mathieu/os-rust
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

optimize char::to_digit and assert radix is at least 2

Browse source 
approved by t-libs: https://github.com/rust-lang/libs-team/issues/475#issuecomment-2457858458
This commit is contained in:
Jacob Lifshay 2024-11-06 12:09:15 -08:00
parent 116fc31c5c
commit aeffff8ecf
No known key found for this signature in database
1 changed files with 31 additions and 13 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

44
library/core/src/char/methods.rs
View file

@ -301,7 +301,7 @@ impl char {
///
/// # Panics
///
/// Panics if given a radix larger than 36.
/// Panics if given a radix smaller than 2 or larger than 36.
///
/// # Examples
///
@ -319,6 +319,13 @@ impl char {
/// // this panics
/// '1'.is_digit(37);
/// ```
///
/// Passing a small radix, causing a panic:
///
/// ```should_panic
/// // this panics
/// '1'.is_digit(1);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_char_classify", issue = "132241")]
#[inline]
@ -345,7 +352,7 @@ impl char {
///
/// # Panics
///
/// Panics if given a radix larger than 36.
/// Panics if given a radix smaller than 2 or larger than 36.
///
/// # Examples
///
@ -369,24 +376,35 @@ impl char {
/// // this panics
/// let _ = '1'.to_digit(37);
/// ```
/// Passing a small radix, causing a panic:
///
/// ```should_panic
/// // this panics
/// let _ = '1'.to_digit(1);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_char_convert", since = "1.67.0")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn to_digit(self, radix: u32) -> Option<u32> {
// If not a digit, a number greater than radix will be created.
let mut digit = (self as u32).wrapping_sub('0' as u32);
if radix > 10 {
assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
if digit < 10 {
return Some(digit);
}
// Force the 6th bit to be set to ensure ascii is lower case.
digit = (self as u32 | 0b10_0000).wrapping_sub('a' as u32).saturating_add(10);
}
assert!(
radix >= 2 && radix <= 36,
"to_digit: invalid radix -- radix must be in the range 2 to 36 inclusive"
);
// check radix to remove letter handling code when radix is a known constant
let value = if self > '9' && radix > 10 {
// convert ASCII letters to lowercase
let lower = self as u32 | 0x20;
// convert an ASCII letter to the corresponding value,
// non-letters convert to values > 36
lower.wrapping_sub('a' as u32) as u64 + 10
} else {
// convert digit to value, non-digits wrap to values > 36
(self as u32).wrapping_sub('0' as u32) as u64
};
// FIXME(const-hack): once then_some is const fn, use it here
if digit < radix { Some(digit) } else { None }
if value < radix as u64 { Some(value as u32) } else { None }
}
/// Returns an iterator that yields the hexadecimal Unicode escape of a