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Slight perf improvement on char::to_ascii_lowercase
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gilescope committed Feb 6, 2021
1 parent 9a9477f commit f165f49
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Showing 2 changed files with 14 additions and 2 deletions.
10 changes: 10 additions & 0 deletions library/core/benches/char/methods.rs
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())
}
6 changes: 4 additions & 2 deletions library/core/src/char/methods.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1090,7 +1090,8 @@ 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 }
// 6th bit dictates ascii case.
if self.is_ascii_lowercase() { ((*self as u8) & !0b10_0000u8) as char } else { *self }
}

/// Makes a copy of the value in its ASCII lower case equivalent.
Expand Down Expand Up @@ -1118,7 +1119,8 @@ 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 }
// 6th bit dictates ascii case.
if self.is_ascii_uppercase() { ((*self as u8) | 0b10_0000u8) as char } else { *self }
}

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

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