static void ec_GFp_simple_mul_single(const EC_GROUP *group, EC_RAW_POINT *r,
const EC_RAW_POINT *p,
const EC_SCALAR *scalar) {
// This is a generic implementation for uncommon curves that not do not
// warrant a tuned one. It uses unsigned digits so that the doubling case in
// |ec_GFp_simple_add| is always unreachable, erring on safety and simplicity.
// Compute a table of the first 32 multiples of |p| (including infinity).
EC_RAW_POINT precomp[32];
ec_GFp_simple_point_set_to_infinity(group, &precomp[0]);
ec_GFp_simple_point_copy(&precomp[1], p);
for (size_t j = 2; j < OPENSSL_ARRAY_SIZE(precomp); j++) {
if (j & 1) {
ec_GFp_simple_add(group, &precomp[j], &precomp[1], &precomp[j - 1]);
} else {
ec_GFp_simple_dbl(group, &precomp[j], &precomp[j / 2]);
}
}
// Divide bits in |scalar| into windows.
unsigned bits = BN_num_bits(&group->order);
int r_is_at_infinity = 1;
for (unsigned i = bits - 1; i < bits; i--) {
if (!r_is_at_infinity) {
ec_GFp_simple_dbl(group, r, r);
}
if (i % 5 == 0) {
// Compute the next window value.
const size_t width = group->order.width;
uint8_t window = bn_is_bit_set_words(scalar->words, width, i + 4) << 4;
window |= bn_is_bit_set_words(scalar->words, width, i + 3) << 3;
window |= bn_is_bit_set_words(scalar->words, width, i + 2) << 2;
window |= bn_is_bit_set_words(scalar->words, width, i + 1) << 1;
window |= bn_is_bit_set_words(scalar->words, width, i);
// Select the entry in constant-time.
EC_RAW_POINT tmp;
OPENSSL_memset(&tmp, 0, sizeof(EC_RAW_POINT));
for (size_t j = 0; j < OPENSSL_ARRAY_SIZE(precomp); j++) {
BN_ULONG mask = constant_time_eq_w(j, window);
ec_felem_select(group, &tmp.X, mask, &precomp[j].X, &tmp.X);
ec_felem_select(group, &tmp.Y, mask, &precomp[j].Y, &tmp.Y);
ec_felem_select(group, &tmp.Z, mask, &precomp[j].Z, &tmp.Z);
}
if (r_is_at_infinity) {
ec_GFp_simple_point_copy(r, &tmp);
r_is_at_infinity = 0;
} else {
ec_GFp_simple_add(group, r, r, &tmp);
}
}
}
if (r_is_at_infinity) {
ec_GFp_simple_point_set_to_infinity(group, r);
}
}
int EC_POINT_set_to_infinity(const EC_GROUP *group, EC_POINT *point) {
if (group->meth != point->meth) {
OPENSSL_PUT_ERROR(EC, EC_R_INCOMPATIBLE_OBJECTS);
return 0;
}
return ec_GFp_simple_point_set_to_infinity(group, point);
}
