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Diffstat (limited to 'third_party/rust/memchr/src/memmem/twoway.rs')
| -rw-r--r-- | third_party/rust/memchr/src/memmem/twoway.rs | 878 |
1 files changed, 878 insertions, 0 deletions
diff --git a/third_party/rust/memchr/src/memmem/twoway.rs b/third_party/rust/memchr/src/memmem/twoway.rs new file mode 100644 index 0000000000..7f82ed15d9 --- /dev/null +++ b/third_party/rust/memchr/src/memmem/twoway.rs @@ -0,0 +1,878 @@ +use core::cmp; + +use crate::memmem::{prefilter::Pre, util}; + +/// Two-Way search in the forward direction. +#[derive(Clone, Copy, Debug)] +pub(crate) struct Forward(TwoWay); + +/// Two-Way search in the reverse direction. +#[derive(Clone, Copy, Debug)] +pub(crate) struct Reverse(TwoWay); + +/// An implementation of the TwoWay substring search algorithm, with heuristics +/// for accelerating search based on frequency analysis. +/// +/// This searcher supports forward and reverse search, although not +/// simultaneously. It runs in O(n + m) time and O(1) space, where +/// `n ~ len(needle)` and `m ~ len(haystack)`. +/// +/// The implementation here roughly matches that which was developed by +/// Crochemore and Perrin in their 1991 paper "Two-way string-matching." The +/// changes in this implementation are 1) the use of zero-based indices, 2) a +/// heuristic skip table based on the last byte (borrowed from Rust's standard +/// library) and 3) the addition of heuristics for a fast skip loop. That is, +/// (3) this will detect bytes that are believed to be rare in the needle and +/// use fast vectorized instructions to find their occurrences quickly. The +/// Two-Way algorithm is then used to confirm whether a match at that location +/// occurred. +/// +/// The heuristic for fast skipping is automatically shut off if it's +/// detected to be ineffective at search time. Generally, this only occurs in +/// pathological cases. But this is generally necessary in order to preserve +/// a `O(n + m)` time bound. +/// +/// The code below is fairly complex and not obviously correct at all. It's +/// likely necessary to read the Two-Way paper cited above in order to fully +/// grok this code. The essence of it is: +/// +/// 1) Do something to detect a "critical" position in the needle. +/// 2) For the current position in the haystack, look if needle[critical..] +/// matches at that position. +/// 3) If so, look if needle[..critical] matches. +/// 4) If a mismatch occurs, shift the search by some amount based on the +/// critical position and a pre-computed shift. +/// +/// This type is wrapped in Forward and Reverse types that expose consistent +/// forward or reverse APIs. +#[derive(Clone, Copy, Debug)] +struct TwoWay { + /// A small bitset used as a quick prefilter (in addition to the faster + /// SIMD based prefilter). Namely, a bit 'i' is set if and only if b%64==i + /// for any b in the needle. + /// + /// When used as a prefilter, if the last byte at the current candidate + /// position is NOT in this set, then we can skip that entire candidate + /// position (the length of the needle). This is essentially the shift + /// trick found in Boyer-Moore, but only applied to bytes that don't appear + /// in the needle. + /// + /// N.B. This trick was inspired by something similar in std's + /// implementation of Two-Way. + byteset: ApproximateByteSet, + /// A critical position in needle. Specifically, this position corresponds + /// to beginning of either the minimal or maximal suffix in needle. (N.B. + /// See SuffixType below for why "minimal" isn't quite the correct word + /// here.) + /// + /// This is the position at which every search begins. Namely, search + /// starts by scanning text to the right of this position, and only if + /// there's a match does the text to the left of this position get scanned. + critical_pos: usize, + /// The amount we shift by in the Two-Way search algorithm. This + /// corresponds to the "small period" and "large period" cases. + shift: Shift, +} + +impl Forward { + /// Create a searcher that uses the Two-Way algorithm by searching forwards + /// through any haystack. + pub(crate) fn new(needle: &[u8]) -> Forward { + if needle.is_empty() { + return Forward(TwoWay::empty()); + } + + let byteset = ApproximateByteSet::new(needle); + let min_suffix = Suffix::forward(needle, SuffixKind::Minimal); + let max_suffix = Suffix::forward(needle, SuffixKind::Maximal); + let (period_lower_bound, critical_pos) = + if min_suffix.pos > max_suffix.pos { + (min_suffix.period, min_suffix.pos) + } else { + (max_suffix.period, max_suffix.pos) + }; + let shift = Shift::forward(needle, period_lower_bound, critical_pos); + Forward(TwoWay { byteset, critical_pos, shift }) + } + + /// Find the position of the first occurrence of this searcher's needle in + /// the given haystack. If one does not exist, then return None. + /// + /// This accepts prefilter state that is useful when using the same + /// searcher multiple times, such as in an iterator. + /// + /// Callers must guarantee that the needle is non-empty and its length is + /// <= the haystack's length. + #[inline(always)] + pub(crate) fn find( + &self, + pre: Option<&mut Pre<'_>>, + haystack: &[u8], + needle: &[u8], + ) -> Option<usize> { + debug_assert!(!needle.is_empty(), "needle should not be empty"); + debug_assert!(needle.len() <= haystack.len(), "haystack too short"); + + match self.0.shift { + Shift::Small { period } => { + self.find_small_imp(pre, haystack, needle, period) + } + Shift::Large { shift } => { + self.find_large_imp(pre, haystack, needle, shift) + } + } + } + + /// Like find, but handles the degenerate substring test cases. This is + /// only useful for conveniently testing this substring implementation in + /// isolation. + #[cfg(test)] + fn find_general( + &self, + pre: Option<&mut Pre<'_>>, + haystack: &[u8], + needle: &[u8], + ) -> Option<usize> { + if needle.is_empty() { + Some(0) + } else if haystack.len() < needle.len() { + None + } else { + self.find(pre, haystack, needle) + } + } + + // Each of the two search implementations below can be accelerated by a + // prefilter, but it is not always enabled. To avoid its overhead when + // its disabled, we explicitly inline each search implementation based on + // whether a prefilter will be used or not. The decision on which to use + // is made in the parent meta searcher. + + #[inline(always)] + fn find_small_imp( + &self, + mut pre: Option<&mut Pre<'_>>, + haystack: &[u8], + needle: &[u8], + period: usize, + ) -> Option<usize> { + let last_byte = needle.len() - 1; + let mut pos = 0; + let mut shift = 0; + while pos + needle.len() <= haystack.len() { + let mut i = cmp::max(self.0.critical_pos, shift); + if let Some(pre) = pre.as_mut() { + if pre.should_call() { + pos += pre.call(&haystack[pos..], needle)?; + shift = 0; + i = self.0.critical_pos; + if pos + needle.len() > haystack.len() { + return None; + } + } + } + if !self.0.byteset.contains(haystack[pos + last_byte]) { + pos += needle.len(); + shift = 0; + continue; + } + while i < needle.len() && needle[i] == haystack[pos + i] { + i += 1; + } + if i < needle.len() { + pos += i - self.0.critical_pos + 1; + shift = 0; + } else { + let mut j = self.0.critical_pos; + while j > shift && needle[j] == haystack[pos + j] { + j -= 1; + } + if j <= shift && needle[shift] == haystack[pos + shift] { + return Some(pos); + } + pos += period; + shift = needle.len() - period; + } + } + None + } + + #[inline(always)] + fn find_large_imp( + &self, + mut pre: Option<&mut Pre<'_>>, + haystack: &[u8], + needle: &[u8], + shift: usize, + ) -> Option<usize> { + let last_byte = needle.len() - 1; + let mut pos = 0; + 'outer: while pos + needle.len() <= haystack.len() { + if let Some(pre) = pre.as_mut() { + if pre.should_call() { + pos += pre.call(&haystack[pos..], needle)?; + if pos + needle.len() > haystack.len() { + return None; + } + } + } + + if !self.0.byteset.contains(haystack[pos + last_byte]) { + pos += needle.len(); + continue; + } + let mut i = self.0.critical_pos; + while i < needle.len() && needle[i] == haystack[pos + i] { + i += 1; + } + if i < needle.len() { + pos += i - self.0.critical_pos + 1; + } else { + for j in (0..self.0.critical_pos).rev() { + if needle[j] != haystack[pos + j] { + pos += shift; + continue 'outer; + } + } + return Some(pos); + } + } + None + } +} + +impl Reverse { + /// Create a searcher that uses the Two-Way algorithm by searching in + /// reverse through any haystack. + pub(crate) fn new(needle: &[u8]) -> Reverse { + if needle.is_empty() { + return Reverse(TwoWay::empty()); + } + + let byteset = ApproximateByteSet::new(needle); + let min_suffix = Suffix::reverse(needle, SuffixKind::Minimal); + let max_suffix = Suffix::reverse(needle, SuffixKind::Maximal); + let (period_lower_bound, critical_pos) = + if min_suffix.pos < max_suffix.pos { + (min_suffix.period, min_suffix.pos) + } else { + (max_suffix.period, max_suffix.pos) + }; + // let critical_pos = needle.len() - critical_pos; + let shift = Shift::reverse(needle, period_lower_bound, critical_pos); + Reverse(TwoWay { byteset, critical_pos, shift }) + } + + /// Find the position of the last occurrence of this searcher's needle + /// in the given haystack. If one does not exist, then return None. + /// + /// This will automatically initialize prefilter state. This should only + /// be used for one-off searches. + /// + /// Callers must guarantee that the needle is non-empty and its length is + /// <= the haystack's length. + #[inline(always)] + pub(crate) fn rfind( + &self, + haystack: &[u8], + needle: &[u8], + ) -> Option<usize> { + debug_assert!(!needle.is_empty(), "needle should not be empty"); + debug_assert!(needle.len() <= haystack.len(), "haystack too short"); + // For the reverse case, we don't use a prefilter. It's plausible that + // perhaps we should, but it's a lot of additional code to do it, and + // it's not clear that it's actually worth it. If you have a really + // compelling use case for this, please file an issue. + match self.0.shift { + Shift::Small { period } => { + self.rfind_small_imp(haystack, needle, period) + } + Shift::Large { shift } => { + self.rfind_large_imp(haystack, needle, shift) + } + } + } + + /// Like rfind, but handles the degenerate substring test cases. This is + /// only useful for conveniently testing this substring implementation in + /// isolation. + #[cfg(test)] + fn rfind_general(&self, haystack: &[u8], needle: &[u8]) -> Option<usize> { + if needle.is_empty() { + Some(haystack.len()) + } else if haystack.len() < needle.len() { + None + } else { + self.rfind(haystack, needle) + } + } + + #[inline(always)] + fn rfind_small_imp( + &self, + haystack: &[u8], + needle: &[u8], + period: usize, + ) -> Option<usize> { + let nlen = needle.len(); + let mut pos = haystack.len(); + let mut shift = nlen; + while pos >= nlen { + if !self.0.byteset.contains(haystack[pos - nlen]) { + pos -= nlen; + shift = nlen; + continue; + } + let mut i = cmp::min(self.0.critical_pos, shift); + while i > 0 && needle[i - 1] == haystack[pos - nlen + i - 1] { + i -= 1; + } + if i > 0 || needle[0] != haystack[pos - nlen] { + pos -= self.0.critical_pos - i + 1; + shift = nlen; + } else { + let mut j = self.0.critical_pos; + while j < shift && needle[j] == haystack[pos - nlen + j] { + j += 1; + } + if j >= shift { + return Some(pos - nlen); + } + pos -= period; + shift = period; + } + } + None + } + + #[inline(always)] + fn rfind_large_imp( + &self, + haystack: &[u8], + needle: &[u8], + shift: usize, + ) -> Option<usize> { + let nlen = needle.len(); + let mut pos = haystack.len(); + while pos >= nlen { + if !self.0.byteset.contains(haystack[pos - nlen]) { + pos -= nlen; + continue; + } + let mut i = self.0.critical_pos; + while i > 0 && needle[i - 1] == haystack[pos - nlen + i - 1] { + i -= 1; + } + if i > 0 || needle[0] != haystack[pos - nlen] { + pos -= self.0.critical_pos - i + 1; + } else { + let mut j = self.0.critical_pos; + while j < nlen && needle[j] == haystack[pos - nlen + j] { + j += 1; + } + if j == nlen { + return Some(pos - nlen); + } + pos -= shift; + } + } + None + } +} + +impl TwoWay { + fn empty() -> TwoWay { + TwoWay { + byteset: ApproximateByteSet::new(b""), + critical_pos: 0, + shift: Shift::Large { shift: 0 }, + } + } +} + +/// A representation of the amount we're allowed to shift by during Two-Way +/// search. +/// +/// When computing a critical factorization of the needle, we find the position +/// of the critical factorization by finding the needle's maximal (or minimal) +/// suffix, along with the period of that suffix. It turns out that the period +/// of that suffix is a lower bound on the period of the needle itself. +/// +/// This lower bound is equivalent to the actual period of the needle in +/// some cases. To describe that case, we denote the needle as `x` where +/// `x = uv` and `v` is the lexicographic maximal suffix of `v`. The lower +/// bound given here is always the period of `v`, which is `<= period(x)`. The +/// case where `period(v) == period(x)` occurs when `len(u) < (len(x) / 2)` and +/// where `u` is a suffix of `v[0..period(v)]`. +/// +/// This case is important because the search algorithm for when the +/// periods are equivalent is slightly different than the search algorithm +/// for when the periods are not equivalent. In particular, when they aren't +/// equivalent, we know that the period of the needle is no less than half its +/// length. In this case, we shift by an amount less than or equal to the +/// period of the needle (determined by the maximum length of the components +/// of the critical factorization of `x`, i.e., `max(len(u), len(v))`).. +/// +/// The above two cases are represented by the variants below. Each entails +/// a different instantiation of the Two-Way search algorithm. +/// +/// N.B. If we could find a way to compute the exact period in all cases, +/// then we could collapse this case analysis and simplify the algorithm. The +/// Two-Way paper suggests this is possible, but more reading is required to +/// grok why the authors didn't pursue that path. +#[derive(Clone, Copy, Debug)] +enum Shift { + Small { period: usize }, + Large { shift: usize }, +} + +impl Shift { + /// Compute the shift for a given needle in the forward direction. + /// + /// This requires a lower bound on the period and a critical position. + /// These can be computed by extracting both the minimal and maximal + /// lexicographic suffixes, and choosing the right-most starting position. + /// The lower bound on the period is then the period of the chosen suffix. + fn forward( + needle: &[u8], + period_lower_bound: usize, + critical_pos: usize, + ) -> Shift { + let large = cmp::max(critical_pos, needle.len() - critical_pos); + if critical_pos * 2 >= needle.len() { + return Shift::Large { shift: large }; + } + + let (u, v) = needle.split_at(critical_pos); + if !util::is_suffix(&v[..period_lower_bound], u) { + return Shift::Large { shift: large }; + } + Shift::Small { period: period_lower_bound } + } + + /// Compute the shift for a given needle in the reverse direction. + /// + /// This requires a lower bound on the period and a critical position. + /// These can be computed by extracting both the minimal and maximal + /// lexicographic suffixes, and choosing the left-most starting position. + /// The lower bound on the period is then the period of the chosen suffix. + fn reverse( + needle: &[u8], + period_lower_bound: usize, + critical_pos: usize, + ) -> Shift { + let large = cmp::max(critical_pos, needle.len() - critical_pos); + if (needle.len() - critical_pos) * 2 >= needle.len() { + return Shift::Large { shift: large }; + } + + let (v, u) = needle.split_at(critical_pos); + if !util::is_prefix(&v[v.len() - period_lower_bound..], u) { + return Shift::Large { shift: large }; + } + Shift::Small { period: period_lower_bound } + } +} + +/// A suffix extracted from a needle along with its period. +#[derive(Debug)] +struct Suffix { + /// The starting position of this suffix. + /// + /// If this is a forward suffix, then `&bytes[pos..]` can be used. If this + /// is a reverse suffix, then `&bytes[..pos]` can be used. That is, for + /// forward suffixes, this is an inclusive starting position, where as for + /// reverse suffixes, this is an exclusive ending position. + pos: usize, + /// The period of this suffix. + /// + /// Note that this is NOT necessarily the period of the string from which + /// this suffix comes from. (It is always less than or equal to the period + /// of the original string.) + period: usize, +} + +impl Suffix { + fn forward(needle: &[u8], kind: SuffixKind) -> Suffix { + debug_assert!(!needle.is_empty()); + + // suffix represents our maximal (or minimal) suffix, along with + // its period. + let mut suffix = Suffix { pos: 0, period: 1 }; + // The start of a suffix in `needle` that we are considering as a + // more maximal (or minimal) suffix than what's in `suffix`. + let mut candidate_start = 1; + // The current offset of our suffixes that we're comparing. + // + // When the characters at this offset are the same, then we mush on + // to the next position since no decision is possible. When the + // candidate's character is greater (or lesser) than the corresponding + // character than our current maximal (or minimal) suffix, then the + // current suffix is changed over to the candidate and we restart our + // search. Otherwise, the candidate suffix is no good and we restart + // our search on the next candidate. + // + // The three cases above correspond to the three cases in the loop + // below. + let mut offset = 0; + + while candidate_start + offset < needle.len() { + let current = needle[suffix.pos + offset]; + let candidate = needle[candidate_start + offset]; + match kind.cmp(current, candidate) { + SuffixOrdering::Accept => { + suffix = Suffix { pos: candidate_start, period: 1 }; + candidate_start += 1; + offset = 0; + } + SuffixOrdering::Skip => { + candidate_start += offset + 1; + offset = 0; + suffix.period = candidate_start - suffix.pos; + } + SuffixOrdering::Push => { + if offset + 1 == suffix.period { + candidate_start += suffix.period; + offset = 0; + } else { + offset += 1; + } + } + } + } + suffix + } + + fn reverse(needle: &[u8], kind: SuffixKind) -> Suffix { + debug_assert!(!needle.is_empty()); + + // See the comments in `forward` for how this works. + let mut suffix = Suffix { pos: needle.len(), period: 1 }; + if needle.len() == 1 { + return suffix; + } + let mut candidate_start = needle.len() - 1; + let mut offset = 0; + + while offset < candidate_start { + let current = needle[suffix.pos - offset - 1]; + let candidate = needle[candidate_start - offset - 1]; + match kind.cmp(current, candidate) { + SuffixOrdering::Accept => { + suffix = Suffix { pos: candidate_start, period: 1 }; + candidate_start -= 1; + offset = 0; + } + SuffixOrdering::Skip => { + candidate_start -= offset + 1; + offset = 0; + suffix.period = suffix.pos - candidate_start; + } + SuffixOrdering::Push => { + if offset + 1 == suffix.period { + candidate_start -= suffix.period; + offset = 0; + } else { + offset += 1; + } + } + } + } + suffix + } +} + +/// The kind of suffix to extract. +#[derive(Clone, Copy, Debug)] +enum SuffixKind { + /// Extract the smallest lexicographic suffix from a string. + /// + /// Technically, this doesn't actually pick the smallest lexicographic + /// suffix. e.g., Given the choice between `a` and `aa`, this will choose + /// the latter over the former, even though `a < aa`. The reasoning for + /// this isn't clear from the paper, but it still smells like a minimal + /// suffix. + Minimal, + /// Extract the largest lexicographic suffix from a string. + /// + /// Unlike `Minimal`, this really does pick the maximum suffix. e.g., Given + /// the choice between `z` and `zz`, this will choose the latter over the + /// former. + Maximal, +} + +/// The result of comparing corresponding bytes between two suffixes. +#[derive(Clone, Copy, Debug)] +enum SuffixOrdering { + /// This occurs when the given candidate byte indicates that the candidate + /// suffix is better than the current maximal (or minimal) suffix. That is, + /// the current candidate suffix should supplant the current maximal (or + /// minimal) suffix. + Accept, + /// This occurs when the given candidate byte excludes the candidate suffix + /// from being better than the current maximal (or minimal) suffix. That + /// is, the current candidate suffix should be dropped and the next one + /// should be considered. + Skip, + /// This occurs when no decision to accept or skip the candidate suffix + /// can be made, e.g., when corresponding bytes are equivalent. In this + /// case, the next corresponding bytes should be compared. + Push, +} + +impl SuffixKind { + /// Returns true if and only if the given candidate byte indicates that + /// it should replace the current suffix as the maximal (or minimal) + /// suffix. + fn cmp(self, current: u8, candidate: u8) -> SuffixOrdering { + use self::SuffixOrdering::*; + + match self { + SuffixKind::Minimal if candidate < current => Accept, + SuffixKind::Minimal if candidate > current => Skip, + SuffixKind::Minimal => Push, + SuffixKind::Maximal if candidate > current => Accept, + SuffixKind::Maximal if candidate < current => Skip, + SuffixKind::Maximal => Push, + } + } +} + +/// A bitset used to track whether a particular byte exists in a needle or not. +/// +/// Namely, bit 'i' is set if and only if byte%64==i for any byte in the +/// needle. If a particular byte in the haystack is NOT in this set, then one +/// can conclude that it is also not in the needle, and thus, one can advance +/// in the haystack by needle.len() bytes. +#[derive(Clone, Copy, Debug)] +struct ApproximateByteSet(u64); + +impl ApproximateByteSet { + /// Create a new set from the given needle. + fn new(needle: &[u8]) -> ApproximateByteSet { + let mut bits = 0; + for &b in needle { + bits |= 1 << (b % 64); + } + ApproximateByteSet(bits) + } + + /// Return true if and only if the given byte might be in this set. This + /// may return a false positive, but will never return a false negative. + #[inline(always)] + fn contains(&self, byte: u8) -> bool { + self.0 & (1 << (byte % 64)) != 0 + } +} + +#[cfg(all(test, feature = "std", not(miri)))] +mod tests { + use quickcheck::quickcheck; + + use super::*; + + define_memmem_quickcheck_tests!( + super::simpletests::twoway_find, + super::simpletests::twoway_rfind + ); + + /// Convenience wrapper for computing the suffix as a byte string. + fn get_suffix_forward(needle: &[u8], kind: SuffixKind) -> (&[u8], usize) { + let s = Suffix::forward(needle, kind); + (&needle[s.pos..], s.period) + } + + /// Convenience wrapper for computing the reverse suffix as a byte string. + fn get_suffix_reverse(needle: &[u8], kind: SuffixKind) -> (&[u8], usize) { + let s = Suffix::reverse(needle, kind); + (&needle[..s.pos], s.period) + } + + /// Return all of the non-empty suffixes in the given byte string. + fn suffixes(bytes: &[u8]) -> Vec<&[u8]> { + (0..bytes.len()).map(|i| &bytes[i..]).collect() + } + + /// Return the lexicographically maximal suffix of the given byte string. + fn naive_maximal_suffix_forward(needle: &[u8]) -> &[u8] { + let mut sufs = suffixes(needle); + sufs.sort(); + sufs.pop().unwrap() + } + + /// Return the lexicographically maximal suffix of the reverse of the given + /// byte string. + fn naive_maximal_suffix_reverse(needle: &[u8]) -> Vec<u8> { + let mut reversed = needle.to_vec(); + reversed.reverse(); + let mut got = naive_maximal_suffix_forward(&reversed).to_vec(); + got.reverse(); + got + } + + #[test] + fn suffix_forward() { + macro_rules! assert_suffix_min { + ($given:expr, $expected:expr, $period:expr) => { + let (got_suffix, got_period) = + get_suffix_forward($given.as_bytes(), SuffixKind::Minimal); + let got_suffix = std::str::from_utf8(got_suffix).unwrap(); + assert_eq!(($expected, $period), (got_suffix, got_period)); + }; + } + + macro_rules! assert_suffix_max { + ($given:expr, $expected:expr, $period:expr) => { + let (got_suffix, got_period) = + get_suffix_forward($given.as_bytes(), SuffixKind::Maximal); + let got_suffix = std::str::from_utf8(got_suffix).unwrap(); + assert_eq!(($expected, $period), (got_suffix, got_period)); + }; + } + + assert_suffix_min!("a", "a", 1); + assert_suffix_max!("a", "a", 1); + + assert_suffix_min!("ab", "ab", 2); + assert_suffix_max!("ab", "b", 1); + + assert_suffix_min!("ba", "a", 1); + assert_suffix_max!("ba", "ba", 2); + + assert_suffix_min!("abc", "abc", 3); + assert_suffix_max!("abc", "c", 1); + + assert_suffix_min!("acb", "acb", 3); + assert_suffix_max!("acb", "cb", 2); + + assert_suffix_min!("cba", "a", 1); + assert_suffix_max!("cba", "cba", 3); + + assert_suffix_min!("abcabc", "abcabc", 3); + assert_suffix_max!("abcabc", "cabc", 3); + + assert_suffix_min!("abcabcabc", "abcabcabc", 3); + assert_suffix_max!("abcabcabc", "cabcabc", 3); + + assert_suffix_min!("abczz", "abczz", 5); + assert_suffix_max!("abczz", "zz", 1); + + assert_suffix_min!("zzabc", "abc", 3); + assert_suffix_max!("zzabc", "zzabc", 5); + + assert_suffix_min!("aaa", "aaa", 1); + assert_suffix_max!("aaa", "aaa", 1); + + assert_suffix_min!("foobar", "ar", 2); + assert_suffix_max!("foobar", "r", 1); + } + + #[test] + fn suffix_reverse() { + macro_rules! assert_suffix_min { + ($given:expr, $expected:expr, $period:expr) => { + let (got_suffix, got_period) = + get_suffix_reverse($given.as_bytes(), SuffixKind::Minimal); + let got_suffix = std::str::from_utf8(got_suffix).unwrap(); + assert_eq!(($expected, $period), (got_suffix, got_period)); + }; + } + + macro_rules! assert_suffix_max { + ($given:expr, $expected:expr, $period:expr) => { + let (got_suffix, got_period) = + get_suffix_reverse($given.as_bytes(), SuffixKind::Maximal); + let got_suffix = std::str::from_utf8(got_suffix).unwrap(); + assert_eq!(($expected, $period), (got_suffix, got_period)); + }; + } + + assert_suffix_min!("a", "a", 1); + assert_suffix_max!("a", "a", 1); + + assert_suffix_min!("ab", "a", 1); + assert_suffix_max!("ab", "ab", 2); + + assert_suffix_min!("ba", "ba", 2); + assert_suffix_max!("ba", "b", 1); + + assert_suffix_min!("abc", "a", 1); + assert_suffix_max!("abc", "abc", 3); + + assert_suffix_min!("acb", "a", 1); + assert_suffix_max!("acb", "ac", 2); + + assert_suffix_min!("cba", "cba", 3); + assert_suffix_max!("cba", "c", 1); + + assert_suffix_min!("abcabc", "abca", 3); + assert_suffix_max!("abcabc", "abcabc", 3); + + assert_suffix_min!("abcabcabc", "abcabca", 3); + assert_suffix_max!("abcabcabc", "abcabcabc", 3); + + assert_suffix_min!("abczz", "a", 1); + assert_suffix_max!("abczz", "abczz", 5); + + assert_suffix_min!("zzabc", "zza", 3); + assert_suffix_max!("zzabc", "zz", 1); + + assert_suffix_min!("aaa", "aaa", 1); + assert_suffix_max!("aaa", "aaa", 1); + } + + quickcheck! { + fn qc_suffix_forward_maximal(bytes: Vec<u8>) -> bool { + if bytes.is_empty() { + return true; + } + + let (got, _) = get_suffix_forward(&bytes, SuffixKind::Maximal); + let expected = naive_maximal_suffix_forward(&bytes); + got == expected + } + + fn qc_suffix_reverse_maximal(bytes: Vec<u8>) -> bool { + if bytes.is_empty() { + return true; + } + + let (got, _) = get_suffix_reverse(&bytes, SuffixKind::Maximal); + let expected = naive_maximal_suffix_reverse(&bytes); + expected == got + } + } +} + +#[cfg(test)] +mod simpletests { + use super::*; + + pub(crate) fn twoway_find( + haystack: &[u8], + needle: &[u8], + ) -> Option<usize> { + Forward::new(needle).find_general(None, haystack, needle) + } + + pub(crate) fn twoway_rfind( + haystack: &[u8], + needle: &[u8], + ) -> Option<usize> { + Reverse::new(needle).rfind_general(haystack, needle) + } + + define_memmem_simple_tests!(twoway_find, twoway_rfind); + + // This is a regression test caught by quickcheck that exercised a bug in + // the reverse small period handling. The bug was that we were using 'if j + // == shift' to determine if a match occurred, but the correct guard is 'if + // j >= shift', which matches the corresponding guard in the forward impl. + #[test] + fn regression_rev_small_period() { + let rfind = super::simpletests::twoway_rfind; + let haystack = "ababaz"; + let needle = "abab"; + assert_eq!(Some(0), rfind(haystack.as_bytes(), needle.as_bytes())); + } +} |