Diff: crc.cpp

Revision:

0:28e16d33040f

Child:

1:ec8513f94d23

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/crc.cpp	Tue May 14 21:54:06 2013 +0000
@@ -0,0 +1,59 @@
+
+#define CRC32_POLYNOMIAL 0xEDB88320L
+
+void CRC32Value(unsigned long &CRC, unsigned char c)
+{
+    /////////////////////////////////////////////////////////////////////////////////////
+    //CRC must be initialized as zero 
+    //c is a character from the sequence that is used to form the CRC
+    //this code is a modification of the code from the Novatel OEM615 specification
+    /////////////////////////////////////////////////////////////////////////////////////
+    unsigned long ulTemp1 = ( CRC >> 8 ) & 0x00FFFFFFL;
+    unsigned long ulCRC = ((int) CRC ^ c ) & 0xff ;
+    for (int  j = 8 ; j > 0; j-- )
+    {
+        if ( ulCRC & 1 )
+            ulCRC = ( ulCRC >> 1 ) ^ CRC32_POLYNOMIAL;
+        else
+            ulCRC >>= 1;
+    }
+    CRC = ulTemp1 ^ ulCRC;
+} 
+
+/* --------------------------------------------------------------------------
+Calculates the CRC-32 of a block of data all at once
+//the CRC is from the complete message (header plus data) 
+//but excluding (of course) the CRC at the end
+-------------------------------------------------------------------------- */
+unsigned long CalculateBlockCRC32(
+        unsigned long ulCount,    /* Number of bytes in the data block */
+        unsigned char *ucBuffer ) /* Data block */
+{
+    //////////////////////////////////////////////////////////////////////
+    //the below code tests the CRC32Value procedure used in a markov form
+    //////////////////////////////////////////////////////////////////////
+    unsigned long CRC = 0;
+    for (int i = 0; i<ulCount; i++)  CRC32Value( CRC, *ucBuffer++ );
+    return  CRC;
+}
+
+/*
+unsigned long CalculateBlockCRC32(
+        unsigned long ulCount, 
+        unsigned char *ucBuffer )
+{
+////////////////////////////////////////////
+//original code from the OEM615 manual
+////////////////////////////////////////////
+    unsigned long ulTemp1;
+    unsigned long ulTemp2;
+    unsigned long ulCRC = 0;
+    while ( ulCount-- != 0 )
+    {
+        ulTemp1 = ( ulCRC >> 8 ) & 0x00FFFFFFL;
+        ulTemp2 = CRC32Value( ((int) ulCRC ^ *ucBuffer++ ) & 0xff );
+        ulCRC = ulTemp1 ^ ulTemp2;
+    }
+    return( ulCRC );
+}
+*/
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