/*
Random number Generator using LFSR
Dhananjay V. Gadre
8 bit LFSR
Taps at 1, 2, 3 and 8

runs under linux, unix.
compile as: gcc filename.c -o executablefilename
*/

#include<stdio.h>
#include<time.h>
#include<ctype.h>
#include<stdlib.h>
#include<string.h>

#define true 1
#define false 0


int main(argc, argv)
int argc;
char *argv[];
{
    int value, temp, temp1, temp2, tap1, tap2, tap3, tap4;
if(argc != 2)
		{printf("\nError... Specify a seed. Aborting");
		printf("\nFormat:  %s seed[a number]\n", argv[0]);
		exit(-1);
		}
value=atoi(argv[1]);
/*read in the seed with which to init the LFSR*/
 
printf("\nSeed = %d\n", value);
value = value & 0x7f;
    for(temp1=0; temp1 < 0x100; temp1 ++)
        {
            temp=value;
            
    tap1 = temp & 0x02;
    tap2 = temp & 0x04;
    tap3 = temp & 0x08;
    tap4 = temp & 0x80;

    tap1 = tap1 >> 1;
    tap2 = tap2 >> 2;
    tap3 = tap3 >> 3;
    tap4 = tap4 >> 7;
    
    temp2 = (tap1 ^ tap2) ^ (tap3 ^ tap4);
    
        /*shift the LFSR left*/
    value = value << 1;

        /*if the XOR result is 0, set bit 0 to 0 else set it to 1*/
    if(temp2 == 0)  (value = value & 0xfffe);
    else value = value | 0x0001;
    
    printf("%x ", 0xff & value); /*just look at the last 8 bits*/
    
    
    
        }
    

return true;
}