A int64_t value overflows in a structure in C - c

Question

I want to create a polynomial with only one term: 6/5 and display it.
It should print this: 6/5X^0
The structure of polynomial is :
typedef struct __poly_struct_t *poly_t;
struct __poly_struct_t{
unsigned int deg;
ratio_t *coeffs;
};
Where ratio_t is an array of rational numbers, it's structure is:
typedef struct __ratio_struct_t{
int64_t num;
int64_t den;
}ratio_t;
I used two functions to construct this polynomial. polyFromRatioArray works: it prints 6/5X^0
poly_t polyFromRatioArray(ratio_t *c, unsigned int degree){
poly_t p = (struct __poly_struct_t*)malloc(sizeof(struct __poly_struct_t));
p->deg = degree;
p->coeffs = c;
return p;
}
The other one made the denominator overflowed: polyFromRatio prints 6/140218959144480X^0
poly_t polyFromRatio(ratio_t c){
return polyFromRatioArray(&c, 0);
}
Main function:
int main(){
ratio_t ra = createRatio((int64_t)6,(int64_t)5);
poly_t p1 = polyFromRatioArray(&ra, 0); // one that works
polyPrint(p1);
poly_t p2 = polyFromRatio(ra); // this doesn't
polyPrint(p2);
free(p1);
free(p2);
return 0;
}
Other fonctions involved:
ratio_t createRatio(int64_t a, int64_t b){
if(b == 0){
printf("Error : a divise by 0 \n");
exit(1);
}
ratio_t r;
int64_t pgcd = gcd(a, b); // gcd(int64_t a, int64_t b) is a function that finds pgcd using Euclid.
r.num = a/pgcd;
r.den = b/pgcd;
return r;
}
int64_t gcd(int64_t a, int64_t b){
int64_t u, v, g;
ext_eucl_div(&u, &v, &g, llabs(a), llabs(b));
return g;
}
void ext_eucl_div(int64_t *u, int64_t *v, int64_t *g, int64_t a, int64_t b){ // this function stocks pgcd of a and b in g
int64_t u1, u2, u3 , v1, v2, v3, q, t1, t2, t3;
int tour = 0;
do{
if(tour == 0){
u1 = 1; u2 = 0; u3 = a; v1 = 0; v2 = 1; v3 = b;
}
else{
u1 = v1; u2 = v2; u3 = v3; v1 = t1; v2 = t2; v3 = t3;
}
q = u3/v3;
t1 = u1 - q*v1;
t2 = u2 - q*v2;
t3 = u3%v3;
tour++;
} while(t3>=1);
*u = v1;
*v = v2;
*g = v3;
}
void polyPrint(poly_t p){
unsigned int i;
for(i=0; i<= p->deg; i++){
if(p->coeffs[i].num != 0){
printRatio(p->coeffs[i]);
if(i != p->deg) printf("X^%u + ", i);
else printf("X^%u\n", i);
}else printf("0\n");
}
}
void printRatio(ratio_t a){
printf("%" PRId64, a.num);
printf("/%" PRId64, a.den);
}
This is very strange, polyFromRatioArray and polyFromRatio seem like doing the same thing but nope.