#include <stdio.h>

#include <gmp.h>

#include <stdlib.h>

void gcd( mpz_t , mpz_t , mpz_t );

main (int argc, char *argv[]) {

mpz_t n, c, x1, x2, product, t, g, t1, t2;

unsigned long max, range, terms, j, ans;

mpz_init (n);

mpz_init (c);

mpz_init (x1);

mpz_init (x2);

mpz_init (product);

mpz_init (t);

mpz_init (g);

mpz_init (t1);

mpz_init (t2);

initialize:

mpz_set_str (n, argv[1], 10);

gmp_printf("n = %Zd\n", n);

mpz_set_str (c, argv[2], 10);

max = atoi(argv[3]);

restart:

mpz_set_ui (x1, 2);

mpz_add_ui (x2, c, 4);

range = 1;

mpz_set_ui (product, 1);

terms = 0;

compute_diff:

while ( terms <= max ) {

for (j=1; j<=range; j++) {

mpz_mul (t, x2, x2);

mpz_add (t, t, c);

mpz_fdiv_r ( x2, t, n );

mpz_sub (t, x1, x2);

mpz_mul (t, product, t);

mpz_fdiv_r (product, t, n);

terms++;

if ((terms%10) == 0) {

mpz_set (t1, n);

mpz_set (t2, product);

gcd (g, t1, t2);

if (mpz_cmp_ui (g, 1) > 0) {

gmp_printf("g = %Zd\n",g);

goto terminate;

}

mpz_set_ui (product, 1);

}

}

reset:

mpz_set (x1, x2);

range = 2*range;

for (j=1; j<=range; j++) {

mpz_mul (t, x2, x2);

mpz_add (t, t, c);

mpz_fdiv_r (x2, t, n);

}

}

gmp_printf("n = %Zd --- no factor found for c = %Zd!!!\n", n, c);

printf("Enter 1 to input new c, 0 to stop\n");

scanf("%d",&ans);

if (ans != 1) goto terminate;

printf("Enter new c value:");

gmp_scanf("%Zd",&c);

goto restart;

terminate:

mpz_clear (g);

mpz_clear (t);

mpz_clear (product);

mpz_clear (x2);

mpz_clear (x1);

mpz_clear (c);

mpz_clear (n);

mpz_clear (t1);

mpz_clear (t2);

exit (0);

}

void gcd( mpz_t g, mpz_t a, mpz_t b ) {

mpz_t temp;

mpz_init (temp);

while ( mpz_cmp_ui (b, 0) > 0 ) {

mpz_set (temp, b);

mpz_fdiv_r (b, a, b);

mpz_set (a, temp);

}

mpz_mul_ui (a, a, mpz_sgn (a));

mpz_set (g, a);

mpz_clear (temp);

return;

}