Attempt to use Intoiterator to abstract over collection types, does not work.

Author: burdges

src/bls12_381/ec.rs

@@ -334,28 +334,31 @@ macro_rules! curve_impl {
                 self.is_zero() || self.z == $basefield::one()
             }
 
-            fn batch_normalization(v: &mut [Self])
+            fn batch_normalization<II: ?Sized>(v: &mut II)
+			where for<'a> &'a mut II: IntoIterator<Item = &'a mut Self>,
+			      for<'a> <&'a mut II as IntoIterator>::IntoIter: DoubleEndedIterator+ExactSizeIterator
             {
                 // Montgomery’s Trick and Fast Implementation of Masked AES
                 // Genelle, Prouff and Quisquater
                 // Section 3.2
 
                 // First pass: compute [a, ab, abc, ...]
-                let mut prod = Vec::with_capacity(v.len());
+                let mut prod = Vec::with_capacity(v.into_iter().len());
                 let mut tmp = $basefield::one();
-                for g in v.iter_mut()
+                for g in v.into_iter()
                           // Ignore normalized elements
                           .filter(|g| !g.is_normalized())
                 {
                     tmp.mul_assign(&g.z);
                     prod.push(tmp);
                 }
+				if prod.is_empty() { return; }
 
                 // Invert `tmp`.
                 tmp = tmp.inverse().unwrap(); // Guaranteed to be nonzero.
 
                 // Second pass: iterate backwards to compute inverses
-                for (g, s) in v.iter_mut()
+                for (g, s) in v.into_iter()
                                // Backwards
                                .rev()
                                // Ignore normalized elements
@@ -372,7 +375,7 @@ macro_rules! curve_impl {
                 }
 
                 // Perform affine transformations
-                for g in v.iter_mut()
+                for g in v.into_iter()
                           .filter(|g| !g.is_normalized())
                 {
                     let mut z = g.z; // 1/z

src/lib.rs

@@ -141,7 +141,10 @@ pub trait CurveProjective:
 
     /// Normalizes a slice of projective elements so that
     /// conversion to affine is cheap.
-    fn batch_normalization(v: &mut [Self]);
+    fn batch_normalization<II: ?Sized>(v: &mut II)
+	where for<'a> &'a mut II: IntoIterator<Item = &'a mut Self>,
+	      for<'a> <&'a mut II as IntoIterator>::IntoIter: DoubleEndedIterator+ExactSizeIterator;
+		  // TODO: Simplify using  https://github.com/rust-lang/rfcs/pull/2289
 
     /// Checks if the point is already "normalized" so that
     /// cheap affine conversion is possible.

src/tests/curve.rs

@@ -375,7 +375,7 @@ fn random_transformation_tests<G: CurveProjective>() {
         let expected_v = v.iter()
             .map(|v| v.into_affine().into_projective())
             .collect::<Vec<_>>();
-        G::batch_normalization(&mut v);
+        G::batch_normalization(v.as_mut_slice());
 
         for i in &v {
             assert!(i.is_normalized());