Add support for AArch64 CRC32 instructions

Author: valpackett

Cargo.toml

@@ -22,6 +22,7 @@ rand = "0.4"
 [features]
 default = ["std"]
 std = []
+nightly = []
 
 [[bench]]
 name = "bench"

README.md

@@ -27,6 +27,7 @@ This crate contains multiple CRC32 implementations:
 
 - A fast baseline implementation which processes up to 16 bytes per iteration
 - An optimized implementation for modern `x86` using `sse` and `pclmulqdq` instructions
+- An optimized implementation for `aarch64` using `crc32` instructions
 
 Calling the `Hasher::new` constructor at runtime will perform a feature detection to select the most
 optimal implementation for the current CPU feature set.

src/lib.rs

@@ -19,6 +19,7 @@
 //! optimal implementation for the current CPU feature set.
 
 #![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(all(feature = "nightly", target_arch = "aarch64"), feature(stdsimd, aarch64_target_feature))]
 
 #[deny(missing_docs)]
 #[cfg(test)]

src/specialized/aarch64.rs

@@ -0,0 +1,85 @@
+use std::arch::aarch64 as arch;
+
+#[derive(Clone)]
+pub struct State {
+    state: u32,
+}
+
+impl State {
+    pub fn new() -> Option<Self> {
+        if is_aarch64_feature_detected!("crc") {
+            // SAFETY: The conditions above ensure that all
+            //         required instructions are supported by the CPU.
+            Some(Self { state: 0 })
+        } else {
+            None
+        }
+    }
+
+    pub fn update(&mut self, buf: &[u8]) {
+        // SAFETY: The `State::new` constructor ensures that all
+        //         required instructions are supported by the CPU.
+        self.state = unsafe { calculate(self.state, buf) }
+    }
+
+    pub fn finalize(self) -> u32 {
+        self.state
+    }
+
+    pub fn reset(&mut self) {
+        self.state = 0;
+    }
+
+    pub fn combine(&mut self, other: u32, amount: u64) {
+        self.state = ::combine::combine(self.state, other, amount);
+    }
+}
+
+// target_feature is necessary to allow rustc to inline the crc32* wrappers
+#[target_feature(enable = "crc")]
+pub unsafe fn calculate(crc: u32, data: &[u8]) -> u32 {
+    let mut c32 = !crc;
+    let (pre_quad, quads, post_quad) = data.align_to::<u64>();
+
+    c32 = pre_quad.iter().fold(c32, |acc, &b| arch::__crc32b(acc, b));
+
+    // unrolling increases performance by a lot
+    let mut quad_iter = quads.chunks_exact(8);
+    for chunk in &mut quad_iter {
+        c32 = arch::__crc32d(c32, chunk[0]);
+        c32 = arch::__crc32d(c32, chunk[1]);
+        c32 = arch::__crc32d(c32, chunk[2]);
+        c32 = arch::__crc32d(c32, chunk[3]);
+        c32 = arch::__crc32d(c32, chunk[4]);
+        c32 = arch::__crc32d(c32, chunk[5]);
+        c32 = arch::__crc32d(c32, chunk[6]);
+        c32 = arch::__crc32d(c32, chunk[7]);
+    }
+    c32 = quad_iter.remainder().iter().fold(c32, |acc, &q| arch::__crc32d(acc, q));
+
+    c32 = post_quad.iter().fold(c32, |acc, &b| arch::__crc32b(acc, b));
+
+    !c32
+}
+
+#[cfg(test)]
+mod test {
+    quickcheck! {
+        fn check_against_baseline(chunks: Vec<(Vec<u8>, usize)>) -> bool {
+            let mut baseline = super::super::super::baseline::State::new();
+            let mut aarch64 = super::State::new().expect("not supported");
+            for (chunk, mut offset) in chunks {
+                // simulate random alignments by offsetting the slice by up to 15 bytes
+                offset = offset & 0xF;
+                if chunk.len() <= offset {
+                    baseline.update(&chunk);
+                    aarch64.update(&chunk);
+                } else {
+                    baseline.update(&chunk[offset..]);
+                    aarch64.update(&chunk[offset..]);
+                }
+            }
+            aarch64.finalize() == baseline.finalize()
+        }
+    }
+}

src/specialized/mod.rs

@@ -5,6 +5,9 @@ cfg_if! {
     ))] {
         mod pclmulqdq;
         pub use self::pclmulqdq::State;
+    } else if #[cfg(all(feature = "nightly", target_arch = "aarch64"))] {
+        mod aarch64;
+        pub use self::aarch64::State;
     } else {
         #[derive(Clone)]
         pub enum State {}