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Slight perf improvement on char::to_ascii_lowercase #81837

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Merged
merged 5 commits into from
Feb 23, 2021
Merged

Slight perf improvement on char::to_ascii_lowercase #81837

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f165f49
Slight perf improvement on char::to_ascii_lowercase
gilescope Feb 6, 2021
f30c51a
Pulling out constant.
gilescope Feb 6, 2021
cadcf5e
Unify way to flip 6th bit. (Same assembly generated)
gilescope Feb 8, 2021
daa55ac
Slightly more explicit
gilescope Feb 12, 2021
33d8b04
Move const def nearer usage.
gilescope Feb 14, 2021
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10 changes: 10 additions & 0 deletions library/core/benches/char/methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,3 +35,13 @@ fn bench_to_digit_radix_var(b: &mut Bencher) {
.min()
})
}

#[bench]
fn bench_to_ascii_uppercase(b: &mut Bencher) {
b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_ascii_uppercase()).min())
}

#[bench]
fn bench_to_ascii_lowercase(b: &mut Bencher) {
b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_ascii_lowercase()).min())
}
7 changes: 5 additions & 2 deletions library/core/src/char/methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,9 @@ use crate::unicode::{self, conversions};

use super::*;

/// If 6th bit set ascii is upper case.
const ASCII_CASE_MASK: u8 = 0b10_0000u8;

#[lang = "char"]
impl char {
/// The highest valid code point a `char` can have.
Expand Down Expand Up @@ -1090,7 +1093,7 @@ impl char {
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn to_ascii_uppercase(&self) -> char {
if self.is_ascii() { (*self as u8).to_ascii_uppercase() as char } else { *self }
if self.is_ascii_lowercase() { ((*self as u8) & !ASCII_CASE_MASK) as char } else { *self }
}

/// Makes a copy of the value in its ASCII lower case equivalent.
Expand Down Expand Up @@ -1118,7 +1121,7 @@ impl char {
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn to_ascii_lowercase(&self) -> char {
if self.is_ascii() { (*self as u8).to_ascii_lowercase() as char } else { *self }
if self.is_ascii_uppercase() { ((*self as u8) | ASCII_CASE_MASK) as char } else { *self }
}

/// Checks that two values are an ASCII case-insensitive match.
Expand Down