Thread: trouble in getting this crc coding right

hi i am stuck with doing crc coding for c programming
i ask for user to define the divisor and dataword
and got the augemented dataword
but have trouble in divinding the augemented dataword with the divisor and getting the remainder result.i am stuck with the algo there
here's my coding

Code:

#include <stdio.h>
#include<stdlib.h>
#include <conio.h>
int main()
{
int a[20],b[20],c[20],i,k,j,n,s=0,t=0;
printf ( "Welcome to the CRC Encoder/Decoder!\n");
printf ( "press n to exit at anytimes\n");
	 /* do{*/
	
		  
printf("enter size of dataword\n");
scanf("%d",&n);
printf("enter dataword to be transfer bit by bit\n");
for (i=0;i<n;i++)
{
scanf("%d",&a[i]);


}
printf("your input dataword is\n");
for (i=0;i<n;i++)
{
	
printf("%d\n",a[i]);
}
printf("enter size of divisor\n");
scanf("%d",&k);
printf("enter divisor to be transfer bit by bit\n");
for (j=0;j<k;j++)
{
scanf("%d",&b[j]);


}
printf("your input divisor is\n");
for (j=0;j<k;j++)
{
	
printf("%d\n",b[j]);
}



for (i=0;i<(k-1);i++)
{
a[n+i]=0;
}
printf("the augmented dataword\n");
for (i=0;i<(k+n-1);i++)
{
printf("%d\n",a[i]);
}

/*i guess this is wrong but i tried to get the remainder by using modulo 2 like ( a ^ b )*/
for (i=0;i<k;i++)
{
c[i]=a[i];
}
for (t=0;t<(n-1);t++)
{
for (j=1;j<k;j++)
{

c[j-1]=c[j]^b[j];
c[j]=a[k+s];


return 0;
}

^ is for xor
% is for modulus

i am in trouble in getting the augmented dataword divided by divisor.it wont work and it will stop running.cna anyone enlighten me here

Code:

#include <stdio.h>
#include<stdlib.h>
#include <conio.h>
int main()
{


int a[20],b[20],c[20],d[20],i,k,j,p,n,s=0,t=0;
int msb;


printf ( "Welcome to the CRC Encoder/Decoder!\n");
printf ( "press n to exit at anytimes\n");
	 /* do{*/
	
		  
printf("enter size of dataword\n");
scanf("%d",&n);
printf("enter dataword to be transfer bit by bit\n");
for (i=0;i<n;i++)
{
scanf("%d",&a[i]);


}
printf("your input dataword is\n");
for (i=0;i<n;i++)
{
	
printf("%d\n",a[i]);
}
printf("enter size of divisor\n");
scanf("%d",&k);
printf("enter divisor to be transfer bit by bit\n");
for (j=0;j<k;j++)
{
scanf("%d",&b[j]);


}
printf("your input divisor is\n");
for (j=0;j<k;j++)
{
	
printf("%d\n",b[j]);
}


for (i=0;i<(k-1);i++)
{
a[n+i]=0;
}
printf("the augmented dataword\n");

for (i=0;i<(k+n-1);i++)
{

printf("%d\n",a[i]);
}

printf("the division and remainder\n");
for (i=k;i<(k-1);i++)
{
a[n+i]=0;
}

for( j = 0;j<(k-1);j++)
{
for (i=0;i<(k+n-1);i++)
{

printf("%d\n",a[i]%b[j]);
}
}

i am in trouble in getting the augmented dataword divided by divisor.it wont work and it will stop running.cna anyone enlighten me here

Well, yeah I can see that's a problem alright... especially since you aren't actually dividing anything anywhere in the entire program.

well thats the part i am stuck,especially with with getting the divisor b[j] to divide with the augemented dataword..
my for loop is absolutely wrong and i am stuck there
can anyone show me how to get the leftmost bit position and check whether it is 0 or 1 if 0 use 0000 divider?
do we have to use a if else statement here also?

How do you expect us to find the error if you don't post the code with the error in it?

well sorry
now from that part
the error making nuts is how to get the remainder from the division in crc
i see the formula is when 1 we use divisor and 0 we use 0000
here is what i have done
but somehow not correct
i taken the last part of the above coding which is divisor and remainder

Code:

printf("the resulting remainder of XOR is \n");
for (j=k-n;j<k;j++){
for (i=k-n;i<k;i++)
{
	if (a[i] != 0) {
		a[i] = a[i]^b[j];
	}
	else 
		a[i]^=0;

}
printf("%d\n",a[i]);
}

the output is 01101 00 1 01100 110
now supposing it has to be only remainder of 110..how to get rid of the initial ones?

You get rid of the initial ones by anding it with 111... a[i] &= 7;

ok
can anyone tell why my output is 111 and not 110 as desired

Code:

printf("the resulting output of modulus is \n");
for (j=0;j<k-1;j++){
for (i=0;i<k-1;i++)
{
if (a[i] !=0)
{
	a[i]^=b[j];

}
else
a[i]^=0;


}
printf("%d\n",a[i]);
}

for the a [i]&=7 where do i put it?on the print f?

nvm.the output i got is nearly exact which is 111 but not 110...
can you telll me why?

Code:

#include <stdio.h>
#include<stdlib.h>
#include <conio.h>
int main()
{


int a[20],b[20],c[20],d[20],i,k,g,j,p,n,s=0,t=0;
int msb;


		  
printf("enter size of dataword\n");
scanf("%d",&n);
printf("enter dataword to be transfer bit by bit\n");
for (i=0;i<n;i++)
{
scanf("%d",&a[i]);


}
printf("your input dataword is\n");
for (i=0;i<n;i++)
{
	
printf("%d\n",a[i]);
}
printf("enter size of divisor\n");
scanf("%d",&g);
printf("enter divisor to be transfer bit by bit\n");
for (j=0;j<g;j++)
{
scanf("%d",&b[j]);


}
printf("your input divisor is\n");
for (j=0;j<g;j++)
{
	
printf("%d\n",b[j]);
}


for (i=0;i<(g-1);i++)
{
a[n+i]=0;
}
printf("the augmented dataword\n");

for (i=0;i<(g+n-1);i++)
{

printf("%d\n",a[i]);
}


printf("the resulting output of modulus is \n");
for (j=0;j<g-1;j++){
for (i=0;i<g-1;i++)
{
if (a[i] !=0)
{
    a[i]^=b[j];
 
}
else
a[i]^=0;
 
 
}
printf("%d\n",a[i]);
}
return 0;
}

/*
for( i=0;i<g;i++)

{
c[i]= a[i];
}
for(t=0;t<(n-1);t++)
{
	for(j=1;j<g;j++)
	{
		c[j-1]=c[j]^b[j];
		c[j]=a[g+s];
}

	for ( i =0;i<g;i++)
		printf("%d",c[i]);
	printf("\n");
	s++;
}
//last loop
for(i=0;i<g;i++)
c[i]=c[i]*b[i];

//print remainder

for(i=0;i<g;i++)
printf("%d",c[i]);


/*


printf("the resulting output of modulus is \n");
for (j=0;j<g-1;j++){
for (i=0;i<g-1;i++)
{
if (a[i] !=0)
{
	a[i]^=b[j];

}
else
a[i]^=0;
}
printf("%d\n",a[i]);
}

for(i=0;i<n;++i)
d[i]= a[i];
for(i=0;i<n;++i)
{
if(a[i]==0)
{
for(j=i;j<g+i;++j)
a[j] = a[j]^0;
}
else
{
a[i] = a[i]^b[0];
a[i+1]=a[i+1]^b[1];
a[i+2]=a[i+2]^b[2];
a[i+3]=a[i+3]^b[3];
}

}
*//*
printf("\n\t The CRC is :");
for(i=n;i<a;++i)
printf("%d",a[i]);
for(i=0;i<g-1;++i)
d[i]=a[i];
s=n+a;
for(i=n;i<s;i++)
c[i]=a[i];
printf("\n");
printf("\n\t The codeword is :");
for(i=0;i<a;i++)
printf("%d",c[i]);
*/

anyoe???