Remove build-time check for stdsimd feature (#183)

* Remove build-time check for `stdsimd` feature This is blocking rust-lang/rust#117372, which replaces `stdsimd` with more fine-grained features. However the auto-detection in aHash breaks when bootstrapping Rust because it detects the `stdsimd` feature on the old toolchain which is not present on the newly build libcore. This PR removes the build-time detection of the `stdsimd` feature and instead just uses the ARM AES intrinsics directly since they are now stable, but only on AArch64. * Add nightly-arm-aes Cargo feature
tkaitchuck · Nov 10, 2023 · b583310 · t-nelson · Jan 1, 2024 · b583310
1 parent 7fbcf0f
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diff --git a/Cargo.toml b/Cargo.toml
@@ -43,6 +43,9 @@ no-rng = []
 # in case this is being used on an architecture lacking core::sync::atomic::AtomicUsize and friends
 atomic-polyfill = [ "dep:atomic-polyfill", "once_cell/atomic-polyfill"]
 
+# Nightly-only support for AES intrinsics on 32-bit ARM
+nightly-arm-aes = []
+
 [[bench]]
 name = "ahash"
 path = "tests/bench.rs"

diff --git a/README.md b/README.md
@@ -57,6 +57,7 @@ The aHash package has the following flags:
 This is done using the [getrandom](https://github.com/rust-random/getrandom) crate.
 * `compile-time-rng`: For OS targets without access to a random number generator, `compile-time-rng` provides an alternative.
 If `getrandom` is unavailable and `compile-time-rng` is enabled, aHash will generate random numbers at compile time and embed them in the binary.
+* `nightly-arm-aes`: To use AES instructions on 32-bit ARM, which requires nightly. This is not needed on AArch64.
 This allows for DOS resistance even if there is no random number generator available at runtime (assuming the compiled binary is not public).
 This makes the binary non-deterministic. (If non-determinism is a problem see [constrandom's documentation](https://github.com/tkaitchuck/constrandom#deterministic-builds))
 

diff --git a/build.rs b/build.rs
@@ -7,9 +7,6 @@ fn main() {
     if let Some(true) = version_check::supports_feature("specialize") {
         println!("cargo:rustc-cfg=feature=\"specialize\"");
     }
-    if let Some(true) = version_check::supports_feature("stdsimd") {
-        println!("cargo:rustc-cfg=feature=\"stdsimd\"");
-    }
     let arch = env::var("CARGO_CFG_TARGET_ARCH").expect("CARGO_CFG_TARGET_ARCH was not set");
     if arch.eq_ignore_ascii_case("x86_64")
         || arch.eq_ignore_ascii_case("aarch64")

diff --git a/src/hash_quality_test.rs b/src/hash_quality_test.rs
@@ -1,5 +1,5 @@
 use core::hash::{Hash, Hasher};
-use std::collections::{HashMap};
+use std::collections::HashMap;
 
 fn assert_sufficiently_different(a: u64, b: u64, tolerance: i32) {
     let (same_byte_count, same_nibble_count) = count_same_bytes_and_nibbles(a, b);
@@ -64,8 +64,7 @@ fn gen_combinations(options: &[u32; 11], depth: u32, so_far: Vec<u32>, combinati
 
 fn test_no_full_collisions<T: Hasher>(gen_hash: impl Fn() -> T) {
     let options: [u32; 11] = [
-        0x00000000, 0x10000000, 0x20000000, 0x40000000, 0x80000000, 0xF0000000,
-        1, 2, 4, 8, 15
+        0x00000000, 0x10000000, 0x20000000, 0x40000000, 0x80000000, 0xF0000000, 1, 2, 4, 8, 15,
     ];
     let mut combinations = Vec::new();
     gen_combinations(&options, 7, Vec::new(), &mut combinations);
@@ -342,9 +341,12 @@ fn test_sparse<T: Hasher>(hasher: impl Fn() -> T) {
     let mut buf = [0u8; 256];
     let mut hashes = HashMap::new();
     for idx_1 in 0..256 {
-        for idx_2 in idx_1+1..256 {
+        for idx_2 in idx_1 + 1..256 {
             for value_1 in [1, 2, 4, 8, 16, 32, 64, 128] {
-                for value_2 in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 17, 18, 20, 24, 31, 32, 33, 48, 64, 96, 127, 128, 129, 192, 254, 255] {
+                for value_2 in [
+                    1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 17, 18, 20, 24, 31, 32, 33, 48, 64, 96, 127, 128, 129,
+                    192, 254, 255,
+                ] {
                     buf[idx_1] = value_1;
                     buf[idx_2] = value_2;
                     let hash_value = hash_with(&buf, &mut hasher());
@@ -437,12 +439,8 @@ mod fallback_tests {
 ///Basic sanity tests of the cypto properties of aHash.
 #[cfg(any(
     all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes", not(miri)),
-    all(
-        any(target_arch = "arm", target_arch = "aarch64"),
-        any(target_feature = "aes", target_feature = "crypto"),
-        not(miri),
-        feature = "stdsimd"
-    )
+    all(target_arch = "aarch64", target_feature = "aes", not(miri)),
+    all(feature = "nightly-arm-aes", target_arch = "arm", target_feature = "aes", not(miri)),
 ))]
 #[cfg(test)]
 mod aes_tests {

diff --git a/src/lib.rs b/src/lib.rs
@@ -13,7 +13,10 @@
 //! But this also means that different computers or computers using different versions of ahash may observe different
 //! hash values for the same input.
 #![cfg_attr(
-    all(feature = "std", any(feature = "compile-time-rng", feature = "runtime-rng", feature = "no-rng")),
+    all(
+        feature = "std",
+        any(feature = "compile-time-rng", feature = "runtime-rng", feature = "no-rng")
+    ),
     doc = r##"
 # Basic Usage
 AHash provides an implementation of the [Hasher] trait.
@@ -95,8 +98,7 @@ Note the import of [HashMapExt]. This is needed for the constructor.
 #![allow(clippy::pedantic, clippy::cast_lossless, clippy::unreadable_literal)]
 #![cfg_attr(all(not(test), not(feature = "std")), no_std)]
 #![cfg_attr(feature = "specialize", feature(min_specialization))]
-#![cfg_attr(feature = "specialize", feature(build_hasher_simple_hash_one))]
-#![cfg_attr(feature = "stdsimd", feature(stdsimd))]
+#![cfg_attr(feature = "nightly-arm-aes", feature(stdarch_arm_neon_intrinsics))]
 
 #[macro_use]
 mod convert;
@@ -106,11 +108,9 @@ mod fallback_hash;
 cfg_if::cfg_if! {
     if #[cfg(any(
             all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes", not(miri)),
-            all(any(target_arch = "arm", target_arch = "aarch64"),
-                any(target_feature = "aes", target_feature = "crypto"),
-                not(miri),
-                feature = "stdsimd")
-            ))] {
+            all(target_arch = "aarch64", target_feature = "aes", not(miri)),
+            all(feature = "nightly-arm-aes", target_arch = "arm", target_feature = "aes", not(miri)),
+        ))] {
         mod aes_hash;
         pub use crate::aes_hash::AHasher;
     } else {

diff --git a/src/operations.rs b/src/operations.rs
@@ -110,11 +110,9 @@ pub(crate) fn aesenc(value: u128, xor: u128) -> u128 {
     }
 }
 
-#[cfg(all(
-    any(target_arch = "arm", target_arch = "aarch64"),
-    any(target_feature = "aes", target_feature = "crypto"),
-    not(miri),
-    feature = "stdsimd"
+#[cfg(any(
+    all(target_arch = "aarch64", target_feature = "aes", not(miri)),
+    all(feature = "nightly-arm-aes", target_arch = "arm", target_feature = "aes", not(miri)),
 ))]
 #[allow(unused)]
 #[inline(always)]
@@ -142,11 +140,9 @@ pub(crate) fn aesdec(value: u128, xor: u128) -> u128 {
     }
 }
 
-#[cfg(all(
-    any(target_arch = "arm", target_arch = "aarch64"),
-    any(target_feature = "aes", target_feature = "crypto"),
-    not(miri),
-    feature = "stdsimd"
+#[cfg(any(
+    all(target_arch = "aarch64", target_feature = "aes", not(miri)),
+    all(feature = "nightly-arm-aes", target_arch = "arm", target_feature = "aes", not(miri)),
 ))]
 #[allow(unused)]
 #[inline(always)]

diff --git a/src/random_state.rs b/src/random_state.rs
@@ -2,7 +2,8 @@ use core::hash::Hash;
 cfg_if::cfg_if! {
     if #[cfg(any(
         all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes", not(miri)),
-         all(any(target_arch = "arm", target_arch = "aarch64"), any(target_feature = "aes", target_feature = "crypto"), not(miri), feature = "stdsimd")
+        all(target_arch = "aarch64", target_feature = "aes", not(miri)),
+        all(feature = "nightly-arm-aes", target_arch = "arm", target_feature = "aes", not(miri)),
     ))] {
         use crate::aes_hash::*;
     } else {
@@ -230,7 +231,6 @@ impl fmt::Debug for RandomState {
 }
 
 impl RandomState {
-
     /// Create a new `RandomState` `BuildHasher` using random keys.
     ///
     /// Each instance will have a unique set of keys derived from [RandomSource].
@@ -317,8 +317,8 @@ impl RandomState {
     /// Calculates the hash of a single value. This provides a more convenient (and faster) way to obtain a hash:
     /// For example:
     #[cfg_attr(
-    feature = "std",
-    doc = r##" # Examples
+        feature = "std",
+        doc = r##" # Examples
 ```
     use std::hash::BuildHasher;
     use ahash::RandomState;
@@ -330,8 +330,8 @@ impl RandomState {
     )]
     /// This is similar to:
     #[cfg_attr(
-    feature = "std",
-    doc = r##" # Examples
+        feature = "std",
+        doc = r##" # Examples
 ```
     use std::hash::{BuildHasher, Hash, Hasher};
     use ahash::RandomState;
@@ -419,12 +419,11 @@ impl BuildHasher for RandomState {
         AHasher::from_random_state(self)
     }
 
-
     /// Calculates the hash of a single value. This provides a more convenient (and faster) way to obtain a hash:
     /// For example:
     #[cfg_attr(
-    feature = "std",
-    doc = r##" # Examples
+        feature = "std",
+        doc = r##" # Examples
 ```
     use std::hash::BuildHasher;
     use ahash::RandomState;
@@ -436,8 +435,8 @@ impl BuildHasher for RandomState {
     )]
     /// This is similar to:
     #[cfg_attr(
-    feature = "std",
-    doc = r##" # Examples
+        feature = "std",
+        doc = r##" # Examples
 ```
     use std::hash::{BuildHasher, Hash, Hasher};
     use ahash::RandomState;

diff --git a/tests/bench.rs b/tests/bench.rs
@@ -14,11 +14,12 @@ const AHASH_IMPL: &str = if cfg!(any(
         target_feature = "aes",
         not(miri),
     ),
+    all(target_arch = "aarch64", target_feature = "aes", not(miri)),
     all(
-        any(target_arch = "arm", target_arch = "aarch64"),
-        any(target_feature = "aes", target_feature = "crypto"),
-        not(miri),
-        feature = "stdsimd",
+        feature = "nightly-arm-aes",
+        target_arch = "arm",
+        target_feature = "aes",
+        not(miri)
     ),
 )) {
     "aeshash"