First attempt at generating basepoint tables at compile time

Cargo.toml

@@ -14,6 +14,7 @@ description = "A low-level cryptographic library for point, group, field, and sc
 exclude = [
     ".gitignore"
 ]
+build = "build.rs"
 
 [package.metadata.docs.rs]
 rustdoc-args = ["--html-in-header", "rustdoc-include-katex-header.html"]
@@ -49,6 +50,17 @@ version = "0.6"
 [dev-dependencies.serde_cbor]
 version = "0.6"
 
+[build-dependencies]
+subtle = "^0.3"
+rand = "0.3"
+generic-array = "^0.8"
+digest = "0.6"
+arrayref = "0.3.4"
+
+[build-dependencies.serde]
+version = "1.0"
+optional = true
+
 [features]
 nightly = ["radix_51", "subtle/nightly"]
 default = ["std"]
@@ -59,3 +71,6 @@ yolocrypto = []
 bench = []
 # 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 = []
+

build.rs

@@ -0,0 +1,89 @@
+#![cfg_attr(feature = "nightly", feature(i128_type))]
+
+extern crate core;
+extern crate subtle;
+extern crate rand;
+extern crate digest;
+extern crate generic_array;
+#[macro_use]
+extern crate arrayref;
+
+use std::env;
+use std::fs::File;
+use std::io::Write;
+use std::path::Path;
+
+// Replicate lib.rs in the build.rs, since we're effectively building the whole crate twice.
+//
+// This should be fixed up by refactoring our code to seperate the "minimal" parts from the rest.
+//
+// For instance, this shouldn't exist here at all, but it does.
+#[cfg(feature = "serde")]
+extern crate serde;
+
+#[path="src/field.rs"]
+mod field;
+#[cfg(not(feature="radix_51"))]
+#[path="src/field_32bit.rs"]
+mod field_32bit;
+#[cfg(feature="radix_51")]
+#[path="src/field_64bit.rs"]
+mod field_64bit;
+
+#[path="src/scalar.rs"]
+mod scalar;
+#[cfg(not(feature="radix_51"))]
+#[path="src/scalar_32bit.rs"]
+mod scalar_32bit;
+#[cfg(feature="radix_51")]
+#[path="src/scalar_64bit.rs"]
+mod scalar_64bit;
+
+#[path="src/montgomery.rs"]
+mod montgomery;
+#[path="src/edwards.rs"]
+mod edwards;
+#[path="src/ristretto.rs"]
+mod ristretto;
+#[path="src/utils.rs"]
+mod utils;
+
+#[path="src/constants.rs"]
+mod constants;
+#[cfg(not(feature="radix_51"))]
+#[path="src/constants_32bit.rs"]
+mod constants_32bit;
+#[cfg(feature="radix_51")]
+#[path="src/constants_64bit.rs"]
+mod constants_64bit;
+
+use edwards::EdwardsBasepointTable;
+
+fn main() {
+    // Enable the "precomputed_tables" feature in the main build stage
+    println!("cargo:rustc-cfg=feature=\"precomputed_tables\"\n");
+
+    let out_dir = env::var("OUT_DIR").unwrap();
+    let dest_path = Path::new(&out_dir).join("basepoint_table.rs");
+    let mut f = File::create(&dest_path).unwrap();
+
+    // Generate a table of precomputed multiples of the basepoint
+    let table = EdwardsBasepointTable::create(&constants::ED25519_BASEPOINT_POINT);
+
+    f.write_all(format!("\n
+#[cfg(feature=\"radix_51\")]
+use field_64bit::FieldElement64;
+
+#[cfg(not(feature=\"radix_51\"))]
+use field_32bit::FieldElement32;
+
+use edwards::AffineNielsPoint;
+use edwards::EdwardsBasepointTable;
+
+/// Table containing precomputed multiples of the basepoint `B = (x,4/5)`.
+///
+/// The table is defined so `constants::base[i][j-1] = j*(16^2i)*B`,
+/// for `0 ≤ i < 32`, `1 ≤ j < 9`.
+pub const ED25519_BASEPOINT_TABLE: EdwardsBasepointTable = {:?};
+        \n\n", &table).as_bytes()).unwrap();
+}

src/constants.rs

@@ -86,7 +86,17 @@ pub const BASEPOINT_ORDER_MINUS_2: Scalar = Scalar([
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,
 ]);
 
+// Precomputed basepoint table is generated into a file by build.rs
+
+/*
+#[cfg(feature="precomputed_tables")]
+pub use generated::ED25519_BASEPOINT_TABLE;
+*/
+#[cfg(feature="precomputed_tables")]
+include!(concat!(env!("OUT_DIR"), "/basepoint_table.rs"));
+
 /// The Ed25519 basepoint, as a RistrettoPoint
+#[cfg(feature="precomputed_tables")]
 pub const RISTRETTO_BASEPOINT_TABLE: RistrettoBasepointTable
     = RistrettoBasepointTable(ED25519_BASEPOINT_TABLE);
 

src/lib.rs

@@ -91,3 +91,4 @@ pub mod constants;
 mod constants_32bit;
 #[cfg(feature="radix_51")]
 mod constants_64bit;
+