ge25519_double_scalarmult_vartime
void ge25519_double_scalarmult_vartime(ge25519 *r, const ge25519 *p1, const sc25519 *s1, const ge25519 *p2, const sc25519 *s2);
ge25519_double_scalarmult_vartime(&get2, &get1, &schram, &ge25519_base, &scs);
ge25519_double_scalarmult_vartime(&get2, &get1, &schram, &ge25519_base, &scs);
static void ge25519_double_scalarmult_vartime(ge25519 *r, const ge25519 *p1, const sc25519 *s1, const ge25519 *p2, const sc25519 *s2);