From 2eed24109eff01ee974fbd1397170e13a939e669 Mon Sep 17 00:00:00 2001
From: Henry de Valence <hdevalence@hdevalence.ca>
Date: Tue, 15 May 2018 11:15:53 -0700
Subject: [PATCH] Move double-base scmul to the EdwardsPoint type

---
 benches/dalek_benchmarks.rs |  2 +-
 src/edwards.rs              | 54 +++++++++++++++----------------------
 2 files changed, 23 insertions(+), 33 deletions(-)

diff --git a/benches/dalek_benchmarks.rs b/benches/dalek_benchmarks.rs
index 35d1a24..0248fdf 100644
--- a/benches/dalek_benchmarks.rs
+++ b/benches/dalek_benchmarks.rs
@@ -59,7 +59,7 @@ mod edwards_benches {
             let a = Scalar::from_u64(298374928).invert();
             let b = Scalar::from_u64(897987897).invert();
             let A = B * (b * a);
-            bench.iter(|| edwards::vartime::double_scalar_mul_basepoint(&a, &A, &b));
+            bench.iter(|| EdwardsPoint::vartime_double_scalar_mul_basepoint(&a, &A, &b));
         });
     }
 
diff --git a/src/edwards.rs b/src/edwards.rs
index 36076cd..5f03929 100644
--- a/src/edwards.rs
+++ b/src/edwards.rs
@@ -584,6 +584,27 @@ impl VartimeMultiscalarMul for EdwardsPoint {
     }
 }
 
+impl EdwardsPoint {
+    /// Compute \\(aA + bB\\) in variable time, where \\(B\\) is the Ed25519 basepoint.
+    ///
+    /// XXX eliminate this function when we have the precomputation API
+    #[cfg(feature = "stage2_build")]
+    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::mul;
+            mul(a, A, b)
+        }
+        // Otherwise, proceed as normal:
+        #[cfg(not(all(feature="avx2_backend", target_feature="avx2")))]
+        {
+            use scalar_mul::vartime_double_base::mul;
+            mul(a, A, b)
+        }
+    }
+}
+
 /// A precomputed table of multiples of a basepoint, for accelerating
 /// fixed-base scalar multiplication.  One table, for the Ed25519
 /// basepoint, is provided in the `constants` module.
@@ -783,37 +804,6 @@ impl Debug for EdwardsBasepointTable {
     }
 }
 
-// ------------------------------------------------------------------------
-// Variable-time functions
-// ------------------------------------------------------------------------
-
-/// Variable-time operations on curve points, useful for non-secret data.
-///
-/// XXX delete this whole module
-pub mod vartime {
-    //! Variable-time operations on curve points, useful for non-secret data.
-    use super::*;
-
-    /// Compute \\(aA + bB\\) in variable time, where \\(B\\) is the Ed25519 basepoint.
-    ///
-    /// XXX eliminate this function when we have the precomputation API
-    #[cfg(feature = "stage2_build")]
-    pub fn 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::mul;
-            mul(a, A, b)
-        }
-        // Otherwise, proceed as normal:
-        #[cfg(not(all(feature="avx2_backend", target_feature="avx2")))]
-        {
-            use scalar_mul::vartime_double_base::mul;
-            mul(a, A, b)
-        }
-    }
-}
-
 // ------------------------------------------------------------------------
 // Tests
 // ------------------------------------------------------------------------
@@ -1143,7 +1133,7 @@ mod test {
         #[test]
         fn double_scalar_mul_basepoint_vs_ed25519py() {
             let A = A_TIMES_BASEPOINT.decompress().unwrap();
-            let result = vartime::double_scalar_mul_basepoint(&A_SCALAR, &A, &B_SCALAR);
+            let result = EdwardsPoint::vartime_double_scalar_mul_basepoint(&A_SCALAR, &A, &B_SCALAR);
             assert_eq!(result.compress(), DOUBLE_SCALAR_MULT_RESULT);
         }