.Printf("create lvv for %s", key)