more doc

base2k/src/sampling.rs

@@ -0,0 +1,94 @@
+use crate::{Infos, VecZnx};
+use rand_distr::{Distribution, Normal};
+use sampling::source::Source;
+
+pub trait Sampling {
+    /// Fills the first `limbs` limbs with uniform values in \[-2^{log_base2k}, 2^{log_base2k}\]
+    fn fill_uniform(&mut self, log_base2k: usize, limbs: usize, source: &mut Source);
+
+    /// Adds vector sampled according to the provided distribution, scaled by 2^{-log_k} and bounded to \[-bound, bound\].
+    fn add_dist_f64<T: Distribution<f64>>(
+        &mut self,
+        log_base2k: usize,
+        log_k: usize,
+        source: &mut Source,
+        dist: T,
+        bound: f64,
+    );
+
+    /// Adds a discrete normal vector scaled by 2^{-log_k} with the provided standard deviation and bounded to \[-bound, bound\].
+    fn add_normal(
+        &mut self,
+        log_base2k: usize,
+        log_k: usize,
+        source: &mut Source,
+        sigma: f64,
+        bound: f64,
+    );
+}
+
+impl Sampling for VecZnx {
+    fn fill_uniform(&mut self, log_base2k: usize, limbs: usize, source: &mut Source) {
+        let base2k: u64 = 1 << log_base2k;
+        let mask: u64 = base2k - 1;
+        let base2k_half: i64 = (base2k >> 1) as i64;
+
+        let size: usize = self.n() * (limbs - 1);
+
+        self.data[..size]
+            .iter_mut()
+            .for_each(|x| *x = (source.next_u64n(base2k, mask) as i64) - base2k_half);
+    }
+
+    fn add_dist_f64<T: Distribution<f64>>(
+        &mut self,
+        log_base2k: usize,
+        log_k: usize,
+        source: &mut Source,
+        dist: T,
+        bound: f64,
+    ) {
+        assert!(
+            (bound.log2().ceil() as i64) < 64,
+            "invalid bound: ceil(log2(bound))={} > 63",
+            (bound.log2().ceil() as i64)
+        );
+
+        let log_base2k_rem: usize = log_k % log_base2k;
+
+        if log_base2k_rem != 0 {
+            self.at_mut(self.limbs() - 1).iter_mut().for_each(|a| {
+                let mut dist_f64: f64 = dist.sample(source);
+                while dist_f64.abs() > bound {
+                    dist_f64 = dist.sample(source)
+                }
+                *a += (dist_f64.round() as i64) << log_base2k_rem
+            });
+        } else {
+            self.at_mut(self.limbs() - 1).iter_mut().for_each(|a| {
+                let mut dist_f64: f64 = dist.sample(source);
+                while dist_f64.abs() > bound {
+                    dist_f64 = dist.sample(source)
+                }
+                *a += dist_f64.round() as i64
+            });
+        }
+    }
+
+    fn add_normal(
+        &mut self,
+        log_base2k: usize,
+        log_k: usize,
+        source: &mut Source,
+        sigma: f64,
+        bound: f64,
+    ) {
+        self.add_dist_f64(
+            log_base2k,
+            log_k,
+            source,
+            Normal::new(0.0, sigma).unwrap(),
+            bound,
+        );
+    }
+}