Slightly more explicit

library/core/src/char/methods.rs

@@ -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::*;
 
@@ -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.
@@ -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.

library/core/src/num/mod.rs

@@ -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 {
@@ -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)`.

library/core/src/unicode/mod.rs

@@ -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,