1use crate::znx_base::ZnxInfos;
 2use crate::{Decoding, VecZnx};
 3use rug::Float;
 4use rug::float::Round;
 5use rug::ops::{AddAssignRound, DivAssignRound, SubAssignRound};
 6
 7pub trait Stats {
 8    /// Returns the standard devaition of the i-th polynomial.
 9    fn std(&self, col_i: usize, log_base2k: usize) -> f64;
10}
11
12impl<D: AsRef<[u8]>> Stats for VecZnx<D> {
13    fn std(&self, col_i: usize, log_base2k: usize) -> f64 {
14        let prec: u32 = (self.size() * log_base2k) as u32;
15        let mut data: Vec<Float> = (0..self.n()).map(|_| Float::with_val(prec, 0)).collect();
16        self.decode_vec_float(col_i, log_base2k, &mut data);
17        // std = sqrt(sum((xi - avg)^2) / n)
18        let mut avg: Float = Float::with_val(prec, 0);
19        data.iter().for_each(|x| {
20            avg.add_assign_round(x, Round::Nearest);
21        });
22        avg.div_assign_round(Float::with_val(prec, data.len()), Round::Nearest);
23        data.iter_mut().for_each(|x| {
24            x.sub_assign_round(&avg, Round::Nearest);
25        });
26        let mut std: Float = Float::with_val(prec, 0);
27        data.iter().for_each(|x| std += x * x);
28        std.div_assign_round(Float::with_val(prec, data.len()), Round::Nearest);
29        std = std.sqrt();
30        std.to_f64()
31    }
32}