Make elligator curve map a static object following revert of revert

of arkworks-rs#679

ec/src/hashing/curve_maps/elligator2/mod.rs → ec/src/hashing/curve_maps/elligator2.rs

@@ -32,7 +32,7 @@ pub trait Elligator2Config: TECurveConfig + MontCurveConfig {
 /// Represents the Elligator2 hash-to-curve map defined by `P`.
 pub struct Elligator2Map<P: TECurveConfig>(PhantomData<fn() -> P>);
 
-impl<P: Elligator2Config> Elligator2Map<P> {
+impl<P: Elligator2Config> MapToCurve<Projective<P>> for Elligator2Map<P> {
     /// Checks if `P` represents a valid Elligator2 map. Panics otherwise.
     fn check_parameters() -> Result<(), HashToCurveError> {
         // We assume that the Montgomery curve is correct and  as such we do
@@ -60,18 +60,9 @@ impl<P: Elligator2Config> Elligator2Map<P> {
         );
         Ok(())
     }
-}
-
-impl<P: Elligator2Config> MapToCurve<Projective<P>> for Elligator2Map<P> {
-    fn new() -> Result<Self, HashToCurveError> {
-        // Checking validity `Elligator2Config` so we actually representing a valid Elligator2 map.
-        Self::check_parameters()?;
-
-        Ok(Elligator2Map(PhantomData))
-    }
 
     /// Map an arbitrary base field element `element` to a curve point.
-    fn map_to_curve(&self, element: P::BaseField) -> Result<Affine<P>, HashToCurveError> {
+    fn map_to_curve(element: P::BaseField) -> Result<Affine<P>, HashToCurveError> {
         // 1. x1 = -(J / K) * inv0(1 + Z * u^2)
         // 2. If x1 == 0, set x1 = -(J / K)
         // 3. gx1 = x1^3 + (J / K) * x1^2 + x1 / K^2
@@ -273,16 +264,16 @@ mod test {
     #[test]
     fn map_field_to_curve_elligator2() {
         Elligator2Map::<TestElligator2MapToCurveConfig>::check_parameters().unwrap();
-        let test_map_to_curve = Elligator2Map::<TestElligator2MapToCurveConfig>::new().unwrap();
 
         let mut map_range: Vec<Affine<TestElligator2MapToCurveConfig>> = vec![];
         // We are mapping all elemnts of the field to the curve, verifying that
         // map is not constant on that set.
         for current_field_element in 0..101 {
             map_range.push(
-                test_map_to_curve
-                    .map_to_curve(F101::from(current_field_element as u64))
-                    .unwrap(),
+                Elligator2Map::<TestElligator2MapToCurveConfig>::map_to_curve(F101::from(
+                    current_field_element as u64,
+                ))
+                .unwrap(),
             );
         }