void ec_multiply (ec_point *p, const vl_point k)
/* sets p := k*p */
{
vl_point h;
int z, hi, ki;
word16 i;
ec_point r;
gf_copy (r.x, p->x); p->x[0] = 0;
gf_copy (r.y, p->y); p->y[0] = 0;
vl_shortmultiply (h, k, 3);
z = vl_numbits (h) - 1; /* so vl_takebit (h, z) == 1 */
i = 1;
for (;;) {
hi = vl_takebit (h, i);
ki = vl_takebit (k, i);
if (hi == 1 && ki == 0) {
ec_add (p, &r);
}
if (hi == 0 && ki == 1) {
ec_sub (p, &r);
}
if (i >= z) {
break;
}
i++;
ec_double (&r);
}
} /* ec_multiply */
void sccd_ec_sub(sccd_ec_t result, const sccd_ec_t a, const sccd_ec_t b) {
#if defined(SCCD_BACKEND_C25519)
sccd_ec_t tmp;
sccd_fp_neg(tmp->x, b->x);
sccd_fp_neg(tmp->t, b->t);
sccd_fp_copy(tmp->y, b->y);
sccd_fp_copy(tmp->z, b->z);
sccd_ec_add(result, a, tmp);
#elif defined(SCCD_BACKEND_RELIC)
ec_sub(result, a, b);
#endif
}
