package crc.java;
import java.io.*;
class Crc
{
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 number 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());
/* System.out.print("Data bits are : ");
for(int i=0; i< data_bits; i++)
System.out.print(data[i]);
System.out.println();
System.out.print("divisor bits are : ");
for(int i=0; i< divisor_bits; i++)
System.out.print(divisor[i]);
System.out.println();
*/ 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) are : ");
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 and ramainder
{
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());
/* System.out.print("crc bits are : ");
for(int i=0; i< crc.length; i++)
System.out.print(crc[i]);
System.out.println();
*/
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");
    }
    System.out.println("THANK YOU.... :)");
    }
    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;
    }
    }