Struct aho_corasick::util::alphabet::ByteClasses

pub(crate) struct ByteClasses([u8; 256]);

A representation of byte oriented equivalence classes.

This is used in finite state machines to reduce the size of the transition table. This can have a particularly large impact not only on the total size of an FSM, but also on FSM build times because it reduces the number of transitions that need to be visited/set.

Tuple Fields

0: [u8; 256]

Implementations

impl ByteClasses

pub(crate) fn empty() -> ByteClasses

Creates a new set of equivalence classes where all bytes are mapped to the same class.

pub(crate) fn singletons() -> ByteClasses

Creates a new set of equivalence classes where each byte belongs to its own equivalence class.

pub(crate) fn set(&mut self, byte: u8, class: u8)

Set the equivalence class for the given byte.

pub(crate) fn get(&self, byte: u8) -> u8

Get the equivalence class for the given byte.

pub(crate) fn alphabet_len(&self) -> usize

Return the total number of elements in the alphabet represented by these equivalence classes. Equivalently, this returns the total number of equivalence classes.

pub(crate) fn stride2(&self) -> usize

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. This is done so that converting between state IDs and indices can be done with shifts alone, which is much faster than integer division. The “stride2” is the exponent. i.e., 2^stride2 = stride.

pub(crate) fn stride(&self) -> usize

Returns the stride for these equivalence classes, which corresponds to the smallest power of 2 greater than or equal to the number of equivalence classes.

pub(crate) fn is_singleton(&self) -> bool

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 exactly one byte (plus the special EOI class).

pub(crate) fn iter(&self) -> ByteClassIter

Returns an iterator over all equivalence classes in this set.

pub(crate) fn elements(&self, class: u8) -> ByteClassElements<'_>

Returns an iterator of the bytes in the given equivalence class.

fn element_ranges(&self, class: u8) -> ByteClassElementRanges<'_>

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.

Trait Implementations

impl Clone for ByteClasses

fn clone(&self) -> ByteClasses

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ByteClasses

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Copy for ByteClasses