import java.util.
*;
class CRC {
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
int n;
// Accept the input
System.out.println("Enter the size of the data:");
n = scan.nextInt();
int data[] = new int[n];
System.out.println("Enter the data, bit by bit:");
for(int i=0 ; i < n ; i++) {
System.out.println("Enter bit number " + (n-i) + ":");
data[i] = scan.nextInt();
}
// Accept the divisor
System.out.println("Enter the size of the divisor:");
n = scan.nextInt();
int divisor[] = new int[n];
System.out.println("Enter the divisor, bit by bit:");
for(int i=0 ; i < n ; i++) {
System.out.println("Enter bit number " + (n-i) + ":");
divisor[i] = scan.nextInt();
}
// Divide the inputted data by the inputted divisor
// Store the remainder that is returned by the method
int remainder[] = divide(data, divisor);
for(int i=0 ; i < remainder.length-1 ; i++) {
System.out.print(remainder[i]);
}
System.out.println("\nThe CRC code generated is:");
for(int i=0 ; i < data.length ; i++) {
System.out.print(data[i]);
}
for(int i=0 ; i < remainder.length-1 ; i++) {
System.out.print(remainder[i]);
}
System.out.println();
// Create a new array
// It will have the remainder generated by the above method
appended
// to the inputted data
int sent_data[] = new int[data.length + remainder.length -
1];
System.out.println("Enter the data to be sent:");
for(int i=0 ; i < sent_data.length ; i++) {
System.out.println("Enter bit number " +
(sent_data.length-i)
+ ":");
sent_data[i] = scan.nextInt();
}
receive(sent_data, divisor);
}
static int[] divide(int old_data[], int divisor[]) {
int remainder[] , i;
int data[] = new int[old_data.length + divisor.length];
System.arraycopy(old_data, 0, data, 0, old_data.length);
// Remainder array stores the remainder
remainder = new int[divisor.length];
// Initially, remainder's bits will be set to the data bits
System.arraycopy(data, 0, remainder, 0, divisor.length);
// Loop runs for same number of times as number of bits of
data
// This loop will continuously exor the bits of the
remainder and
// divisor
for(i=0 ; i < old_data.length ; i++) {
System.out.println((i+1) + ".) First data bit is : "
+ remainder[0]);
System.out.print("Remainder : ");
if(remainder[0] == 1) {
// We have to exor the remainder bits with
divisor bits
for(int j=1 ; j < divisor.length ; j++) {
remainder[j-1] = exor(remainder[j],
divisor[j]);
System.out.print(remainder[j-1]);
}
}
else {
// We have to exor the remainder bits with 0
for(int j=1 ; j < divisor.length ; j++) {
remainder[j-1] = exor(remainder[j], 0);
System.out.print(remainder[j-1]);
}
}
// The last bit of the remainder will be taken from
the data
// This is the 'carry' taken from the dividend after
every step
// of division
remainder[divisor.length-1] = data[i+divisor.length];
System.out.println(remainder[divisor.length-1]);
}
return remainder;
}
static int exor(int a, int b) {
// This simple function returns the exor of two bits
if(a == b) {
return 0;
}
return 1;
}
static void receive(int data[], int divisor[]) {
// This is the receiver method
// It accepts the data and divisor (although the receiver
already has
// the divisor value stored, with no need for the sender to
resend it)
int remainder[] = divide(data, divisor);
// Division is done
for(int i=0 ; i < remainder.length ; i++) {
if(remainder[i] != 0) {
// If remainder is not zero then there is an
error
System.out.println("There is an error in received
data...");
return;
}
}
//Otherwise there is no error in the received data
System.out.println("Data was received without any error.");
}
}
