#![allow(non_snake_case)]
use crate::backend::vector::{CachedPoint, ExtendedPoint};
use crate::edwards::EdwardsPoint;
use crate::scalar::Scalar;
use crate::traits::Identity;
use crate::window::LookupTable;
/// Perform constant-time, variable-base scalar multiplication.
pub fn mul(point: &EdwardsPoint, scalar: &Scalar) -> EdwardsPoint {
// Construct a lookup table of [P,2P,3P,4P,5P,6P,7P,8P]
let lookup_table = LookupTable::<CachedPoint>::from(point);
// Setting s = scalar, compute
//
// s = s_0 + s_1*16^1 + ... + s_63*16^63,
//
// with `-8 ≤ s_i < 8` for `0 ≤ i < 63` and `-8 ≤ s_63 ≤ 8`.
let scalar_digits = scalar.as_radix_16();
// Compute s*P as
//
// s*P = P*(s_0 + s_1*16^1 + s_2*16^2 + ... + s_63*16^63)
// s*P = P*s_0 + P*s_1*16^1 + P*s_2*16^2 + ... + P*s_63*16^63
// s*P = P*s_0 + 16*(P*s_1 + 16*(P*s_2 + 16*( ... + P*s_63)...))
//
// We sum right-to-left.
let mut Q = ExtendedPoint::identity();
for i in (0..64).rev() {
Q = Q.mul_by_pow_2(4);
Q = &Q + &lookup_table.select(scalar_digits[i]);
}
Q.into()
}