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Auto merge of rust-lang#122616 - Jules-Bertholet:casemappingiter-layo…
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…ut, r=Nilstrieb

Optimize `core::char::CaseMappingIter`

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`@rustbot` label T-libs A-layout C-optimization
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@bors
bors committed Mar 29, 2024
2 parents 760e567 + 2f1ab2c commit 1c19595
Showing 1 changed file with 181 additions and 128 deletions.
309 changes: 181 additions & 128 deletions library/core/src/char/mod.rs
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Expand Up @@ -42,7 +42,7 @@ use crate::ascii;
use crate::error::Error;
use crate::escape;
use crate::fmt::{self, Write};
use crate::iter::FusedIterator;
use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
use crate::num::NonZero;

pub(crate) use self::methods::EscapeDebugExtArgs;
Expand Down Expand Up @@ -373,176 +373,229 @@ impl fmt::Display for EscapeDebug {
}
}

/// Returns an iterator that yields the lowercase equivalent of a `char`.
///
/// This `struct` is created by the [`to_lowercase`] method on [`char`]. See
/// its documentation for more.
///
/// [`to_lowercase`]: char::to_lowercase
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug, Clone)]
pub struct ToLowercase(CaseMappingIter);
macro_rules! casemappingiter_impls {
($(#[$attr:meta])* $ITER_NAME:ident) => {
$(#[$attr])*
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug, Clone)]
pub struct $ITER_NAME(CaseMappingIter);

#[stable(feature = "rust1", since = "1.0.0")]
impl Iterator for $ITER_NAME {
type Item = char;
fn next(&mut self) -> Option<char> {
self.0.next()
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Iterator for ToLowercase {
type Item = char;
fn next(&mut self) -> Option<char> {
self.0.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.0.size_hint()
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.0.size_hint()
}

#[stable(feature = "case_mapping_double_ended", since = "1.59.0")]
impl DoubleEndedIterator for ToLowercase {
fn next_back(&mut self) -> Option<char> {
self.0.next_back()
}
}
fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.0.fold(init, fold)
}

#[stable(feature = "fused", since = "1.26.0")]
impl FusedIterator for ToLowercase {}
fn count(self) -> usize {
self.0.count()
}

#[stable(feature = "exact_size_case_mapping_iter", since = "1.35.0")]
impl ExactSizeIterator for ToLowercase {}
fn last(self) -> Option<Self::Item> {
self.0.last()
}

/// Returns an iterator that yields the uppercase equivalent of a `char`.
///
/// This `struct` is created by the [`to_uppercase`] method on [`char`]. See
/// its documentation for more.
///
/// [`to_uppercase`]: char::to_uppercase
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug, Clone)]
pub struct ToUppercase(CaseMappingIter);
fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
self.0.advance_by(n)
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Iterator for ToUppercase {
type Item = char;
fn next(&mut self) -> Option<char> {
self.0.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.0.size_hint()
}
}
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
// SAFETY: just forwarding requirements to caller
unsafe { self.0.__iterator_get_unchecked(idx) }
}
}

#[stable(feature = "case_mapping_double_ended", since = "1.59.0")]
impl DoubleEndedIterator for ToUppercase {
fn next_back(&mut self) -> Option<char> {
self.0.next_back()
#[stable(feature = "case_mapping_double_ended", since = "1.59.0")]
impl DoubleEndedIterator for $ITER_NAME {
fn next_back(&mut self) -> Option<char> {
self.0.next_back()
}

fn rfold<Acc, Fold>(self, init: Acc, rfold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.0.rfold(init, rfold)
}

fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
self.0.advance_back_by(n)
}
}

#[stable(feature = "fused", since = "1.26.0")]
impl FusedIterator for $ITER_NAME {}

#[stable(feature = "exact_size_case_mapping_iter", since = "1.35.0")]
impl ExactSizeIterator for $ITER_NAME {
fn len(&self) -> usize {
self.0.len()
}

fn is_empty(&self) -> bool {
self.0.is_empty()
}
}

// SAFETY: forwards to inner `array::IntoIter`
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl TrustedLen for $ITER_NAME {}

// SAFETY: forwards to inner `array::IntoIter`
#[doc(hidden)]
#[unstable(feature = "std_internals", issue = "none")]
unsafe impl TrustedRandomAccessNoCoerce for $ITER_NAME {
const MAY_HAVE_SIDE_EFFECT: bool = false;
}

// SAFETY: this iter has no subtypes/supertypes
#[doc(hidden)]
#[unstable(feature = "std_internals", issue = "none")]
unsafe impl TrustedRandomAccess for $ITER_NAME {}

#[stable(feature = "char_struct_display", since = "1.16.0")]
impl fmt::Display for $ITER_NAME {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&self.0, f)
}
}
}
}

#[stable(feature = "fused", since = "1.26.0")]
impl FusedIterator for ToUppercase {}
casemappingiter_impls! {
/// Returns an iterator that yields the lowercase equivalent of a `char`.
///
/// This `struct` is created by the [`to_lowercase`] method on [`char`]. See
/// its documentation for more.
///
/// [`to_lowercase`]: char::to_lowercase
ToLowercase
}

#[stable(feature = "exact_size_case_mapping_iter", since = "1.35.0")]
impl ExactSizeIterator for ToUppercase {}
casemappingiter_impls! {
/// Returns an iterator that yields the uppercase equivalent of a `char`.
///
/// This `struct` is created by the [`to_uppercase`] method on [`char`]. See
/// its documentation for more.
///
/// [`to_uppercase`]: char::to_uppercase
ToUppercase
}

#[derive(Debug, Clone)]
enum CaseMappingIter {
Three(char, char, char),
Two(char, char),
One(char),
Zero,
}
struct CaseMappingIter(core::array::IntoIter<char, 3>);

impl CaseMappingIter {
#[inline]
fn new(chars: [char; 3]) -> CaseMappingIter {
let mut iter = chars.into_iter();
if chars[2] == '\0' {
iter.next_back();
if chars[1] == '\0' {
CaseMappingIter::One(chars[0]) // Including if chars[0] == '\0'
} else {
CaseMappingIter::Two(chars[0], chars[1])
iter.next_back();

// Deliberately don't check `chars[0]`,
// as '\0' lowercases to itself
}
} else {
CaseMappingIter::Three(chars[0], chars[1], chars[2])
}
CaseMappingIter(iter)
}
}

impl Iterator for CaseMappingIter {
type Item = char;

fn next(&mut self) -> Option<char> {
match *self {
CaseMappingIter::Three(a, b, c) => {
*self = CaseMappingIter::Two(b, c);
Some(a)
}
CaseMappingIter::Two(b, c) => {
*self = CaseMappingIter::One(c);
Some(b)
}
CaseMappingIter::One(c) => {
*self = CaseMappingIter::Zero;
Some(c)
}
CaseMappingIter::Zero => None,
}
self.0.next()
}

fn size_hint(&self) -> (usize, Option<usize>) {
let size = match self {
CaseMappingIter::Three(..) => 3,
CaseMappingIter::Two(..) => 2,
CaseMappingIter::One(_) => 1,
CaseMappingIter::Zero => 0,
};
(size, Some(size))
self.0.size_hint()
}

fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.0.fold(init, fold)
}

fn count(self) -> usize {
self.0.count()
}

fn last(self) -> Option<Self::Item> {
self.0.last()
}

fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
self.0.advance_by(n)
}

unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
// SAFETY: just forwarding requirements to caller
unsafe { self.0.__iterator_get_unchecked(idx) }
}
}

impl DoubleEndedIterator for CaseMappingIter {
fn next_back(&mut self) -> Option<char> {
match *self {
CaseMappingIter::Three(a, b, c) => {
*self = CaseMappingIter::Two(a, b);
Some(c)
}
CaseMappingIter::Two(b, c) => {
*self = CaseMappingIter::One(b);
Some(c)
}
CaseMappingIter::One(c) => {
*self = CaseMappingIter::Zero;
Some(c)
}
CaseMappingIter::Zero => None,
}
self.0.next_back()
}
}

impl fmt::Display for CaseMappingIter {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match *self {
CaseMappingIter::Three(a, b, c) => {
f.write_char(a)?;
f.write_char(b)?;
f.write_char(c)
}
CaseMappingIter::Two(b, c) => {
f.write_char(b)?;
f.write_char(c)
}
CaseMappingIter::One(c) => f.write_char(c),
CaseMappingIter::Zero => Ok(()),
}
fn rfold<Acc, Fold>(self, init: Acc, rfold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.0.rfold(init, rfold)
}

fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
self.0.advance_back_by(n)
}
}

#[stable(feature = "char_struct_display", since = "1.16.0")]
impl fmt::Display for ToLowercase {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&self.0, f)
impl ExactSizeIterator for CaseMappingIter {
fn len(&self) -> usize {
self.0.len()
}

fn is_empty(&self) -> bool {
self.0.is_empty()
}
}

#[stable(feature = "char_struct_display", since = "1.16.0")]
impl fmt::Display for ToUppercase {
impl FusedIterator for CaseMappingIter {}

// SAFETY: forwards to inner `array::IntoIter`
unsafe impl TrustedLen for CaseMappingIter {}

// SAFETY: forwards to inner `array::IntoIter`
unsafe impl TrustedRandomAccessNoCoerce for CaseMappingIter {
const MAY_HAVE_SIDE_EFFECT: bool = false;
}

// SAFETY: `CaseMappingIter` has no subtypes/supertypes
unsafe impl TrustedRandomAccess for CaseMappingIter {}

impl fmt::Display for CaseMappingIter {
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&self.0, f)
for c in self.0.clone() {
f.write_char(c)?;
}
Ok(())
}
}

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