1 files changed, 82 insertions, 0 deletions
diff --git a/library/core/benches/ascii/is_ascii.rs b/library/core/benches/ascii/is_ascii.rs
new file mode 100644
index 000000000..a42a1dcfe
--- /dev/null
+++ b/library/core/benches/ascii/is_ascii.rs
@@ -0,0 +1,82 @@
+use super::{LONG, MEDIUM, SHORT};
+use test::black_box;
+use test::Bencher;
+
+macro_rules! benches {
+    ($( fn $name: ident($arg: ident: &[u8]) $body: block )+) => {
+        benches!(mod short SHORT[..] $($name $arg $body)+);
+        benches!(mod medium MEDIUM[..] $($name $arg $body)+);
+        benches!(mod long LONG[..] $($name $arg $body)+);
+        // Ensure we benchmark cases where the functions are called with strings
+        // that are not perfectly aligned or have a length which is not a
+        // multiple of size_of::<usize>() (or both)
+        benches!(mod unaligned_head MEDIUM[1..] $($name $arg $body)+);
+        benches!(mod unaligned_tail MEDIUM[..(MEDIUM.len() - 1)] $($name $arg $body)+);
+        benches!(mod unaligned_both MEDIUM[1..(MEDIUM.len() - 1)] $($name $arg $body)+);
+    };
+
+    (mod $mod_name: ident $input: ident [$range: expr] $($name: ident $arg: ident $body: block)+) => {
+        mod $mod_name {
+            use super::*;
+            $(
+                #[bench]
+                fn $name(bencher: &mut Bencher) {
+                    bencher.bytes = $input[$range].len() as u64;
+                    let mut vec = $input.as_bytes().to_vec();
+                    bencher.iter(|| {
+                        let $arg: &[u8] = &black_box(&mut vec)[$range];
+                        black_box($body)
+                    })
+                }
+            )+
+        }
+    };
+}
+
+benches! {
+    fn case00_libcore(bytes: &[u8]) {
+        bytes.is_ascii()
+    }
+
+    fn case01_iter_all(bytes: &[u8]) {
+        bytes.iter().all(|b| b.is_ascii())
+    }
+
+    fn case02_align_to(bytes: &[u8]) {
+        is_ascii_align_to(bytes)
+    }
+
+    fn case03_align_to_unrolled(bytes: &[u8]) {
+        is_ascii_align_to_unrolled(bytes)
+    }
+}
+
+// These are separate since it's easier to debug errors if they don't go through
+// macro expansion first.
+fn is_ascii_align_to(bytes: &[u8]) -> bool {
+    if bytes.len() < core::mem::size_of::<usize>() {
+        return bytes.iter().all(|b| b.is_ascii());
+    }
+    // SAFETY: transmuting a sequence of `u8` to `usize` is always fine
+    let (head, body, tail) = unsafe { bytes.align_to::<usize>() };
+    head.iter().all(|b| b.is_ascii())
+        && body.iter().all(|w| !contains_nonascii(*w))
+        && tail.iter().all(|b| b.is_ascii())
+}
+
+fn is_ascii_align_to_unrolled(bytes: &[u8]) -> bool {
+    if bytes.len() < core::mem::size_of::<usize>() {
+        return bytes.iter().all(|b| b.is_ascii());
+    }
+    // SAFETY: transmuting a sequence of `u8` to `[usize; 2]` is always fine
+    let (head, body, tail) = unsafe { bytes.align_to::<[usize; 2]>() };
+    head.iter().all(|b| b.is_ascii())
+        && body.iter().all(|w| !contains_nonascii(w[0] | w[1]))
+        && tail.iter().all(|b| b.is_ascii())
+}
+
+#[inline]
+fn contains_nonascii(v: usize) -> bool {
+    const NONASCII_MASK: usize = usize::from_ne_bytes([0x80; core::mem::size_of::<usize>()]);
+    (NONASCII_MASK & v) != 0
+}