| // Copyright 2015 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! The string Pattern API. |
| //! |
| //! For more details, see the traits `Pattern`, `Searcher`, |
| //! `ReverseSearcher` and `DoubleEndedSearcher`. |
| |
| #![unstable(feature = "pattern", |
| reason = "API not fully fleshed out and ready to be stabilized", |
| issue = "27721")] |
| |
| use prelude::v1::*; |
| |
| use cmp; |
| use fmt; |
| use usize; |
| |
| // Pattern |
| |
| /// A string pattern. |
| /// |
| /// A `Pattern<'a>` expresses that the implementing type |
| /// can be used as a string pattern for searching in a `&'a str`. |
| /// |
| /// For example, both `'a'` and `"aa"` are patterns that |
| /// would match at index `1` in the string `"baaaab"`. |
| /// |
| /// The trait itself acts as a builder for an associated |
| /// `Searcher` type, which does the actual work of finding |
| /// occurrences of the pattern in a string. |
| pub trait Pattern<'a>: Sized { |
| /// Associated searcher for this pattern |
| type Searcher: Searcher<'a>; |
| |
| /// Constructs the associated searcher from |
| /// `self` and the `haystack` to search in. |
| fn into_searcher(self, haystack: &'a str) -> Self::Searcher; |
| |
| /// Checks whether the pattern matches anywhere in the haystack |
| #[inline] |
| fn is_contained_in(self, haystack: &'a str) -> bool { |
| self.into_searcher(haystack).next_match().is_some() |
| } |
| |
| /// Checks whether the pattern matches at the front of the haystack |
| #[inline] |
| fn is_prefix_of(self, haystack: &'a str) -> bool { |
| match self.into_searcher(haystack).next() { |
| SearchStep::Match(0, _) => true, |
| _ => false, |
| } |
| } |
| |
| /// Checks whether the pattern matches at the back of the haystack |
| #[inline] |
| fn is_suffix_of(self, haystack: &'a str) -> bool |
| where Self::Searcher: ReverseSearcher<'a> |
| { |
| match self.into_searcher(haystack).next_back() { |
| SearchStep::Match(_, j) if haystack.len() == j => true, |
| _ => false, |
| } |
| } |
| } |
| |
| // Searcher |
| |
| /// Result of calling `Searcher::next()` or `ReverseSearcher::next_back()`. |
| #[derive(Copy, Clone, Eq, PartialEq, Debug)] |
| pub enum SearchStep { |
| /// Expresses that a match of the pattern has been found at |
| /// `haystack[a..b]`. |
| Match(usize, usize), |
| /// Expresses that `haystack[a..b]` has been rejected as a possible match |
| /// of the pattern. |
| /// |
| /// Note that there might be more than one `Reject` between two `Match`es, |
| /// there is no requirement for them to be combined into one. |
| Reject(usize, usize), |
| /// Expresses that every byte of the haystack has been visted, ending |
| /// the iteration. |
| Done |
| } |
| |
| /// A searcher for a string pattern. |
| /// |
| /// This trait provides methods for searching for non-overlapping |
| /// matches of a pattern starting from the front (left) of a string. |
| /// |
| /// It will be implemented by associated `Searcher` |
| /// types of the `Pattern` trait. |
| /// |
| /// The trait is marked unsafe because the indices returned by the |
| /// `next()` methods are required to lie on valid utf8 boundaries in |
| /// the haystack. This enables consumers of this trait to |
| /// slice the haystack without additional runtime checks. |
| pub unsafe trait Searcher<'a> { |
| /// Getter for the underlaying string to be searched in |
| /// |
| /// Will always return the same `&str` |
| fn haystack(&self) -> &'a str; |
| |
| /// Performs the next search step starting from the front. |
| /// |
| /// - Returns `Match(a, b)` if `haystack[a..b]` matches the pattern. |
| /// - Returns `Reject(a, b)` if `haystack[a..b]` can not match the |
| /// pattern, even partially. |
| /// - Returns `Done` if every byte of the haystack has been visited |
| /// |
| /// The stream of `Match` and `Reject` values up to a `Done` |
| /// will contain index ranges that are adjacent, non-overlapping, |
| /// covering the whole haystack, and laying on utf8 boundaries. |
| /// |
| /// A `Match` result needs to contain the whole matched pattern, |
| /// however `Reject` results may be split up into arbitrary |
| /// many adjacent fragments. Both ranges may have zero length. |
| /// |
| /// As an example, the pattern `"aaa"` and the haystack `"cbaaaaab"` |
| /// might produce the stream |
| /// `[Reject(0, 1), Reject(1, 2), Match(2, 5), Reject(5, 8)]` |
| fn next(&mut self) -> SearchStep; |
| |
| /// Find the next `Match` result. See `next()` |
| #[inline] |
| fn next_match(&mut self) -> Option<(usize, usize)> { |
| loop { |
| match self.next() { |
| SearchStep::Match(a, b) => return Some((a, b)), |
| SearchStep::Done => return None, |
| _ => continue, |
| } |
| } |
| } |
| |
| /// Find the next `Reject` result. See `next()` |
| #[inline] |
| fn next_reject(&mut self) -> Option<(usize, usize)> { |
| loop { |
| match self.next() { |
| SearchStep::Reject(a, b) => return Some((a, b)), |
| SearchStep::Done => return None, |
| _ => continue, |
| } |
| } |
| } |
| } |
| |
| /// A reverse searcher for a string pattern. |
| /// |
| /// This trait provides methods for searching for non-overlapping |
| /// matches of a pattern starting from the back (right) of a string. |
| /// |
| /// It will be implemented by associated `Searcher` |
| /// types of the `Pattern` trait if the pattern supports searching |
| /// for it from the back. |
| /// |
| /// The index ranges returned by this trait are not required |
| /// to exactly match those of the forward search in reverse. |
| /// |
| /// For the reason why this trait is marked unsafe, see them |
| /// parent trait `Searcher`. |
| pub unsafe trait ReverseSearcher<'a>: Searcher<'a> { |
| /// Performs the next search step starting from the back. |
| /// |
| /// - Returns `Match(a, b)` if `haystack[a..b]` matches the pattern. |
| /// - Returns `Reject(a, b)` if `haystack[a..b]` can not match the |
| /// pattern, even partially. |
| /// - Returns `Done` if every byte of the haystack has been visited |
| /// |
| /// The stream of `Match` and `Reject` values up to a `Done` |
| /// will contain index ranges that are adjacent, non-overlapping, |
| /// covering the whole haystack, and laying on utf8 boundaries. |
| /// |
| /// A `Match` result needs to contain the whole matched pattern, |
| /// however `Reject` results may be split up into arbitrary |
| /// many adjacent fragments. Both ranges may have zero length. |
| /// |
| /// As an example, the pattern `"aaa"` and the haystack `"cbaaaaab"` |
| /// might produce the stream |
| /// `[Reject(7, 8), Match(4, 7), Reject(1, 4), Reject(0, 1)]` |
| fn next_back(&mut self) -> SearchStep; |
| |
| /// Find the next `Match` result. See `next_back()` |
| #[inline] |
| fn next_match_back(&mut self) -> Option<(usize, usize)>{ |
| loop { |
| match self.next_back() { |
| SearchStep::Match(a, b) => return Some((a, b)), |
| SearchStep::Done => return None, |
| _ => continue, |
| } |
| } |
| } |
| |
| /// Find the next `Reject` result. See `next_back()` |
| #[inline] |
| fn next_reject_back(&mut self) -> Option<(usize, usize)>{ |
| loop { |
| match self.next_back() { |
| SearchStep::Reject(a, b) => return Some((a, b)), |
| SearchStep::Done => return None, |
| _ => continue, |
| } |
| } |
| } |
| } |
| |
| /// A marker trait to express that a `ReverseSearcher` |
| /// can be used for a `DoubleEndedIterator` implementation. |
| /// |
| /// For this, the impl of `Searcher` and `ReverseSearcher` need |
| /// to follow these conditions: |
| /// |
| /// - All results of `next()` need to be identical |
| /// to the results of `next_back()` in reverse order. |
| /// - `next()` and `next_back()` need to behave as |
| /// the two ends of a range of values, that is they |
| /// can not "walk past each other". |
| /// |
| /// # Examples |
| /// |
| /// `char::Searcher` is a `DoubleEndedSearcher` because searching for a |
| /// `char` only requires looking at one at a time, which behaves the same |
| /// from both ends. |
| /// |
| /// `(&str)::Searcher` is not a `DoubleEndedSearcher` because |
| /// the pattern `"aa"` in the haystack `"aaa"` matches as either |
| /// `"[aa]a"` or `"a[aa]"`, depending from which side it is searched. |
| pub trait DoubleEndedSearcher<'a>: ReverseSearcher<'a> {} |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // Impl for a CharEq wrapper |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| #[doc(hidden)] |
| trait CharEq { |
| fn matches(&mut self, char) -> bool; |
| fn only_ascii(&self) -> bool; |
| } |
| |
| impl CharEq for char { |
| #[inline] |
| fn matches(&mut self, c: char) -> bool { *self == c } |
| |
| #[inline] |
| fn only_ascii(&self) -> bool { (*self as u32) < 128 } |
| } |
| |
| impl<F> CharEq for F where F: FnMut(char) -> bool { |
| #[inline] |
| fn matches(&mut self, c: char) -> bool { (*self)(c) } |
| |
| #[inline] |
| fn only_ascii(&self) -> bool { false } |
| } |
| |
| impl<'a> CharEq for &'a [char] { |
| #[inline] |
| fn matches(&mut self, c: char) -> bool { |
| self.iter().any(|&m| { let mut m = m; m.matches(c) }) |
| } |
| |
| #[inline] |
| fn only_ascii(&self) -> bool { |
| self.iter().all(|m| m.only_ascii()) |
| } |
| } |
| |
| struct CharEqPattern<C: CharEq>(C); |
| |
| #[derive(Clone, Debug)] |
| struct CharEqSearcher<'a, C: CharEq> { |
| char_eq: C, |
| haystack: &'a str, |
| char_indices: super::CharIndices<'a>, |
| #[allow(dead_code)] |
| ascii_only: bool, |
| } |
| |
| impl<'a, C: CharEq> Pattern<'a> for CharEqPattern<C> { |
| type Searcher = CharEqSearcher<'a, C>; |
| |
| #[inline] |
| fn into_searcher(self, haystack: &'a str) -> CharEqSearcher<'a, C> { |
| CharEqSearcher { |
| ascii_only: self.0.only_ascii(), |
| haystack: haystack, |
| char_eq: self.0, |
| char_indices: haystack.char_indices(), |
| } |
| } |
| } |
| |
| unsafe impl<'a, C: CharEq> Searcher<'a> for CharEqSearcher<'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: CharEq> ReverseSearcher<'a> for CharEqSearcher<'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: CharEq> DoubleEndedSearcher<'a> for CharEqSearcher<'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 is_suffix_of(self, haystack: &'a str) -> bool |
| where $t: ReverseSearcher<'a> |
| { |
| ($pmap)(self).is_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() |
| } |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // Impl for char |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| /// Associated type for `<char as Pattern<'a>>::Searcher`. |
| #[derive(Clone, Debug)] |
| pub struct CharSearcher<'a>(<CharEqPattern<char> as Pattern<'a>>::Searcher); |
| |
| unsafe impl<'a> Searcher<'a> for CharSearcher<'a> { |
| searcher_methods!(forward); |
| } |
| |
| unsafe impl<'a> ReverseSearcher<'a> for CharSearcher<'a> { |
| searcher_methods!(reverse); |
| } |
| |
| impl<'a> DoubleEndedSearcher<'a> for CharSearcher<'a> {} |
| |
| /// Searches for chars that are equal to a given char |
| impl<'a> Pattern<'a> for char { |
| pattern_methods!(CharSearcher<'a>, CharEqPattern, CharSearcher); |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // 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>(<CharEqPattern<&'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 chars in the array |
| impl<'a, 'b> Pattern<'a> for &'b [char] { |
| pattern_methods!(CharSliceSearcher<'a, 'b>, CharEqPattern, CharSliceSearcher); |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // Impl for F: FnMut(char) -> bool |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| /// Associated type for `<F as Pattern<'a>>::Searcher`. |
| #[derive(Clone)] |
| pub struct CharPredicateSearcher<'a, F>(<CharEqPattern<F> as Pattern<'a>>::Searcher) |
| where F: FnMut(char) -> bool; |
| |
| impl<'a, F> fmt::Debug for CharPredicateSearcher<'a, 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) |
| .field("ascii_only", &self.0.ascii_only) |
| .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 chars that match the given predicate |
| impl<'a, F> Pattern<'a> for F where F: FnMut(char) -> bool { |
| pattern_methods!(CharPredicateSearcher<'a, F>, CharEqPattern, 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. |
| 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.is_char_boundary(self.len()) && |
| self == &haystack[..self.len()] |
| } |
| |
| /// Checks whether the pattern matches at the back of the haystack |
| #[inline] |
| fn is_suffix_of(self, haystack: &'a str) -> bool { |
| self.len() <= haystack.len() && |
| haystack.is_char_boundary(haystack.len() - self.len()) && |
| self == &haystack[haystack.len() - self.len()..] |
| } |
| } |
| |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // 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, |
| } |
| |
| impl<'a, 'b> StrSearcher<'a, 'b> { |
| fn new(haystack: &'a str, needle: &'b str) -> StrSearcher<'a, 'b> { |
| if needle.is_empty() { |
| StrSearcher { |
| haystack: haystack, |
| needle: needle, |
| searcher: StrSearcherImpl::Empty(EmptyNeedle { |
| position: 0, |
| end: haystack.len(), |
| is_match_fw: true, |
| is_match_bw: true, |
| }), |
| } |
| } else { |
| StrSearcher { |
| haystack: haystack, |
| needle: needle, |
| searcher: StrSearcherImpl::TwoWay( |
| TwoWaySearcher::new(needle.as_bytes(), haystack.len()) |
| ), |
| } |
| } |
| } |
| } |
| |
| unsafe impl<'a, 'b> Searcher<'a> for StrSearcher<'a, 'b> { |
| fn haystack(&self) -> &'a str { self.haystack } |
| |
| #[inline] |
| fn next(&mut self) -> SearchStep { |
| match self.searcher { |
| StrSearcherImpl::Empty(ref mut searcher) => { |
| // 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 => 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(always)] |
| 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) => { |
| 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 => 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, |
| crit_pos_back: crit_pos_back, |
| period: period, |
| byteset: Self::byteset_create(&needle[..period]), |
| |
| position: 0, |
| end: 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, |
| crit_pos_back: crit_pos, |
| period: cmp::max(crit_pos, needle.len() - crit_pos) + 1, |
| byteset: Self::byteset_create(needle), |
| |
| position: 0, |
| end: 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(always)] |
| 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(always)] |
| 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 immedately 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(usize, usize) -> Self::Output; |
| fn matching(usize, 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) } |
| } |
