Struct aho_corasick::util::prefilter::RareBytesBuilder

struct RareBytesBuilder {
    ascii_case_insensitive: bool,
    rare_set: ByteSet,
    byte_offsets: RareByteOffsets,
    available: bool,
    count: usize,
    rank_sum: u16,
}

A builder for constructing a rare byte prefilter.

A rare byte prefilter attempts to pick out a small set of rare bytes that occurr in the patterns, and then quickly scan to matches of those rare bytes.

Fields

ascii_case_insensitive: bool

Whether this prefilter should account for ASCII case insensitivity or not.

rare_set: ByteSet

A set of rare bytes, indexed by byte value.

byte_offsets: RareByteOffsets

A set of byte offsets associated with bytes in a pattern. An entry corresponds to a particular bytes (its index) and is only non-zero if the byte occurred at an offset greater than 0 in at least one pattern.

If a byte’s offset is not representable in 8 bits, then the rare bytes prefilter becomes inert.

available: bool

Whether this is available as a prefilter or not. This can be set to false during construction if a condition is seen that invalidates the use of the rare-byte prefilter.

count: usize

The number of bytes set to an active value in byte_offsets.

rank_sum: u16

The sum of frequency ranks for the rare bytes detected. This is intended to give a heuristic notion of how rare the bytes are.

Implementations

impl RareBytesBuilder

fn new() -> RareBytesBuilder

Create a new builder for constructing a rare byte prefilter.

fn ascii_case_insensitive(self, yes: bool) -> RareBytesBuilder

Enable ASCII case insensitivity. When set, byte strings added to this builder will be interpreted without respect to ASCII case.

fn build(&self) -> Option<Prefilter>

Build the rare bytes prefilter.

If there are more than 3 distinct rare bytes found, or if heuristics otherwise determine that this prefilter should not be used, then None is returned.

fn add(&mut self, bytes: &[u8])

Add a byte string to this builder.

All patterns added to an Aho-Corasick automaton should be added to this builder before attempting to construct the prefilter.

fn set_offset(&mut self, pos: usize, byte: u8)

fn add_rare_byte(&mut self, byte: u8)

fn add_one_rare_byte(&mut self, byte: u8)

Trait Implementations

impl Clone for RareBytesBuilder

fn clone(&self) -> RareBytesBuilder

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for RareBytesBuilder

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

Formats the value using the given formatter.