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//! Operations on ASCII `[u8]`.
use crate::ascii;
use crate::fmt::{self, Write};
use crate::iter;
use crate::mem;
use crate::ops;
use core::ascii::EscapeDefault;
#[cfg(not(test))]
impl [u8] {
/// Checks if all bytes in this slice are within the ASCII range.
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[rustc_const_stable(feature = "const_slice_is_ascii", since = "1.74.0")]
#[must_use]
#[inline]
pub const fn is_ascii(&self) -> bool {
is_ascii(self)
}
/// If this slice [`is_ascii`](Self::is_ascii), returns it as a slice of
/// [ASCII characters](`ascii::Char`), otherwise returns `None`.
#[unstable(feature = "ascii_char", issue = "110998")]
#[must_use]
#[inline]
pub const fn as_ascii(&self) -> Option<&[ascii::Char]> {
if self.is_ascii() {
// SAFETY: Just checked that it's ASCII
Some(unsafe { self.as_ascii_unchecked() })
} else {
None
}
}
/// Converts this slice of bytes into a slice of ASCII characters,
/// without checking whether they're valid.
///
/// # Safety
///
/// Every byte in the slice must be in `0..=127`, or else this is UB.
#[unstable(feature = "ascii_char", issue = "110998")]
#[must_use]
#[inline]
pub const unsafe fn as_ascii_unchecked(&self) -> &[ascii::Char] {
let byte_ptr: *const [u8] = self;
let ascii_ptr = byte_ptr as *const [ascii::Char];
// SAFETY: The caller promised all the bytes are ASCII
unsafe { &*ascii_ptr }
}
/// Checks that two slices are an ASCII case-insensitive match.
///
/// Same as `to_ascii_lowercase(a) == to_ascii_lowercase(b)`,
/// but without allocating and copying temporaries.
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[must_use]
#[inline]
pub fn eq_ignore_ascii_case(&self, other: &[u8]) -> bool {
self.len() == other.len() && iter::zip(self, other).all(|(a, b)| a.eq_ignore_ascii_case(b))
}
/// Converts this slice to its ASCII upper case equivalent in-place.
///
/// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
/// but non-ASCII letters are unchanged.
///
/// To return a new uppercased value without modifying the existing one, use
/// [`to_ascii_uppercase`].
///
/// [`to_ascii_uppercase`]: #method.to_ascii_uppercase
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn make_ascii_uppercase(&mut self) {
for byte in self {
byte.make_ascii_uppercase();
}
}
/// Converts this slice to its ASCII lower case equivalent in-place.
///
/// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
/// but non-ASCII letters are unchanged.
///
/// To return a new lowercased value without modifying the existing one, use
/// [`to_ascii_lowercase`].
///
/// [`to_ascii_lowercase`]: #method.to_ascii_lowercase
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[inline]
pub fn make_ascii_lowercase(&mut self) {
for byte in self {
byte.make_ascii_lowercase();
}
}
/// Returns an iterator that produces an escaped version of this slice,
/// treating it as an ASCII string.
///
/// # Examples
///
/// ```
///
/// let s = b"0\t\r\n'\"\\\x9d";
/// let escaped = s.escape_ascii().to_string();
/// assert_eq!(escaped, "0\\t\\r\\n\\'\\\"\\\\\\x9d");
/// ```
#[must_use = "this returns the escaped bytes as an iterator, \
without modifying the original"]
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
pub fn escape_ascii(&self) -> EscapeAscii<'_> {
EscapeAscii { inner: self.iter().flat_map(EscapeByte) }
}
/// Returns a byte slice with leading ASCII whitespace bytes removed.
///
/// 'Whitespace' refers to the definition used by
/// `u8::is_ascii_whitespace`.
///
/// # Examples
///
/// ```
/// #![feature(byte_slice_trim_ascii)]
///
/// assert_eq!(b" \t hello world\n".trim_ascii_start(), b"hello world\n");
/// assert_eq!(b" ".trim_ascii_start(), b"");
/// assert_eq!(b"".trim_ascii_start(), b"");
/// ```
#[unstable(feature = "byte_slice_trim_ascii", issue = "94035")]
#[inline]
pub const fn trim_ascii_start(&self) -> &[u8] {
let mut bytes = self;
// Note: A pattern matching based approach (instead of indexing) allows
// making the function const.
while let [first, rest @ ..] = bytes {
if first.is_ascii_whitespace() {
bytes = rest;
} else {
break;
}
}
bytes
}
/// Returns a byte slice with trailing ASCII whitespace bytes removed.
///
/// 'Whitespace' refers to the definition used by
/// `u8::is_ascii_whitespace`.
///
/// # Examples
///
/// ```
/// #![feature(byte_slice_trim_ascii)]
///
/// assert_eq!(b"\r hello world\n ".trim_ascii_end(), b"\r hello world");
/// assert_eq!(b" ".trim_ascii_end(), b"");
/// assert_eq!(b"".trim_ascii_end(), b"");
/// ```
#[unstable(feature = "byte_slice_trim_ascii", issue = "94035")]
#[inline]
pub const fn trim_ascii_end(&self) -> &[u8] {
let mut bytes = self;
// Note: A pattern matching based approach (instead of indexing) allows
// making the function const.
while let [rest @ .., last] = bytes {
if last.is_ascii_whitespace() {
bytes = rest;
} else {
break;
}
}
bytes
}
/// Returns a byte slice with leading and trailing ASCII whitespace bytes
/// removed.
///
/// 'Whitespace' refers to the definition used by
/// `u8::is_ascii_whitespace`.
///
/// # Examples
///
/// ```
/// #![feature(byte_slice_trim_ascii)]
///
/// assert_eq!(b"\r hello world\n ".trim_ascii(), b"hello world");
/// assert_eq!(b" ".trim_ascii(), b"");
/// assert_eq!(b"".trim_ascii(), b"");
/// ```
#[unstable(feature = "byte_slice_trim_ascii", issue = "94035")]
#[inline]
pub const fn trim_ascii(&self) -> &[u8] {
self.trim_ascii_start().trim_ascii_end()
}
}
impl_fn_for_zst! {
#[derive(Clone)]
struct EscapeByte impl Fn = |byte: &u8| -> ascii::EscapeDefault {
ascii::escape_default(*byte)
};
}
/// An iterator over the escaped version of a byte slice.
///
/// This `struct` is created by the [`slice::escape_ascii`] method. See its
/// documentation for more information.
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
#[derive(Clone)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
pub struct EscapeAscii<'a> {
inner: iter::FlatMap<super::Iter<'a, u8>, ascii::EscapeDefault, EscapeByte>,
}
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
impl<'a> iter::Iterator for EscapeAscii<'a> {
type Item = u8;
#[inline]
fn next(&mut self) -> Option<u8> {
self.inner.next()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.inner.size_hint()
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Fold: FnMut(Acc, Self::Item) -> R,
R: ops::Try<Output = Acc>,
{
self.inner.try_fold(init, fold)
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where
Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.inner.fold(init, fold)
}
#[inline]
fn last(mut self) -> Option<u8> {
self.next_back()
}
}
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
impl<'a> iter::DoubleEndedIterator for EscapeAscii<'a> {
fn next_back(&mut self) -> Option<u8> {
self.inner.next_back()
}
}
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
impl<'a> iter::FusedIterator for EscapeAscii<'a> {}
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
impl<'a> fmt::Display for EscapeAscii<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// disassemble iterator, including front/back parts of flatmap in case it has been partially consumed
let (front, slice, back) = self.clone().inner.into_parts();
let front = front.unwrap_or(EscapeDefault::empty());
let mut bytes = slice.unwrap_or_default().as_slice();
let back = back.unwrap_or(EscapeDefault::empty());
// usually empty, so the formatter won't have to do any work
for byte in front {
f.write_char(byte as char)?;
}
fn needs_escape(b: u8) -> bool {
b > 0x7E || b < 0x20 || b == b'\\' || b == b'\'' || b == b'"'
}
while bytes.len() > 0 {
// fast path for the printable, non-escaped subset of ascii
let prefix = bytes.iter().take_while(|&&b| !needs_escape(b)).count();
// SAFETY: prefix length was derived by counting bytes in the same splice, so it's in-bounds
let (prefix, remainder) = unsafe { bytes.split_at_unchecked(prefix) };
// SAFETY: prefix is a valid utf8 sequence, as it's a subset of ASCII
let prefix = unsafe { crate::str::from_utf8_unchecked(prefix) };
f.write_str(prefix)?; // the fast part
bytes = remainder;
if let Some(&b) = bytes.first() {
// guaranteed to be non-empty, better to write it as a str
f.write_str(ascii::escape_default(b).as_str())?;
bytes = &bytes[1..];
}
}
// also usually empty
for byte in back {
f.write_char(byte as char)?;
}
Ok(())
}
}
#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
impl<'a> fmt::Debug for EscapeAscii<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("EscapeAscii").finish_non_exhaustive()
}
}
/// Returns `true` if any byte in the word `v` is nonascii (>= 128). Snarfed
/// from `../str/mod.rs`, which does something similar for utf8 validation.
#[inline]
const fn contains_nonascii(v: usize) -> bool {
const NONASCII_MASK: usize = usize::repeat_u8(0x80);
(NONASCII_MASK & v) != 0
}
/// ASCII test *without* the chunk-at-a-time optimizations.
///
/// This is carefully structured to produce nice small code -- it's smaller in
/// `-O` than what the "obvious" ways produces under `-C opt-level=s`. If you
/// touch it, be sure to run (and update if needed) the assembly test.
#[unstable(feature = "str_internals", issue = "none")]
#[doc(hidden)]
#[inline]
pub const fn is_ascii_simple(mut bytes: &[u8]) -> bool {
while let [rest @ .., last] = bytes {
if !last.is_ascii() {
break;
}
bytes = rest;
}
bytes.is_empty()
}
/// Optimized ASCII test that will use usize-at-a-time operations instead of
/// byte-at-a-time operations (when possible).
///
/// The algorithm we use here is pretty simple. If `s` is too short, we just
/// check each byte and be done with it. Otherwise:
///
/// - Read the first word with an unaligned load.
/// - Align the pointer, read subsequent words until end with aligned loads.
/// - Read the last `usize` from `s` with an unaligned load.
///
/// If any of these loads produces something for which `contains_nonascii`
/// (above) returns true, then we know the answer is false.
#[inline]
const fn is_ascii(s: &[u8]) -> bool {
const USIZE_SIZE: usize = mem::size_of::<usize>();
let len = s.len();
let align_offset = s.as_ptr().align_offset(USIZE_SIZE);
// If we wouldn't gain anything from the word-at-a-time implementation, fall
// back to a scalar loop.
//
// We also do this for architectures where `size_of::<usize>()` isn't
// sufficient alignment for `usize`, because it's a weird edge case.
if len < USIZE_SIZE || len < align_offset || USIZE_SIZE < mem::align_of::<usize>() {
return is_ascii_simple(s);
}
// We always read the first word unaligned, which means `align_offset` is
// 0, we'd read the same value again for the aligned read.
let offset_to_aligned = if align_offset == 0 { USIZE_SIZE } else { align_offset };
let start = s.as_ptr();
// SAFETY: We verify `len < USIZE_SIZE` above.
let first_word = unsafe { (start as *const usize).read_unaligned() };
if contains_nonascii(first_word) {
return false;
}
// We checked this above, somewhat implicitly. Note that `offset_to_aligned`
// is either `align_offset` or `USIZE_SIZE`, both of are explicitly checked
// above.
debug_assert!(offset_to_aligned <= len);
// SAFETY: word_ptr is the (properly aligned) usize ptr we use to read the
// middle chunk of the slice.
let mut word_ptr = unsafe { start.add(offset_to_aligned) as *const usize };
// `byte_pos` is the byte index of `word_ptr`, used for loop end checks.
let mut byte_pos = offset_to_aligned;
// Paranoia check about alignment, since we're about to do a bunch of
// unaligned loads. In practice this should be impossible barring a bug in
// `align_offset` though.
// While this method is allowed to spuriously fail in CTFE, if it doesn't
// have alignment information it should have given a `usize::MAX` for
// `align_offset` earlier, sending things through the scalar path instead of
// this one, so this check should pass if it's reachable.
debug_assert!(word_ptr.is_aligned_to(mem::align_of::<usize>()));
// Read subsequent words until the last aligned word, excluding the last
// aligned word by itself to be done in tail check later, to ensure that
// tail is always one `usize` at most to extra branch `byte_pos == len`.
while byte_pos < len - USIZE_SIZE {
// Sanity check that the read is in bounds
debug_assert!(byte_pos + USIZE_SIZE <= len);
// And that our assumptions about `byte_pos` hold.
debug_assert!(matches!(
word_ptr.cast::<u8>().guaranteed_eq(start.wrapping_add(byte_pos)),
// These are from the same allocation, so will hopefully always be
// known to match even in CTFE, but if it refuses to compare them
// that's ok since it's just a debug check anyway.
None | Some(true),
));
// SAFETY: We know `word_ptr` is properly aligned (because of
// `align_offset`), and we know that we have enough bytes between `word_ptr` and the end
let word = unsafe { word_ptr.read() };
if contains_nonascii(word) {
return false;
}
byte_pos += USIZE_SIZE;
// SAFETY: We know that `byte_pos <= len - USIZE_SIZE`, which means that
// after this `add`, `word_ptr` will be at most one-past-the-end.
word_ptr = unsafe { word_ptr.add(1) };
}
// Sanity check to ensure there really is only one `usize` left. This should
// be guaranteed by our loop condition.
debug_assert!(byte_pos <= len && len - byte_pos <= USIZE_SIZE);
// SAFETY: This relies on `len >= USIZE_SIZE`, which we check at the start.
let last_word = unsafe { (start.add(len - USIZE_SIZE) as *const usize).read_unaligned() };
!contains_nonascii(last_word)
}