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Diffstat (limited to 'third_party/rust/regex-automata/src/util/alphabet.rs')
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diff --git a/third_party/rust/regex-automata/src/util/alphabet.rs b/third_party/rust/regex-automata/src/util/alphabet.rs new file mode 100644 index 0000000000..22b5a76446 --- /dev/null +++ b/third_party/rust/regex-automata/src/util/alphabet.rs @@ -0,0 +1,1139 @@ +/*! +This module provides APIs for dealing with the alphabets of finite state +machines. + +There are two principal types in this module, [`ByteClasses`] and [`Unit`]. +The former defines the alphabet of a finite state machine while the latter +represents an element of that alphabet. + +To a first approximation, the alphabet of all automata in this crate is just +a `u8`. Namely, every distinct byte value. All 256 of them. In practice, this +can be quite wasteful when building a transition table for a DFA, since it +requires storing a state identifier for each element in the alphabet. Instead, +we collapse the alphabet of an automaton down into equivalence classes, where +every byte in the same equivalence class never discriminates between a match or +a non-match from any other byte in the same class. For example, in the regex +`[a-z]+`, then you could consider it having an alphabet consisting of two +equivalence classes: `a-z` and everything else. In terms of the transitions on +an automaton, it doesn't actually require representing every distinct byte. +Just the equivalence classes. + +The downside of equivalence classes is that, of course, searching a haystack +deals with individual byte values. Those byte values need to be mapped to +their corresponding equivalence class. This is what `ByteClasses` does. In +practice, doing this for every state transition has negligible impact on modern +CPUs. Moreover, it helps make more efficient use of the CPU cache by (possibly +considerably) shrinking the size of the transition table. + +One last hiccup concerns `Unit`. Namely, because of look-around and how the +DFAs in this crate work, we need to add a sentinel value to our alphabet +of equivalence classes that represents the "end" of a search. We call that +sentinel [`Unit::eoi`] or "end of input." Thus, a `Unit` is either an +equivalence class corresponding to a set of bytes, or it is a special "end of +input" sentinel. + +In general, you should not expect to need either of these types unless you're +doing lower level shenanigans with DFAs, or even building your own DFAs. +(Although, you don't have to use these types to build your own DFAs of course.) +For example, if you're walking a DFA's state graph, it's probably useful to +make use of [`ByteClasses`] to visit each element in the DFA's alphabet instead +of just visiting every distinct `u8` value. The latter isn't necessarily wrong, +but it could be potentially very wasteful. +*/ +use crate::util::{ + escape::DebugByte, + wire::{self, DeserializeError, SerializeError}, +}; + +/// Unit represents a single unit of haystack for DFA based regex engines. +/// +/// It is not expected for consumers of this crate to need to use this type +/// unless they are implementing their own DFA. And even then, it's not +/// required: implementors may use other techniques to handle haystack units. +/// +/// Typically, a single unit of haystack for a DFA would be a single byte. +/// However, for the DFAs in this crate, matches are delayed by a single byte +/// in order to handle look-ahead assertions (`\b`, `$` and `\z`). Thus, once +/// we have consumed the haystack, we must run the DFA through one additional +/// transition using a unit that indicates the haystack has ended. +/// +/// There is no way to represent a sentinel with a `u8` since all possible +/// values *may* be valid haystack units to a DFA, therefore this type +/// explicitly adds room for a sentinel value. +/// +/// The sentinel EOI value is always its own equivalence class and is +/// ultimately represented by adding 1 to the maximum equivalence class value. +/// So for example, the regex `^[a-z]+$` might be split into the following +/// equivalence classes: +/// +/// ```text +/// 0 => [\x00-`] +/// 1 => [a-z] +/// 2 => [{-\xFF] +/// 3 => [EOI] +/// ``` +/// +/// Where EOI is the special sentinel value that is always in its own +/// singleton equivalence class. +#[derive(Clone, Copy, Eq, PartialEq, PartialOrd, Ord)] +pub struct Unit(UnitKind); + +#[derive(Clone, Copy, Eq, PartialEq, PartialOrd, Ord)] +enum UnitKind { + /// Represents a byte value, or more typically, an equivalence class + /// represented as a byte value. + U8(u8), + /// Represents the "end of input" sentinel. We regretably use a `u16` + /// here since the maximum sentinel value is `256`. Thankfully, we don't + /// actually store a `Unit` anywhere, so this extra space shouldn't be too + /// bad. + EOI(u16), +} + +impl Unit { + /// Create a new haystack unit from a byte value. + /// + /// All possible byte values are legal. However, when creating a haystack + /// unit for a specific DFA, one should be careful to only construct units + /// that are in that DFA's alphabet. Namely, one way to compact a DFA's + /// in-memory representation is to collapse its transitions to a set of + /// equivalence classes into a set of all possible byte values. If a DFA + /// uses equivalence classes instead of byte values, then the byte given + /// here should be the equivalence class. + pub fn u8(byte: u8) -> Unit { + Unit(UnitKind::U8(byte)) + } + + /// Create a new "end of input" haystack unit. + /// + /// The value given is the sentinel value used by this unit to represent + /// the "end of input." The value should be the total number of equivalence + /// classes in the corresponding alphabet. Its maximum value is `256`, + /// which occurs when every byte is its own equivalence class. + /// + /// # Panics + /// + /// This panics when `num_byte_equiv_classes` is greater than `256`. + pub fn eoi(num_byte_equiv_classes: usize) -> Unit { + assert!( + num_byte_equiv_classes <= 256, + "max number of byte-based equivalent classes is 256, but got {}", + num_byte_equiv_classes, + ); + Unit(UnitKind::EOI(u16::try_from(num_byte_equiv_classes).unwrap())) + } + + /// If this unit is not an "end of input" sentinel, then returns its + /// underlying byte value. Otherwise return `None`. + pub fn as_u8(self) -> Option<u8> { + match self.0 { + UnitKind::U8(b) => Some(b), + UnitKind::EOI(_) => None, + } + } + + /// If this unit is an "end of input" sentinel, then return the underlying + /// sentinel value that was given to [`Unit::eoi`]. Otherwise return + /// `None`. + pub fn as_eoi(self) -> Option<u16> { + match self.0 { + UnitKind::U8(_) => None, + UnitKind::EOI(sentinel) => Some(sentinel), + } + } + + /// Return this unit as a `usize`, regardless of whether it is a byte value + /// or an "end of input" sentinel. In the latter case, the underlying + /// sentinel value given to [`Unit::eoi`] is returned. + pub fn as_usize(self) -> usize { + match self.0 { + UnitKind::U8(b) => usize::from(b), + UnitKind::EOI(eoi) => usize::from(eoi), + } + } + + /// Returns true if and only of this unit is a byte value equivalent to the + /// byte given. This always returns false when this is an "end of input" + /// sentinel. + pub fn is_byte(self, byte: u8) -> bool { + self.as_u8().map_or(false, |b| b == byte) + } + + /// Returns true when this unit represents an "end of input" sentinel. + pub fn is_eoi(self) -> bool { + self.as_eoi().is_some() + } + + /// Returns true when this unit corresponds to an ASCII word byte. + /// + /// This always returns false when this unit represents an "end of input" + /// sentinel. + pub fn is_word_byte(self) -> bool { + self.as_u8().map_or(false, crate::util::utf8::is_word_byte) + } +} + +impl core::fmt::Debug for Unit { + fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result { + match self.0 { + UnitKind::U8(b) => write!(f, "{:?}", DebugByte(b)), + UnitKind::EOI(_) => write!(f, "EOI"), + } + } +} + +/// A representation of byte oriented equivalence classes. +/// +/// This is used in a DFA to reduce the size of the transition table. This can +/// have a particularly large impact not only on the total size of a dense DFA, +/// but also on compile times. +/// +/// The essential idea here is that the alphabet of a DFA is shrunk from the +/// usual 256 distinct byte values down to a set of equivalence classes. The +/// guarantee you get is that any byte belonging to the same equivalence class +/// can be treated as if it were any other byte in the same class, and the +/// result of a search wouldn't change. +/// +/// # Example +/// +/// This example shows how to get byte classes from an +/// [`NFA`](crate::nfa::thompson::NFA) and ask for the class of various bytes. +/// +/// ``` +/// use regex_automata::nfa::thompson::NFA; +/// +/// let nfa = NFA::new("[a-z]+")?; +/// let classes = nfa.byte_classes(); +/// // 'a' and 'z' are in the same class for this regex. +/// assert_eq!(classes.get(b'a'), classes.get(b'z')); +/// // But 'a' and 'A' are not. +/// assert_ne!(classes.get(b'a'), classes.get(b'A')); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone, Copy)] +pub struct ByteClasses([u8; 256]); + +impl ByteClasses { + /// Creates a new set of equivalence classes where all bytes are mapped to + /// the same class. + #[inline] + pub fn empty() -> ByteClasses { + ByteClasses([0; 256]) + } + + /// Creates a new set of equivalence classes where each byte belongs to + /// its own equivalence class. + #[inline] + pub fn singletons() -> ByteClasses { + let mut classes = ByteClasses::empty(); + for b in 0..=255 { + classes.set(b, b); + } + classes + } + + /// Deserializes a byte class map from the given slice. If the slice is of + /// insufficient length or otherwise contains an impossible mapping, then + /// an error is returned. Upon success, the number of bytes read along with + /// the map are returned. The number of bytes read is always a multiple of + /// 8. + pub(crate) fn from_bytes( + slice: &[u8], + ) -> Result<(ByteClasses, usize), DeserializeError> { + wire::check_slice_len(slice, 256, "byte class map")?; + let mut classes = ByteClasses::empty(); + for (b, &class) in slice[..256].iter().enumerate() { + classes.set(u8::try_from(b).unwrap(), class); + } + // We specifically don't use 'classes.iter()' here because that + // iterator depends on 'classes.alphabet_len()' being correct. But that + // is precisely the thing we're trying to verify below! + for &b in classes.0.iter() { + if usize::from(b) >= classes.alphabet_len() { + return Err(DeserializeError::generic( + "found equivalence class greater than alphabet len", + )); + } + } + Ok((classes, 256)) + } + + /// Writes this byte class map to the given byte buffer. if the given + /// buffer is too small, then an error is returned. Upon success, the total + /// number of bytes written is returned. The number of bytes written is + /// guaranteed to be a multiple of 8. + pub(crate) fn write_to( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("byte class map")); + } + for b in 0..=255 { + dst[0] = self.get(b); + dst = &mut dst[1..]; + } + Ok(nwrite) + } + + /// Returns the total number of bytes written by `write_to`. + pub(crate) fn write_to_len(&self) -> usize { + 256 + } + + /// Set the equivalence class for the given byte. + #[inline] + pub fn set(&mut self, byte: u8, class: u8) { + self.0[usize::from(byte)] = class; + } + + /// Get the equivalence class for the given byte. + #[inline] + pub fn get(&self, byte: u8) -> u8 { + self.0[usize::from(byte)] + } + + /// Get the equivalence class for the given haystack unit and return the + /// class as a `usize`. + #[inline] + pub fn get_by_unit(&self, unit: Unit) -> usize { + match unit.0 { + UnitKind::U8(b) => usize::from(self.get(b)), + UnitKind::EOI(b) => usize::from(b), + } + } + + /// Create a unit that represents the "end of input" sentinel based on the + /// number of equivalence classes. + #[inline] + pub fn eoi(&self) -> Unit { + // The alphabet length already includes the EOI sentinel, hence why + // we subtract 1. + Unit::eoi(self.alphabet_len().checked_sub(1).unwrap()) + } + + /// Return the total number of elements in the alphabet represented by + /// these equivalence classes. Equivalently, this returns the total number + /// of equivalence classes. + #[inline] + pub fn alphabet_len(&self) -> usize { + // Add one since the number of equivalence classes is one bigger than + // the last one. But add another to account for the final EOI class + // that isn't explicitly represented. + usize::from(self.0[255]) + 1 + 1 + } + + /// Returns the stride, as a base-2 exponent, required for these + /// equivalence classes. + /// + /// The stride is always the smallest power of 2 that is greater than or + /// equal to the alphabet length, and the `stride2` returned here is the + /// exponent applied to `2` to get the smallest power. This is done so that + /// converting between premultiplied state IDs and indices can be done with + /// shifts alone, which is much faster than integer division. + #[inline] + pub fn stride2(&self) -> usize { + let zeros = self.alphabet_len().next_power_of_two().trailing_zeros(); + usize::try_from(zeros).unwrap() + } + + /// Returns true if and only if every byte in this class maps to its own + /// equivalence class. Equivalently, there are 257 equivalence classes + /// and each class contains either exactly one byte or corresponds to the + /// singleton class containing the "end of input" sentinel. + #[inline] + pub fn is_singleton(&self) -> bool { + self.alphabet_len() == 257 + } + + /// Returns an iterator over all equivalence classes in this set. + #[inline] + pub fn iter(&self) -> ByteClassIter<'_> { + ByteClassIter { classes: self, i: 0 } + } + + /// Returns an iterator over a sequence of representative bytes from each + /// equivalence class within the range of bytes given. + /// + /// When the given range is unbounded on both sides, the iterator yields + /// exactly N items, where N is equivalent to the number of equivalence + /// classes. Each item is an arbitrary byte drawn from each equivalence + /// class. + /// + /// This is useful when one is determinizing an NFA and the NFA's alphabet + /// hasn't been converted to equivalence classes. Picking an arbitrary byte + /// from each equivalence class then permits a full exploration of the NFA + /// instead of using every possible byte value and thus potentially saves + /// quite a lot of redundant work. + /// + /// # Example + /// + /// This shows an example of what a complete sequence of representatives + /// might look like from a real example. + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, util::alphabet::Unit}; + /// + /// let nfa = NFA::new("[a-z]+")?; + /// let classes = nfa.byte_classes(); + /// let reps: Vec<Unit> = classes.representatives(..).collect(); + /// // Note that the specific byte values yielded are not guaranteed! + /// let expected = vec![ + /// Unit::u8(b'\x00'), + /// Unit::u8(b'a'), + /// Unit::u8(b'{'), + /// Unit::eoi(3), + /// ]; + /// assert_eq!(expected, reps); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Note though, that you can ask for an arbitrary range of bytes, and only + /// representatives for that range will be returned: + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, util::alphabet::Unit}; + /// + /// let nfa = NFA::new("[a-z]+")?; + /// let classes = nfa.byte_classes(); + /// let reps: Vec<Unit> = classes.representatives(b'A'..=b'z').collect(); + /// // Note that the specific byte values yielded are not guaranteed! + /// let expected = vec![ + /// Unit::u8(b'A'), + /// Unit::u8(b'a'), + /// ]; + /// assert_eq!(expected, reps); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn representatives<R: core::ops::RangeBounds<u8>>( + &self, + range: R, + ) -> ByteClassRepresentatives<'_> { + use core::ops::Bound; + + let cur_byte = match range.start_bound() { + Bound::Included(&i) => usize::from(i), + Bound::Excluded(&i) => usize::from(i).checked_add(1).unwrap(), + Bound::Unbounded => 0, + }; + let end_byte = match range.end_bound() { + Bound::Included(&i) => { + Some(usize::from(i).checked_add(1).unwrap()) + } + Bound::Excluded(&i) => Some(usize::from(i)), + Bound::Unbounded => None, + }; + assert_ne!( + cur_byte, + usize::MAX, + "start range must be less than usize::MAX", + ); + ByteClassRepresentatives { + classes: self, + cur_byte, + end_byte, + last_class: None, + } + } + + /// Returns an iterator of the bytes in the given equivalence class. + /// + /// This is useful when one needs to know the actual bytes that belong to + /// an equivalence class. For example, conceptually speaking, accelerating + /// a DFA state occurs when a state only has a few outgoing transitions. + /// But in reality, what is required is that there are only a small + /// number of distinct bytes that can lead to an outgoing transition. The + /// difference is that any one transition can correspond to an equivalence + /// class which may contains many bytes. Therefore, DFA state acceleration + /// considers the actual elements in each equivalence class of each + /// outgoing transition. + /// + /// # Example + /// + /// This shows an example of how to get all of the elements in an + /// equivalence class. + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, util::alphabet::Unit}; + /// + /// let nfa = NFA::new("[a-z]+")?; + /// let classes = nfa.byte_classes(); + /// let elements: Vec<Unit> = classes.elements(Unit::u8(1)).collect(); + /// let expected: Vec<Unit> = (b'a'..=b'z').map(Unit::u8).collect(); + /// assert_eq!(expected, elements); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn elements(&self, class: Unit) -> ByteClassElements { + ByteClassElements { classes: self, class, byte: 0 } + } + + /// Returns an iterator of byte ranges in the given equivalence class. + /// + /// That is, a sequence of contiguous ranges are returned. Typically, every + /// class maps to a single contiguous range. + fn element_ranges(&self, class: Unit) -> ByteClassElementRanges { + ByteClassElementRanges { elements: self.elements(class), range: None } + } +} + +impl Default for ByteClasses { + fn default() -> ByteClasses { + ByteClasses::singletons() + } +} + +impl core::fmt::Debug for ByteClasses { + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { + if self.is_singleton() { + write!(f, "ByteClasses({{singletons}})") + } else { + write!(f, "ByteClasses(")?; + for (i, class) in self.iter().enumerate() { + if i > 0 { + write!(f, ", ")?; + } + write!(f, "{:?} => [", class.as_usize())?; + for (start, end) in self.element_ranges(class) { + if start == end { + write!(f, "{:?}", start)?; + } else { + write!(f, "{:?}-{:?}", start, end)?; + } + } + write!(f, "]")?; + } + write!(f, ")") + } + } +} + +/// An iterator over each equivalence class. +/// +/// The last element in this iterator always corresponds to [`Unit::eoi`]. +/// +/// This is created by the [`ByteClasses::iter`] method. +/// +/// The lifetime `'a` refers to the lifetime of the byte classes that this +/// iterator was created from. +#[derive(Debug)] +pub struct ByteClassIter<'a> { + classes: &'a ByteClasses, + i: usize, +} + +impl<'a> Iterator for ByteClassIter<'a> { + type Item = Unit; + + fn next(&mut self) -> Option<Unit> { + if self.i + 1 == self.classes.alphabet_len() { + self.i += 1; + Some(self.classes.eoi()) + } else if self.i < self.classes.alphabet_len() { + let class = u8::try_from(self.i).unwrap(); + self.i += 1; + Some(Unit::u8(class)) + } else { + None + } + } +} + +/// An iterator over representative bytes from each equivalence class. +/// +/// This is created by the [`ByteClasses::representatives`] method. +/// +/// The lifetime `'a` refers to the lifetime of the byte classes that this +/// iterator was created from. +#[derive(Debug)] +pub struct ByteClassRepresentatives<'a> { + classes: &'a ByteClasses, + cur_byte: usize, + end_byte: Option<usize>, + last_class: Option<u8>, +} + +impl<'a> Iterator for ByteClassRepresentatives<'a> { + type Item = Unit; + + fn next(&mut self) -> Option<Unit> { + while self.cur_byte < self.end_byte.unwrap_or(256) { + let byte = u8::try_from(self.cur_byte).unwrap(); + let class = self.classes.get(byte); + self.cur_byte += 1; + + if self.last_class != Some(class) { + self.last_class = Some(class); + return Some(Unit::u8(byte)); + } + } + if self.cur_byte != usize::MAX && self.end_byte.is_none() { + // Using usize::MAX as a sentinel is OK because we ban usize::MAX + // from appearing as a start bound in iterator construction. But + // why do it this way? Well, we want to return the EOI class + // whenever the end of the given range is unbounded because EOI + // isn't really a "byte" per se, so the only way it should be + // excluded is if there is a bounded end to the range. Therefore, + // when the end is unbounded, we just need to know whether we've + // reported EOI or not. When we do, we set cur_byte to a value it + // can never otherwise be. + self.cur_byte = usize::MAX; + return Some(self.classes.eoi()); + } + None + } +} + +/// An iterator over all elements in an equivalence class. +/// +/// This is created by the [`ByteClasses::elements`] method. +/// +/// The lifetime `'a` refers to the lifetime of the byte classes that this +/// iterator was created from. +#[derive(Debug)] +pub struct ByteClassElements<'a> { + classes: &'a ByteClasses, + class: Unit, + byte: usize, +} + +impl<'a> Iterator for ByteClassElements<'a> { + type Item = Unit; + + fn next(&mut self) -> Option<Unit> { + while self.byte < 256 { + let byte = u8::try_from(self.byte).unwrap(); + self.byte += 1; + if self.class.is_byte(self.classes.get(byte)) { + return Some(Unit::u8(byte)); + } + } + if self.byte < 257 { + self.byte += 1; + if self.class.is_eoi() { + return Some(Unit::eoi(256)); + } + } + None + } +} + +/// An iterator over all elements in an equivalence class expressed as a +/// sequence of contiguous ranges. +#[derive(Debug)] +struct ByteClassElementRanges<'a> { + elements: ByteClassElements<'a>, + range: Option<(Unit, Unit)>, +} + +impl<'a> Iterator for ByteClassElementRanges<'a> { + type Item = (Unit, Unit); + + fn next(&mut self) -> Option<(Unit, Unit)> { + loop { + let element = match self.elements.next() { + None => return self.range.take(), + Some(element) => element, + }; + match self.range.take() { + None => { + self.range = Some((element, element)); + } + Some((start, end)) => { + if end.as_usize() + 1 != element.as_usize() + || element.is_eoi() + { + self.range = Some((element, element)); + return Some((start, end)); + } + self.range = Some((start, element)); + } + } + } + } +} + +/// A partitioning of bytes into equivalence classes. +/// +/// A byte class set keeps track of an *approximation* of equivalence classes +/// of bytes during NFA construction. That is, every byte in an equivalence +/// class cannot discriminate between a match and a non-match. +/// +/// For example, in the regex `[ab]+`, the bytes `a` and `b` would be in the +/// same equivalence class because it never matters whether an `a` or a `b` is +/// seen, and no combination of `a`s and `b`s in the text can discriminate a +/// match. +/// +/// Note though that this does not compute the minimal set of equivalence +/// classes. For example, in the regex `[ac]+`, both `a` and `c` are in the +/// same equivalence class for the same reason that `a` and `b` are in the +/// same equivalence class in the aforementioned regex. However, in this +/// implementation, `a` and `c` are put into distinct equivalence classes. The +/// reason for this is implementation complexity. In the future, we should +/// endeavor to compute the minimal equivalence classes since they can have a +/// rather large impact on the size of the DFA. (Doing this will likely require +/// rethinking how equivalence classes are computed, including changing the +/// representation here, which is only able to group contiguous bytes into the +/// same equivalence class.) +#[cfg(feature = "alloc")] +#[derive(Clone, Debug)] +pub(crate) struct ByteClassSet(ByteSet); + +#[cfg(feature = "alloc")] +impl Default for ByteClassSet { + fn default() -> ByteClassSet { + ByteClassSet::empty() + } +} + +#[cfg(feature = "alloc")] +impl ByteClassSet { + /// Create a new set of byte classes where all bytes are part of the same + /// equivalence class. + pub(crate) fn empty() -> Self { + ByteClassSet(ByteSet::empty()) + } + + /// Indicate the the range of byte given (inclusive) can discriminate a + /// match between it and all other bytes outside of the range. + pub(crate) fn set_range(&mut self, start: u8, end: u8) { + debug_assert!(start <= end); + if start > 0 { + self.0.add(start - 1); + } + self.0.add(end); + } + + /// Add the contiguous ranges in the set given to this byte class set. + pub(crate) fn add_set(&mut self, set: &ByteSet) { + for (start, end) in set.iter_ranges() { + self.set_range(start, end); + } + } + + /// Convert this boolean set to a map that maps all byte values to their + /// corresponding equivalence class. The last mapping indicates the largest + /// equivalence class identifier (which is never bigger than 255). + pub(crate) fn byte_classes(&self) -> ByteClasses { + let mut classes = ByteClasses::empty(); + let mut class = 0u8; + let mut b = 0u8; + loop { + classes.set(b, class); + if b == 255 { + break; + } + if self.0.contains(b) { + class = class.checked_add(1).unwrap(); + } + b = b.checked_add(1).unwrap(); + } + classes + } +} + +/// A simple set of bytes that is reasonably cheap to copy and allocation free. +#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)] +pub(crate) struct ByteSet { + bits: BitSet, +} + +/// The representation of a byte set. Split out so that we can define a +/// convenient Debug impl for it while keeping "ByteSet" in the output. +#[derive(Clone, Copy, Default, Eq, PartialEq)] +struct BitSet([u128; 2]); + +impl ByteSet { + /// Create an empty set of bytes. + pub(crate) fn empty() -> ByteSet { + ByteSet { bits: BitSet([0; 2]) } + } + + /// Add a byte to this set. + /// + /// If the given byte already belongs to this set, then this is a no-op. + pub(crate) fn add(&mut self, byte: u8) { + let bucket = byte / 128; + let bit = byte % 128; + self.bits.0[usize::from(bucket)] |= 1 << bit; + } + + /// Remove a byte from this set. + /// + /// If the given byte is not in this set, then this is a no-op. + pub(crate) fn remove(&mut self, byte: u8) { + let bucket = byte / 128; + let bit = byte % 128; + self.bits.0[usize::from(bucket)] &= !(1 << bit); + } + + /// Return true if and only if the given byte is in this set. + pub(crate) fn contains(&self, byte: u8) -> bool { + let bucket = byte / 128; + let bit = byte % 128; + self.bits.0[usize::from(bucket)] & (1 << bit) > 0 + } + + /// Return true if and only if the given inclusive range of bytes is in + /// this set. + pub(crate) fn contains_range(&self, start: u8, end: u8) -> bool { + (start..=end).all(|b| self.contains(b)) + } + + /// Returns an iterator over all bytes in this set. + pub(crate) fn iter(&self) -> ByteSetIter { + ByteSetIter { set: self, b: 0 } + } + + /// Returns an iterator over all contiguous ranges of bytes in this set. + pub(crate) fn iter_ranges(&self) -> ByteSetRangeIter { + ByteSetRangeIter { set: self, b: 0 } + } + + /// Return true if and only if this set is empty. + #[cfg_attr(feature = "perf-inline", inline(always))] + pub(crate) fn is_empty(&self) -> bool { + self.bits.0 == [0, 0] + } + + /// Deserializes a byte set from the given slice. If the slice is of + /// incorrect length or is otherwise malformed, then an error is returned. + /// Upon success, the number of bytes read along with the set are returned. + /// The number of bytes read is always a multiple of 8. + pub(crate) fn from_bytes( + slice: &[u8], + ) -> Result<(ByteSet, usize), DeserializeError> { + use core::mem::size_of; + + wire::check_slice_len(slice, 2 * size_of::<u128>(), "byte set")?; + let mut nread = 0; + let (low, nr) = wire::try_read_u128(slice, "byte set low bucket")?; + nread += nr; + let (high, nr) = wire::try_read_u128(slice, "byte set high bucket")?; + nread += nr; + Ok((ByteSet { bits: BitSet([low, high]) }, nread)) + } + + /// Writes this byte set to the given byte buffer. If the given buffer is + /// too small, then an error is returned. Upon success, the total number of + /// bytes written is returned. The number of bytes written is guaranteed to + /// be a multiple of 8. + pub(crate) fn write_to<E: crate::util::wire::Endian>( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + use core::mem::size_of; + + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("byte set")); + } + let mut nw = 0; + E::write_u128(self.bits.0[0], &mut dst[nw..]); + nw += size_of::<u128>(); + E::write_u128(self.bits.0[1], &mut dst[nw..]); + nw += size_of::<u128>(); + assert_eq!(nwrite, nw, "expected to write certain number of bytes",); + assert_eq!( + nw % 8, + 0, + "expected to write multiple of 8 bytes for byte set", + ); + Ok(nw) + } + + /// Returns the total number of bytes written by `write_to`. + pub(crate) fn write_to_len(&self) -> usize { + 2 * core::mem::size_of::<u128>() + } +} + +impl core::fmt::Debug for BitSet { + fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result { + let mut fmtd = f.debug_set(); + for b in 0u8..=255 { + if (ByteSet { bits: *self }).contains(b) { + fmtd.entry(&b); + } + } + fmtd.finish() + } +} + +#[derive(Debug)] +pub(crate) struct ByteSetIter<'a> { + set: &'a ByteSet, + b: usize, +} + +impl<'a> Iterator for ByteSetIter<'a> { + type Item = u8; + + fn next(&mut self) -> Option<u8> { + while self.b <= 255 { + let b = u8::try_from(self.b).unwrap(); + self.b += 1; + if self.set.contains(b) { + return Some(b); + } + } + None + } +} + +#[derive(Debug)] +pub(crate) struct ByteSetRangeIter<'a> { + set: &'a ByteSet, + b: usize, +} + +impl<'a> Iterator for ByteSetRangeIter<'a> { + type Item = (u8, u8); + + fn next(&mut self) -> Option<(u8, u8)> { + let asu8 = |n: usize| u8::try_from(n).unwrap(); + while self.b <= 255 { + let start = asu8(self.b); + self.b += 1; + if !self.set.contains(start) { + continue; + } + + let mut end = start; + while self.b <= 255 && self.set.contains(asu8(self.b)) { + end = asu8(self.b); + self.b += 1; + } + return Some((start, end)); + } + None + } +} + +#[cfg(all(test, feature = "alloc"))] +mod tests { + use alloc::{vec, vec::Vec}; + + use super::*; + + #[test] + fn byte_classes() { + let mut set = ByteClassSet::empty(); + set.set_range(b'a', b'z'); + + let classes = set.byte_classes(); + assert_eq!(classes.get(0), 0); + assert_eq!(classes.get(1), 0); + assert_eq!(classes.get(2), 0); + assert_eq!(classes.get(b'a' - 1), 0); + assert_eq!(classes.get(b'a'), 1); + assert_eq!(classes.get(b'm'), 1); + assert_eq!(classes.get(b'z'), 1); + assert_eq!(classes.get(b'z' + 1), 2); + assert_eq!(classes.get(254), 2); + assert_eq!(classes.get(255), 2); + + let mut set = ByteClassSet::empty(); + set.set_range(0, 2); + set.set_range(4, 6); + let classes = set.byte_classes(); + assert_eq!(classes.get(0), 0); + assert_eq!(classes.get(1), 0); + assert_eq!(classes.get(2), 0); + assert_eq!(classes.get(3), 1); + assert_eq!(classes.get(4), 2); + assert_eq!(classes.get(5), 2); + assert_eq!(classes.get(6), 2); + assert_eq!(classes.get(7), 3); + assert_eq!(classes.get(255), 3); + } + + #[test] + fn full_byte_classes() { + let mut set = ByteClassSet::empty(); + for b in 0u8..=255 { + set.set_range(b, b); + } + assert_eq!(set.byte_classes().alphabet_len(), 257); + } + + #[test] + fn elements_typical() { + let mut set = ByteClassSet::empty(); + set.set_range(b'b', b'd'); + set.set_range(b'g', b'm'); + set.set_range(b'z', b'z'); + let classes = set.byte_classes(); + // class 0: \x00-a + // class 1: b-d + // class 2: e-f + // class 3: g-m + // class 4: n-y + // class 5: z-z + // class 6: \x7B-\xFF + // class 7: EOI + assert_eq!(classes.alphabet_len(), 8); + + let elements = classes.elements(Unit::u8(0)).collect::<Vec<_>>(); + assert_eq!(elements.len(), 98); + assert_eq!(elements[0], Unit::u8(b'\x00')); + assert_eq!(elements[97], Unit::u8(b'a')); + + let elements = classes.elements(Unit::u8(1)).collect::<Vec<_>>(); + assert_eq!( + elements, + vec![Unit::u8(b'b'), Unit::u8(b'c'), Unit::u8(b'd')], + ); + + let elements = classes.elements(Unit::u8(2)).collect::<Vec<_>>(); + assert_eq!(elements, vec![Unit::u8(b'e'), Unit::u8(b'f')],); + + let elements = classes.elements(Unit::u8(3)).collect::<Vec<_>>(); + assert_eq!( + elements, + vec![ + Unit::u8(b'g'), + Unit::u8(b'h'), + Unit::u8(b'i'), + Unit::u8(b'j'), + Unit::u8(b'k'), + Unit::u8(b'l'), + Unit::u8(b'm'), + ], + ); + + let elements = classes.elements(Unit::u8(4)).collect::<Vec<_>>(); + assert_eq!(elements.len(), 12); + assert_eq!(elements[0], Unit::u8(b'n')); + assert_eq!(elements[11], Unit::u8(b'y')); + + let elements = classes.elements(Unit::u8(5)).collect::<Vec<_>>(); + assert_eq!(elements, vec![Unit::u8(b'z')]); + + let elements = classes.elements(Unit::u8(6)).collect::<Vec<_>>(); + assert_eq!(elements.len(), 133); + assert_eq!(elements[0], Unit::u8(b'\x7B')); + assert_eq!(elements[132], Unit::u8(b'\xFF')); + + let elements = classes.elements(Unit::eoi(7)).collect::<Vec<_>>(); + assert_eq!(elements, vec![Unit::eoi(256)]); + } + + #[test] + fn elements_singletons() { + let classes = ByteClasses::singletons(); + assert_eq!(classes.alphabet_len(), 257); + + let elements = classes.elements(Unit::u8(b'a')).collect::<Vec<_>>(); + assert_eq!(elements, vec![Unit::u8(b'a')]); + + let elements = classes.elements(Unit::eoi(5)).collect::<Vec<_>>(); + assert_eq!(elements, vec![Unit::eoi(256)]); + } + + #[test] + fn elements_empty() { + let classes = ByteClasses::empty(); + assert_eq!(classes.alphabet_len(), 2); + + let elements = classes.elements(Unit::u8(0)).collect::<Vec<_>>(); + assert_eq!(elements.len(), 256); + assert_eq!(elements[0], Unit::u8(b'\x00')); + assert_eq!(elements[255], Unit::u8(b'\xFF')); + + let elements = classes.elements(Unit::eoi(1)).collect::<Vec<_>>(); + assert_eq!(elements, vec![Unit::eoi(256)]); + } + + #[test] + fn representatives() { + let mut set = ByteClassSet::empty(); + set.set_range(b'b', b'd'); + set.set_range(b'g', b'm'); + set.set_range(b'z', b'z'); + let classes = set.byte_classes(); + + let got: Vec<Unit> = classes.representatives(..).collect(); + let expected = vec![ + Unit::u8(b'\x00'), + Unit::u8(b'b'), + Unit::u8(b'e'), + Unit::u8(b'g'), + Unit::u8(b'n'), + Unit::u8(b'z'), + Unit::u8(b'\x7B'), + Unit::eoi(7), + ]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(..0).collect(); + assert!(got.is_empty()); + let got: Vec<Unit> = classes.representatives(1..1).collect(); + assert!(got.is_empty()); + let got: Vec<Unit> = classes.representatives(255..255).collect(); + assert!(got.is_empty()); + + // A weird case that is the only guaranteed to way to get an iterator + // of just the EOI class by excluding all possible byte values. + let got: Vec<Unit> = classes + .representatives(( + core::ops::Bound::Excluded(255), + core::ops::Bound::Unbounded, + )) + .collect(); + let expected = vec![Unit::eoi(7)]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(..=255).collect(); + let expected = vec![ + Unit::u8(b'\x00'), + Unit::u8(b'b'), + Unit::u8(b'e'), + Unit::u8(b'g'), + Unit::u8(b'n'), + Unit::u8(b'z'), + Unit::u8(b'\x7B'), + ]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(b'b'..=b'd').collect(); + let expected = vec![Unit::u8(b'b')]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(b'a'..=b'd').collect(); + let expected = vec![Unit::u8(b'a'), Unit::u8(b'b')]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(b'b'..=b'e').collect(); + let expected = vec![Unit::u8(b'b'), Unit::u8(b'e')]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(b'A'..=b'Z').collect(); + let expected = vec![Unit::u8(b'A')]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(b'A'..=b'z').collect(); + let expected = vec![ + Unit::u8(b'A'), + Unit::u8(b'b'), + Unit::u8(b'e'), + Unit::u8(b'g'), + Unit::u8(b'n'), + Unit::u8(b'z'), + ]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(b'z'..).collect(); + let expected = vec![Unit::u8(b'z'), Unit::u8(b'\x7B'), Unit::eoi(7)]; + assert_eq!(expected, got); + + let got: Vec<Unit> = classes.representatives(b'z'..=0xFF).collect(); + let expected = vec![Unit::u8(b'z'), Unit::u8(b'\x7B')]; + assert_eq!(expected, got); + } +} |