Add aarch64 SIMD specialization

.github/workflows/ci.yml

@@ -22,6 +22,7 @@ jobs:
         arch:
           - i686
           - x86_64
+          - aarch64
         features:
           - default
           - runtime-dispatch-simd

src/integer_simd.rs

@@ -13,7 +13,7 @@ unsafe fn usize_load_unchecked(bytes: &[u8], offset: usize) -> usize {
     ptr::copy_nonoverlapping(
         bytes.as_ptr().add(offset),
         &mut output as *mut usize as *mut u8,
-        mem::size_of::<usize>()
+        mem::size_of::<usize>(),
     );
     output
 }
@@ -65,11 +65,17 @@ pub fn chunk_count(haystack: &[u8], needle: u8) -> usize {
         // 8
         let mut counts = 0;
         for i in 0..(haystack.len() - offset) / chunksize {
-            counts += bytewise_equal(usize_load_unchecked(haystack, offset + i * chunksize), needles);
+            counts += bytewise_equal(
+                usize_load_unchecked(haystack, offset + i * chunksize),
+                needles,
+            );
         }
         if haystack.len() % 8 != 0 {
             let mask = usize::from_le(!(!0 >> ((haystack.len() % chunksize) * 8)));
-            counts += bytewise_equal(usize_load_unchecked(haystack, haystack.len() - chunksize), needles) & mask;
+            counts += bytewise_equal(
+                usize_load_unchecked(haystack, haystack.len() - chunksize),
+                needles,
+            ) & mask;
         }
         count += sum_usize(counts);
 
@@ -98,11 +104,15 @@ pub fn chunk_num_chars(utf8_chars: &[u8]) -> usize {
         // 8
         let mut counts = 0;
         for i in 0..(utf8_chars.len() - offset) / chunksize {
-            counts += is_leading_utf8_byte(usize_load_unchecked(utf8_chars, offset + i * chunksize));
+            counts +=
+                is_leading_utf8_byte(usize_load_unchecked(utf8_chars, offset + i * chunksize));
         }
         if utf8_chars.len() % 8 != 0 {
             let mask = usize::from_le(!(!0 >> ((utf8_chars.len() % chunksize) * 8)));
-            counts += is_leading_utf8_byte(usize_load_unchecked(utf8_chars, utf8_chars.len() - chunksize)) & mask;
+            counts += is_leading_utf8_byte(usize_load_unchecked(
+                utf8_chars,
+                utf8_chars.len() - chunksize,
+            )) & mask;
         }
         count += sum_usize(counts);
 

src/lib.rs

@@ -32,7 +32,6 @@
 //! still on small strings.
 
 #![deny(missing_docs)]
-
 #![cfg_attr(not(feature = "runtime-dispatch-simd"), no_std)]
 
 #[cfg(not(feature = "runtime-dispatch-simd"))]
@@ -45,7 +44,11 @@ pub use naive::*;
 mod integer_simd;
 
 #[cfg(any(
-    all(feature = "runtime-dispatch-simd", any(target_arch = "x86", target_arch = "x86_64")),
+    all(
+        feature = "runtime-dispatch-simd",
+        any(target_arch = "x86", target_arch = "x86_64")
+    ),
+    target_arch = "aarch64",
     feature = "generic-simd"
 ))]
 mod simd;
@@ -64,7 +67,9 @@ pub fn count(haystack: &[u8], needle: u8) -> usize {
         #[cfg(all(feature = "runtime-dispatch-simd", target_arch = "x86_64"))]
         {
             if is_x86_feature_detected!("avx2") {
-                unsafe { return simd::x86_avx2::chunk_count(haystack, needle); }
+                unsafe {
+                    return simd::x86_avx2::chunk_count(haystack, needle);
+                }
             }
         }
 
@@ -80,7 +85,15 @@ pub fn count(haystack: &[u8], needle: u8) -> usize {
         ))]
         {
             if is_x86_feature_detected!("sse2") {
-                unsafe { return simd::x86_sse2::chunk_count(haystack, needle); }
+                unsafe {
+                    return simd::x86_sse2::chunk_count(haystack, needle);
+                }
+            }
+        }
+        #[cfg(all(target_arch = "aarch64", not(feature = "generic_simd")))]
+        {
+            unsafe {
+                return simd::aarch64::chunk_count(haystack, needle);
             }
         }
     }
@@ -109,7 +122,9 @@ pub fn num_chars(utf8_chars: &[u8]) -> usize {
         #[cfg(all(feature = "runtime-dispatch-simd", target_arch = "x86_64"))]
         {
             if is_x86_feature_detected!("avx2") {
-                unsafe { return simd::x86_avx2::chunk_num_chars(utf8_chars); }
+                unsafe {
+                    return simd::x86_avx2::chunk_num_chars(utf8_chars);
+                }
             }
         }
 
@@ -125,7 +140,15 @@ pub fn num_chars(utf8_chars: &[u8]) -> usize {
         ))]
         {
             if is_x86_feature_detected!("sse2") {
-                unsafe { return simd::x86_sse2::chunk_num_chars(utf8_chars); }
+                unsafe {
+                    return simd::x86_sse2::chunk_num_chars(utf8_chars);
+                }
+            }
+        }
+        #[cfg(all(target_arch = "aarch64", not(feature = "generic_simd")))]
+        {
+            unsafe {
+                return simd::aarch64::chunk_num_chars(utf8_chars);
             }
         }
     }

src/naive.rs

@@ -22,7 +22,9 @@ pub fn naive_count_32(haystack: &[u8], needle: u8) -> usize {
 /// assert_eq!(number_of_spaces, 6);
 /// ```
 pub fn naive_count(utf8_chars: &[u8], needle: u8) -> usize {
-    utf8_chars.iter().fold(0, |n, c| n + (*c == needle) as usize)
+    utf8_chars
+        .iter()
+        .fold(0, |n, c| n + (*c == needle) as usize)
 }
 
 /// Count the number of UTF-8 encoded Unicode codepoints in a slice of bytes, simple
@@ -38,5 +40,8 @@ pub fn naive_count(utf8_chars: &[u8], needle: u8) -> usize {
 /// assert_eq!(char_count, 4);
 /// ```
 pub fn naive_num_chars(utf8_chars: &[u8]) -> usize {
-    utf8_chars.iter().filter(|&&byte| (byte >> 6) != 0b10).count()
+    utf8_chars
+        .iter()
+        .filter(|&&byte| (byte >> 6) != 0b10)
+        .count()
 }

src/simd/aarch64.rs

@@ -0,0 +1,157 @@
+use core::arch::aarch64::{
+    uint8x16_t, uint8x16x4_t, vaddlvq_u8, vandq_u8, vceqq_u8, vdupq_n_u8, vld1q_u8, vld1q_u8_x4,
+    vmvnq_u8, vsubq_u8,
+};
+
+const MASK: [u8; 32] = [
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+    255, 255, 255, 255, 255, 255, 255,
+];
+
+#[target_feature(enable = "neon")]
+unsafe fn u8x16_from_offset(slice: &[u8], offset: usize) -> uint8x16_t {
+    debug_assert!(
+        offset + 16 <= slice.len(),
+        "{} + 16 ≥ {}",
+        offset,
+        slice.len()
+    );
+    vld1q_u8(slice.as_ptr().add(offset) as *const _) // TODO: does this need to be aligned?
+}
+
+#[target_feature(enable = "neon")]
+unsafe fn u8x16_x4_from_offset(slice: &[u8], offset: usize) -> uint8x16x4_t {
+    debug_assert!(
+        offset + 64 <= slice.len(),
+        "{} + 64 ≥ {}",
+        offset,
+        slice.len()
+    );
+    vld1q_u8_x4(slice.as_ptr().add(offset) as *const _)
+}
+
+#[target_feature(enable = "neon")]
+unsafe fn sum(u8s: uint8x16_t) -> usize {
+    vaddlvq_u8(u8s) as usize
+}
+
+#[target_feature(enable = "neon")]
+pub unsafe fn chunk_count(haystack: &[u8], needle: u8) -> usize {
+    assert!(haystack.len() >= 16);
+
+    let mut offset = 0;
+    let mut count = 0;
+
+    let needles = vdupq_n_u8(needle);
+
+    // 16320
+    while haystack.len() >= offset + 64 * 255 {
+        let (mut count1, mut count2, mut count3, mut count4) =
+            (vdupq_n_u8(0), vdupq_n_u8(0), vdupq_n_u8(0), vdupq_n_u8(0));
+        for _ in 0..255 {
+            let uint8x16x4_t(h1, h2, h3, h4) = u8x16_x4_from_offset(haystack, offset);
+            count1 = vsubq_u8(count1, vceqq_u8(h1, needles));
+            count2 = vsubq_u8(count2, vceqq_u8(h2, needles));
+            count3 = vsubq_u8(count3, vceqq_u8(h3, needles));
+            count4 = vsubq_u8(count4, vceqq_u8(h4, needles));
+            offset += 64;
+        }
+        count += sum(count1) + sum(count2) + sum(count3) + sum(count4);
+    }
+
+    // 64
+    let (mut count1, mut count2, mut count3, mut count4) =
+        (vdupq_n_u8(0), vdupq_n_u8(0), vdupq_n_u8(0), vdupq_n_u8(0));
+    for _ in 0..(haystack.len() - offset) / 64 {
+        let uint8x16x4_t(h1, h2, h3, h4) = u8x16_x4_from_offset(haystack, offset);
+        count1 = vsubq_u8(count1, vceqq_u8(h1, needles));
+        count2 = vsubq_u8(count2, vceqq_u8(h2, needles));
+        count3 = vsubq_u8(count3, vceqq_u8(h3, needles));
+        count4 = vsubq_u8(count4, vceqq_u8(h4, needles));
+        offset += 64;
+    }
+    count += sum(count1) + sum(count2) + sum(count3) + sum(count4);
+
+    let mut counts = vdupq_n_u8(0);
+    // 16
+    for i in 0..(haystack.len() - offset) / 16 {
+        counts = vsubq_u8(
+            counts,
+            vceqq_u8(u8x16_from_offset(haystack, offset + i * 16), needles),
+        );
+    }
+    if haystack.len() % 16 != 0 {
+        counts = vsubq_u8(
+            counts,
+            vandq_u8(
+                vceqq_u8(u8x16_from_offset(haystack, haystack.len() - 16), needles),
+                u8x16_from_offset(&MASK, haystack.len() % 16),
+            ),
+        );
+    }
+    count + sum(counts)
+}
+
+#[target_feature(enable = "neon")]
+unsafe fn is_leading_utf8_byte(u8s: uint8x16_t) -> uint8x16_t {
+    vmvnq_u8(vceqq_u8(
+        vandq_u8(u8s, vdupq_n_u8(0b1100_0000)),
+        vdupq_n_u8(0b1000_0000),
+    ))
+}
+
+#[target_feature(enable = "neon")]
+pub unsafe fn chunk_num_chars(utf8_chars: &[u8]) -> usize {
+    assert!(utf8_chars.len() >= 16);
+
+    let mut offset = 0;
+    let mut count = 0;
+
+    // 4080
+    while utf8_chars.len() >= offset + 16 * 255 {
+        let mut counts = vdupq_n_u8(0);
+
+        for _ in 0..255 {
+            counts = vsubq_u8(
+                counts,
+                is_leading_utf8_byte(u8x16_from_offset(utf8_chars, offset)),
+            );
+            offset += 16;
+        }
+        count += sum(counts);
+    }
+
+    // 2048
+    if utf8_chars.len() >= offset + 16 * 128 {
+        let mut counts = vdupq_n_u8(0);
+        for _ in 0..128 {
+            counts = vsubq_u8(
+                counts,
+                is_leading_utf8_byte(u8x16_from_offset(utf8_chars, offset)),
+            );
+            offset += 16;
+        }
+        count += sum(counts);
+    }
+
+    // 16
+    let mut counts = vdupq_n_u8(0);
+    for i in 0..(utf8_chars.len() - offset) / 16 {
+        counts = vsubq_u8(
+            counts,
+            is_leading_utf8_byte(u8x16_from_offset(utf8_chars, offset + i * 16)),
+        );
+    }
+    if utf8_chars.len() % 16 != 0 {
+        counts = vsubq_u8(
+            counts,
+            vandq_u8(
+                is_leading_utf8_byte(u8x16_from_offset(utf8_chars, utf8_chars.len() - 16)),
+                u8x16_from_offset(&MASK, utf8_chars.len() % 16),
+            ),
+        );
+    }
+    count += sum(counts);
+
+    count
+}

src/simd/generic.rs

@@ -8,10 +8,9 @@ use std::mem;
 use self::packed_simd::{u8x32, u8x64, FromCast};
 
 const MASK: [u8; 64] = [
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
-    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 ];
 
 unsafe fn u8x64_from_offset(slice: &[u8], offset: usize) -> u8x64 {
@@ -66,15 +65,17 @@ pub fn chunk_count(haystack: &[u8], needle: u8) -> usize {
         // 32
         let mut counts = u8x32::splat(0);
         for i in 0..(haystack.len() - offset) / 32 {
-            counts -= u8x32::from_cast(u8x32_from_offset(haystack, offset + i * 32).eq(needles_x32));
+            counts -=
+                u8x32::from_cast(u8x32_from_offset(haystack, offset + i * 32).eq(needles_x32));
         }
         count += sum_x32(&counts);
 
         // Straggler; need to reset counts because prior loop can run 255 times
         counts = u8x32::splat(0);
         if haystack.len() % 32 != 0 {
-            counts -= u8x32::from_cast(u8x32_from_offset(haystack, haystack.len() - 32).eq(needles_x32)) &
-                      u8x32_from_offset(&MASK, haystack.len() % 32);
+            counts -=
+                u8x32::from_cast(u8x32_from_offset(haystack, haystack.len() - 32).eq(needles_x32))
+                    & u8x32_from_offset(&MASK, haystack.len() % 32);
         }
         count += sum_x32(&counts);
 
@@ -127,8 +128,9 @@ pub fn chunk_num_chars(utf8_chars: &[u8]) -> usize {
         // Straggler; need to reset counts because prior loop can run 255 times
         counts = u8x32::splat(0);
         if utf8_chars.len() % 32 != 0 {
-            counts -= is_leading_utf8_byte_x32(u8x32_from_offset(utf8_chars, utf8_chars.len() - 32)) &
-                      u8x32_from_offset(&MASK, utf8_chars.len() % 32);
+            counts -=
+                is_leading_utf8_byte_x32(u8x32_from_offset(utf8_chars, utf8_chars.len() - 32))
+                    & u8x32_from_offset(&MASK, utf8_chars.len() % 32);
         }
         count += sum_x32(&counts);
 

src/simd/mod.rs

@@ -15,3 +15,7 @@ pub mod x86_sse2;
 // Runtime feature detection is not available with no_std.
 #[cfg(all(feature = "runtime-dispatch-simd", target_arch = "x86_64"))]
 pub mod x86_avx2;
+
+/// Modern ARM machines are also quite capable thanks to NEON
+#[cfg(target_arch = "aarch64")]
+pub mod aarch64;