added vec_znx_split and vec_znx_merge

base2k/src/vec_znx.rs

@@ -406,9 +406,28 @@ pub trait VecZnxOps {
 
     /// a <- phi_k(a) where phi_k: X^i -> X^{i*k} (mod (X^{n} + 1))
     fn vec_znx_automorphism_inplace(&self, k: i64, a: &mut VecZnx);
+
+    /// Splits b into subrings and copies them them into a.
+    /// 
+    /// # Panics
+    /// 
+    /// This method requires that all [VecZnx] of b have the same ring degree
+    /// and that b.n() * b.len() <= a.n()
+    fn vec_znx_split(&self, b: &mut Vec<VecZnx>, a: &VecZnx, buf: &mut VecZnx);
+
+
+    /// Merges the subrings a into b.
+    /// 
+    /// # Panics
+    /// 
+    /// This method requires that all [VecZnx] of a have the same ring degree
+    /// and that a.n() * a.len() <= b.n()
+    fn vec_znx_merge(&self, b: &mut VecZnx, a: &Vec<VecZnx>);
+
 }
 
 impl VecZnxOps for Module {
+
     fn new_vec_znx(&self, limbs: usize) -> VecZnx {
         VecZnx::new(self.n(), limbs)
     }
@@ -572,4 +591,39 @@ impl VecZnxOps for Module {
             );
         }
     }
+
+    fn vec_znx_split(&self, b: &mut Vec<VecZnx>, a: &VecZnx, buf: &mut VecZnx){
+        let (n_in, n_out) = (a.n(), b[0].n());
+
+        assert!(n_out < n_in, "invalid a: output ring degree should be smaller");
+        b[1..].iter().for_each(|bi|{
+            assert_eq!(bi.n(), n_out, "invalid input a: all VecZnx must have the same degree")
+        });
+
+        b.iter_mut().enumerate().for_each(|(i, bi)|{
+            if i == 0{
+                a.switch_degree(bi);
+                self.vec_znx_rotate(-1, buf, a);
+            }else{
+                buf.switch_degree(bi);
+                self.vec_znx_rotate_inplace(-1, buf);
+            }
+        })
+    }
+
+    fn vec_znx_merge(&self, b: &mut VecZnx, a: &Vec<VecZnx>){
+        let (n_in, n_out) = (b.n(), a[0].n());
+
+        assert!(n_out < n_in, "invalid a: output ring degree should be smaller");
+        a[1..].iter().for_each(|ai|{
+            assert_eq!(ai.n(), n_out, "invalid input a: all VecZnx must have the same degree")
+        });
+
+        a.iter().enumerate().for_each(|(i, ai)|{
+            ai.switch_degree(b);
+            self.vec_znx_rotate_inplace(-1, b);
+        });
+
+        self.vec_znx_rotate_inplace(a.len() as i64, b);
+    }
 }