Zoltan Hudak / CRC16_CCITT

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Diff: CRC16_CCITT.cpp

Revision:
1:6ecc3a64bf7b
Parent:
0:253105d48c3c
--- a/CRC16_CCITT.cpp	Sat Sep 02 08:26:22 2017 +0000
+++ b/CRC16_CCITT.cpp	Sun Sep 03 08:29:38 2017 +0000
@@ -4,7 +4,7 @@
  *
  * Modified by Zoltan Hudak to implement CRC16-CCITT
  * using the polynomial 0x1021: X^16 + X^15 + X^2 + 1.
- * Initial CRC register = 0x0000
+ * Default initial CRC value = 0x0000
  */
 
 #include "CRC16_CCITT.h"
@@ -46,14 +46,15 @@
     0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
 };
 
-unsigned short CRC16_CCITT::calc(char input[], int length) {
-    unsigned short  result = 0;
+unsigned short CRC16_CCITT::calc(char input[], int length, unsigned short crc /*=0x0000*/) {
     for(int i = 0; i < length; i++) {
-        unsigned short  tableValue = TABLE[((result >> 8) ^ *(char*)input++) & SHIFTER];
-        result = (result << 8) ^ tableValue;
+        unsigned short  tableValue = TABLE[((crc >> 8) ^ *(char*)input++) & SHIFTER];
+        crc = (crc << 8) ^ tableValue;
     }
 
-    return result;
+    return crc;
 }
 
 
+
+