1921 lines
70 KiB
Rust
1921 lines
70 KiB
Rust
//! The string Pattern API.
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//!
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//! The Pattern API provides a generic mechanism for using different pattern
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//! types when searching through a string.
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//!
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//! For more details, see the traits [`Pattern`], [`Searcher`],
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//! [`ReverseSearcher`], and [`DoubleEndedSearcher`].
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//!
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//! Although this API is unstable, it is exposed via stable APIs on the
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//! [`str`] type.
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//!
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//! # Examples
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//!
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//! [`Pattern`] is [implemented][pattern-impls] in the stable API for
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//! [`&str`][`str`], [`char`], slices of [`char`], and functions and closures
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//! implementing `FnMut(char) -> bool`.
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//!
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//! ```
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//! let s = "Can you find a needle in a haystack?";
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//!
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//! // &str pattern
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//! assert_eq!(s.find("you"), Some(4));
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//! // char pattern
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//! assert_eq!(s.find('n'), Some(2));
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//! // array of chars pattern
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//! assert_eq!(s.find(&['a', 'e', 'i', 'o', 'u']), Some(1));
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//! // slice of chars pattern
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//! assert_eq!(s.find(&['a', 'e', 'i', 'o', 'u'][..]), Some(1));
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//! // closure pattern
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//! assert_eq!(s.find(|c: char| c.is_ascii_punctuation()), Some(35));
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//! ```
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//!
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//! [pattern-impls]: Pattern#implementors
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#![unstable(
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feature = "pattern",
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reason = "API not fully fleshed out and ready to be stabilized",
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issue = "27721"
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)]
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use crate::cmp;
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use crate::cmp::Ordering;
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use crate::fmt;
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use crate::slice::memchr;
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// Pattern
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/// A string pattern.
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///
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/// A `Pattern<'a>` expresses that the implementing type
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/// can be used as a string pattern for searching in a [`&'a str`][str].
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///
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/// For example, both `'a'` and `"aa"` are patterns that
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/// would match at index `1` in the string `"baaaab"`.
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///
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/// The trait itself acts as a builder for an associated
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/// [`Searcher`] type, which does the actual work of finding
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/// occurrences of the pattern in a string.
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///
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/// Depending on the type of the pattern, the behaviour of methods like
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/// [`str::find`] and [`str::contains`] can change. The table below describes
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/// some of those behaviours.
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///
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/// | Pattern type | Match condition |
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/// |--------------------------|-------------------------------------------|
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/// | `&str` | is substring |
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/// | `char` | is contained in string |
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/// | `&[char]` | any char in slice is contained in string |
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/// | `F: FnMut(char) -> bool` | `F` returns `true` for a char in string |
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/// | `&&str` | is substring |
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/// | `&String` | is substring |
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///
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/// # Examples
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///
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/// ```
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/// // &str
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/// assert_eq!("abaaa".find("ba"), Some(1));
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/// assert_eq!("abaaa".find("bac"), None);
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///
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/// // char
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/// assert_eq!("abaaa".find('a'), Some(0));
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/// assert_eq!("abaaa".find('b'), Some(1));
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/// assert_eq!("abaaa".find('c'), None);
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///
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/// // &[char; N]
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/// assert_eq!("ab".find(&['b', 'a']), Some(0));
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/// assert_eq!("abaaa".find(&['a', 'z']), Some(0));
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/// assert_eq!("abaaa".find(&['c', 'd']), None);
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///
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/// // &[char]
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/// assert_eq!("ab".find(&['b', 'a'][..]), Some(0));
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/// assert_eq!("abaaa".find(&['a', 'z'][..]), Some(0));
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/// assert_eq!("abaaa".find(&['c', 'd'][..]), None);
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///
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/// // FnMut(char) -> bool
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/// assert_eq!("abcdef_z".find(|ch| ch > 'd' && ch < 'y'), Some(4));
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/// assert_eq!("abcddd_z".find(|ch| ch > 'd' && ch < 'y'), None);
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/// ```
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pub trait Pattern<'a>: Sized {
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/// Associated searcher for this pattern
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type Searcher: Searcher<'a>;
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/// Constructs the associated searcher from
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/// `self` and the `haystack` to search in.
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fn into_searcher(self, haystack: &'a str) -> Self::Searcher;
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/// Checks whether the pattern matches anywhere in the haystack
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#[inline]
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fn is_contained_in(self, haystack: &'a str) -> bool {
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self.into_searcher(haystack).next_match().is_some()
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}
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/// Checks whether the pattern matches at the front of the haystack
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#[inline]
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fn is_prefix_of(self, haystack: &'a str) -> bool {
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matches!(self.into_searcher(haystack).next(), SearchStep::Match(0, _))
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}
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/// Checks whether the pattern matches at the back of the haystack
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#[inline]
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fn is_suffix_of(self, haystack: &'a str) -> bool
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where
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Self::Searcher: ReverseSearcher<'a>,
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{
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matches!(self.into_searcher(haystack).next_back(), SearchStep::Match(_, j) if haystack.len() == j)
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}
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/// Removes the pattern from the front of haystack, if it matches.
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#[inline]
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fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
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if let SearchStep::Match(start, len) = self.into_searcher(haystack).next() {
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debug_assert_eq!(
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start, 0,
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"The first search step from Searcher \
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must include the first character"
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);
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// SAFETY: `Searcher` is known to return valid indices.
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unsafe { Some(haystack.get_unchecked(len..)) }
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} else {
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None
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}
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}
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/// Removes the pattern from the back of haystack, if it matches.
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#[inline]
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fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>
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where
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Self::Searcher: ReverseSearcher<'a>,
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{
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if let SearchStep::Match(start, end) = self.into_searcher(haystack).next_back() {
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debug_assert_eq!(
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end,
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haystack.len(),
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"The first search step from ReverseSearcher \
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must include the last character"
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);
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// SAFETY: `Searcher` is known to return valid indices.
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unsafe { Some(haystack.get_unchecked(..start)) }
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} else {
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None
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}
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}
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}
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// Searcher
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/// Result of calling [`Searcher::next()`] or [`ReverseSearcher::next_back()`].
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#[derive(Copy, Clone, Eq, PartialEq, Debug)]
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pub enum SearchStep {
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/// Expresses that a match of the pattern has been found at
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/// `haystack[a..b]`.
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Match(usize, usize),
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/// Expresses that `haystack[a..b]` has been rejected as a possible match
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/// of the pattern.
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///
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/// Note that there might be more than one `Reject` between two `Match`es,
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/// there is no requirement for them to be combined into one.
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Reject(usize, usize),
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/// Expresses that every byte of the haystack has been visited, ending
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/// the iteration.
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Done,
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}
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/// A searcher for a string pattern.
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///
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/// This trait provides methods for searching for non-overlapping
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/// matches of a pattern starting from the front (left) of a string.
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///
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/// It will be implemented by associated `Searcher`
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/// types of the [`Pattern`] trait.
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///
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/// The trait is marked unsafe because the indices returned by the
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/// [`next()`][Searcher::next] methods are required to lie on valid utf8
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/// boundaries in the haystack. This enables consumers of this trait to
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/// slice the haystack without additional runtime checks.
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pub unsafe trait Searcher<'a> {
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/// Getter for the underlying string to be searched in
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///
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/// Will always return the same [`&str`][str].
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fn haystack(&self) -> &'a str;
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/// Performs the next search step starting from the front.
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///
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/// - Returns [`Match(a, b)`][SearchStep::Match] if `haystack[a..b]` matches
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/// the pattern.
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/// - Returns [`Reject(a, b)`][SearchStep::Reject] if `haystack[a..b]` can
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/// not match the pattern, even partially.
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/// - Returns [`Done`][SearchStep::Done] if every byte of the haystack has
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/// been visited.
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///
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/// The stream of [`Match`][SearchStep::Match] and
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/// [`Reject`][SearchStep::Reject] values up to a [`Done`][SearchStep::Done]
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/// will contain index ranges that are adjacent, non-overlapping,
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/// covering the whole haystack, and laying on utf8 boundaries.
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///
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/// A [`Match`][SearchStep::Match] result needs to contain the whole matched
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/// pattern, however [`Reject`][SearchStep::Reject] results may be split up
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/// into arbitrary many adjacent fragments. Both ranges may have zero length.
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///
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/// As an example, the pattern `"aaa"` and the haystack `"cbaaaaab"`
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/// might produce the stream
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/// `[Reject(0, 1), Reject(1, 2), Match(2, 5), Reject(5, 8)]`
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fn next(&mut self) -> SearchStep;
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/// Finds the next [`Match`][SearchStep::Match] result. See [`next()`][Searcher::next].
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///
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/// Unlike [`next()`][Searcher::next], there is no guarantee that the returned ranges
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/// of this and [`next_reject`][Searcher::next_reject] will overlap. This will return
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/// `(start_match, end_match)`, where start_match is the index of where
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/// the match begins, and end_match is the index after the end of the match.
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#[inline]
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fn next_match(&mut self) -> Option<(usize, usize)> {
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loop {
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match self.next() {
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SearchStep::Match(a, b) => return Some((a, b)),
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SearchStep::Done => return None,
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_ => continue,
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}
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}
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}
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/// Finds the next [`Reject`][SearchStep::Reject] result. See [`next()`][Searcher::next]
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/// and [`next_match()`][Searcher::next_match].
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///
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/// Unlike [`next()`][Searcher::next], there is no guarantee that the returned ranges
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/// of this and [`next_match`][Searcher::next_match] will overlap.
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#[inline]
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fn next_reject(&mut self) -> Option<(usize, usize)> {
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loop {
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match self.next() {
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SearchStep::Reject(a, b) => return Some((a, b)),
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SearchStep::Done => return None,
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_ => continue,
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}
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}
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}
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}
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/// A reverse searcher for a string pattern.
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///
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/// This trait provides methods for searching for non-overlapping
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/// matches of a pattern starting from the back (right) of a string.
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///
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/// It will be implemented by associated [`Searcher`]
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/// types of the [`Pattern`] trait if the pattern supports searching
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/// for it from the back.
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///
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/// The index ranges returned by this trait are not required
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/// to exactly match those of the forward search in reverse.
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///
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/// For the reason why this trait is marked unsafe, see the
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/// parent trait [`Searcher`].
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pub unsafe trait ReverseSearcher<'a>: Searcher<'a> {
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/// Performs the next search step starting from the back.
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///
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/// - Returns [`Match(a, b)`][SearchStep::Match] if `haystack[a..b]`
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/// matches the pattern.
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/// - Returns [`Reject(a, b)`][SearchStep::Reject] if `haystack[a..b]`
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/// can not match the pattern, even partially.
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/// - Returns [`Done`][SearchStep::Done] if every byte of the haystack
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/// has been visited
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///
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/// The stream of [`Match`][SearchStep::Match] and
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/// [`Reject`][SearchStep::Reject] values up to a [`Done`][SearchStep::Done]
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/// will contain index ranges that are adjacent, non-overlapping,
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/// covering the whole haystack, and laying on utf8 boundaries.
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///
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/// A [`Match`][SearchStep::Match] result needs to contain the whole matched
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/// pattern, however [`Reject`][SearchStep::Reject] results may be split up
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/// into arbitrary many adjacent fragments. Both ranges may have zero length.
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///
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/// As an example, the pattern `"aaa"` and the haystack `"cbaaaaab"`
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/// might produce the stream
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/// `[Reject(7, 8), Match(4, 7), Reject(1, 4), Reject(0, 1)]`.
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fn next_back(&mut self) -> SearchStep;
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/// Finds the next [`Match`][SearchStep::Match] result.
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/// See [`next_back()`][ReverseSearcher::next_back].
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#[inline]
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fn next_match_back(&mut self) -> Option<(usize, usize)> {
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loop {
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match self.next_back() {
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SearchStep::Match(a, b) => return Some((a, b)),
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SearchStep::Done => return None,
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_ => continue,
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}
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}
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}
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/// Finds the next [`Reject`][SearchStep::Reject] result.
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/// See [`next_back()`][ReverseSearcher::next_back].
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#[inline]
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fn next_reject_back(&mut self) -> Option<(usize, usize)> {
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loop {
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match self.next_back() {
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SearchStep::Reject(a, b) => return Some((a, b)),
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SearchStep::Done => return None,
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_ => continue,
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}
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}
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}
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}
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/// A marker trait to express that a [`ReverseSearcher`]
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/// can be used for a [`DoubleEndedIterator`] implementation.
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///
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/// For this, the impl of [`Searcher`] and [`ReverseSearcher`] need
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/// to follow these conditions:
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///
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/// - All results of `next()` need to be identical
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/// to the results of `next_back()` in reverse order.
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/// - `next()` and `next_back()` need to behave as
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/// the two ends of a range of values, that is they
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/// can not "walk past each other".
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///
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/// # Examples
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///
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/// `char::Searcher` is a `DoubleEndedSearcher` because searching for a
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/// [`char`] only requires looking at one at a time, which behaves the same
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/// from both ends.
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///
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/// `(&str)::Searcher` is not a `DoubleEndedSearcher` because
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/// the pattern `"aa"` in the haystack `"aaa"` matches as either
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/// `"[aa]a"` or `"a[aa]"`, depending from which side it is searched.
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pub trait DoubleEndedSearcher<'a>: ReverseSearcher<'a> {}
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/////////////////////////////////////////////////////////////////////////////
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// Impl for char
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/////////////////////////////////////////////////////////////////////////////
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/// Associated type for `<char as Pattern<'a>>::Searcher`.
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#[derive(Clone, Debug)]
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pub struct CharSearcher<'a> {
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haystack: &'a str,
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// safety invariant: `finger`/`finger_back` must be a valid utf8 byte index of `haystack`
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// This invariant can be broken *within* next_match and next_match_back, however
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// they must exit with fingers on valid code point boundaries.
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/// `finger` is the current byte index of the forward search.
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/// Imagine that it exists before the byte at its index, i.e.
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/// `haystack[finger]` is the first byte of the slice we must inspect during
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/// forward searching
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finger: usize,
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/// `finger_back` is the current byte index of the reverse search.
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/// Imagine that it exists after the byte at its index, i.e.
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/// haystack[finger_back - 1] is the last byte of the slice we must inspect during
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/// forward searching (and thus the first byte to be inspected when calling next_back()).
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finger_back: usize,
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/// The character being searched for
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needle: char,
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// safety invariant: `utf8_size` must be less than 5
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/// The number of bytes `needle` takes up when encoded in utf8.
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utf8_size: usize,
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/// A utf8 encoded copy of the `needle`
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utf8_encoded: [u8; 4],
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}
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unsafe impl<'a> Searcher<'a> for CharSearcher<'a> {
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#[inline]
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fn haystack(&self) -> &'a str {
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self.haystack
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}
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#[inline]
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fn next(&mut self) -> SearchStep {
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let old_finger = self.finger;
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// SAFETY: 1-4 guarantee safety of `get_unchecked`
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// 1. `self.finger` and `self.finger_back` are kept on unicode boundaries
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// (this is invariant)
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// 2. `self.finger >= 0` since it starts at 0 and only increases
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// 3. `self.finger < self.finger_back` because otherwise the char `iter`
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// would return `SearchStep::Done`
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// 4. `self.finger` comes before the end of the haystack because `self.finger_back`
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// starts at the end and only decreases
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let slice = unsafe { self.haystack.get_unchecked(old_finger..self.finger_back) };
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let mut iter = slice.chars();
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let old_len = iter.iter.len();
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if let Some(ch) = iter.next() {
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// add byte offset of current character
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// without re-encoding as utf-8
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self.finger += old_len - iter.iter.len();
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if ch == self.needle {
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SearchStep::Match(old_finger, self.finger)
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} else {
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SearchStep::Reject(old_finger, self.finger)
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}
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} else {
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SearchStep::Done
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}
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}
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#[inline]
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fn next_match(&mut self) -> Option<(usize, usize)> {
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loop {
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// get the haystack after the last character found
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let bytes = self.haystack.as_bytes().get(self.finger..self.finger_back)?;
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// the last byte of the utf8 encoded needle
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// SAFETY: we have an invariant that `utf8_size < 5`
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let last_byte = unsafe { *self.utf8_encoded.get_unchecked(self.utf8_size - 1) };
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if let Some(index) = memchr::memchr(last_byte, bytes) {
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// The new finger is the index of the byte we found,
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// plus one, since we memchr'd for the last byte of the character.
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//
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// Note that this doesn't always give us a finger on a UTF8 boundary.
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// If we *didn't* find our character
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// we may have indexed to the non-last byte of a 3-byte or 4-byte character.
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// We can't just skip to the next valid starting byte because a character like
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// ꁁ (U+A041 YI SYLLABLE PA), utf-8 `EA 81 81` will have us always find
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// the second byte when searching for the third.
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//
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// However, this is totally okay. While we have the invariant that
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// self.finger is on a UTF8 boundary, this invariant is not relied upon
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// within this method (it is relied upon in CharSearcher::next()).
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//
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// We only exit this method when we reach the end of the string, or if we
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// find something. When we find something the `finger` will be set
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// to a UTF8 boundary.
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self.finger += index + 1;
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if self.finger >= self.utf8_size {
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let found_char = self.finger - self.utf8_size;
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if let Some(slice) = self.haystack.as_bytes().get(found_char..self.finger) {
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if slice == &self.utf8_encoded[0..self.utf8_size] {
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return Some((found_char, self.finger));
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}
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}
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}
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} else {
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// found nothing, exit
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self.finger = self.finger_back;
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return None;
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}
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}
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}
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// let next_reject use the default implementation from the Searcher trait
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}
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|
|
unsafe impl<'a> ReverseSearcher<'a> for CharSearcher<'a> {
|
|
#[inline]
|
|
fn next_back(&mut self) -> SearchStep {
|
|
let old_finger = self.finger_back;
|
|
// SAFETY: see the comment for next() above
|
|
let slice = unsafe { self.haystack.get_unchecked(self.finger..old_finger) };
|
|
let mut iter = slice.chars();
|
|
let old_len = iter.iter.len();
|
|
if let Some(ch) = iter.next_back() {
|
|
// subtract byte offset of current character
|
|
// without re-encoding as utf-8
|
|
self.finger_back -= old_len - iter.iter.len();
|
|
if ch == self.needle {
|
|
SearchStep::Match(self.finger_back, old_finger)
|
|
} else {
|
|
SearchStep::Reject(self.finger_back, old_finger)
|
|
}
|
|
} else {
|
|
SearchStep::Done
|
|
}
|
|
}
|
|
#[inline]
|
|
fn next_match_back(&mut self) -> Option<(usize, usize)> {
|
|
let haystack = self.haystack.as_bytes();
|
|
loop {
|
|
// get the haystack up to but not including the last character searched
|
|
let bytes = haystack.get(self.finger..self.finger_back)?;
|
|
// the last byte of the utf8 encoded needle
|
|
// SAFETY: we have an invariant that `utf8_size < 5`
|
|
let last_byte = unsafe { *self.utf8_encoded.get_unchecked(self.utf8_size - 1) };
|
|
if let Some(index) = memchr::memrchr(last_byte, bytes) {
|
|
// we searched a slice that was offset by self.finger,
|
|
// add self.finger to recoup the original index
|
|
let index = self.finger + index;
|
|
// memrchr will return the index of the byte we wish to
|
|
// find. In case of an ASCII character, this is indeed
|
|
// were we wish our new finger to be ("after" the found
|
|
// char in the paradigm of reverse iteration). For
|
|
// multibyte chars we need to skip down by the number of more
|
|
// bytes they have than ASCII
|
|
let shift = self.utf8_size - 1;
|
|
if index >= shift {
|
|
let found_char = index - shift;
|
|
if let Some(slice) = haystack.get(found_char..(found_char + self.utf8_size)) {
|
|
if slice == &self.utf8_encoded[0..self.utf8_size] {
|
|
// move finger to before the character found (i.e., at its start index)
|
|
self.finger_back = found_char;
|
|
return Some((self.finger_back, self.finger_back + self.utf8_size));
|
|
}
|
|
}
|
|
}
|
|
// We can't use finger_back = index - size + 1 here. If we found the last char
|
|
// of a different-sized character (or the middle byte of a different character)
|
|
// we need to bump the finger_back down to `index`. This similarly makes
|
|
// `finger_back` have the potential to no longer be on a boundary,
|
|
// but this is OK since we only exit this function on a boundary
|
|
// or when the haystack has been searched completely.
|
|
//
|
|
// Unlike next_match this does not
|
|
// have the problem of repeated bytes in utf-8 because
|
|
// we're searching for the last byte, and we can only have
|
|
// found the last byte when searching in reverse.
|
|
self.finger_back = index;
|
|
} else {
|
|
self.finger_back = self.finger;
|
|
// found nothing, exit
|
|
return None;
|
|
}
|
|
}
|
|
}
|
|
|
|
// let next_reject_back use the default implementation from the Searcher trait
|
|
}
|
|
|
|
impl<'a> DoubleEndedSearcher<'a> for CharSearcher<'a> {}
|
|
|
|
/// Searches for chars that are equal to a given [`char`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// assert_eq!("Hello world".find('o'), Some(4));
|
|
/// ```
|
|
impl<'a> Pattern<'a> for char {
|
|
type Searcher = CharSearcher<'a>;
|
|
|
|
#[inline]
|
|
fn into_searcher(self, haystack: &'a str) -> Self::Searcher {
|
|
let mut utf8_encoded = [0; 4];
|
|
let utf8_size = self.encode_utf8(&mut utf8_encoded).len();
|
|
CharSearcher {
|
|
haystack,
|
|
finger: 0,
|
|
finger_back: haystack.len(),
|
|
needle: self,
|
|
utf8_size,
|
|
utf8_encoded,
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn is_contained_in(self, haystack: &'a str) -> bool {
|
|
if (self as u32) < 128 {
|
|
haystack.as_bytes().contains(&(self as u8))
|
|
} else {
|
|
let mut buffer = [0u8; 4];
|
|
self.encode_utf8(&mut buffer).is_contained_in(haystack)
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn is_prefix_of(self, haystack: &'a str) -> bool {
|
|
self.encode_utf8(&mut [0u8; 4]).is_prefix_of(haystack)
|
|
}
|
|
|
|
#[inline]
|
|
fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
|
|
self.encode_utf8(&mut [0u8; 4]).strip_prefix_of(haystack)
|
|
}
|
|
|
|
#[inline]
|
|
fn is_suffix_of(self, haystack: &'a str) -> bool
|
|
where
|
|
Self::Searcher: ReverseSearcher<'a>,
|
|
{
|
|
self.encode_utf8(&mut [0u8; 4]).is_suffix_of(haystack)
|
|
}
|
|
|
|
#[inline]
|
|
fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>
|
|
where
|
|
Self::Searcher: ReverseSearcher<'a>,
|
|
{
|
|
self.encode_utf8(&mut [0u8; 4]).strip_suffix_of(haystack)
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Impl for a MultiCharEq wrapper
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
#[doc(hidden)]
|
|
trait MultiCharEq {
|
|
fn matches(&mut self, c: char) -> bool;
|
|
}
|
|
|
|
impl<F> MultiCharEq for F
|
|
where
|
|
F: FnMut(char) -> bool,
|
|
{
|
|
#[inline]
|
|
fn matches(&mut self, c: char) -> bool {
|
|
(*self)(c)
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> MultiCharEq for [char; N] {
|
|
#[inline]
|
|
fn matches(&mut self, c: char) -> bool {
|
|
self.iter().any(|&m| m == c)
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> MultiCharEq for &[char; N] {
|
|
#[inline]
|
|
fn matches(&mut self, c: char) -> bool {
|
|
self.iter().any(|&m| m == c)
|
|
}
|
|
}
|
|
|
|
impl MultiCharEq for &[char] {
|
|
#[inline]
|
|
fn matches(&mut self, c: char) -> bool {
|
|
self.iter().any(|&m| m == c)
|
|
}
|
|
}
|
|
|
|
struct MultiCharEqPattern<C: MultiCharEq>(C);
|
|
|
|
#[derive(Clone, Debug)]
|
|
struct MultiCharEqSearcher<'a, C: MultiCharEq> {
|
|
char_eq: C,
|
|
haystack: &'a str,
|
|
char_indices: super::CharIndices<'a>,
|
|
}
|
|
|
|
impl<'a, C: MultiCharEq> Pattern<'a> for MultiCharEqPattern<C> {
|
|
type Searcher = MultiCharEqSearcher<'a, C>;
|
|
|
|
#[inline]
|
|
fn into_searcher(self, haystack: &'a str) -> MultiCharEqSearcher<'a, C> {
|
|
MultiCharEqSearcher { haystack, char_eq: self.0, char_indices: haystack.char_indices() }
|
|
}
|
|
}
|
|
|
|
unsafe impl<'a, C: MultiCharEq> Searcher<'a> for MultiCharEqSearcher<'a, C> {
|
|
#[inline]
|
|
fn haystack(&self) -> &'a str {
|
|
self.haystack
|
|
}
|
|
|
|
#[inline]
|
|
fn next(&mut self) -> SearchStep {
|
|
let s = &mut self.char_indices;
|
|
// Compare lengths of the internal byte slice iterator
|
|
// to find length of current char
|
|
let pre_len = s.iter.iter.len();
|
|
if let Some((i, c)) = s.next() {
|
|
let len = s.iter.iter.len();
|
|
let char_len = pre_len - len;
|
|
if self.char_eq.matches(c) {
|
|
return SearchStep::Match(i, i + char_len);
|
|
} else {
|
|
return SearchStep::Reject(i, i + char_len);
|
|
}
|
|
}
|
|
SearchStep::Done
|
|
}
|
|
}
|
|
|
|
unsafe impl<'a, C: MultiCharEq> ReverseSearcher<'a> for MultiCharEqSearcher<'a, C> {
|
|
#[inline]
|
|
fn next_back(&mut self) -> SearchStep {
|
|
let s = &mut self.char_indices;
|
|
// Compare lengths of the internal byte slice iterator
|
|
// to find length of current char
|
|
let pre_len = s.iter.iter.len();
|
|
if let Some((i, c)) = s.next_back() {
|
|
let len = s.iter.iter.len();
|
|
let char_len = pre_len - len;
|
|
if self.char_eq.matches(c) {
|
|
return SearchStep::Match(i, i + char_len);
|
|
} else {
|
|
return SearchStep::Reject(i, i + char_len);
|
|
}
|
|
}
|
|
SearchStep::Done
|
|
}
|
|
}
|
|
|
|
impl<'a, C: MultiCharEq> DoubleEndedSearcher<'a> for MultiCharEqSearcher<'a, C> {}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
macro_rules! pattern_methods {
|
|
($t:ty, $pmap:expr, $smap:expr) => {
|
|
type Searcher = $t;
|
|
|
|
#[inline]
|
|
fn into_searcher(self, haystack: &'a str) -> $t {
|
|
($smap)(($pmap)(self).into_searcher(haystack))
|
|
}
|
|
|
|
#[inline]
|
|
fn is_contained_in(self, haystack: &'a str) -> bool {
|
|
($pmap)(self).is_contained_in(haystack)
|
|
}
|
|
|
|
#[inline]
|
|
fn is_prefix_of(self, haystack: &'a str) -> bool {
|
|
($pmap)(self).is_prefix_of(haystack)
|
|
}
|
|
|
|
#[inline]
|
|
fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
|
|
($pmap)(self).strip_prefix_of(haystack)
|
|
}
|
|
|
|
#[inline]
|
|
fn is_suffix_of(self, haystack: &'a str) -> bool
|
|
where
|
|
$t: ReverseSearcher<'a>,
|
|
{
|
|
($pmap)(self).is_suffix_of(haystack)
|
|
}
|
|
|
|
#[inline]
|
|
fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>
|
|
where
|
|
$t: ReverseSearcher<'a>,
|
|
{
|
|
($pmap)(self).strip_suffix_of(haystack)
|
|
}
|
|
};
|
|
}
|
|
|
|
macro_rules! searcher_methods {
|
|
(forward) => {
|
|
#[inline]
|
|
fn haystack(&self) -> &'a str {
|
|
self.0.haystack()
|
|
}
|
|
#[inline]
|
|
fn next(&mut self) -> SearchStep {
|
|
self.0.next()
|
|
}
|
|
#[inline]
|
|
fn next_match(&mut self) -> Option<(usize, usize)> {
|
|
self.0.next_match()
|
|
}
|
|
#[inline]
|
|
fn next_reject(&mut self) -> Option<(usize, usize)> {
|
|
self.0.next_reject()
|
|
}
|
|
};
|
|
(reverse) => {
|
|
#[inline]
|
|
fn next_back(&mut self) -> SearchStep {
|
|
self.0.next_back()
|
|
}
|
|
#[inline]
|
|
fn next_match_back(&mut self) -> Option<(usize, usize)> {
|
|
self.0.next_match_back()
|
|
}
|
|
#[inline]
|
|
fn next_reject_back(&mut self) -> Option<(usize, usize)> {
|
|
self.0.next_reject_back()
|
|
}
|
|
};
|
|
}
|
|
|
|
/// Associated type for `<[char; N] as Pattern<'a>>::Searcher`.
|
|
#[derive(Clone, Debug)]
|
|
pub struct CharArraySearcher<'a, const N: usize>(
|
|
<MultiCharEqPattern<[char; N]> as Pattern<'a>>::Searcher,
|
|
);
|
|
|
|
/// Associated type for `<&[char; N] as Pattern<'a>>::Searcher`.
|
|
#[derive(Clone, Debug)]
|
|
pub struct CharArrayRefSearcher<'a, 'b, const N: usize>(
|
|
<MultiCharEqPattern<&'b [char; N]> as Pattern<'a>>::Searcher,
|
|
);
|
|
|
|
/// Searches for chars that are equal to any of the [`char`]s in the array.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// assert_eq!("Hello world".find(['l', 'l']), Some(2));
|
|
/// assert_eq!("Hello world".find(['l', 'l']), Some(2));
|
|
/// ```
|
|
impl<'a, const N: usize> Pattern<'a> for [char; N] {
|
|
pattern_methods!(CharArraySearcher<'a, N>, MultiCharEqPattern, CharArraySearcher);
|
|
}
|
|
|
|
unsafe impl<'a, const N: usize> Searcher<'a> for CharArraySearcher<'a, N> {
|
|
searcher_methods!(forward);
|
|
}
|
|
|
|
unsafe impl<'a, const N: usize> ReverseSearcher<'a> for CharArraySearcher<'a, N> {
|
|
searcher_methods!(reverse);
|
|
}
|
|
|
|
/// Searches for chars that are equal to any of the [`char`]s in the array.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// assert_eq!("Hello world".find(&['l', 'l']), Some(2));
|
|
/// assert_eq!("Hello world".find(&['l', 'l']), Some(2));
|
|
/// ```
|
|
impl<'a, 'b, const N: usize> Pattern<'a> for &'b [char; N] {
|
|
pattern_methods!(CharArrayRefSearcher<'a, 'b, N>, MultiCharEqPattern, CharArrayRefSearcher);
|
|
}
|
|
|
|
unsafe impl<'a, 'b, const N: usize> Searcher<'a> for CharArrayRefSearcher<'a, 'b, N> {
|
|
searcher_methods!(forward);
|
|
}
|
|
|
|
unsafe impl<'a, 'b, const N: usize> ReverseSearcher<'a> for CharArrayRefSearcher<'a, 'b, N> {
|
|
searcher_methods!(reverse);
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Impl for &[char]
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
// Todo: Change / Remove due to ambiguity in meaning.
|
|
|
|
/// Associated type for `<&[char] as Pattern<'a>>::Searcher`.
|
|
#[derive(Clone, Debug)]
|
|
pub struct CharSliceSearcher<'a, 'b>(<MultiCharEqPattern<&'b [char]> as Pattern<'a>>::Searcher);
|
|
|
|
unsafe impl<'a, 'b> Searcher<'a> for CharSliceSearcher<'a, 'b> {
|
|
searcher_methods!(forward);
|
|
}
|
|
|
|
unsafe impl<'a, 'b> ReverseSearcher<'a> for CharSliceSearcher<'a, 'b> {
|
|
searcher_methods!(reverse);
|
|
}
|
|
|
|
impl<'a, 'b> DoubleEndedSearcher<'a> for CharSliceSearcher<'a, 'b> {}
|
|
|
|
/// Searches for chars that are equal to any of the [`char`]s in the slice.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// assert_eq!("Hello world".find(&['l', 'l'] as &[_]), Some(2));
|
|
/// assert_eq!("Hello world".find(&['l', 'l'][..]), Some(2));
|
|
/// ```
|
|
impl<'a, 'b> Pattern<'a> for &'b [char] {
|
|
pattern_methods!(CharSliceSearcher<'a, 'b>, MultiCharEqPattern, CharSliceSearcher);
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Impl for F: FnMut(char) -> bool
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Associated type for `<F as Pattern<'a>>::Searcher`.
|
|
#[derive(Clone)]
|
|
pub struct CharPredicateSearcher<'a, F>(<MultiCharEqPattern<F> as Pattern<'a>>::Searcher)
|
|
where
|
|
F: FnMut(char) -> bool;
|
|
|
|
impl<F> fmt::Debug for CharPredicateSearcher<'_, F>
|
|
where
|
|
F: FnMut(char) -> bool,
|
|
{
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
f.debug_struct("CharPredicateSearcher")
|
|
.field("haystack", &self.0.haystack)
|
|
.field("char_indices", &self.0.char_indices)
|
|
.finish()
|
|
}
|
|
}
|
|
unsafe impl<'a, F> Searcher<'a> for CharPredicateSearcher<'a, F>
|
|
where
|
|
F: FnMut(char) -> bool,
|
|
{
|
|
searcher_methods!(forward);
|
|
}
|
|
|
|
unsafe impl<'a, F> ReverseSearcher<'a> for CharPredicateSearcher<'a, F>
|
|
where
|
|
F: FnMut(char) -> bool,
|
|
{
|
|
searcher_methods!(reverse);
|
|
}
|
|
|
|
impl<'a, F> DoubleEndedSearcher<'a> for CharPredicateSearcher<'a, F> where F: FnMut(char) -> bool {}
|
|
|
|
/// Searches for [`char`]s that match the given predicate.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// assert_eq!("Hello world".find(char::is_uppercase), Some(0));
|
|
/// assert_eq!("Hello world".find(|c| "aeiou".contains(c)), Some(1));
|
|
/// ```
|
|
impl<'a, F> Pattern<'a> for F
|
|
where
|
|
F: FnMut(char) -> bool,
|
|
{
|
|
pattern_methods!(CharPredicateSearcher<'a, F>, MultiCharEqPattern, CharPredicateSearcher);
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Impl for &&str
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Delegates to the `&str` impl.
|
|
impl<'a, 'b, 'c> Pattern<'a> for &'c &'b str {
|
|
pattern_methods!(StrSearcher<'a, 'b>, |&s| s, |s| s);
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Impl for &str
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Non-allocating substring search.
|
|
///
|
|
/// Will handle the pattern `""` as returning empty matches at each character
|
|
/// boundary.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// assert_eq!("Hello world".find("world"), Some(6));
|
|
/// ```
|
|
impl<'a, 'b> Pattern<'a> for &'b str {
|
|
type Searcher = StrSearcher<'a, 'b>;
|
|
|
|
#[inline]
|
|
fn into_searcher(self, haystack: &'a str) -> StrSearcher<'a, 'b> {
|
|
StrSearcher::new(haystack, self)
|
|
}
|
|
|
|
/// Checks whether the pattern matches at the front of the haystack.
|
|
#[inline]
|
|
fn is_prefix_of(self, haystack: &'a str) -> bool {
|
|
haystack.as_bytes().starts_with(self.as_bytes())
|
|
}
|
|
|
|
/// Checks whether the pattern matches anywhere in the haystack
|
|
#[inline]
|
|
fn is_contained_in(self, haystack: &'a str) -> bool {
|
|
if self.len() == 0 {
|
|
return true;
|
|
}
|
|
|
|
match self.len().cmp(&haystack.len()) {
|
|
Ordering::Less => {
|
|
if self.len() == 1 {
|
|
return haystack.as_bytes().contains(&self.as_bytes()[0]);
|
|
}
|
|
|
|
#[cfg(all(target_arch = "x86_64", target_feature = "sse2"))]
|
|
if self.len() <= 32 {
|
|
if let Some(result) = simd_contains(self, haystack) {
|
|
return result;
|
|
}
|
|
}
|
|
|
|
self.into_searcher(haystack).next_match().is_some()
|
|
}
|
|
_ => self == haystack,
|
|
}
|
|
}
|
|
|
|
/// Removes the pattern from the front of haystack, if it matches.
|
|
#[inline]
|
|
fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> {
|
|
if self.is_prefix_of(haystack) {
|
|
// SAFETY: prefix was just verified to exist.
|
|
unsafe { Some(haystack.get_unchecked(self.as_bytes().len()..)) }
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
|
|
/// Checks whether the pattern matches at the back of the haystack.
|
|
#[inline]
|
|
fn is_suffix_of(self, haystack: &'a str) -> bool {
|
|
haystack.as_bytes().ends_with(self.as_bytes())
|
|
}
|
|
|
|
/// Removes the pattern from the back of haystack, if it matches.
|
|
#[inline]
|
|
fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str> {
|
|
if self.is_suffix_of(haystack) {
|
|
let i = haystack.len() - self.as_bytes().len();
|
|
// SAFETY: suffix was just verified to exist.
|
|
unsafe { Some(haystack.get_unchecked(..i)) }
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Two Way substring searcher
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
#[derive(Clone, Debug)]
|
|
/// Associated type for `<&str as Pattern<'a>>::Searcher`.
|
|
pub struct StrSearcher<'a, 'b> {
|
|
haystack: &'a str,
|
|
needle: &'b str,
|
|
|
|
searcher: StrSearcherImpl,
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
enum StrSearcherImpl {
|
|
Empty(EmptyNeedle),
|
|
TwoWay(TwoWaySearcher),
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
struct EmptyNeedle {
|
|
position: usize,
|
|
end: usize,
|
|
is_match_fw: bool,
|
|
is_match_bw: bool,
|
|
// Needed in case of an empty haystack, see #85462
|
|
is_finished: bool,
|
|
}
|
|
|
|
impl<'a, 'b> StrSearcher<'a, 'b> {
|
|
fn new(haystack: &'a str, needle: &'b str) -> StrSearcher<'a, 'b> {
|
|
if needle.is_empty() {
|
|
StrSearcher {
|
|
haystack,
|
|
needle,
|
|
searcher: StrSearcherImpl::Empty(EmptyNeedle {
|
|
position: 0,
|
|
end: haystack.len(),
|
|
is_match_fw: true,
|
|
is_match_bw: true,
|
|
is_finished: false,
|
|
}),
|
|
}
|
|
} else {
|
|
StrSearcher {
|
|
haystack,
|
|
needle,
|
|
searcher: StrSearcherImpl::TwoWay(TwoWaySearcher::new(
|
|
needle.as_bytes(),
|
|
haystack.len(),
|
|
)),
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
unsafe impl<'a, 'b> Searcher<'a> for StrSearcher<'a, 'b> {
|
|
#[inline]
|
|
fn haystack(&self) -> &'a str {
|
|
self.haystack
|
|
}
|
|
|
|
#[inline]
|
|
fn next(&mut self) -> SearchStep {
|
|
match self.searcher {
|
|
StrSearcherImpl::Empty(ref mut searcher) => {
|
|
if searcher.is_finished {
|
|
return SearchStep::Done;
|
|
}
|
|
// empty needle rejects every char and matches every empty string between them
|
|
let is_match = searcher.is_match_fw;
|
|
searcher.is_match_fw = !searcher.is_match_fw;
|
|
let pos = searcher.position;
|
|
match self.haystack[pos..].chars().next() {
|
|
_ if is_match => SearchStep::Match(pos, pos),
|
|
None => {
|
|
searcher.is_finished = true;
|
|
SearchStep::Done
|
|
}
|
|
Some(ch) => {
|
|
searcher.position += ch.len_utf8();
|
|
SearchStep::Reject(pos, searcher.position)
|
|
}
|
|
}
|
|
}
|
|
StrSearcherImpl::TwoWay(ref mut searcher) => {
|
|
// TwoWaySearcher produces valid *Match* indices that split at char boundaries
|
|
// as long as it does correct matching and that haystack and needle are
|
|
// valid UTF-8
|
|
// *Rejects* from the algorithm can fall on any indices, but we will walk them
|
|
// manually to the next character boundary, so that they are utf-8 safe.
|
|
if searcher.position == self.haystack.len() {
|
|
return SearchStep::Done;
|
|
}
|
|
let is_long = searcher.memory == usize::MAX;
|
|
match searcher.next::<RejectAndMatch>(
|
|
self.haystack.as_bytes(),
|
|
self.needle.as_bytes(),
|
|
is_long,
|
|
) {
|
|
SearchStep::Reject(a, mut b) => {
|
|
// skip to next char boundary
|
|
while !self.haystack.is_char_boundary(b) {
|
|
b += 1;
|
|
}
|
|
searcher.position = cmp::max(b, searcher.position);
|
|
SearchStep::Reject(a, b)
|
|
}
|
|
otherwise => otherwise,
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn next_match(&mut self) -> Option<(usize, usize)> {
|
|
match self.searcher {
|
|
StrSearcherImpl::Empty(..) => loop {
|
|
match self.next() {
|
|
SearchStep::Match(a, b) => return Some((a, b)),
|
|
SearchStep::Done => return None,
|
|
SearchStep::Reject(..) => {}
|
|
}
|
|
},
|
|
StrSearcherImpl::TwoWay(ref mut searcher) => {
|
|
let is_long = searcher.memory == usize::MAX;
|
|
// write out `true` and `false` cases to encourage the compiler
|
|
// to specialize the two cases separately.
|
|
if is_long {
|
|
searcher.next::<MatchOnly>(
|
|
self.haystack.as_bytes(),
|
|
self.needle.as_bytes(),
|
|
true,
|
|
)
|
|
} else {
|
|
searcher.next::<MatchOnly>(
|
|
self.haystack.as_bytes(),
|
|
self.needle.as_bytes(),
|
|
false,
|
|
)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
unsafe impl<'a, 'b> ReverseSearcher<'a> for StrSearcher<'a, 'b> {
|
|
#[inline]
|
|
fn next_back(&mut self) -> SearchStep {
|
|
match self.searcher {
|
|
StrSearcherImpl::Empty(ref mut searcher) => {
|
|
if searcher.is_finished {
|
|
return SearchStep::Done;
|
|
}
|
|
let is_match = searcher.is_match_bw;
|
|
searcher.is_match_bw = !searcher.is_match_bw;
|
|
let end = searcher.end;
|
|
match self.haystack[..end].chars().next_back() {
|
|
_ if is_match => SearchStep::Match(end, end),
|
|
None => {
|
|
searcher.is_finished = true;
|
|
SearchStep::Done
|
|
}
|
|
Some(ch) => {
|
|
searcher.end -= ch.len_utf8();
|
|
SearchStep::Reject(searcher.end, end)
|
|
}
|
|
}
|
|
}
|
|
StrSearcherImpl::TwoWay(ref mut searcher) => {
|
|
if searcher.end == 0 {
|
|
return SearchStep::Done;
|
|
}
|
|
let is_long = searcher.memory == usize::MAX;
|
|
match searcher.next_back::<RejectAndMatch>(
|
|
self.haystack.as_bytes(),
|
|
self.needle.as_bytes(),
|
|
is_long,
|
|
) {
|
|
SearchStep::Reject(mut a, b) => {
|
|
// skip to next char boundary
|
|
while !self.haystack.is_char_boundary(a) {
|
|
a -= 1;
|
|
}
|
|
searcher.end = cmp::min(a, searcher.end);
|
|
SearchStep::Reject(a, b)
|
|
}
|
|
otherwise => otherwise,
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn next_match_back(&mut self) -> Option<(usize, usize)> {
|
|
match self.searcher {
|
|
StrSearcherImpl::Empty(..) => loop {
|
|
match self.next_back() {
|
|
SearchStep::Match(a, b) => return Some((a, b)),
|
|
SearchStep::Done => return None,
|
|
SearchStep::Reject(..) => {}
|
|
}
|
|
},
|
|
StrSearcherImpl::TwoWay(ref mut searcher) => {
|
|
let is_long = searcher.memory == usize::MAX;
|
|
// write out `true` and `false`, like `next_match`
|
|
if is_long {
|
|
searcher.next_back::<MatchOnly>(
|
|
self.haystack.as_bytes(),
|
|
self.needle.as_bytes(),
|
|
true,
|
|
)
|
|
} else {
|
|
searcher.next_back::<MatchOnly>(
|
|
self.haystack.as_bytes(),
|
|
self.needle.as_bytes(),
|
|
false,
|
|
)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// The internal state of the two-way substring search algorithm.
|
|
#[derive(Clone, Debug)]
|
|
struct TwoWaySearcher {
|
|
// constants
|
|
/// critical factorization index
|
|
crit_pos: usize,
|
|
/// critical factorization index for reversed needle
|
|
crit_pos_back: usize,
|
|
period: usize,
|
|
/// `byteset` is an extension (not part of the two way algorithm);
|
|
/// it's a 64-bit "fingerprint" where each set bit `j` corresponds
|
|
/// to a (byte & 63) == j present in the needle.
|
|
byteset: u64,
|
|
|
|
// variables
|
|
position: usize,
|
|
end: usize,
|
|
/// index into needle before which we have already matched
|
|
memory: usize,
|
|
/// index into needle after which we have already matched
|
|
memory_back: usize,
|
|
}
|
|
|
|
/*
|
|
This is the Two-Way search algorithm, which was introduced in the paper:
|
|
Crochemore, M., Perrin, D., 1991, Two-way string-matching, Journal of the ACM 38(3):651-675.
|
|
|
|
Here's some background information.
|
|
|
|
A *word* is a string of symbols. The *length* of a word should be a familiar
|
|
notion, and here we denote it for any word x by |x|.
|
|
(We also allow for the possibility of the *empty word*, a word of length zero).
|
|
|
|
If x is any non-empty word, then an integer p with 0 < p <= |x| is said to be a
|
|
*period* for x iff for all i with 0 <= i <= |x| - p - 1, we have x[i] == x[i+p].
|
|
For example, both 1 and 2 are periods for the string "aa". As another example,
|
|
the only period of the string "abcd" is 4.
|
|
|
|
We denote by period(x) the *smallest* period of x (provided that x is non-empty).
|
|
This is always well-defined since every non-empty word x has at least one period,
|
|
|x|. We sometimes call this *the period* of x.
|
|
|
|
If u, v and x are words such that x = uv, where uv is the concatenation of u and
|
|
v, then we say that (u, v) is a *factorization* of x.
|
|
|
|
Let (u, v) be a factorization for a word x. Then if w is a non-empty word such
|
|
that both of the following hold
|
|
|
|
- either w is a suffix of u or u is a suffix of w
|
|
- either w is a prefix of v or v is a prefix of w
|
|
|
|
then w is said to be a *repetition* for the factorization (u, v).
|
|
|
|
Just to unpack this, there are four possibilities here. Let w = "abc". Then we
|
|
might have:
|
|
|
|
- w is a suffix of u and w is a prefix of v. ex: ("lolabc", "abcde")
|
|
- w is a suffix of u and v is a prefix of w. ex: ("lolabc", "ab")
|
|
- u is a suffix of w and w is a prefix of v. ex: ("bc", "abchi")
|
|
- u is a suffix of w and v is a prefix of w. ex: ("bc", "a")
|
|
|
|
Note that the word vu is a repetition for any factorization (u,v) of x = uv,
|
|
so every factorization has at least one repetition.
|
|
|
|
If x is a string and (u, v) is a factorization for x, then a *local period* for
|
|
(u, v) is an integer r such that there is some word w such that |w| = r and w is
|
|
a repetition for (u, v).
|
|
|
|
We denote by local_period(u, v) the smallest local period of (u, v). We sometimes
|
|
call this *the local period* of (u, v). Provided that x = uv is non-empty, this
|
|
is well-defined (because each non-empty word has at least one factorization, as
|
|
noted above).
|
|
|
|
It can be proven that the following is an equivalent definition of a local period
|
|
for a factorization (u, v): any positive integer r such that x[i] == x[i+r] for
|
|
all i such that |u| - r <= i <= |u| - 1 and such that both x[i] and x[i+r] are
|
|
defined. (i.e., i > 0 and i + r < |x|).
|
|
|
|
Using the above reformulation, it is easy to prove that
|
|
|
|
1 <= local_period(u, v) <= period(uv)
|
|
|
|
A factorization (u, v) of x such that local_period(u,v) = period(x) is called a
|
|
*critical factorization*.
|
|
|
|
The algorithm hinges on the following theorem, which is stated without proof:
|
|
|
|
**Critical Factorization Theorem** Any word x has at least one critical
|
|
factorization (u, v) such that |u| < period(x).
|
|
|
|
The purpose of maximal_suffix is to find such a critical factorization.
|
|
|
|
If the period is short, compute another factorization x = u' v' to use
|
|
for reverse search, chosen instead so that |v'| < period(x).
|
|
|
|
*/
|
|
impl TwoWaySearcher {
|
|
fn new(needle: &[u8], end: usize) -> TwoWaySearcher {
|
|
let (crit_pos_false, period_false) = TwoWaySearcher::maximal_suffix(needle, false);
|
|
let (crit_pos_true, period_true) = TwoWaySearcher::maximal_suffix(needle, true);
|
|
|
|
let (crit_pos, period) = if crit_pos_false > crit_pos_true {
|
|
(crit_pos_false, period_false)
|
|
} else {
|
|
(crit_pos_true, period_true)
|
|
};
|
|
|
|
// A particularly readable explanation of what's going on here can be found
|
|
// in Crochemore and Rytter's book "Text Algorithms", ch 13. Specifically
|
|
// see the code for "Algorithm CP" on p. 323.
|
|
//
|
|
// What's going on is we have some critical factorization (u, v) of the
|
|
// needle, and we want to determine whether u is a suffix of
|
|
// &v[..period]. If it is, we use "Algorithm CP1". Otherwise we use
|
|
// "Algorithm CP2", which is optimized for when the period of the needle
|
|
// is large.
|
|
if needle[..crit_pos] == needle[period..period + crit_pos] {
|
|
// short period case -- the period is exact
|
|
// compute a separate critical factorization for the reversed needle
|
|
// x = u' v' where |v'| < period(x).
|
|
//
|
|
// This is sped up by the period being known already.
|
|
// Note that a case like x = "acba" may be factored exactly forwards
|
|
// (crit_pos = 1, period = 3) while being factored with approximate
|
|
// period in reverse (crit_pos = 2, period = 2). We use the given
|
|
// reverse factorization but keep the exact period.
|
|
let crit_pos_back = needle.len()
|
|
- cmp::max(
|
|
TwoWaySearcher::reverse_maximal_suffix(needle, period, false),
|
|
TwoWaySearcher::reverse_maximal_suffix(needle, period, true),
|
|
);
|
|
|
|
TwoWaySearcher {
|
|
crit_pos,
|
|
crit_pos_back,
|
|
period,
|
|
byteset: Self::byteset_create(&needle[..period]),
|
|
|
|
position: 0,
|
|
end,
|
|
memory: 0,
|
|
memory_back: needle.len(),
|
|
}
|
|
} else {
|
|
// long period case -- we have an approximation to the actual period,
|
|
// and don't use memorization.
|
|
//
|
|
// Approximate the period by lower bound max(|u|, |v|) + 1.
|
|
// The critical factorization is efficient to use for both forward and
|
|
// reverse search.
|
|
|
|
TwoWaySearcher {
|
|
crit_pos,
|
|
crit_pos_back: crit_pos,
|
|
period: cmp::max(crit_pos, needle.len() - crit_pos) + 1,
|
|
byteset: Self::byteset_create(needle),
|
|
|
|
position: 0,
|
|
end,
|
|
memory: usize::MAX, // Dummy value to signify that the period is long
|
|
memory_back: usize::MAX,
|
|
}
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn byteset_create(bytes: &[u8]) -> u64 {
|
|
bytes.iter().fold(0, |a, &b| (1 << (b & 0x3f)) | a)
|
|
}
|
|
|
|
#[inline]
|
|
fn byteset_contains(&self, byte: u8) -> bool {
|
|
(self.byteset >> ((byte & 0x3f) as usize)) & 1 != 0
|
|
}
|
|
|
|
// One of the main ideas of Two-Way is that we factorize the needle into
|
|
// two halves, (u, v), and begin trying to find v in the haystack by scanning
|
|
// left to right. If v matches, we try to match u by scanning right to left.
|
|
// How far we can jump when we encounter a mismatch is all based on the fact
|
|
// that (u, v) is a critical factorization for the needle.
|
|
#[inline]
|
|
fn next<S>(&mut self, haystack: &[u8], needle: &[u8], long_period: bool) -> S::Output
|
|
where
|
|
S: TwoWayStrategy,
|
|
{
|
|
// `next()` uses `self.position` as its cursor
|
|
let old_pos = self.position;
|
|
let needle_last = needle.len() - 1;
|
|
'search: loop {
|
|
// Check that we have room to search in
|
|
// position + needle_last can not overflow if we assume slices
|
|
// are bounded by isize's range.
|
|
let tail_byte = match haystack.get(self.position + needle_last) {
|
|
Some(&b) => b,
|
|
None => {
|
|
self.position = haystack.len();
|
|
return S::rejecting(old_pos, self.position);
|
|
}
|
|
};
|
|
|
|
if S::use_early_reject() && old_pos != self.position {
|
|
return S::rejecting(old_pos, self.position);
|
|
}
|
|
|
|
// Quickly skip by large portions unrelated to our substring
|
|
if !self.byteset_contains(tail_byte) {
|
|
self.position += needle.len();
|
|
if !long_period {
|
|
self.memory = 0;
|
|
}
|
|
continue 'search;
|
|
}
|
|
|
|
// See if the right part of the needle matches
|
|
let start =
|
|
if long_period { self.crit_pos } else { cmp::max(self.crit_pos, self.memory) };
|
|
for i in start..needle.len() {
|
|
if needle[i] != haystack[self.position + i] {
|
|
self.position += i - self.crit_pos + 1;
|
|
if !long_period {
|
|
self.memory = 0;
|
|
}
|
|
continue 'search;
|
|
}
|
|
}
|
|
|
|
// See if the left part of the needle matches
|
|
let start = if long_period { 0 } else { self.memory };
|
|
for i in (start..self.crit_pos).rev() {
|
|
if needle[i] != haystack[self.position + i] {
|
|
self.position += self.period;
|
|
if !long_period {
|
|
self.memory = needle.len() - self.period;
|
|
}
|
|
continue 'search;
|
|
}
|
|
}
|
|
|
|
// We have found a match!
|
|
let match_pos = self.position;
|
|
|
|
// Note: add self.period instead of needle.len() to have overlapping matches
|
|
self.position += needle.len();
|
|
if !long_period {
|
|
self.memory = 0; // set to needle.len() - self.period for overlapping matches
|
|
}
|
|
|
|
return S::matching(match_pos, match_pos + needle.len());
|
|
}
|
|
}
|
|
|
|
// Follows the ideas in `next()`.
|
|
//
|
|
// The definitions are symmetrical, with period(x) = period(reverse(x))
|
|
// and local_period(u, v) = local_period(reverse(v), reverse(u)), so if (u, v)
|
|
// is a critical factorization, so is (reverse(v), reverse(u)).
|
|
//
|
|
// For the reverse case we have computed a critical factorization x = u' v'
|
|
// (field `crit_pos_back`). We need |u| < period(x) for the forward case and
|
|
// thus |v'| < period(x) for the reverse.
|
|
//
|
|
// To search in reverse through the haystack, we search forward through
|
|
// a reversed haystack with a reversed needle, matching first u' and then v'.
|
|
#[inline]
|
|
fn next_back<S>(&mut self, haystack: &[u8], needle: &[u8], long_period: bool) -> S::Output
|
|
where
|
|
S: TwoWayStrategy,
|
|
{
|
|
// `next_back()` uses `self.end` as its cursor -- so that `next()` and `next_back()`
|
|
// are independent.
|
|
let old_end = self.end;
|
|
'search: loop {
|
|
// Check that we have room to search in
|
|
// end - needle.len() will wrap around when there is no more room,
|
|
// but due to slice length limits it can never wrap all the way back
|
|
// into the length of haystack.
|
|
let front_byte = match haystack.get(self.end.wrapping_sub(needle.len())) {
|
|
Some(&b) => b,
|
|
None => {
|
|
self.end = 0;
|
|
return S::rejecting(0, old_end);
|
|
}
|
|
};
|
|
|
|
if S::use_early_reject() && old_end != self.end {
|
|
return S::rejecting(self.end, old_end);
|
|
}
|
|
|
|
// Quickly skip by large portions unrelated to our substring
|
|
if !self.byteset_contains(front_byte) {
|
|
self.end -= needle.len();
|
|
if !long_period {
|
|
self.memory_back = needle.len();
|
|
}
|
|
continue 'search;
|
|
}
|
|
|
|
// See if the left part of the needle matches
|
|
let crit = if long_period {
|
|
self.crit_pos_back
|
|
} else {
|
|
cmp::min(self.crit_pos_back, self.memory_back)
|
|
};
|
|
for i in (0..crit).rev() {
|
|
if needle[i] != haystack[self.end - needle.len() + i] {
|
|
self.end -= self.crit_pos_back - i;
|
|
if !long_period {
|
|
self.memory_back = needle.len();
|
|
}
|
|
continue 'search;
|
|
}
|
|
}
|
|
|
|
// See if the right part of the needle matches
|
|
let needle_end = if long_period { needle.len() } else { self.memory_back };
|
|
for i in self.crit_pos_back..needle_end {
|
|
if needle[i] != haystack[self.end - needle.len() + i] {
|
|
self.end -= self.period;
|
|
if !long_period {
|
|
self.memory_back = self.period;
|
|
}
|
|
continue 'search;
|
|
}
|
|
}
|
|
|
|
// We have found a match!
|
|
let match_pos = self.end - needle.len();
|
|
// Note: sub self.period instead of needle.len() to have overlapping matches
|
|
self.end -= needle.len();
|
|
if !long_period {
|
|
self.memory_back = needle.len();
|
|
}
|
|
|
|
return S::matching(match_pos, match_pos + needle.len());
|
|
}
|
|
}
|
|
|
|
// Compute the maximal suffix of `arr`.
|
|
//
|
|
// The maximal suffix is a possible critical factorization (u, v) of `arr`.
|
|
//
|
|
// Returns (`i`, `p`) where `i` is the starting index of v and `p` is the
|
|
// period of v.
|
|
//
|
|
// `order_greater` determines if lexical order is `<` or `>`. Both
|
|
// orders must be computed -- the ordering with the largest `i` gives
|
|
// a critical factorization.
|
|
//
|
|
// For long period cases, the resulting period is not exact (it is too short).
|
|
#[inline]
|
|
fn maximal_suffix(arr: &[u8], order_greater: bool) -> (usize, usize) {
|
|
let mut left = 0; // Corresponds to i in the paper
|
|
let mut right = 1; // Corresponds to j in the paper
|
|
let mut offset = 0; // Corresponds to k in the paper, but starting at 0
|
|
// to match 0-based indexing.
|
|
let mut period = 1; // Corresponds to p in the paper
|
|
|
|
while let Some(&a) = arr.get(right + offset) {
|
|
// `left` will be inbounds when `right` is.
|
|
let b = arr[left + offset];
|
|
if (a < b && !order_greater) || (a > b && order_greater) {
|
|
// Suffix is smaller, period is entire prefix so far.
|
|
right += offset + 1;
|
|
offset = 0;
|
|
period = right - left;
|
|
} else if a == b {
|
|
// Advance through repetition of the current period.
|
|
if offset + 1 == period {
|
|
right += offset + 1;
|
|
offset = 0;
|
|
} else {
|
|
offset += 1;
|
|
}
|
|
} else {
|
|
// Suffix is larger, start over from current location.
|
|
left = right;
|
|
right += 1;
|
|
offset = 0;
|
|
period = 1;
|
|
}
|
|
}
|
|
(left, period)
|
|
}
|
|
|
|
// Compute the maximal suffix of the reverse of `arr`.
|
|
//
|
|
// The maximal suffix is a possible critical factorization (u', v') of `arr`.
|
|
//
|
|
// Returns `i` where `i` is the starting index of v', from the back;
|
|
// returns immediately when a period of `known_period` is reached.
|
|
//
|
|
// `order_greater` determines if lexical order is `<` or `>`. Both
|
|
// orders must be computed -- the ordering with the largest `i` gives
|
|
// a critical factorization.
|
|
//
|
|
// For long period cases, the resulting period is not exact (it is too short).
|
|
fn reverse_maximal_suffix(arr: &[u8], known_period: usize, order_greater: bool) -> usize {
|
|
let mut left = 0; // Corresponds to i in the paper
|
|
let mut right = 1; // Corresponds to j in the paper
|
|
let mut offset = 0; // Corresponds to k in the paper, but starting at 0
|
|
// to match 0-based indexing.
|
|
let mut period = 1; // Corresponds to p in the paper
|
|
let n = arr.len();
|
|
|
|
while right + offset < n {
|
|
let a = arr[n - (1 + right + offset)];
|
|
let b = arr[n - (1 + left + offset)];
|
|
if (a < b && !order_greater) || (a > b && order_greater) {
|
|
// Suffix is smaller, period is entire prefix so far.
|
|
right += offset + 1;
|
|
offset = 0;
|
|
period = right - left;
|
|
} else if a == b {
|
|
// Advance through repetition of the current period.
|
|
if offset + 1 == period {
|
|
right += offset + 1;
|
|
offset = 0;
|
|
} else {
|
|
offset += 1;
|
|
}
|
|
} else {
|
|
// Suffix is larger, start over from current location.
|
|
left = right;
|
|
right += 1;
|
|
offset = 0;
|
|
period = 1;
|
|
}
|
|
if period == known_period {
|
|
break;
|
|
}
|
|
}
|
|
debug_assert!(period <= known_period);
|
|
left
|
|
}
|
|
}
|
|
|
|
// TwoWayStrategy allows the algorithm to either skip non-matches as quickly
|
|
// as possible, or to work in a mode where it emits Rejects relatively quickly.
|
|
trait TwoWayStrategy {
|
|
type Output;
|
|
fn use_early_reject() -> bool;
|
|
fn rejecting(a: usize, b: usize) -> Self::Output;
|
|
fn matching(a: usize, b: usize) -> Self::Output;
|
|
}
|
|
|
|
/// Skip to match intervals as quickly as possible
|
|
enum MatchOnly {}
|
|
|
|
impl TwoWayStrategy for MatchOnly {
|
|
type Output = Option<(usize, usize)>;
|
|
|
|
#[inline]
|
|
fn use_early_reject() -> bool {
|
|
false
|
|
}
|
|
#[inline]
|
|
fn rejecting(_a: usize, _b: usize) -> Self::Output {
|
|
None
|
|
}
|
|
#[inline]
|
|
fn matching(a: usize, b: usize) -> Self::Output {
|
|
Some((a, b))
|
|
}
|
|
}
|
|
|
|
/// Emit Rejects regularly
|
|
enum RejectAndMatch {}
|
|
|
|
impl TwoWayStrategy for RejectAndMatch {
|
|
type Output = SearchStep;
|
|
|
|
#[inline]
|
|
fn use_early_reject() -> bool {
|
|
true
|
|
}
|
|
#[inline]
|
|
fn rejecting(a: usize, b: usize) -> Self::Output {
|
|
SearchStep::Reject(a, b)
|
|
}
|
|
#[inline]
|
|
fn matching(a: usize, b: usize) -> Self::Output {
|
|
SearchStep::Match(a, b)
|
|
}
|
|
}
|
|
|
|
/// SIMD search for short needles based on
|
|
/// Wojciech Muła's "SIMD-friendly algorithms for substring searching"[0]
|
|
///
|
|
/// It skips ahead by the vector width on each iteration (rather than the needle length as two-way
|
|
/// does) by probing the first and last byte of the needle for the whole vector width
|
|
/// and only doing full needle comparisons when the vectorized probe indicated potential matches.
|
|
///
|
|
/// Since the x86_64 baseline only offers SSE2 we only use u8x16 here.
|
|
/// If we ever ship std with for x86-64-v3 or adapt this for other platforms then wider vectors
|
|
/// should be evaluated.
|
|
///
|
|
/// For haystacks smaller than vector-size + needle length it falls back to
|
|
/// a naive O(n*m) search so this implementation should not be called on larger needles.
|
|
///
|
|
/// [0]: http://0x80.pl/articles/simd-strfind.html#sse-avx2
|
|
#[cfg(all(target_arch = "x86_64", target_feature = "sse2"))]
|
|
#[inline]
|
|
fn simd_contains(needle: &str, haystack: &str) -> Option<bool> {
|
|
let needle = needle.as_bytes();
|
|
let haystack = haystack.as_bytes();
|
|
|
|
debug_assert!(needle.len() > 1);
|
|
|
|
use crate::ops::BitAnd;
|
|
use crate::simd::mask8x16 as Mask;
|
|
use crate::simd::u8x16 as Block;
|
|
use crate::simd::{SimdPartialEq, ToBitMask};
|
|
|
|
let first_probe = needle[0];
|
|
let last_byte_offset = needle.len() - 1;
|
|
|
|
// the offset used for the 2nd vector
|
|
let second_probe_offset = if needle.len() == 2 {
|
|
// never bail out on len=2 needles because the probes will fully cover them and have
|
|
// no degenerate cases.
|
|
1
|
|
} else {
|
|
// try a few bytes in case first and last byte of the needle are the same
|
|
let Some(second_probe_offset) = (needle.len().saturating_sub(4)..needle.len()).rfind(|&idx| needle[idx] != first_probe) else {
|
|
// fall back to other search methods if we can't find any different bytes
|
|
// since we could otherwise hit some degenerate cases
|
|
return None;
|
|
};
|
|
second_probe_offset
|
|
};
|
|
|
|
// do a naive search if the haystack is too small to fit
|
|
if haystack.len() < Block::LANES + last_byte_offset {
|
|
return Some(haystack.windows(needle.len()).any(|c| c == needle));
|
|
}
|
|
|
|
let first_probe: Block = Block::splat(first_probe);
|
|
let second_probe: Block = Block::splat(needle[second_probe_offset]);
|
|
// first byte are already checked by the outer loop. to verify a match only the
|
|
// remainder has to be compared.
|
|
let trimmed_needle = &needle[1..];
|
|
|
|
// this #[cold] is load-bearing, benchmark before removing it...
|
|
let check_mask = #[cold]
|
|
|idx, mask: u16, skip: bool| -> bool {
|
|
if skip {
|
|
return false;
|
|
}
|
|
|
|
// and so is this. optimizations are weird.
|
|
let mut mask = mask;
|
|
|
|
while mask != 0 {
|
|
let trailing = mask.trailing_zeros();
|
|
let offset = idx + trailing as usize + 1;
|
|
// SAFETY: mask is between 0 and 15 trailing zeroes, we skip one additional byte that was already compared
|
|
// and then take trimmed_needle.len() bytes. This is within the bounds defined by the outer loop
|
|
unsafe {
|
|
let sub = haystack.get_unchecked(offset..).get_unchecked(..trimmed_needle.len());
|
|
if small_slice_eq(sub, trimmed_needle) {
|
|
return true;
|
|
}
|
|
}
|
|
mask &= !(1 << trailing);
|
|
}
|
|
return false;
|
|
};
|
|
|
|
let test_chunk = |idx| -> u16 {
|
|
// SAFETY: this requires at least LANES bytes being readable at idx
|
|
// that is ensured by the loop ranges (see comments below)
|
|
let a: Block = unsafe { haystack.as_ptr().add(idx).cast::<Block>().read_unaligned() };
|
|
// SAFETY: this requires LANES + block_offset bytes being readable at idx
|
|
let b: Block = unsafe {
|
|
haystack.as_ptr().add(idx).add(second_probe_offset).cast::<Block>().read_unaligned()
|
|
};
|
|
let eq_first: Mask = a.simd_eq(first_probe);
|
|
let eq_last: Mask = b.simd_eq(second_probe);
|
|
let both = eq_first.bitand(eq_last);
|
|
let mask = both.to_bitmask();
|
|
|
|
return mask;
|
|
};
|
|
|
|
let mut i = 0;
|
|
let mut result = false;
|
|
// The loop condition must ensure that there's enough headroom to read LANE bytes,
|
|
// and not only at the current index but also at the index shifted by block_offset
|
|
const UNROLL: usize = 4;
|
|
while i + last_byte_offset + UNROLL * Block::LANES < haystack.len() && !result {
|
|
let mut masks = [0u16; UNROLL];
|
|
for j in 0..UNROLL {
|
|
masks[j] = test_chunk(i + j * Block::LANES);
|
|
}
|
|
for j in 0..UNROLL {
|
|
let mask = masks[j];
|
|
if mask != 0 {
|
|
result |= check_mask(i + j * Block::LANES, mask, result);
|
|
}
|
|
}
|
|
i += UNROLL * Block::LANES;
|
|
}
|
|
while i + last_byte_offset + Block::LANES < haystack.len() && !result {
|
|
let mask = test_chunk(i);
|
|
if mask != 0 {
|
|
result |= check_mask(i, mask, result);
|
|
}
|
|
i += Block::LANES;
|
|
}
|
|
|
|
// Process the tail that didn't fit into LANES-sized steps.
|
|
// This simply repeats the same procedure but as right-aligned chunk instead
|
|
// of a left-aligned one. The last byte must be exactly flush with the string end so
|
|
// we don't miss a single byte or read out of bounds.
|
|
let i = haystack.len() - last_byte_offset - Block::LANES;
|
|
let mask = test_chunk(i);
|
|
if mask != 0 {
|
|
result |= check_mask(i, mask, result);
|
|
}
|
|
|
|
Some(result)
|
|
}
|
|
|
|
/// Compares short slices for equality.
|
|
///
|
|
/// It avoids a call to libc's memcmp which is faster on long slices
|
|
/// due to SIMD optimizations but it incurs a function call overhead.
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// Both slices must have the same length.
|
|
#[cfg(all(target_arch = "x86_64", target_feature = "sse2"))] // only called on x86
|
|
#[inline]
|
|
unsafe fn small_slice_eq(x: &[u8], y: &[u8]) -> bool {
|
|
debug_assert_eq!(x.len(), y.len());
|
|
// This function is adapted from
|
|
// https://github.com/BurntSushi/memchr/blob/8037d11b4357b0f07be2bb66dc2659d9cf28ad32/src/memmem/util.rs#L32
|
|
|
|
// If we don't have enough bytes to do 4-byte at a time loads, then
|
|
// fall back to the naive slow version.
|
|
//
|
|
// Potential alternative: We could do a copy_nonoverlapping combined with a mask instead
|
|
// of a loop. Benchmark it.
|
|
if x.len() < 4 {
|
|
for (&b1, &b2) in x.iter().zip(y) {
|
|
if b1 != b2 {
|
|
return false;
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
// When we have 4 or more bytes to compare, then proceed in chunks of 4 at
|
|
// a time using unaligned loads.
|
|
//
|
|
// Also, why do 4 byte loads instead of, say, 8 byte loads? The reason is
|
|
// that this particular version of memcmp is likely to be called with tiny
|
|
// needles. That means that if we do 8 byte loads, then a higher proportion
|
|
// of memcmp calls will use the slower variant above. With that said, this
|
|
// is a hypothesis and is only loosely supported by benchmarks. There's
|
|
// likely some improvement that could be made here. The main thing here
|
|
// though is to optimize for latency, not throughput.
|
|
|
|
// SAFETY: Via the conditional above, we know that both `px` and `py`
|
|
// have the same length, so `px < pxend` implies that `py < pyend`.
|
|
// Thus, derefencing both `px` and `py` in the loop below is safe.
|
|
//
|
|
// Moreover, we set `pxend` and `pyend` to be 4 bytes before the actual
|
|
// end of `px` and `py`. Thus, the final dereference outside of the
|
|
// loop is guaranteed to be valid. (The final comparison will overlap with
|
|
// the last comparison done in the loop for lengths that aren't multiples
|
|
// of four.)
|
|
//
|
|
// Finally, we needn't worry about alignment here, since we do unaligned
|
|
// loads.
|
|
unsafe {
|
|
let (mut px, mut py) = (x.as_ptr(), y.as_ptr());
|
|
let (pxend, pyend) = (px.add(x.len() - 4), py.add(y.len() - 4));
|
|
while px < pxend {
|
|
let vx = (px as *const u32).read_unaligned();
|
|
let vy = (py as *const u32).read_unaligned();
|
|
if vx != vy {
|
|
return false;
|
|
}
|
|
px = px.add(4);
|
|
py = py.add(4);
|
|
}
|
|
let vx = (pxend as *const u32).read_unaligned();
|
|
let vy = (pyend as *const u32).read_unaligned();
|
|
vx == vy
|
|
}
|
|
}
|