Add associated type bounds and other PR suggestions

ec/src/lib.rs

@@ -282,7 +282,7 @@ pub trait AffineCurve:
     #[must_use]
     #[inline]
     fn mul<S: Into<<Self::ScalarField as PrimeField>::BigInt>>(&self, by: S) -> Self::Projective {
-        self.mul_bits(BitIteratorBE::new(by.into()))
+        self.mul_bits(BitIteratorBE::without_leading_zeros(by.into()))
     }
 
     /// Multiplies this element by the cofactor and output the

ec/src/models/mod.rs

@@ -10,26 +10,26 @@ pub mod short_weierstrass_jacobian;
 pub mod twisted_edwards_extended;
 
 /// Model parameters for an elliptic curve.
-pub trait ModelParameters: Send + Sync + 'static {
+pub trait ModelParameters: Send + Sync + Sized + 'static {
     type BaseField: Field + SquareRootField;
     type ScalarField: PrimeField + SquareRootField + Into<<Self::ScalarField as PrimeField>::BigInt>;
-    type Affine: AffineCurve;
+    type Affine: AffineCurve<BaseField = Self::BaseField, ScalarField = Self::ScalarField>;
 
     const COFACTOR: &'static [u64];
     const COFACTOR_INV: Self::ScalarField;
 
     /// Checks that the current point is in the prime order subgroup given
     /// the point on the curve.
-    /// Requires type parameters G: the type of point passed in, and H: the type of
-    /// point that results from multiplying G by a scalar.
     fn is_in_correct_subgroup_assuming_on_curve(item: &Self::Affine) -> bool {
         item.mul_bits(BitIteratorBE::new(Self::ScalarField::characteristic()))
             .is_zero()
     }
 }
 
 /// Model parameters for a Short Weierstrass curve.
-pub trait SWModelParameters: ModelParameters {
+pub trait SWModelParameters:
+    ModelParameters<Affine = short_weierstrass_jacobian::GroupAffine<Self>>
+{
     const COEFF_A: Self::BaseField;
     const COEFF_B: Self::BaseField;
     const AFFINE_GENERATOR_COEFFS: (Self::BaseField, Self::BaseField);
@@ -53,7 +53,9 @@ pub trait SWModelParameters: ModelParameters {
 }
 
 /// Model parameters for a Twisted Edwards curve.
-pub trait TEModelParameters: ModelParameters {
+pub trait TEModelParameters:
+    ModelParameters<Affine = twisted_edwards_extended::GroupAffine<Self>>
+{
     const COEFF_A: Self::BaseField;
     const COEFF_D: Self::BaseField;
     const AFFINE_GENERATOR_COEFFS: (Self::BaseField, Self::BaseField);

ec/src/models/short_weierstrass_jacobian.rs

@@ -119,9 +119,11 @@ impl<P: Parameters> GroupAffine<P> {
             y2 == x3b
         }
     }
+}
 
-    /// Checks if `self` is in the subgroup having order that equaling that of
-    /// `P::ScalarField`.
+impl<P: Parameters> GroupAffine<P> {
+    /// Checks if `self` is in the subgroup having order equaling that of
+    /// `P::ScalarField` given it is on the curve.
     pub fn is_in_correct_subgroup_assuming_on_curve(&self) -> bool {
         P::is_in_correct_subgroup_assuming_on_curve(self)
     }

ec/src/models/twisted_edwards_extended.rs

@@ -100,9 +100,11 @@ impl<P: Parameters> GroupAffine<P> {
 
         lhs == rhs
     }
+}
 
-    /// Checks that the current point is in the prime order subgroup given
-    /// the point on the curve.
+impl<P: Parameters> GroupAffine<P> {
+    /// Checks if `self` is in the subgroup having order equaling that of
+    /// `P::ScalarField` given it is on the curve.
     pub fn is_in_correct_subgroup_assuming_on_curve(&self) -> bool {
         P::is_in_correct_subgroup_assuming_on_curve(self)
     }
@@ -293,7 +295,7 @@ mod group_impl {
 
 //////////////////////////////////////////////////////////////////////////////
 
-/// `GroupProjective` implements Extended Twisted Edwards (Jacobian) Coordinates
+/// `GroupProjective` implements Extended Twisted Edwards Coordinates
 /// as described in [\[HKCD08\]](https://eprint.iacr.org/2008/522.pdf).
 ///
 /// This implementation uses the unified addition formulae from that paper (see

test-curves/src/bls12_381/g1.rs

@@ -14,6 +14,7 @@ pub struct Parameters;
 impl ModelParameters for Parameters {
     type BaseField = Fq;
     type ScalarField = Fr;
+    type Affine = GroupAffine<Self>;
 
     /// COFACTOR = (x - 1)^2 / 3  = 76329603384216526031706109802092473003
     const COFACTOR: &'static [u64] = &[0x8c00aaab0000aaab, 0x396c8c005555e156];

test-curves/src/bn384_small_two_adicity/g1.rs

@@ -15,6 +15,7 @@ pub struct Parameters;
 impl ModelParameters for Parameters {
     type BaseField = Fq;
     type ScalarField = Fr;
+    type Affine = GroupAffine<Self>;
 
     /// COFACTOR = 1
     const COFACTOR: &'static [u64] = &[0x1];

test-curves/src/mnt4_753/g1.rs

@@ -15,6 +15,7 @@ pub struct Parameters;
 impl ModelParameters for Parameters {
     type BaseField = Fq;
     type ScalarField = Fr;
+    type Affine = GroupAffine<Self>;
 
     /// COFACTOR = 1
     const COFACTOR: &'static [u64] = &[1];