Update comment for consistent context logic.

Author: ksw2000

library/core/src/num/mod.rs

@@ -549,7 +549,7 @@ impl u8 {
     #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
     #[inline]
     pub const fn to_ascii_uppercase(&self) -> u8 {
-        // Toggle the fifth bit if this is a lowercase letter
+        // Toggle the 6th bit if this is a lowercase letter
         *self ^ ((self.is_ascii_lowercase() as u8) * ASCII_CASE_MASK)
     }
 
@@ -574,7 +574,7 @@ impl u8 {
     #[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.52.0")]
     #[inline]
     pub const fn to_ascii_lowercase(&self) -> u8 {
-        // Set the fifth bit if this is an uppercase letter
+        // Set the 6th bit if this is an uppercase letter
         *self | (self.is_ascii_uppercase() as u8 * ASCII_CASE_MASK)
     }