Initial import of regex-automata-0.1.9.
Bug: 155309706
Change-Id: I20031167cbe49d12754936285a0781eb7a3b8bfd
diff --git a/src/classes.rs b/src/classes.rs
new file mode 100644
index 0000000..143908b
--- /dev/null
+++ b/src/classes.rs
@@ -0,0 +1,271 @@
+use core::fmt;
+
+/// 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.
+#[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.
+ pub fn empty() -> ByteClasses {
+ ByteClasses([0; 256])
+ }
+
+ /// Creates a new set of equivalence classes where each byte belongs to
+ /// its own equivalence class.
+ pub fn singletons() -> ByteClasses {
+ let mut classes = ByteClasses::empty();
+ for i in 0..256 {
+ classes.set(i as u8, i as u8);
+ }
+ classes
+ }
+
+ /// Copies the byte classes given. The given slice must have length 0 or
+ /// length 256. Slices of length 0 are treated as singletons (every byte
+ /// is its own class).
+ pub fn from_slice(slice: &[u8]) -> ByteClasses {
+ assert!(slice.is_empty() || slice.len() == 256);
+
+ if slice.is_empty() {
+ ByteClasses::singletons()
+ } else {
+ let mut classes = ByteClasses::empty();
+ for (b, &class) in slice.iter().enumerate() {
+ classes.set(b as u8, class);
+ }
+ classes
+ }
+ }
+
+ /// Set the equivalence class for the given byte.
+ #[inline]
+ pub fn set(&mut self, byte: u8, class: u8) {
+ self.0[byte as usize] = class;
+ }
+
+ /// Get the equivalence class for the given byte.
+ #[inline]
+ pub fn get(&self, byte: u8) -> u8 {
+ self.0[byte as usize]
+ }
+
+ /// Get the equivalence class for the given byte while forcefully
+ /// eliding bounds checks.
+ #[inline]
+ pub unsafe fn get_unchecked(&self, byte: u8) -> u8 {
+ *self.0.get_unchecked(byte as usize)
+ }
+
+ /// 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 {
+ self.0[255] as usize + 1
+ }
+
+ /// Returns true if and only if every byte in this class maps to its own
+ /// equivalence class. Equivalently, there are 256 equivalence classes
+ /// and each class contains exactly one byte.
+ #[inline]
+ pub fn is_singleton(&self) -> bool {
+ self.alphabet_len() == 256
+ }
+
+ /// Returns an iterator over a sequence of representative bytes from each
+ /// equivalence class. Namely, this 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 yet. Picking an arbitrary
+ /// byte from each equivalence class then permits a full exploration of
+ /// the NFA instead of using every possible byte value.
+ #[cfg(feature = "std")]
+ pub fn representatives(&self) -> ByteClassRepresentatives {
+ ByteClassRepresentatives { classes: self, byte: 0, last_class: None }
+ }
+
+ /// Returns all of the bytes in the given equivalence class.
+ ///
+ /// The second element in the tuple indicates the number of elements in
+ /// the array.
+ fn elements(&self, equiv: u8) -> ([u8; 256], usize) {
+ let (mut array, mut len) = ([0; 256], 0);
+ for b in 0..256 {
+ if self.get(b as u8) == equiv {
+ array[len] = b as u8;
+ len += 1;
+ }
+ }
+ (array, len)
+ }
+}
+
+impl fmt::Debug for ByteClasses {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ if self.is_singleton() {
+ write!(f, "ByteClasses({{singletons}})")
+ } else {
+ write!(f, "ByteClasses(")?;
+ for equiv in 0..self.alphabet_len() {
+ let (members, len) = self.elements(equiv as u8);
+ write!(f, "{} => {:?}", equiv, &members[..len])?;
+ }
+ write!(f, ")")
+ }
+ }
+}
+
+/// An iterator over representative bytes from each equivalence class.
+#[cfg(feature = "std")]
+#[derive(Debug)]
+pub struct ByteClassRepresentatives<'a> {
+ classes: &'a ByteClasses,
+ byte: usize,
+ last_class: Option<u8>,
+}
+
+#[cfg(feature = "std")]
+impl<'a> Iterator for ByteClassRepresentatives<'a> {
+ type Item = u8;
+
+ fn next(&mut self) -> Option<u8> {
+ while self.byte < 256 {
+ let byte = self.byte as u8;
+ let class = self.classes.get(byte);
+ self.byte += 1;
+
+ if self.last_class != Some(class) {
+ self.last_class = Some(class);
+ return Some(byte);
+ }
+ }
+ None
+ }
+}
+
+/// 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.
+///
+/// The representation here is 256 booleans, all initially set to false. Each
+/// boolean maps to its corresponding byte based on position. A `true` value
+/// indicates the end of an equivalence class, where its corresponding byte
+/// and all of the bytes corresponding to all previous contiguous `false`
+/// values are in the same equivalence class.
+///
+/// This particular representation only permits contiguous ranges of bytes to
+/// be in the same equivalence class, which means that we can never discover
+/// the true minimal set of equivalence classes.
+#[cfg(feature = "std")]
+#[derive(Debug)]
+pub struct ByteClassSet(Vec<bool>);
+
+#[cfg(feature = "std")]
+impl ByteClassSet {
+ /// Create a new set of byte classes where all bytes are part of the same
+ /// equivalence class.
+ pub fn new() -> Self {
+ ByteClassSet(vec![false; 256])
+ }
+
+ /// Indicate the the range of byte given (inclusive) can discriminate a
+ /// match between it and all other bytes outside of the range.
+ pub fn set_range(&mut self, start: u8, end: u8) {
+ debug_assert!(start <= end);
+ if start > 0 {
+ self.0[start as usize - 1] = true;
+ }
+ self.0[end as usize] = true;
+ }
+
+ /// 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 fn byte_classes(&self) -> ByteClasses {
+ let mut classes = ByteClasses::empty();
+ let mut class = 0u8;
+ let mut i = 0;
+ loop {
+ classes.set(i as u8, class as u8);
+ if i >= 255 {
+ break;
+ }
+ if self.0[i] {
+ class = class.checked_add(1).unwrap();
+ }
+ i += 1;
+ }
+ classes
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ #[cfg(feature = "std")]
+ #[test]
+ fn byte_classes() {
+ use super::ByteClassSet;
+
+ let mut set = ByteClassSet::new();
+ 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::new();
+ 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);
+ }
+
+ #[cfg(feature = "std")]
+ #[test]
+ fn full_byte_classes() {
+ use super::ByteClassSet;
+
+ let mut set = ByteClassSet::new();
+ for i in 0..256u16 {
+ set.set_range(i as u8, i as u8);
+ }
+ assert_eq!(set.byte_classes().alphabet_len(), 256);
+ }
+}