keccak: replace asm/simd features with --cfg keccak_backend (#106)

Replaces these non-additive "features" with a 1-of-n backend selection
enabled by using `cfg` instead.

- `asm` => `--cfg keccak_backend="armv8_asm"`
- `simd` => `--cfg keccak_backend="simd"`

Closes #85

.github/workflows/keccak.yml

@@ -50,7 +50,6 @@ jobs:
     uses: RustCrypto/actions/.github/workflows/minimal-versions.yml@master
     with:
       working-directory: ${{ github.workflow }}
-      stable-cmd: cargo hack test --release --feature-powerset --skip simd # `simd` requires nightly
 
   test:
     needs: set-msrv
@@ -79,25 +78,27 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
           targets: ${{ matrix.target }}
-      - run: cargo check --features asm --target ${{ matrix.target }}
-      - run: cargo test --no-default-features --target ${{ matrix.target }}
+      - run: cargo check --target ${{ matrix.target }}
       - run: cargo test --target ${{ matrix.target }}
-      - run: cargo test --features asm --target ${{ matrix.target }}
-      - run: cargo test --features asm --release --target ${{ matrix.target }}
+      - run: cargo test --release --target ${{ matrix.target }}
+      - env:
+          RUSTFLAGS: '-Dwarnings --cfg keccak_backend="armv8_asm"'
+        run: cargo test --release --target ${{ matrix.target }}
       - env:
           RUSTFLAGS: '-Dwarnings --cfg keccak_backend="soft-compact"'
         run: cargo test --release --target ${{ matrix.target }}
 
   test-simd:
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: '-Dwarnings --cfg keccak_backend="simd"'
     steps:
       - uses: actions/checkout@v4
       - uses: RustCrypto/actions/cargo-cache@master
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: nightly
-      - run: cargo check --features simd
-      - run: cargo test --features simd
+      - run: cargo test
 
   test-miri:
     runs-on: ubuntu-latest
@@ -113,15 +114,15 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: nightly
-      - name: Install Miri
-        run: |
-          rustup component add miri
-          cargo miri setup
-      - name: Test with Miri
-        run: |
-          cargo miri test --target ${{ matrix.target }} --no-default-features
-          cargo miri test --target ${{ matrix.target }}
-          cargo miri test --target ${{ matrix.target }} --features simd
+          components: miri
+      - run: cargo miri setup
+      - run: cargo miri test --target ${{ matrix.target }}
+      - env:
+          RUSTFLAGS: '-Dwarnings --cfg keccak_backend="armv8_asm"'
+        run: cargo miri test --release --target ${{ matrix.target }}
+      - env:
+          RUSTFLAGS: '-Dwarnings --cfg keccak_backend="simd"'
+        run: cargo miri test --release --target ${{ matrix.target }}
       - env:
           RUSTFLAGS: '-Dwarnings --cfg keccak_backend="soft-compact"'
         run: cargo miri test --release --target ${{ matrix.target }}
@@ -152,9 +153,9 @@ jobs:
           tar -C /tmp -xzf /tmp/binaries.tar.gz
           mv /tmp/cross ~/.cargo/bin
         shell: bash
-      - name: cross test
+      - env:
+          RUSTFLAGS: '-C target-feature=+sha3 --cfg keccak_backend="armv8_asm"'
         run: |
           cd keccak
           # Cross doesn't enable `sha3` by default, but QEMU supports it.
-          export RUSTFLAGS="-C target-feature=+sha3"
           cross test --target aarch64-unknown-linux-gnu --no-default-features

keccak/Cargo.toml

@@ -16,10 +16,6 @@ readme = "README.md"
 edition = "2024"
 rust-version = "1.85"
 
-[features]
-asm = []  # Use optimized assembly when available (currently only ARMv8)
-simd = [] # Use core::simd (nightly-only)
-
 [target.'cfg(target_arch = "aarch64")'.dependencies]
 cpufeatures = "0.3"
 
@@ -34,7 +30,7 @@ unused_qualifications = "warn"
 
 [lints.rust.unexpected_cfgs]
 level = "warn"
-check-cfg = ['cfg(keccak_backend, values("soft-compact"))']
+check-cfg = ['cfg(keccak_backend, values("armv8_asm", "simd", "soft-compact"))']
 
 [lints.clippy]
 borrow_as_ptr = "warn"

keccak/src/lib.rs

@@ -1,6 +1,6 @@
 #![no_std]
 #![cfg_attr(docsrs, feature(doc_cfg))]
-#![cfg_attr(feature = "simd", feature(portable_simd))]
+#![cfg_attr(keccak_backend = "simd", feature(portable_simd))]
 #![doc = include_str!("../README.md")]
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg",
@@ -51,10 +51,10 @@ use core::{
 #[rustfmt::skip]
 mod unroll;
 
-#[cfg(all(target_arch = "aarch64", feature = "asm"))]
+#[cfg(all(target_arch = "aarch64", keccak_backend = "armv8_asm"))]
 mod armv8;
 
-#[cfg(all(target_arch = "aarch64", feature = "asm"))]
+#[cfg(all(target_arch = "aarch64", keccak_backend = "armv8_asm"))]
 cpufeatures::new!(armv8_sha3_intrinsics, "sha3");
 
 const PLEN: usize = 25;
@@ -166,11 +166,11 @@ impl_keccak!(p200, f200, u8);
 impl_keccak!(p400, f400, u16);
 impl_keccak!(p800, f800, u32);
 
-#[cfg(not(all(target_arch = "aarch64", feature = "asm")))]
+#[cfg(not(all(target_arch = "aarch64", keccak_backend = "armv8_asm")))]
 impl_keccak!(p1600, f1600, u64);
 
 /// `Keccak-p[1600, rc]` permutation.
-#[cfg(all(target_arch = "aarch64", feature = "asm"))]
+#[cfg(all(target_arch = "aarch64", keccak_backend = "armv8_asm"))]
 pub fn p1600(state: &mut [u64; PLEN], round_count: usize) {
     if armv8_sha3_intrinsics::get() {
         // SAFETY: we just performed runtime CPU feature detection above
@@ -181,7 +181,7 @@ pub fn p1600(state: &mut [u64; PLEN], round_count: usize) {
 }
 
 /// `Keccak-f[1600]` permutation.
-#[cfg(all(target_arch = "aarch64", feature = "asm"))]
+#[cfg(all(target_arch = "aarch64", keccak_backend = "armv8_asm"))]
 pub fn f1600(state: &mut [u64; PLEN]) {
     if armv8_sha3_intrinsics::get() {
         // SAFETY: we just performed runtime CPU feature detection above
@@ -191,7 +191,7 @@ pub fn f1600(state: &mut [u64; PLEN]) {
     }
 }
 
-#[cfg(feature = "simd")]
+#[cfg(keccak_backend = "simd")]
 /// SIMD implementations for Keccak-f1600 sponge function
 pub mod simd {
     use crate::{LaneSize, PLEN, keccak_p};
@@ -413,7 +413,7 @@ mod tests {
         keccak_f::<u64>(state_first, state_second);
     }
 
-    #[cfg(feature = "simd")]
+    #[cfg(keccak_backend = "simd")]
     mod simd {
         use super::keccak_f;
         use core::simd::{u64x2, u64x4, u64x8};