Algorithm
1. Read number of data bits.
2. Read the data bit-by-bit
3. Read number of divisor bits
4. Enter the divisor bit-by-bit
5. Append zeroes to the message
6. Generate remainder by using XOR division
7. Subtract remainder from message using XOR
8. Display the CRC code word
9. Accept transmitted message as receiver side data
10. Peroform polynomial division using XOR
11. If remainder is zero then display “No error” else display “Error”
12. Stop
import java.io.*;
class crc_gen
{
public static void main(String args[]) throws IOException
{
BufferedReader br=new BufferedReader(new
InputStreamReader(System.in));
int[] data;
int[] div;
int[] divisor;
int[] rem;
int[] crc;
int data_bits, divisor_bits, tot_length;
System.out.println("Enter number of data bits : ");
data_bits=Integer.parseInt(br.readLine());
data=new int[data_bits];
System.out.println("Enter data bits : ");
for(int i=0; i<data_bits; i++)
data[i]=Integer.parseInt(br.readLine());
System.out.println("Enter no. of bits in divisor: ");
divisor_bits=Integer.parseInt(br.readLine());
divisor=new int[divisor_bits];
System.out.println("Enter Divisor bits : ");
for(int i=0; i<divisor_bits; i++)
divisor[i]=Integer.parseInt(br.readLine());
tot_length=data_bits+divisor_bits-1;
div=new int[tot_length];
rem=new int[tot_length];
crc=new int[tot_length];
/*------------------ CRC GENERATION---------------------*/
for(int i=0;i<data.length;i++)
div[i]=data[i];
System.out.print("Dividend (after appending 0's): ");
for(int i=0; i< div.length; i++)
System.out.print(div[i]);
System.out.println();
for(int j=0; j<div.length; j++)
rem[j] = div[j];
rem=divide(div, divisor, rem);
for(int i=0;i<div.length;i++) //append dividend & rem
{
crc[i]=(div[i]^rem[i]);
}
System.out.println();
System.out.println("CRC code : ");
for(int i=0;i<crc.length;i++)
System.out.print(crc[i]);
/*-------------------ERROR DETECTION---------------------*/
System.out.println();
System.out.println("Enter CRC code of " + tot_length
+ " bits : ");
for(int i=0; i<crc.length; i++)
crc[i]=Integer.parseInt(br.readLine());
for(int j=0; j<crc.length; j++)
rem[j] = crc[j];
rem=divide(crc, divisor, rem);
for(int i=0; i< rem.length; i++)
{
if(rem[i]!=0)
{
System.out.println("Error");
break;
}
if(i==rem.length-1)
System.out.println("No Error");
}
}
static int[] divide(int div[],int divisor[], int rem[])
{
int cur=0;
while(true)
{
for(int i=0;i<divisor.length;i++)
rem[cur+i]=(rem[cur+i]^divisor[i]);
while(rem[cur]==0 && cur!=rem.length-1)
cur++;
if((rem.length-cur)<divisor.length)
break;
}
return rem;
}
}
Output
$javac crc_gen.java
$java crc_gen
Enter number of data bits :
8
Enter data bits :
1
0
0
1
1
0
1
0
Enter no. of bits in divisor:
4
Enter Divisor bits :
1
1
0
1
Dividend (after appending 0's): 10011010000
CRC code :
10011010101
Enter CRC code of 11 bits :
1
0
0
1
1
0
1
0
1
0
1
No Error
Laksh Think 