Generate CRC code for a given data frame Algorithm
1. A string of n as is appended to the data unit. The length of predetermined divisor is n+ 1.
2. The newly formed data unit 1. A string of n as is appended to the data unit. The length of predetermined divisor is n+ 1.
i.e. original data + string of n as are divided by the divisor using binary division and remainder is obtained. This remainder is called CRC.
3. Now, string of n Os appended to data unit is replaced by the CRC remainder (which is also of n bit).
4. The data unit + CRC is then transmitted to receiver.
5. The receiver on receiving it divides data unit + CRC by the same divisor & checks the remainder.
6. If the remainder of division is zero, receiver assumes that there is no error in data and it accepts it.
7. If remainder is non-zero then there is an error in data and receiver rejects it.
PROGRAM:
#include<stdio.h>
#include<math.h>
main()
{
int i,j,k,m,n,cl;
char a[10],b[100],c[100];
clrscr();
printf("\n ENTER POLYNANOMIAL:");
scanf("%s",a);
printf("\n ENTER THE FRAME:");
scanf("%s",b); m=strlen(a);
n=strlen(b);
for(i=0;i<m;i++) /* To eliminat first zeros in polynomial */
{
if(a[i]=='1')
{
m=m-i;
break;
}
}
for(k=0;k<m;k++) /* To Adjust the polynomial
*/ a[k]=a[k+i];
cl=m+n-1;
for(i=0;i<n;i++) /* To copy the original frame to c[]*/
c[i]=b[i];
for(i=n;i<cl;i++) /* To add n-1 zeros at the end of frame */
c[i]='0';
c[i]='\0'; /*To make it as a string */
for(i=0;i<n;i++) /* To set polynomial remainder at end of c[]*/
if(c[i]=='1')
{
for(j=i,k=0;k<m;k++,j++)
if(a[k]==c[j])
c[j]='0';
else c[j]='1';
}
for(i=0;i<n;i++) /* To copy original data in c[] */
c[i]=b[i];
printf("\n THE MESSAGE IS: %s",c);
getch();
}
INPUT/OUTPUT:
ENTER POLYNANOMIAL:1011 ENTER THE FRAME:10011101 THE MESSAGE IS: 10011101011
ENTER POLYNANOMIAL:00101 ENTER THE FRAME:10101011 THE MESSAGE IS: 1010101101
