Allow to overwrite the default implementation of msm

ec/src/models/short_weierstrass/group.rs

@@ -634,6 +634,24 @@ impl<P: SWCurveConfig> ScalarMul for Projective<P> {
     }
 }
 
+#[cfg(feature = "specialization")]
+pub trait CustomMSM: SWCurveConfig {
+    fn msm_bigint(
+        bases: &[Affine<Self>],
+        bigints: &[<Self::ScalarField as PrimeField>::BigInt],
+    ) -> Projective<Self>;
+}
+
+#[cfg(feature = "specialization")]
+impl<P: SWCurveConfig> VariableBaseMSM for Projective<P> where P: CustomMSM {
+    fn msm_bigint(
+        bases: &[Self::MulBase],
+        bigints: &[<Self::ScalarField as PrimeField>::BigInt],
+    ) -> Self {
+        P::msm_bigint(bases, bigints)
+    }
+}
+
 impl<P: SWCurveConfig> VariableBaseMSM for Projective<P> {}
 
 impl<P: SWCurveConfig, T: Borrow<Affine<P>>> core::iter::Sum<T> for Projective<P> {

ec/src/models/short_weierstrass/mod.rs

@@ -4,9 +4,9 @@ use ark_serialize::{
 };
 use ark_std::io::{Read, Write};
 
-use ark_ff::fields::Field;
+use ark_ff::{fields::Field, PrimeField};
 
-use crate::{AffineRepr, Group};
+use crate::{scalar_mul::variable_base::VariableBaseMSM, AffineRepr, Group};
 
 use num_traits::Zero;
 

test-templates/src/msm.rs

@@ -3,6 +3,7 @@ use ark_ec::{
     ScalarMul,
 };
 use ark_ff::{PrimeField, UniformRand};
+use ark_std::vec::Vec;
 
 fn naive_var_base_msm<G: ScalarMul>(bases: &[G::MulBase], scalars: &[G::ScalarField]) -> G {
     let mut acc = G::zero();