Diff: CRCheader.h

Revision:

1:743a1d709fe0

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/CRCheader.h	Fri Jul 17 12:36:51 2015 +0000
@@ -0,0 +1,80 @@
+//EDITS
+//changed the initial remainder from 0x0000 to 0xffff according to the standards
+//made two seperate functions crc16_gen and crc8_gen
+ 
+#define TOPBIT16 (1 << 15)
+#define TOPBIT8 (1 << 7)
+#define POLYNOMIAL16 0x1021
+#define POLYNOMIAL8 0xEA
+ 
+namespace CRC{
+    typedef unsigned short int crctype16; 
+    crctype16 crc16_gen(const unsigned char message[], unsigned int nBytes){
+        crctype16 remainder = 0xffff;
+        int byte;
+        char bit;
+        
+        for( byte = 0 ; byte < nBytes ; byte++ ){
+            /*
+            Bring the data byte by byte
+            each time only one byte is brought
+            0 xor x = x
+            */
+            remainder = remainder ^ ( message[byte] << 8 );
+            
+            for( bit = 8 ; bit > 0 ; bit--){
+                /*
+                for each bit, xor the remainder with polynomial
+                if the MSB is 1
+                */
+                if(remainder & TOPBIT16){
+                    remainder = (remainder << 1) ^ POLYNOMIAL16;
+                    /*
+                    each time the remainder is xor-ed with polynomial, the MSB is made zero
+                    hence the first digit of the remainder is ignored in the loop
+                    */
+                }
+                else{
+                    remainder = (remainder << 1);
+                }
+            }
+        }
+        
+        return remainder;
+    }
+    
+    typedef unsigned char crctype8;
+    crctype8 crc8_gen(const unsigned char message[], unsigned int nBytes){
+        
+        crctype8 remainder = 0xff;
+        
+        for(int byte = 0 ; byte < nBytes ; byte++ ){
+            /*
+            Bring the data byte by byte
+            each time only one byte is brought
+            0 xor x = x
+            */
+            remainder = remainder ^ ( message[byte] );
+            
+            for(int bit = 8 ; bit > 0 ; bit--){
+                /*
+                for each bit, xor the remainder with polynomial
+                if the MSB is 1
+                */
+                if(remainder & TOPBIT8){
+                    remainder = (remainder << 1) ^ POLYNOMIAL8;
+                    /*
+                    each time the remainder is xor-ed with polynomial, the MSB is made zero
+                    hence the first digit of the remainder is ignored in the loop
+                    */
+                }
+                else{
+                    remainder = (remainder << 1);
+                }
+            }
+        }
+        
+        return remainder;
+    }
+}
+ 
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