1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666
//! `str` 原始类型的实用工具。
//!
//! *[See also the `str` primitive type](str).*
#![stable(feature = "rust1", since = "1.0.0")]
// 该模块中的许多用法仅在测试配置中使用。
// 仅关闭 unused_imports 警告比解决它们更干净。
#![allow(unused_imports)]
use core::borrow::{Borrow, BorrowMut};
use core::iter::FusedIterator;
use core::mem;
use core::ptr;
use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
use core::unicode::conversions;
use crate::borrow::ToOwned;
use crate::boxed::Box;
use crate::slice::{Concat, Join, SliceIndex};
use crate::string::String;
use crate::vec::Vec;
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::pattern;
#[stable(feature = "encode_utf16", since = "1.8.0")]
pub use core::str::EncodeUtf16;
#[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
pub use core::str::SplitAsciiWhitespace;
#[stable(feature = "split_inclusive", since = "1.51.0")]
pub use core::str::SplitInclusive;
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::SplitWhitespace;
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
#[stable(feature = "str_escape", since = "1.34.0")]
pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{FromStr, Utf8Error};
#[allow(deprecated)]
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{Lines, LinesAny};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{MatchIndices, RMatchIndices};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{Matches, RMatches};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{RSplit, Split};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{RSplitN, SplitN};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::str::{RSplitTerminator, SplitTerminator};
#[unstable(feature = "utf8_chunks", issue = "99543")]
pub use core::str::{Utf8Chunk, Utf8Chunks};
/// Note: `Concat<str>` 中的 `str` 在这里没有意义。
/// trait 的这个类型参数的存在只是为了启用另一个 impl。
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "slice_concat_ext", issue = "27747")]
impl<S: Borrow<str>> Concat<str> for [S] {
type Output = String;
fn concat(slice: &Self) -> String {
Join::join(slice, "")
}
}
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "slice_concat_ext", issue = "27747")]
impl<S: Borrow<str>> Join<&str> for [S] {
type Output = String;
fn join(slice: &Self, sep: &str) -> String {
unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
}
}
#[cfg(not(no_global_oom_handling))]
macro_rules! specialize_for_lengths {
($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {{
let mut target = $target;
let iter = $iter;
let sep_bytes = $separator;
match $separator.len() {
$(
// 具有硬编码大小的循环运行得更快,专门针对分隔符长度较小的情况
//
$num => {
for s in iter {
copy_slice_and_advance!(target, sep_bytes);
let content_bytes = s.borrow().as_ref();
copy_slice_and_advance!(target, content_bytes);
}
},
)*
_ => {
// 任意非零大小的回退
for s in iter {
copy_slice_and_advance!(target, sep_bytes);
let content_bytes = s.borrow().as_ref();
copy_slice_and_advance!(target, content_bytes);
}
}
}
target
}}
}
#[cfg(not(no_global_oom_handling))]
macro_rules! copy_slice_and_advance {
($target:expr, $bytes:expr) => {
let len = $bytes.len();
let (head, tail) = { $target }.split_at_mut(len);
head.copy_from_slice($bytes);
$target = tail;
};
}
// 适用于 Vec<T> (T: Copy) 和 String 的内部 vec 的优化联接实现这个函数。
// 在固定的时间将其保留在原位。
//
// 字符串连接的边界是 S: Borrow<str> 和 Vec-join Borrow<[T]> [T] 和 str 都暗示 AsRef<[T]> 对于某些 T
// => s.borrow().as_ref() 并且我们总是有切片
//
//
//
#[cfg(not(no_global_oom_handling))]
fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
where
T: Copy,
B: AsRef<[T]> + ?Sized,
S: Borrow<B>,
{
let sep_len = sep.len();
let mut iter = slice.iter();
// 第一个切片是唯一没有分隔符的切片
let first = match iter.next() {
Some(first) => first,
None => return vec![],
};
// 如果 `len` 计算溢出,则计算连接的 Vec 的确切总长度,否则我们将 panic 耗尽内存,并且该函数的剩余部分需要为安全起见预先分配整个 Vec
//
//
//
let reserved_len = sep_len
.checked_mul(iter.len())
.and_then(|n| {
slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
})
.expect("attempt to join into collection with len > usize::MAX");
// 准备一个未初始化的缓冲区
let mut result = Vec::with_capacity(reserved_len);
debug_assert!(result.capacity() >= reserved_len);
result.extend_from_slice(first.borrow().as_ref());
unsafe {
let pos = result.len();
let target = result.spare_capacity_mut().get_unchecked_mut(..reserved_len - pos);
// 将分隔符和切片转换为 MaybeUninit 的切片以简化 specialize_for_lengths 中的实现
//
let sep_uninit = core::slice::from_raw_parts(sep.as_ptr().cast(), sep.len());
let iter_uninit = iter.map(|it| {
let it = it.borrow().as_ref();
core::slice::from_raw_parts(it.as_ptr().cast(), it.len())
});
// 复制分隔符和切片无边界检查会生成带有硬编码偏移量的循环,用于较小的分隔符 (可能需要大量改进)
//
//
let remain = specialize_for_lengths!(sep_uninit, target, iter_uninit; 0, 1, 2, 3, 4);
// 奇怪的借用实现可能会返回不同的切片来进行长度计算和实际复制。
//
// 确保我们不向调用者公开未初始化的字节。
let result_len = reserved_len - remain.len();
result.set_len(result_len);
}
result
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Borrow<str> for String {
#[inline]
fn borrow(&self) -> &str {
&self[..]
}
}
#[stable(feature = "string_borrow_mut", since = "1.36.0")]
impl BorrowMut<str> for String {
#[inline]
fn borrow_mut(&mut self) -> &mut str {
&mut self[..]
}
}
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl ToOwned for str {
type Owned = String;
#[inline]
fn to_owned(&self) -> String {
unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
}
fn clone_into(&self, target: &mut String) {
let mut b = mem::take(target).into_bytes();
self.as_bytes().clone_into(&mut b);
*target = unsafe { String::from_utf8_unchecked(b) }
}
}
/// 字符串切片的方法。
#[cfg(not(test))]
impl str {
/// 无需复制或分配即可将 `Box<str>` 转换为 `Box<[u8]>`。
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// let s = "this is a string";
/// let boxed_str = s.to_owned().into_boxed_str();
/// let boxed_bytes = boxed_str.into_boxed_bytes();
/// assert_eq!(*boxed_bytes, *s.as_bytes());
/// ```
#[rustc_allow_incoherent_impl]
#[stable(feature = "str_box_extras", since = "1.20.0")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
self.into()
}
/// 用另一个字符串替换模式的所有匹配项。
///
/// `replace` 创建一个新的 [`String`],并将此字符串切片中的数据复制到其中。
/// 这样做时,它将尝试查找某个模式的匹配项。
/// 如果找到,则将其替换为替换字符串切片。
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// let s = "this is old";
///
/// assert_eq!("this is new", s.replace("old", "new"));
/// assert_eq!("than an old", s.replace("is", "an"));
/// ```
///
/// 当模式不匹配时,它将此字符串切片作为 [`String`] 返回:
///
/// ```
/// let s = "this is old";
/// assert_eq!(s, s.replace("cookie monster", "little lamb"));
/// ```
#[cfg(not(no_global_oom_handling))]
#[rustc_allow_incoherent_impl]
#[must_use = "this returns the replaced string as a new allocation, \
without modifying the original"]
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
let mut result = String::new();
let mut last_end = 0;
for (start, part) in self.match_indices(from) {
result.push_str(unsafe { self.get_unchecked(last_end..start) });
result.push_str(to);
last_end = start + part.len();
}
result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
result
}
/// 用另一个字符串替换模式的前 N 个匹配项。
///
/// `replacen` 创建一个新的 [`String`],并将此字符串切片中的数据复制到其中。
/// 这样做时,它将尝试查找某个模式的匹配项。
/// 如果找到任何内容,则最多 `count` 次将它们替换为替换字符串切片。
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// let s = "foo foo 123 foo";
/// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
/// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
/// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
/// ```
///
/// 当模式不匹配时,它将此字符串切片作为 [`String`] 返回:
///
/// ```
/// let s = "this is old";
/// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
/// ```
#[cfg(not(no_global_oom_handling))]
#[rustc_allow_incoherent_impl]
#[must_use = "this returns the replaced string as a new allocation, \
without modifying the original"]
#[stable(feature = "str_replacen", since = "1.16.0")]
pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
// 希望减少重新分配的时间
let mut result = String::with_capacity(32);
let mut last_end = 0;
for (start, part) in self.match_indices(pat).take(count) {
result.push_str(unsafe { self.get_unchecked(last_end..start) });
result.push_str(to);
last_end = start + part.len();
}
result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
result
}
/// 以新的 [`String`] 返回等效于此字符串切片的小写字母。
///
/// 'Lowercase' 是根据 Unicode 派生核心属性 `Lowercase` 的术语定义的。
///
/// 由于更改大小写时某些字符可以扩展为多个字符,因此此函数返回 [`String`] 而不是就地修改参数。
///
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// let s = "HELLO";
///
/// assert_eq!("hello", s.to_lowercase());
/// ```
///
/// 一个棘手的示例,使用 sigma:
///
/// ```
/// let sigma = "Σ";
///
/// assert_eq!("σ", sigma.to_lowercase());
///
/// // 但在单词结尾时,它是 ς,而不是 σ:
/// let odysseus = "ὈΔΥΣΣΕΎΣ";
///
/// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
/// ```
///
/// 不区分大小写的语言不会更改:
///
/// ```
/// let new_year = "农历新年";
///
/// assert_eq!(new_year, new_year.to_lowercase());
/// ```
///
///
#[cfg(not(no_global_oom_handling))]
#[rustc_allow_incoherent_impl]
#[must_use = "this returns the lowercase string as a new String, \
without modifying the original"]
#[stable(feature = "unicode_case_mapping", since = "1.2.0")]
pub fn to_lowercase(&self) -> String {
let out = convert_while_ascii(self.as_bytes(), u8::to_ascii_lowercase);
// 安全性: 我们知道这是一个有效的字符边界,因为 out.len() 只有在找到 ascii 字节时才会进行
//
let rest = unsafe { self.get_unchecked(out.len()..) };
// 安全性: 我们只向我们的 vec 写入了有效的 ASCII
let mut s = unsafe { String::from_utf8_unchecked(out) };
for (i, c) in rest[..].char_indices() {
if c == 'Σ' {
// Σ maps 到 σ,但单词 maps 到 ς 的末尾除外。
// 这是 `SpecialCasing.txt` 中唯一的条件 (contextual),但与语言无关的映射,因此请对其进行硬编码,而不要使用泛型 "condition" 机制。
//
// See https://github.com/rust-lang/rust/issues/26035
//
map_uppercase_sigma(rest, i, &mut s)
} else {
match conversions::to_lower(c) {
[a, '\0', _] => s.push(a),
[a, b, '\0'] => {
s.push(a);
s.push(b);
}
[a, b, c] => {
s.push(a);
s.push(b);
s.push(c);
}
}
}
}
return s;
fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
// See https://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
// `Final_Sigma` 的定义。
debug_assert!('Σ'.len_utf8() == 2);
let is_word_final = case_ignorable_then_cased(from[..i].chars().rev())
&& !case_ignorable_then_cased(from[i + 2..].chars());
to.push_str(if is_word_final { "ς" } else { "σ" });
}
fn case_ignorable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
use core::unicode::{Case_Ignorable, Cased};
match iter.skip_while(|&c| Case_Ignorable(c)).next() {
Some(c) => Cased(c),
None => false,
}
}
}
/// 返回此字符串切片的大写等效项,作为新的 [`String`]。
///
/// 'Uppercase' 是根据 Unicode 派生核心属性 `Uppercase` 的术语定义的。
///
/// 由于更改大小写时某些字符可以扩展为多个字符,因此此函数返回 [`String`] 而不是就地修改参数。
///
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// let s = "hello";
///
/// assert_eq!("HELLO", s.to_uppercase());
/// ```
///
/// 不区分大小写的脚本不会更改:
///
/// ```
/// let new_year = "农历新年";
///
/// assert_eq!(new_year, new_year.to_uppercase());
/// ```
///
/// 一个字符可以变成多个:
///
/// ```
/// let s = "tschüß";
///
/// assert_eq!("TSCHÜSS", s.to_uppercase());
/// ```
///
#[cfg(not(no_global_oom_handling))]
#[rustc_allow_incoherent_impl]
#[must_use = "this returns the uppercase string as a new String, \
without modifying the original"]
#[stable(feature = "unicode_case_mapping", since = "1.2.0")]
pub fn to_uppercase(&self) -> String {
let out = convert_while_ascii(self.as_bytes(), u8::to_ascii_uppercase);
// 安全性: 我们知道这是一个有效的字符边界,因为 out.len() 只有在找到 ascii 字节时才会进行
//
let rest = unsafe { self.get_unchecked(out.len()..) };
// 安全性: 我们只向我们的 vec 写入了有效的 ASCII
let mut s = unsafe { String::from_utf8_unchecked(out) };
for c in rest.chars() {
match conversions::to_upper(c) {
[a, '\0', _] => s.push(a),
[a, b, '\0'] => {
s.push(a);
s.push(b);
}
[a, b, c] => {
s.push(a);
s.push(b);
s.push(c);
}
}
}
s
}
/// 无需复制或分配即可将 [`Box<str>`] 转换为 [`String`]。
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// let string = String::from("birthday gift");
/// let boxed_str = string.clone().into_boxed_str();
///
/// assert_eq!(boxed_str.into_string(), string);
/// ```
#[stable(feature = "box_str", since = "1.4.0")]
#[rustc_allow_incoherent_impl]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub fn into_string(self: Box<str>) -> String {
let slice = Box::<[u8]>::from(self);
unsafe { String::from_utf8_unchecked(slice.into_vec()) }
}
/// 通过重复字符串 `n` 次来创建新的 [`String`]。
///
/// # Panics
///
/// 如果容量溢出,此函数将为 panic。
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
/// ```
///
/// 溢出时为 panic:
///
/// ```should_panic
/// // 这将在运行时 panic
/// let huge = "0123456789abcdef".repeat(usize::MAX);
/// ```
#[cfg(not(no_global_oom_handling))]
#[rustc_allow_incoherent_impl]
#[must_use]
#[stable(feature = "repeat_str", since = "1.16.0")]
pub fn repeat(&self, n: usize) -> String {
unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
}
/// 返回此字符串的副本,其中每个字符都映射为其等效的 ASCII 大写字母。
///
///
/// ASCII 字母 'a' 到 'z' 映射到 'A' 到 'Z',但是非 ASCII 字母不变。
///
/// 要就地将值大写,请使用 [`make_ascii_uppercase`]。
///
/// 要除非 ASCII 字符外还使用大写 ASCII 字符,请使用 [`to_uppercase`]。
///
/// # Examples
///
/// ```
/// let s = "Grüße, Jürgen ❤";
///
/// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
/// ```
///
/// [`make_ascii_uppercase`]: str::make_ascii_uppercase
/// [`to_uppercase`]: #method.to_uppercase
///
///
#[cfg(not(no_global_oom_handling))]
#[rustc_allow_incoherent_impl]
#[must_use = "to uppercase the value in-place, use `make_ascii_uppercase()`"]
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn to_ascii_uppercase(&self) -> String {
let mut s = self.to_owned();
s.make_ascii_uppercase();
s
}
/// 返回此字符串的副本,其中每个字符都映射为其等效的 ASCII 小写字母。
///
///
/// ASCII 字母 'A' 到 'Z' 映射到 'a' 到 'z',但是非 ASCII 字母不变。
///
/// 要就地小写该值,请使用 [`make_ascii_lowercase`]。
///
/// 要除非 ASCII 字符外还使用小写 ASCII 字符,请使用 [`to_lowercase`]。
///
/// # Examples
///
/// ```
/// let s = "Grüße, Jürgen ❤";
///
/// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
/// ```
///
/// [`make_ascii_lowercase`]: str::make_ascii_lowercase
/// [`to_lowercase`]: #method.to_lowercase
///
///
#[cfg(not(no_global_oom_handling))]
#[rustc_allow_incoherent_impl]
#[must_use = "to lowercase the value in-place, use `make_ascii_lowercase()`"]
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn to_ascii_lowercase(&self) -> String {
let mut s = self.to_owned();
s.make_ascii_lowercase();
s
}
}
/// 将字节的 boxed 切片转换为 boxed 字符串切片,而无需检查该字符串是否包含有效的 UTF-8。
///
///
/// # Examples
///
/// 基本用法:
///
/// ```
/// let smile_utf8 = Box::new([226, 152, 186]);
/// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
///
/// assert_eq!("☺", &*smile);
/// ```
#[stable(feature = "str_box_extras", since = "1.20.0")]
#[must_use]
#[inline]
pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
}
/// 在字节仍然是 ascii 时转换字节。
/// 为了获得更好的平均性能,这发生在 `2*size_of::<usize>()` 的块中。
/// 返回带有转换后的字节的 vec。
#[inline]
#[cfg(not(test))]
#[cfg(not(no_global_oom_handling))]
fn convert_while_ascii(b: &[u8], convert: fn(&u8) -> u8) -> Vec<u8> {
let mut out = Vec::with_capacity(b.len());
const USIZE_SIZE: usize = mem::size_of::<usize>();
const MAGIC_UNROLL: usize = 2;
const N: usize = USIZE_SIZE * MAGIC_UNROLL;
const NONASCII_MASK: usize = usize::from_ne_bytes([0x80; USIZE_SIZE]);
let mut i = 0;
unsafe {
while i + N <= b.len() {
// 安全: 我们检查了 `b` 和 `out` 的尺寸,以了解我们的
let in_chunk = b.get_unchecked(i..i + N);
let out_chunk = out.spare_capacity_mut().get_unchecked_mut(i..i + N);
let mut bits = 0;
for j in 0..MAGIC_UNROLL {
// 一次读取 1 个字节 (未对齐,因为我们没有检查对齐) 安全性: in_chunk 是范围内的有效字节
//
bits |= in_chunk.as_ptr().cast::<usize>().add(j).read_unaligned();
}
// 如果我们的块不是 ascii,则只返回前面的字节作为 init
if bits & NONASCII_MASK != 0 {
break;
}
// 对 N 个字节执行大小写转换 (大量自动处理)
for j in 0..N {
// 安全性: in_chunk 和 out_chunk 是范围内的有效字节
let out = out_chunk.get_unchecked_mut(j);
out.write(convert(in_chunk.get_unchecked(j)));
}
// 将这些字节标记为已初始化
i += N;
}
out.set_len(i);
}
out
}