Diff: source/CRC16.cpp

Revision:

15:91b3c572d9df

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/source/CRC16.cpp	Wed Apr 22 19:27:44 2015 +0000
@@ -0,0 +1,76 @@
+#include "CRC16.h"
+
+/*
+ * FUNCTION: calcCRC calculates a 2-byte CRC on serial data using
+ * CRC-CCITT 16-bit standard maintained by the ITU
+ * ARGUMENTS: queue_ptr is pointer to queue holding are a to be CRCed
+ * queue_size is offset into buffer where to stop CRC calculation
+ * RETURNS: 2-byte CRC
+ */
+
+#define POLY 0x8005//0x8408
+/*
+//                                      16   12   5
+// this is the CCITT CRC 16 polynomial X  + X  + X  + 1.
+// This works out to be 0x1021, but the way the algorithm works
+// lets us use 0x8408 (the reverse of the bit pattern).  The high
+// bit is always assumed to be set, thus we only use 16 bits to
+// represent the 17 bit value.
+*/
+
+
+uint16_t CRC16_BUYPASS(const char *data, size_t len) { 
+  uint16_t crc = 0x0000; 
+  size_t j; 
+  int i; 
+  for (j=len; j>0; j--) { 
+    crc ^= (uint16_t)(*data++) << 8; 
+    for (i=0; i<8; i++) { 
+      if (crc & 0x8000) crc = (crc<<1) ^ 0x8005; 
+      else crc <<= 1; 
+    } 
+  } 
+  return (crc); 
+} 
+
+/*int main() { 
+  uint8_t test[9]  = {0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39}; 
+  uint8_t tgil[29] = {0x00,0x0B,0x01,0x0E,0x01,0xC6,0x00,0x00,0x00,0x00, 
+                      0x00,0x00,0x33,0x31,0x30,0x31,0x34,0x31,0x30,0x30, 
+                      0x41,0x00,0x00,0x04,0x24,0x14,0x16,0x06,0x49}; 
+  uint16_t crc; 
+  crc = CRC16_BUYPASS(test, 9); 
+  //printf("Rocksoft check value: 0x%04X, test ", crc); 
+  //if (crc==0xFEE8) printf("passed.\n"); else printf("failed!\n"); 
+  crc = CRC16_BUYPASS(tgil, 29); 
+  //printf("CRC gil's data: 0x%04X\n", crc); 
+  return 0; 
+} */
+
+unsigned short calculateCRC16(const char *data_p, unsigned short length)
+{
+    unsigned char i;
+    unsigned int data;
+    unsigned int crc = 0xffff;
+
+    if (length == 0)
+    return (~crc);
+
+    do
+    {
+        for (i=0, data=(unsigned int)0xff & *data_p++;
+        i < 8;
+        i++, data >>= 1)
+        {
+            if ((crc & 0x0001) ^ (data & 0x0001))
+            crc = (crc >> 1) ^ POLY;
+            else  crc >>= 1;
+        }
+    } while (--length);
+
+    crc = ~crc;
+    data = crc;
+    crc = (crc << 8) | (data >> 8 & 0xff);
+
+    return (crc);
+}
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