Add missing Ristretto vartime-double-base fn

src/edwards.rs

@@ -587,16 +587,12 @@ impl EdwardsPoint {
     pub fn vartime_double_scalar_mul_basepoint(a: &Scalar, A: &EdwardsPoint, b: &Scalar) -> EdwardsPoint {
         // If we built with AVX2, use the AVX2 backend.
         #[cfg(all(feature="avx2_backend", target_feature="avx2"))]
-        {
+        use backend::avx2::scalar_mul::vartime_double_base;
-            use backend::avx2::scalar_mul::vartime_double_base::mul;
+        // Otherwise, use the serial backend:
-            mul(a, A, b)
-        }
-        // Otherwise, proceed as normal:
         #[cfg(not(all(feature="avx2_backend", target_feature="avx2")))]
-        {
+        use scalar_mul::vartime_double_base;
-            use scalar_mul::vartime_double_base::mul;
+
-            mul(a, A, b)
+        vartime_double_base::mul(a, A, b)
-        }
     }
 }
 

src/ristretto.rs

@@ -830,6 +830,21 @@ impl VartimeMultiscalarMul for RistrettoPoint {
     }
 }
 
+impl RistrettoPoint {
+    /// Compute \\(aA + bB\\) in variable time, where \\(B\\) is the
+    /// Ristretto basepoint.
+    #[cfg(feature = "stage2_build")]
+    pub fn vartime_double_scalar_mul_basepoint(
+        a: &Scalar,
+        A: &RistrettoPoint,
+        b: &Scalar,
+    ) -> RistrettoPoint {
+        RistrettoPoint(
+            EdwardsPoint::vartime_double_scalar_mul_basepoint(a, &A.0, b)
+        )
+    }
+}
+
 /// A precomputed table of multiples of a basepoint, used to accelerate
 /// scalar multiplication.
 ///