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Benchmark the unaligned case for is_ascii, and add missing SAFETY

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This commit is contained in:
Thom Chiovoloni 2020-07-05 14:51:05 -07:00
parent e1d4db6055
commit 13e380d798
1 changed files with 21 additions and 3 deletions
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24
src/libcore/benches/ascii.rs
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@ -65,6 +65,23 @@ macro_rules! benches {
benches!(@ro mod short_readonly SHORT $($name $arg $body)+);
benches!(@ro mod medium_readonly MEDIUM $($name $arg $body)+);
benches!(@ro mod long_readonly LONG $($name $arg $body)+);
// Add another `MEDIUM` bench, but trim the ends so that we can (try to)
// benchmark a case where the function has to handle misalignment.
mod medium_unaligned {
use super::*;
$(
#[bench]
fn $name(bencher: &mut Bencher) {
bencher.bytes = MEDIUM.len() as u64 - 2;
let mut vec = MEDIUM.as_bytes().to_vec();
bencher.iter(|| {
black_box(&mut vec);
let $arg = black_box(&vec[1..(vec.len() - 1)]);
black_box($body)
})
}
)+
}
};
(@ro mod $mod_name: ident $input: ident $($name: ident $arg: ident $body: block)+) => {
mod $mod_name {
@ -291,10 +308,11 @@ fn is_ascii_align_to_impl(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())
head.iter().all(|b| b.is_ascii())
&& body.iter().all(|w| !contains_nonascii(*w))
&& tail.iter().all(|b| b.is_ascii())
}
#[inline]