[ring]: added ring degree switching

2026-02-10 13:16:44 +01:00 · 2025-01-20 11:44:27 +01:00
parent 3b7d889971
commit 1cc38b3042
5 changed files with 153 additions and 4 deletions
--- a/math/src/ring/impl_u64/ring_switch.rs
+++ b/math/src/ring/impl_u64/ring_switch.rs
@@ -0,0 +1,43 @@
+use crate::poly::Poly;
+use crate::ring::Ring;
+
+impl Ring<u64> {
+    pub fn switch_degree<const NTT: bool>(
+        &self,
+        a: &Poly<u64>,
+        buf: &mut Poly<u64>,
+        b: &mut Poly<u64>,
+    ) {
+        let (n_in, n_out) = (a.n(), b.n());
+
+        if n_in > n_out {
+            let (gap_in, gap_out) = (1, n_in / n_out);
+            if NTT {
+                self.intt::<false>(&a, buf);
+                b.0.iter_mut()
+                    .step_by(gap_in)
+                    .zip(buf.0.iter().step_by(gap_out))
+                    .for_each(|(x_out, x_in)| *x_out = *x_in);
+                self.ntt_inplace::<false>(b);
+            } else {
+                b.0.iter_mut()
+                    .step_by(gap_in)
+                    .zip(a.0.iter().step_by(gap_out))
+                    .for_each(|(x_out, x_in)| *x_out = *x_in);
+            }
+        } else {
+            let gap: usize = n_out / n_in;
+
+            if NTT {
+                a.0.iter()
+                    .enumerate()
+                    .for_each(|(i, &c)| (0..gap).for_each(|j| b.0[i * gap + j] = c));
+            } else {
+                b.0.iter_mut()
+                    .step_by(gap)
+                    .zip(a.0.iter())
+                    .for_each(|(x_out, x_in)| *x_out = *x_in);
+            }
+        }
+    }
+}