Diff: crc.h

Revision:

0:f016e9e8d48b

Child:

6:79d422d1ed42

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/crc.h	Tue Dec 01 10:56:10 2015 +0000
@@ -0,0 +1,77 @@
+//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
+
+typedef uint16_t 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 uint8_t 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;
+}
\ No newline at end of file