Rename 'precomputed_tables' to the more accurate 'stage2_build'

Cargo.toml

@@ -67,7 +67,10 @@ alloc = []
 yolocrypto = ["avx2_backend"]
 # Radix-51 arithmetic using u128
 radix_51 = []
-# Include precomputed basepoint tables.  This is off by default so that build.rs can generate the tables, and then re-enabled by build.rs in the main-stage compilation.
-precomputed_tables = []
 # experimental avx2 support
 avx2_backend = ["nightly"]
+# Signals that we're in the main build stage.  This is off by default,
+# to signal stage 1 of the build, where build.rs loads the library
+# into the build script. Then, the build.rs emits the stage2_build
+# feature before the main-stage compilation.
+stage2_build = []

build.rs

@@ -62,8 +62,8 @@ use curve_models::AffineNielsPoint;
 use scalar_mul::window::NafLookupTable8;
 
 fn main() {
-    // Enable the "precomputed_tables" feature in the main build stage
-    println!("cargo:rustc-cfg=feature=\"precomputed_tables\"\n");
+    // Enable the "stage2_build" feature in the main build stage
+    println!("cargo:rustc-cfg=feature=\"stage2_build\"\n");
 
     let out_dir = env::var("OUT_DIR").unwrap();
     let dest_path = Path::new(&out_dir).join("basepoint_table.rs");

src/backend/avx2/mod.rs

@@ -9,7 +9,9 @@
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
 // See the comment above the ristretto::notes module.
-#![cfg_attr(all(feature = "nightly", feature="precomputed_tables"), doc(include = "../docs/avx2-notes.md"))]
+#![cfg_attr(
+    all(feature = "nightly", feature = "stage2_build"), doc(include = "../docs/avx2-notes.md")
+)]
 
 pub(crate) mod field;
 

src/backend/avx2/scalar_mul/mod.rs

@@ -10,7 +10,7 @@
 
 pub mod variable_base;
 
-#[cfg(feature="precomputed_tables")]
+#[cfg(feature = "stage2_build")]
 pub mod vartime_double_base;
 
 #[cfg(any(feature = "alloc", feature = "std"))]

src/constants.rs

@@ -85,14 +85,14 @@ pub const BASEPOINT_ORDER: Scalar = Scalar{
 
 // Precomputed basepoint table is generated into a file by build.rs
 
-#[cfg(feature="precomputed_tables")]
+#[cfg(feature = "stage2_build")]
 include!(concat!(env!("OUT_DIR"), "/basepoint_table.rs"));
 
-#[cfg(feature="precomputed_tables")]
+#[cfg(feature = "stage2_build")]
 use ristretto::RistrettoBasepointTable;
 
 /// The Ristretto basepoint, as a `RistrettoBasepointTable` for scalar multiplication.
-#[cfg(feature="precomputed_tables")]
+#[cfg(feature = "stage2_build")]
 pub const RISTRETTO_BASEPOINT_TABLE: RistrettoBasepointTable
     = RistrettoBasepointTable(ED25519_BASEPOINT_TABLE);
 

src/edwards.rs

@@ -858,7 +858,7 @@ pub mod vartime {
     }
 
     /// Compute \\(aA + bB\\) in variable time, where \\(B\\) is the Ed25519 basepoint.
-    #[cfg(feature="precomputed_tables")]
+    #[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="nightly", all(feature="avx2_backend", target_feature="avx2")))]
@@ -879,7 +879,7 @@ pub mod vartime {
 // Tests
 // ------------------------------------------------------------------------
 
-#[cfg(test)]
+#[cfg(all(test, feature = "stage2_build"))]
 mod test {
     use field::FieldElement;
     use scalar::Scalar;
@@ -971,7 +971,6 @@ mod test {
 
     /// Test that computing 1*basepoint gives the correct basepoint.
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn basepoint_mult_one_vs_basepoint() {
         let bp = &constants::ED25519_BASEPOINT_TABLE * &Scalar::one();
         let compressed = bp.compress();
@@ -980,7 +979,6 @@ mod test {
 
     /// Test that `EdwardsBasepointTable::basepoint()` gives the correct basepoint.
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn basepoint_table_basepoint_function_correct() {
         let bp = constants::ED25519_BASEPOINT_TABLE.basepoint();
         assert_eq!(bp.compress(), constants::ED25519_BASEPOINT_COMPRESSED);
@@ -1031,7 +1029,6 @@ mod test {
 
     /// Sanity check for conversion to precomputed points
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn to_affine_niels_clears_denominators() {
         // construct a point as aB so it has denominators (ie. Z != 1)
         let aB = &constants::ED25519_BASEPOINT_TABLE * &A_SCALAR;
@@ -1043,7 +1040,6 @@ mod test {
 
     /// Test basepoint_mult versus a known scalar multiple from ed25519.py
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn basepoint_mult_vs_ed25519py() {
         let aB = &constants::ED25519_BASEPOINT_TABLE * &A_SCALAR;
         assert_eq!(aB.compress(), A_TIMES_BASEPOINT);
@@ -1051,7 +1047,6 @@ mod test {
 
     /// Test that multiplication by the basepoint order kills the basepoint
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn basepoint_mult_by_basepoint_order() {
         let B = &constants::ED25519_BASEPOINT_TABLE;
         let should_be_id = B * &constants::BASEPOINT_ORDER;
@@ -1060,11 +1055,9 @@ mod test {
 
     /// Test precomputed basepoint mult
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn test_precomputed_basepoint_mult() {
-        let table = EdwardsBasepointTable::create(&constants::ED25519_BASEPOINT_POINT);
         let aB_1 = &constants::ED25519_BASEPOINT_TABLE * &A_SCALAR;
-        let aB_2 = &table * &A_SCALAR;
+        let aB_2 = &constants::ED25519_BASEPOINT_POINT * &A_SCALAR;
         assert_eq!(aB_1.compress(), aB_2.compress());
     }
 
@@ -1084,7 +1077,6 @@ mod test {
 
     /// Test that computing 2*basepoint is the same as basepoint.double()
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn basepoint_mult_two_vs_basepoint2() {
         let two = Scalar::from_u64(2);
         let bp2 = &constants::ED25519_BASEPOINT_TABLE * &two;
@@ -1210,7 +1202,6 @@ mod test {
 
         /// Test double_scalar_mul_vartime vs ed25519.py
         #[test]
-        #[cfg(feature="precomputed_tables")]
         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);

src/montgomery.rs

@@ -279,7 +279,7 @@ impl<'a, 'b> Mul<&'b MontgomeryPoint> for &'a Scalar {
 // Tests
 // ------------------------------------------------------------------------
 
-#[cfg(test)]
+#[cfg(all(test, feature = "stage2_build"))]
 mod test {
     use constants;
     use super::*;
@@ -338,7 +338,6 @@ mod test {
     }
 
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn montgomery_ladder_matches_edwards_scalarmult() {
         let mut csprng: OsRng = OsRng::new().unwrap();
 

src/ristretto.rs

@@ -161,7 +161,7 @@
 // missing).
 //
 // This hack is also used in the avx2 notes.
-#[cfg_attr(all(feature = "nightly", feature="precomputed_tables"), doc(include = "../docs/ristretto-notes.md"))]
+#[cfg_attr(all(feature = "nightly", feature = "stage2_build"), doc(include = "../docs/ristretto-notes.md"))]
 mod notes {
 }
 
@@ -1014,7 +1014,7 @@ pub mod vartime {
 // Tests
 // ------------------------------------------------------------------------
 
-#[cfg(test)]
+#[cfg(all(test, feature = "stage2_build"))]
 mod test {
     use rand::OsRng;
 
@@ -1152,7 +1152,6 @@ mod test {
     }
 
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn four_torsion_random() {
         let mut rng = OsRng::new().unwrap();
         let B = &constants::RISTRETTO_BASEPOINT_TABLE;
@@ -1215,7 +1214,6 @@ mod test {
     }
 
     #[test]
-    #[cfg(feature="precomputed_tables")]
     fn random_roundtrip() {
         let mut rng = OsRng::new().unwrap();
         let B = &constants::RISTRETTO_BASEPOINT_TABLE;

src/scalar_mul/mod.rs

@@ -12,7 +12,7 @@ pub mod window;
 
 pub mod variable_base;
 
-#[cfg(feature="precomputed_tables")]
+#[cfg(feature = "stage2_build")]
 pub mod vartime_double_base;
 
 #[cfg(any(feature = "alloc", feature = "std"))]