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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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Slightly more explicit
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@gilescope
gilescope committed Feb 12, 2021
commit daa55acdb0bd174bb0bca1f88d5920289808a8f1
14 changes: 11 additions & 3 deletions library/core/src/char/methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@
use crate::slice;
use crate::str::from_utf8_unchecked_mut;
use crate::unicode::printable::is_printable;
use crate::unicode::{self, conversions, ASCII_CASE_MASK};
use crate::unicode::{self, conversions};

use super::*;

Expand Down Expand Up @@ -1090,7 +1090,11 @@ impl char {
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn to_ascii_uppercase(&self) -> char {
if self.is_ascii_lowercase() { ((*self as u8) & !ASCII_CASE_MASK) as char } else { *self }
if self.is_ascii_lowercase() {
(*self as u8).ascii_change_case_unchecked() as char
} else {
*self
}
}

/// Makes a copy of the value in its ASCII lower case equivalent.
Expand Down Expand Up @@ -1118,7 +1122,11 @@ impl char {
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn to_ascii_lowercase(&self) -> char {
if self.is_ascii_uppercase() { ((*self as u8) | ASCII_CASE_MASK) as char } else { *self }
if self.is_ascii_uppercase() {
(*self as u8).ascii_change_case_unchecked() as char
} else {
*self
}
}

/// Checks that two values are an ASCII case-insensitive match.
Expand Down
10 changes: 9 additions & 1 deletion library/core/src/num/mod.rs
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Expand Up @@ -5,7 +5,9 @@
use crate::intrinsics;
use crate::mem;
use crate::str::FromStr;
use crate::unicode::ASCII_CASE_MASK;

/// If 6th bit set ascii is upper case.
const ASCII_CASE_MASK: u8 = 0b0010_0000;

// Used because the `?` operator is not allowed in a const context.
macro_rules! try_opt {
Expand Down Expand Up @@ -222,6 +224,12 @@ impl u8 {
*self | (self.is_ascii_uppercase() as u8 * ASCII_CASE_MASK)
}

/// Assumes self is ascii
#[inline]
pub(crate) fn ascii_change_case_unchecked(&self) -> u8 {
*self ^ ASCII_CASE_MASK
}

/// Checks that two values are an ASCII case-insensitive match.
///
/// This is equivalent to `to_ascii_lowercase(a) == to_ascii_lowercase(b)`.
Expand Down
3 changes: 0 additions & 3 deletions library/core/src/unicode/mod.rs
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Expand Up @@ -17,9 +17,6 @@ mod unicode_data;
#[stable(feature = "unicode_version", since = "1.45.0")]
pub const UNICODE_VERSION: (u8, u8, u8) = unicode_data::UNICODE_VERSION;

/// If 6th bit set ascii is upper case.
pub(crate) const ASCII_CASE_MASK: u8 = 0b0010_0000;

// For use in liballoc, not re-exported in libstd.
pub use unicode_data::{
case_ignorable::lookup as Case_Ignorable, cased::lookup as Cased, conversions,
Expand Down