int main(void) {
/*this program computes primes*/
bint prime[MAX_PRIMES];
int primes;
bint testprime,zero;
/* we have to enter at least 1 prime */
primes=1;
uint_to_bint(2,&prime[primes-1]);
/*make zero 0*/
uint_to_bint(0,&zero);
/*we start testing at the last prime in table +1*/
testprime=prime[primes-1];
printf("Prime generator:\n");
printf("Primes number 2-%d\n",MAX_PRIMES);
while(primes<MAX_PRIMES) {
bint testsqrt;
int primeptr;
int is_a_prime=1;
bint_inc(&testprime); /* increase*/
bint_sqrt(&testprime,&testsqrt); /* compute square root of
test - this speed up the
algorithm due to the fact
we dont have to test
division more than to the
square root of the number
*/
bint_inc(&testsqrt);
primeptr=0;
while(primeptr<primes &&
is_a_prime &&
bint_cmp(&prime[primeptr],&testsqrt)<=0) {
bint remainder;
bint_mod(&testprime,&prime[primeptr],&remainder);
if(bint_cmp(&remainder,&zero)==0)
is_a_prime=0;
else
primeptr++;
}
if(is_a_prime) {
/*got a prime*/
char s[100];
prime[primes++]=testprime;
/*convert to string*/
bint_to_string(&testprime,s);
/*print out the prime*/
printf("%4.4d: %12.12s ",primes,s);
}
}
putchar('\n');
return 0;/*Ok*/
}
t_bint * bint_add_dst(t_bint ** dst, t_bint * a, t_bint * b) {
int a_zero = bint_is_zero(a);
int b_zero = bint_is_zero(b);
//if a and b are 0
if (a_zero && b_zero) {
//return 0
return (BINT_ZERO);
}
if (a_zero) {
return (bint_clone(b));
}
if (b_zero) {
return (bint_clone(a));
}
//the size to store the result
size_t size = (a == NULL || a_zero) ? b->size : (b == NULL || b_zero) ? a->size : (a->size > b->size) ? a->size : b->size;
//ensure that 'dst' bint has the given size
t_bint * r = bint_ensure_size(dst, size);
//if allocation failed
if (r == NULL) {
return (NULL);
}
//do the addition, r has now a correct size to store the result
//compare the two integers
int cmp = bint_cmp(a, b);
//if a == b, then return 2 * a
if (cmp == 0) {
//dst = a << 1 = 2 * a
bint_shift_left_dst(&r, a, 1);
return (r);
}
//else, if a < b
if (cmp < 0) {
//swap them, so we always then have a > b
t_bint * tmp = a;
a = b;
b = tmp;
}
//' a + (-b) ' becomes ' a - b '
//notice that the case '(-a) + b ' becoming ' b - a' is impossible here: a > b
if (a->sign == 1 && b->sign == -1) {
//TODO : a - abs(b)
puts("warning: addition sign issue");
} else {
//a and b have the same size, and a > b
//set the sign
r->sign = a->sign;
//finally do the addition
_bint_add_dst_raw(r, a, b);
}
//return it
return (r);
}
