From c873f72ed5ee61562a46849ca9efb0b9076b117f Mon Sep 17 00:00:00 2001
From: pinkforest <36498018+pinkforest@users.noreply.github.com>
Date: Fri, 9 Dec 2022 21:53:02 +1100
Subject: [PATCH] Set well known defaults for wasm and arm

As discussed in #456 this sets well known defaults for cfg(target_family = "wasm")
and cfg(target_arch = "arm") for 64 bit arithmetric via cfg(curve25519_dalek_bits = "64")
---
 .github/workflows/rust.yml | 33 +++++++++++++++++++++++++
 CHANGELOG.md               |  1 +
 Cargo.toml                 |  3 +++
 build.rs                   | 50 +++++++++++++++++++++++++++++---------
 4 files changed, 76 insertions(+), 11 deletions(-)

diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
index 57330f6a6..e3132388c 100644
--- a/.github/workflows/rust.yml
+++ b/.github/workflows/rust.yml
@@ -48,6 +48,39 @@ jobs:
         RUSTFLAGS: '--cfg curve25519_dalek_backend="simd" -C target_feature=+avx512ifma'
       run: cargo build --target x86_64-unknown-linux-gnu
 
+  cross:
+    strategy:
+      matrix:
+        include:
+          # ARM32
+          - target: armv7-unknown-linux-gnueabihf
+            rust: 1.56.1 # MSRV (cross)
+          - target: armv7-unknown-linux-gnueabihf
+            rust: stable
+
+          # ARM64
+          - target: aarch64-unknown-linux-gnu
+            rust: 1.56.1 # MSRV (cross)
+          - target: aarch64-unknown-linux-gnu
+            rust: stable
+
+          # PPC32
+          - target: powerpc-unknown-linux-gnu
+            rust: 1.56.1 # MSRV (cross)
+          - target: powerpc-unknown-linux-gnu
+            rust: stable
+
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - run: ${{ matrix.deps }}
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+          targets: ${{ matrix.target }}
+      - run: cargo install cross
+      - run: cross test --release --target ${{ matrix.target }}
+
   nightly:
     name: Test nightly compiler
     runs-on: ubuntu-latest
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 841d3809f..cb1572d85 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@ major series.
 
 #### Other changes
 
+* Set well known defaults for wasm and arm
 * Update Maintenance Policies for SemVer
 * Migrate documentation to docs.rs hosted
 * Fix backend documentation generation
diff --git a/Cargo.toml b/Cargo.toml
index 17ba12ea8..8b7db7831 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -38,6 +38,9 @@ hex = "0.4.2"
 rand = "0.8"
 rand_core = { version = "0.6", default-features = false, features = ["getrandom"] }
 
+[build-dependencies]
+platforms = "3.0.2"
+
 [[bench]]
 name = "dalek_benchmarks"
 harness = false
diff --git a/build.rs b/build.rs
index cb896efd6..d4b4af050 100644
--- a/build.rs
+++ b/build.rs
@@ -1,15 +1,43 @@
 //! This selects the curve25519_dalek_bits either by default from target_pointer_width or explicitly set
 
+#[allow(non_camel_case_types)]
+enum DalekBits {
+    Dalek32,
+    Dalek64,
+}
+
+#[cfg(all(not(curve25519_dalek_bits = "64"), not(curve25519_dalek_bits = "32")))]
+#[deny(dead_code)]
+fn lotto_curve25519_dalek_bits() -> DalekBits {
+    use platforms::target::{Arch, PointerWidth};
+
+    let target_triplet = std::env::var("TARGET").unwrap();
+    let platform = platforms::Platform::find(&target_triplet).unwrap();
+
+    match platform.target_arch {
+        Arch::Arm => DalekBits::Dalek64,
+        //TODO: Needs tests + benchmarks to back it up across
+        //Arch::Wasm32 => DalekBits::Dalek64,
+        _ => match platform.target_pointer_width {
+            PointerWidth::U64 => DalekBits::Dalek64,
+            PointerWidth::U32 => DalekBits::Dalek32,
+            _ => DalekBits::Dalek32,
+        },
+    }
+}
+
 fn main() {
-    #[cfg(any(
-        all(not(target_pointer_width = "64"), not(curve25519_dalek_bits = "64")),
-        curve25519_dalek_bits = "32"
-    ))]
-    println!("cargo:rustc-cfg=curve25519_dalek_bits=\"32\"");
-
-    #[cfg(any(
-        all(target_pointer_width = "64", not(curve25519_dalek_bits = "32")),
-        curve25519_dalek_bits = "64"
-    ))]
-    println!("cargo:rustc-cfg=curve25519_dalek_bits=\"64\"");
+    #[cfg(curve25519_dalek_bits = "32")]
+    let curve25519_dalek_bits = DalekBits::Dalek32;
+
+    #[cfg(curve25519_dalek_bits = "64")]
+    let curve25519_dalek_bits = DalekBits::Dalek64;
+
+    #[cfg(all(not(curve25519_dalek_bits = "64"), not(curve25519_dalek_bits = "32")))]
+    let curve25519_dalek_bits = lotto_curve25519_dalek_bits();
+
+    match curve25519_dalek_bits {
+        DalekBits::Dalek64 => println!("cargo:rustc-cfg=curve25519_dalek_bits=\"64\""),
+        DalekBits::Dalek32 => println!("cargo:rustc-cfg=curve25519_dalek_bits=\"32\""),
+    }
 }