add aarch64

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/simd/aarch64.rs

@@ -0,0 +1,139 @@
+use core::arch::aarch64::{
+    uint8x16_t, vaddlvq_u8, vandq_u8, vceqq_u8, vcgtq_u8, vdupq_n_u8, vld1q_u8, 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 {
+    vld1q_u8(slice.as_ptr().add(offset) as *const _) // TODO: does this need to be aligned?
+}
+
+#[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);
+
+    // 4080
+    while haystack.len() >= offset + 16 * 255 {
+        let mut counts = vdupq_n_u8(0);
+        for _ in 0..255 {
+            counts = vsubq_u8(
+                counts,
+                vceqq_u8(u8x16_from_offset(haystack, offset), needles),
+            );
+            offset += 16;
+        }
+        count += sum(&counts);
+    }
+
+    // 2048
+    if haystack.len() >= offset + 16 * 128 {
+        let mut counts = vdupq_n_u8(0);
+        for _ in 0..128 {
+            counts = vsubq_u8(
+                counts,
+                vceqq_u8(u8x16_from_offset(haystack, offset), needles),
+            );
+            offset += 16;
+        }
+        count += sum(&counts);
+    }
+
+    // 16
+    let mut counts = vdupq_n_u8(0);
+    for i in 0..(haystack.len() - offset) / 16 {
+        counts = vsubq_u8(
+            counts,
+            vcgtq_u8(u8x16_from_offset(haystack, offset + i * 32), 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);
+
+    count
+}
+
+#[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 * 32)),
+        );
+    }
+    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/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;