void Egcd(ll a, ll b, ll &x, ll &y)
{
if(b == 0) {
x = 1, y = 0;
return ;
}
Egcd(b, a%b, x, y);
ll t = x; x = y, y = t - a/b*y;
}
ll mod_inv(ll a, ll P)
{
ll x, y;
Egcd(a, P, x, y);
return (x % P + P) % P;
}
//old
BIGNUM *Egcd(const BIGNUM *n, const BIGNUM *m, BIGNUM *x, BIGNUM *y)
{
//print_bn("n", n);
//print_bn("m", m);
BIGNUM *value = BN_new();
BIGNUM *temp = BN_new();
BIGNUM *t1 = BN_new();
BIGNUM *t2 = BN_new();
BIGNUM *new_m = BN_new();
BN_CTX *ctx = BN_CTX_new();
if (BN_is_zero(m))
{
BN_set_word(x, 1);
BN_set_word(y, 0);
value = BN_dup(n);
//print_bn("x", x);
//print_bn("y", y);
return value;
}
BN_mod(new_m, n, m, ctx);
//printf("called once\n");
value = BN_dup(Egcd(m, new_m, x, y));
print_bn("n", n);
print_bn("m", m);
print_bn("old_x", x);
print_bn("old_y", y);
temp = BN_dup(x);
x = BN_dup(y);
/* y = temp - (n/m) * y */
BN_div(t1, NULL, n, m, ctx);
BN_mul(t2, t1, y, ctx);
BN_sub(y, temp, t2);
print_bn("x", x);
print_bn("y", y);
return value;
}