INNER CODE UNIT · Rust

sum_n

IronCoreLabs/recrypt-rs · src/internal/mod.rs:386

fn sum_n<T: Add<Output = T> + Copy + Zero + PartialEq>(t: T, n: u32) -> T {
    if n == 0 {
        Zero::zero()
    } else {
        sum_n_loop(t, n - 1, t)
    }
}

fn sum_n_loop<T: Add<Output = T> + Copy>(t: T, k: u32, extra: T) -> T {
    if k == 1 {
        t + extra
    } else {
        let x = if (k & 1) == 1 { t + extra } else { extra };
        sum_n_loop(t + t, k >> 1, x)
    }
}

/// This is not constant time, it reveals the n, but if the t has a constant time square and multiply, doesn't reveal the t.

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