Wednesday, July 4, 2012

Calculate CRC

Program to calculate CRC in C language.......

1:   #include<stdio.h>  
2:   #define MS 14  
3:  // MS Message Size in Bits  
4:  // DS Divisor Size in Bits  
5:  int main() {  
6:     int divisor4[50] = {1,0,0,1,1};  
7:     int divisor24[50] = {1,0,1,0,1,1,1,0,1,0,1,1,0,1,1,0,1,1,1,0,0,1,0,1,1 };  
8:     int message[150] = {1,1,0,0,0,1,1,0,1,0,1,1,0,1};  
9:     int msgcopy[150];  
10:     int divisor[50];  
11:     int i,j,DS;  
12:     printf("At sender side\n");  
13:     printf("Enter the CRC you want to use in Bits 4Bit,8Bit,16Bit,24Bit,32Bit\n");  
14:     scanf("%d",&DS);  
15:   // Checking the Size of the divisor in bits  
16:     if(DS == 4) {  
17:         for(i = 0 ; i < DS+1 ; i++) {  
18:               divisor[i] = divisor4[i];  
19:          }  
20:     }  
21:     else if(DS == 24) {  
22:          for(i = 0 ;i < DS+1 ; i++) {  
23:                divisor[i] = divisor24[i];  
24:           }  
25:     }  
26:    // Copying message to another array  
27:     for(i = 0 ; i < MS ; i++) {  
28:           msgcopy[i] = message[i];  
29:      }  
30:    // Appending zero's at the end of the message  
31:     for(i = MS ; i < MS+DS-1 ; i++) {  
32:           message[MS] = 0;  
33:      }  
34:    // Calculating CRC  
35:      i = 0;  
36:      while(i < MS) {  
37:         if(message[i] == 0) {  
38:            i++;  
39:         }  
40:         else {  
41:            for(j = 0 ; j < DS+1 ; j++) {  
42:                  message[i+j] = message[i+j]^divisor[j];  
43:               //  printf("message[%d+%d] = %d\n",i,j,message[i+j]);  
44:             }  
45:          }  
46:      }  
47:     //Appending CRC at the end of the message  
48:      printf("CRC is\n");  
49:      for(i = MS ; i < MS+DS ; i++) {  
50:              msgcopy[i] = message[i];  
51:              printf("msgcopy[%d] = %d\n",i,msgcopy[i]);  
52:      }  
53:     printf("Message after appending CRC at the end\n");  
54:     for(i = 0 ; i < MS+DS ; i++) {  
55:              printf("msgcopy[%d] = %d\n",i,msgcopy[i]);  
56:      }  
57:      for(i = 0 ; i < MS+DS ; i++) {  
58:              message[i] = msgcopy[i];  
59:      }  
60:    // Checking that CRC is correct or not  
61:     printf("At receiver end\nChecking that CRC is correct or not\n");  
62:     i = 0;  
63:     while(i < MS+DS) {  
64:             if(message[i] == 0) {  
65:               i++;  
66:             }  
67:             else {  
68:               for(j = 0 ; j < DS+1 ; j++) {  
69:                   message[i+j] = message[i+j]^divisor[j];  
70:                //  printf("message[%d+%d] = %d\n",i,j,message[i+j]);  
71:               }  
72:            }  
73:      }  
74:   // CRC, After appending CRC at the end of the message  
75:     printf("CRC after appending Original CRC at the end of the message\n");  
76:     for(i = MS ; i < MS+DS ; i++) {  
77:              printf("message[%d] = %d\n",i,message[i]);  
78:     }  
79:  }  
Output :-
1:  At sender side  
2:  Enter the CRC you want to use in Bits 4Bit,24Bit  
3:  4  
4:  CRC is  
5:  msgcopy[14] = 1  
6:  msgcopy[15] = 0  
7:  msgcopy[16] = 0  
8:  msgcopy[17] = 1  
9:  Message after appending CRC at the end  
10:  msgcopy[0] = 1  
11:  msgcopy[1] = 1  
12:  msgcopy[2] = 0  
13:  msgcopy[3] = 0  
14:  msgcopy[4] = 0  
15:  msgcopy[5] = 1  
16:  msgcopy[6] = 1  
17:  msgcopy[7] = 0  
18:  msgcopy[8] = 1  
19:  msgcopy[9] = 0  
20:  msgcopy[10] = 1  
21:  msgcopy[11] = 1  
22:  msgcopy[12] = 0  
23:  msgcopy[13] = 1  
24:  msgcopy[14] = 1  
25:  msgcopy[15] = 0  
26:  msgcopy[16] = 0  
27:  msgcopy[17] = 1  
28:  At receiver end  
29:  Checking that CRC is correct or not  
30:  CRC after appending Original CRC at the end of the message  
31:  message[14] = 0  
32:  message[15] = 0  
33:  message[16] = 0  
34:  message[17] = 0  

Note :- This is for 4 and 24 Bit polynomial if you want to calculate CRC for 8,16,32 and 64 Bits then this code requires some changes . Try it youself.........
This code is calculating CRC for 14 Bits long message, you can use it for another length but don not forget to change Macro definition i.e 

#define MS 14
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