Diff: CRC.cpp

Revision:

6:ac7c0ccf9b5d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/CRC.cpp	Tue Oct 24 02:33:50 2017 +0000
@@ -0,0 +1,50 @@
+#include "CRC.h"
+
+const unsigned short CRCPOLYNOM = 0x8005;
+
+// The last two bytes of data corresponds to the remainder. If they are of 0,0, this function will return the remainder to put into them.
+// If the two last bytes contains the crc received, the return should be of 0
+int crc16Remainder(std::vector<unsigned char> data, unsigned short generator)
+{   
+    // shift generator
+    unsigned int polynom = generator <<  16;
+    
+    if (data.empty())
+    {
+        return -1;
+    }
+
+    unsigned int remainder = data[0] << 24 | data[1] << 16;
+
+    for (int i = 2; i < data.size(); i++)
+    {
+        remainder = remainder | data[i] << 8;
+        for (int j = 0; j < 8; j++)
+        {
+            // if msb is 1, shift and xor
+            if (remainder >> 31 ==1)
+            {
+                remainder = (remainder << 1) ^ polynom;
+            }
+            else
+            {
+                remainder = remainder << 1;
+            }
+        }
+    }
+    // Calculates remainder of last 16 bits 
+    for (int i = 0; i < 16; i++)
+    {
+        // if msb is 1, shift and xor
+        if (remainder >> 31 == 1)
+        {
+            remainder = (remainder << 1) ^ polynom;
+        }
+        else
+        {
+            remainder = remainder << 1;
+        }
+    }
+    return remainder >> 16;
+
+}