Revision 0:99467adee231, committed 2013-03-17

Comitter:

Mike951

Date:

Sun Mar 17 20:12:29 2013 +0000

Commit message:

No changes

Changed in this revision

diff -r 000000000000 -r 99467adee231 crc16.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/crc16.cpp	Sun Mar 17 20:12:29 2013 +0000
@@ -0,0 +1,45 @@
+#include "crc16.h"
+
+/*
+CRC16 generation algorithm taken from J.G. Harston at
+http://mdfs.net/Info/Comp/Comms/CRC16.htm
+*/
+
+// Refer to crc16.h for overall function details
+
+#define poly 0x11021 // Define polynomial generating CRC tag
+
+int     crc16 (char* dataIn, int numberOfBytes) {
+    if (numberOfBytes > 16)     // Keep numberOfBytes under 16
+        return 0;
+    int i, j;
+    int crc = 0;                // Initialize CRC to zero
+    
+    for (j = numberOfBytes ; j > 0; j--) {  // Execute numberOfBytes times
+        crc = crc ^ (*dataIn++ << 8);   // Get byte and XOR with crc
+        for (i = 0; i < 8; i++) {
+            crc = crc << 1;             // Rotate
+            if (crc & 0x10000)          // If bit 15 is set
+                crc ^= poly;            // XOR with polynomial            
+        }
+    }
+    return crc;             // Return CRC tag       
+}
+
+void    crc16_attach (char* dataIn, int numberOfBytes) {
+    int crc = crc16(dataIn, numberOfBytes);             // Generate CRC tag from first numberOfBytes elements of DataIn
+    dataIn[numberOfBytes] = ((crc >> 8) & 0xFF);        // Store 8 MSbits as the next element in dataIn
+    dataIn[numberOfBytes + 1] = (crc & 0xFF);           // Store the 8 LSbits is the last element in dataIn
+}
+
+bool    crc16_match (char* dataIn, int numberOfBytes) {
+    int crcData = crc16(dataIn, numberOfBytes);         // Generate CRC tag from the first numberOfBytes elements of dataIn
+    int a,b;
+    a = dataIn[numberOfBytes];                          // Extract the last two 8 bit elements of dataIn as integers
+    b = dataIn[numberOfBytes + 1];
+    int crcExpect = (a << 8) + b;                       // Recombine into a single 16 bit element
+    if (crcData == crcExpect)                           // Compare the generated with the expected
+        return true;                                    // If they match, data is intact
+    else
+        return false;                                   // Otherwise, data is not intact
+}            

diff -r 000000000000 -r 99467adee231 crc16.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/crc16.h	Sun Mar 17 20:12:29 2013 +0000
@@ -0,0 +1,44 @@
+#ifndef CRC16_H_
+#define CRC16_H_
+
+/* General Layout Design taken from Erik van Wijk's crc8 library found at
+http://mbed.org/users/evwijk/code/crc8/
+*/
+ 
+/* Takes in a character array with a given number of bytes. Returns the
+16 bit CRC tag as a 32 bit integer. numberOfBytes exceeds 16, function returns 0.
+*/ 
+
+int     crc16 (char* dataIn, int numberOfBytes);
+
+/* Takes in a character array with at least (numberOfBytes + 2) entries. A 16-bit
+CRC tag is created from the first numberOfBytes elements of dataIn. The 16-bit tag is then
+broken into two 8 bit tags. The most significant is stored in dataIn at (numberOfBytes+1) 
+and the least significant is stored in dataIn at (numberOfBytes+2)
+
+*******************************************************************************
+Note: numberOfBytes indicates the number of data elements to generate the CRC.
+dataIn must be at least of length numberOfBytes + 2 for the two bytes of CRC
+*******************************************************************************
+*/
+
+void    crc16_attach (char* dataIn, int numberOfBytes);
+
+/* Takes in a character array of length (numberOfBytes + 2). A 16-bit CRC is created from the first
+numberOfBytes elements of dataIn. The elements at numberOfBytes + 1 and numberOfBytes + 2 are assumed
+to be a CRC tag created in the form described above and are reassembled into a single integer.
+
+The calculated CRC and the input CRC are compared
+
+If they match, funtion is true.
+If the two CRC tags to not match, function is false.
+
+*******************************************************************************
+Note: numberOfBytes indicates the number of data elements to generate the CRC.
+dataIn must be at least of length numberOfBytes + 2 for the two bytes of CRC
+*******************************************************************************
+*/
+bool    crc16_match (char* dataIn, int numberOfBytes);
+
+ 
+#endif
\ No newline at end of file