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/*!
Provides a contiguous NFA implementation of Aho-Corasick.
This is a low-level API that generally only needs to be used in niche
circumstances. When possible, prefer using [`AhoCorasick`](crate::AhoCorasick)
instead of a contiguous NFA directly. Using an `NFA` directly is typically only
necessary when one needs access to the [`Automaton`] trait implementation.
*/
use alloc::{vec, vec::Vec};
use crate::{
automaton::Automaton,
nfa::noncontiguous,
util::{
alphabet::ByteClasses,
error::{BuildError, MatchError},
int::{Usize, U16, U32},
prefilter::Prefilter,
primitives::{IteratorIndexExt, PatternID, SmallIndex, StateID},
search::{Anchored, MatchKind},
special::Special,
},
};
/// A contiguous NFA implementation of Aho-Corasick.
///
/// When possible, prefer using [`AhoCorasick`](crate::AhoCorasick) instead of
/// this type directly. Using an `NFA` directly is typically only necessary
/// when one needs access to the [`Automaton`] trait implementation.
///
/// This NFA can only be built by first constructing a [`noncontiguous::NFA`].
/// Both [`NFA::new`] and [`Builder::build`] do this for you automatically, but
/// [`Builder::build_from_noncontiguous`] permits doing it explicitly.
///
/// The main difference between a noncontiguous NFA and a contiguous NFA is
/// that the latter represents all of its states and transitions in a single
/// allocation, where as the former uses a separate allocation for each state.
/// Doing this at construction time while keeping a low memory footprint isn't
/// feasible, which is primarily why there are two different NFA types: one
/// that does the least amount of work possible to build itself, and another
/// that does a little extra work to compact itself and make state transitions
/// faster by making some states use a dense representation.
///
/// Because a contiguous NFA uses a single allocation, there is a lot more
/// opportunity for compression tricks to reduce the heap memory used. Indeed,
/// it is not uncommon for a contiguous NFA to use an order of magnitude less
/// heap memory than a noncontiguous NFA. Since building a contiguous NFA
/// usually only takes a fraction of the time it takes to build a noncontiguous
/// NFA, the overall build time is not much slower. Thus, in most cases, a
/// contiguous NFA is the best choice.
///
/// Since a contiguous NFA uses various tricks for compression and to achieve
/// faster state transitions, currently, its limit on the number of states
/// is somewhat smaller than what a noncontiguous NFA can achieve. Generally
/// speaking, you shouldn't expect to run into this limit if the number of
/// patterns is under 1 million. It is plausible that this limit will be
/// increased in the future. If the limit is reached, building a contiguous NFA
/// will return an error. Often, since building a contiguous NFA is relatively
/// cheap, it can make sense to always try it even if you aren't sure if it
/// will fail or not. If it does, you can always fall back to a noncontiguous
/// NFA. (Indeed, the main [`AhoCorasick`](crate::AhoCorasick) type employs a
/// strategy similar to this at construction time.)
///
/// # Example
///
/// This example shows how to build an `NFA` directly and use it to execute
/// [`Automaton::try_find`]:
///
/// ```
/// use aho_corasick::{
/// automaton::Automaton,
/// nfa::contiguous::NFA,
/// Input, Match,
/// };
///
/// let patterns = &["b", "abc", "abcd"];
/// let haystack = "abcd";
///
/// let nfa = NFA::new(patterns).unwrap();
/// assert_eq!(
/// Some(Match::must(0, 1..2)),
/// nfa.try_find(&Input::new(haystack))?,
/// );
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// It is also possible to implement your own version of `try_find`. See the
/// [`Automaton`] documentation for an example.
#[derive(Clone)]
pub struct NFA {
/// The raw NFA representation. Each state is packed with a header
/// (containing the format of the state, the failure transition and, for
/// a sparse state, the number of transitions), its transitions and any
/// matching pattern IDs for match states.
repr: Vec<u32>,
/// The length of each pattern. This is used to compute the start offset
/// of a match.
pattern_lens: Vec<SmallIndex>,
/// The total number of states in this NFA.
state_len: usize,
/// A prefilter for accelerating searches, if one exists.
prefilter: Option<Prefilter>,
/// The match semantics built into this NFA.
match_kind: MatchKind,
/// The alphabet size, or total number of equivalence classes, for this
/// NFA. Dense states always have this many transitions.
alphabet_len: usize,
/// The equivalence classes for this NFA. All transitions, dense and
/// sparse, are defined on equivalence classes and not on the 256 distinct
/// byte values.
byte_classes: ByteClasses,
/// The length of the shortest pattern in this automaton.
min_pattern_len: usize,
/// The length of the longest pattern in this automaton.
max_pattern_len: usize,
/// The information required to deduce which states are "special" in this
/// NFA.
special: Special,
}
impl NFA {
/// Create a new Aho-Corasick contiguous NFA using the default
/// configuration.
///
/// Use a [`Builder`] if you want to change the configuration.
pub fn new<I, P>(patterns: I) -> Result<NFA, BuildError>
where
I: IntoIterator<Item = P>,
P: AsRef<[u8]>,
{
NFA::builder().build(patterns)
}
/// A convenience method for returning a new Aho-Corasick contiguous NFA
/// builder.
///
/// This usually permits one to just import the `NFA` type.
pub fn builder() -> Builder {
Builder::new()
}
}
impl NFA {
/// A sentinel state ID indicating that a search should stop once it has
/// entered this state. When a search stops, it returns a match if one
/// has been found, otherwise no match. A contiguous NFA always has an
/// actual dead state at this ID.
const DEAD: StateID = StateID::new_unchecked(0);
/// Another sentinel state ID indicating that a search should move through
/// current state's failure transition.
///
/// Note that unlike DEAD, this does not actually point to a valid state
/// in a contiguous NFA. (noncontiguous::NFA::FAIL does point to a valid
/// state.) Instead, this points to the position that is guaranteed to
/// never be a valid state ID (by making sure it points to a place in the
/// middle of the encoding of the DEAD state). Since we never need to
/// actually look at the FAIL state itself, this works out.
///
/// By why do it this way? So that FAIL is a constant. I don't have any
/// concrete evidence that this materially helps matters, but it's easy to
/// do. The alternative would be making the FAIL ID point to the second
/// state, which could be made a constant but is a little trickier to do.
/// The easiest path is to just make the FAIL state a runtime value, but
/// since comparisons with FAIL occur in perf critical parts of the search,
/// we want it to be as tight as possible and not waste any registers.
///
/// Very hand wavy... But the code complexity that results from this is
/// very mild.
const FAIL: StateID = StateID::new_unchecked(1);
}
// SAFETY: 'start_state' always returns a valid state ID, 'next_state' always
// returns a valid state ID given a valid state ID. We otherwise claim that
// all other methods are correct as well.
unsafe impl Automaton for NFA {
#[inline(always)]
fn start_state(&self, anchored: Anchored) -> Result<StateID, MatchError> {
match anchored {
Anchored::No => Ok(self.special.start_unanchored_id),
Anchored::Yes => Ok(self.special.start_anchored_id),
}
}
#[inline(always)]
fn next_state(
&self,
anchored: Anchored,
mut sid: StateID,
byte: u8,
) -> StateID {
let repr = &self.repr;
let class = self.byte_classes.get(byte);
let u32tosid = StateID::from_u32_unchecked;
loop {
let o = sid.as_usize();
let kind = repr[o] & 0xFF;
// I tried to encapsulate the "next transition" logic into its own
// function, but it seemed to always result in sub-optimal codegen
// that led to real and significant slowdowns. So we just inline
// the logic here.
//
// I've also tried a lot of different ways to speed up this
// routine, and most of them have failed.
if kind == State::KIND_DENSE {
let next = u32tosid(repr[o + 2 + usize::from(class)]);
if next != NFA::FAIL {
return next;
}
} else if kind == State::KIND_ONE {
if class == repr[o].low_u16().high_u8() {
return u32tosid(repr[o + 2]);
}
} else {
// NOTE: I tried a SWAR technique in the loop below, but found
// it slower. See the 'swar' test in the tests for this module.
let trans_len = kind.as_usize();
let classes_len = u32_len(trans_len);
let trans_offset = o + 2 + classes_len;
for (i, &chunk) in
repr[o + 2..][..classes_len].iter().enumerate()
{
let classes = chunk.to_ne_bytes();
if classes[0] == class {
return u32tosid(repr[trans_offset + i * 4]);
}
if classes[1] == class {
return u32tosid(repr[trans_offset + i * 4 + 1]);
}
if classes[2] == class {
return u32tosid(repr[trans_offset + i * 4 + 2]);
}
if classes[3] == class {
return u32tosid(repr[trans_offset + i * 4 + 3]);
}
}
}
// For an anchored search, we never follow failure transitions
// because failure transitions lead us down a path to matching
// a *proper* suffix of the path we were on. Thus, it can only
// produce matches that appear after the beginning of the search.
if anchored.is_anchored() {
return NFA::DEAD;
}
sid = u32tosid(repr[o + 1]);
}
}
#[inline(always)]
fn is_special(&self, sid: StateID) -> bool {
sid <= self.special.max_special_id
}
#[inline(always)]
fn is_dead(&self, sid: StateID) -> bool {
sid == NFA::DEAD
}
#[inline(always)]
fn is_match(&self, sid: StateID) -> bool {
!self.is_dead(sid) && sid <= self.special.max_match_id
}
#[inline(always)]
fn is_start(&self, sid: StateID) -> bool {
sid == self.special.start_unanchored_id
|| sid == self.special.start_anchored_id
}
#[inline(always)]
fn match_kind(&self) -> MatchKind {
self.match_kind
}
#[inline(always)]
fn patterns_len(&self) -> usize {
self.pattern_lens.len()
}
#[inline(always)]
fn pattern_len(&self, pid: PatternID) -> usize {
self.pattern_lens[pid].as_usize()
}
#[inline(always)]
fn min_pattern_len(&self) -> usize {
self.min_pattern_len
}
#[inline(always)]
fn max_pattern_len(&self) -> usize {
self.max_pattern_len
}
#[inline(always)]
fn match_len(&self, sid: StateID) -> usize {
State::match_len(self.alphabet_len, &self.repr[sid.as_usize()..])
}
#[inline(always)]
fn match_pattern(&self, sid: StateID, index: usize) -> PatternID {
State::match_pattern(
self.alphabet_len,
&self.repr[sid.as_usize()..],
index,
)
}
#[inline(always)]
fn memory_usage(&self) -> usize {
use core::mem::size_of;
(self.repr.len() * size_of::<u32>())
+ (self.pattern_lens.len() * size_of::<SmallIndex>())
+ self.prefilter.as_ref().map_or(0, |p| p.memory_usage())
}
#[inline(always)]
fn prefilter(&self) -> Option<&Prefilter> {
self.prefilter.as_ref()
}
}
impl core::fmt::Debug for NFA {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
use crate::automaton::fmt_state_indicator;
writeln!(f, "contiguous::NFA(")?;
let mut sid = NFA::DEAD; // always the first state and always present
loop {
let raw = &self.repr[sid.as_usize()..];
if raw.is_empty() {
break;
}
let is_match = self.is_match(sid);
let state = State::read(self.alphabet_len, is_match, raw);
fmt_state_indicator(f, self, sid)?;
write!(
f,
"{:06}({:06}): ",
sid.as_usize(),
state.fail.as_usize()
)?;
state.fmt(f)?;
write!(f, "\n")?;
if self.is_match(sid) {
write!(f, " matches: ")?;
for i in 0..state.match_len {
let pid = State::match_pattern(self.alphabet_len, raw, i);
if i > 0 {
write!(f, ", ")?;
}
write!(f, "{}", pid.as_usize())?;
}
write!(f, "\n")?;
}
// The FAIL state doesn't actually have space for a state allocated
// for it, so we have to treat it as a special case. write below
// the DEAD state.
if sid == NFA::DEAD {
writeln!(f, "F {:06}:", NFA::FAIL.as_usize())?;
}
let len = State::len(self.alphabet_len, is_match, raw);
sid = StateID::new(sid.as_usize().checked_add(len).unwrap())
.unwrap();
}
writeln!(f, "match kind: {:?}", self.match_kind)?;
writeln!(f, "prefilter: {:?}", self.prefilter.is_some())?;
writeln!(f, "state length: {:?}", self.state_len)?;
writeln!(f, "pattern length: {:?}", self.patterns_len())?;
writeln!(f, "shortest pattern length: {:?}", self.min_pattern_len)?;
writeln!(f, "longest pattern length: {:?}", self.max_pattern_len)?;
writeln!(f, "alphabet length: {:?}", self.alphabet_len)?;
writeln!(f, "byte classes: {:?}", self.byte_classes)?;
writeln!(f, "memory usage: {:?}", self.memory_usage())?;
writeln!(f, ")")?;
Ok(())
}
}
/// The "in memory" representation a single dense or sparse state.
///
/// A `State`'s in memory representation is not ever actually materialized
/// during a search with a contiguous NFA. Doing so would be too slow. (Indeed,
/// the only time a `State` is actually constructed is in `Debug` impls.)
/// Instead, a `State` exposes a number of static methods for reading certain
/// things from the raw binary encoding of the state.
#[derive(Clone)]
struct State<'a> {
/// The state to transition to when 'class_to_next' yields a transition
/// to the FAIL state.
fail: StateID,
/// The number of pattern IDs in this state. For a non-match state, this is
/// always zero. Otherwise it is always bigger than zero.
match_len: usize,
/// The sparse or dense representation of the transitions for this state.
trans: StateTrans<'a>,
}
/// The underlying representation of sparse or dense transitions for a state.
///
/// Note that like `State`, we don't typically construct values of this type
/// during a search since we don't always need all values and thus would
/// represent a lot of wasteful work.
#[derive(Clone)]
enum StateTrans<'a> {
/// A sparse representation of transitions for a state, where only non-FAIL
/// transitions are explicitly represented.
Sparse {
classes: &'a [u32],
/// The transitions for this state, where each transition is packed
/// into a u32. The low 8 bits correspond to the byte class for the
/// transition, and the high 24 bits correspond to the next state ID.
///
/// This packing is why the max state ID allowed for a contiguous
/// NFA is 2^24-1.
nexts: &'a [u32],
},
/// A "one transition" state that is never a match state.
///
/// These are by far the most common state, so we use a specialized and
/// very compact representation for them.
One {
/// The element of this NFA's alphabet that this transition is
/// defined for.
class: u8,
/// The state this should transition to if the current symbol is
/// equal to 'class'.
next: u32,
},
/// A dense representation of transitions for a state, where all
/// transitions are explicitly represented, including transitions to the
/// FAIL state.
Dense {
/// A dense set of transitions to other states. The transitions may
/// point to a FAIL state, in which case, the search should try the
/// same transition lookup at 'fail'.
///
/// Note that this is indexed by byte equivalence classes and not
/// byte values. That means 'class_to_next[byte]' is wrong and
/// 'class_to_next[classes.get(byte)]' is correct. The number of
/// transitions is always equivalent to 'classes.alphabet_len()'.
class_to_next: &'a [u32],
},
}
impl<'a> State<'a> {
/// The offset of where the "kind" of a state is stored. If it isn't one
/// of the sentinel values below, then it's a sparse state and the kind
/// corresponds to the number of transitions in the state.
const KIND: usize = 0;
/// A sentinel value indicating that the state uses a dense representation.
const KIND_DENSE: u32 = 0xFF;
/// A sentinel value indicating that the state uses a special "one
/// transition" encoding. In practice, non-match states with one transition
/// make up the overwhelming majority of all states in any given
/// Aho-Corasick automaton, so we can specialize them using a very compact
/// representation.
const KIND_ONE: u32 = 0xFE;
/// The maximum number of transitions to encode as a sparse state. Usually
/// states with a lot of transitions are either very rare, or occur near
/// the start state. In the latter case, they are probably dense already
/// anyway. In the former case, making them dense is fine because they're
/// rare.
///
/// This needs to be small enough to permit each of the sentinel values for
/// 'KIND' above. Namely, a sparse state embeds the number of transitions
/// into the 'KIND'. Basically, "sparse" is a state kind too, but it's the
/// "else" branch.
///
/// N.B. There isn't anything particularly magical about 127 here. I
/// just picked it because I figured any sparse state with this many
/// transitions is going to be exceptionally rare, and if it did have this
/// many transitions, then it would be quite slow to do a linear scan on
/// the transitions during a search anyway.
const MAX_SPARSE_TRANSITIONS: usize = 127;
/// Remap state IDs in-place.
///
/// `state` should be the the raw binary encoding of a state. (The start
/// of the slice must correspond to the start of the state, but the slice
/// may extend past the end of the encoding of the state.)
fn remap(
alphabet_len: usize,
old_to_new: &[StateID],
state: &mut [u32],
) -> Result<(), BuildError> {
let kind = State::kind(state);
if kind == State::KIND_DENSE {
state[1] = old_to_new[state[1].as_usize()].as_u32();
for next in state[2..][..alphabet_len].iter_mut() {
*next = old_to_new[next.as_usize()].as_u32();
}
} else if kind == State::KIND_ONE {
state[1] = old_to_new[state[1].as_usize()].as_u32();
state[2] = old_to_new[state[2].as_usize()].as_u32();
} else {
let trans_len = State::sparse_trans_len(state);
let classes_len = u32_len(trans_len);
state[1] = old_to_new[state[1].as_usize()].as_u32();
for next in state[2 + classes_len..][..trans_len].iter_mut() {
*next = old_to_new[next.as_usize()].as_u32();
}
}
Ok(())
}
/// Returns the length, in number of u32s, of this state.
///
/// This is useful for reading states consecutively, e.g., in the Debug
/// impl without needing to store a separate map from state index to state
/// identifier.
///
/// `state` should be the the raw binary encoding of a state. (The start
/// of the slice must correspond to the start of the state, but the slice
/// may extend past the end of the encoding of the state.)
fn len(alphabet_len: usize, is_match: bool, state: &[u32]) -> usize {
let kind_len = 1;
let fail_len = 1;
let kind = State::kind(state);
let (classes_len, trans_len) = if kind == State::KIND_DENSE {
(0, alphabet_len)
} else if kind == State::KIND_ONE {
(0, 1)
} else {
let trans_len = State::sparse_trans_len(state);
let classes_len = u32_len(trans_len);
(classes_len, trans_len)
};
let match_len = if !is_match {
0
} else if State::match_len(alphabet_len, state) == 1 {
// This is a special case because when there is one pattern ID for
// a match state, it is represented by a single u32 with its high
// bit set (which is impossible for a valid pattern ID).
1
} else {
// We add 1 to include the u32 that indicates the number of
// pattern IDs that follow.
1 + State::match_len(alphabet_len, state)
};
kind_len + fail_len + classes_len + trans_len + match_len
}
/// Returns the kind of this state.
///
/// This only includes the low byte.
#[inline(always)]
fn kind(state: &[u32]) -> u32 {
state[State::KIND] & 0xFF
}
/// Get the number of sparse transitions in this state. This can never
/// be more than State::MAX_SPARSE_TRANSITIONS, as all states with more
/// transitions are encoded as dense states.
///
/// `state` should be the the raw binary encoding of a sparse state. (The
/// start of the slice must correspond to the start of the state, but the
/// slice may extend past the end of the encoding of the state.) If this
/// isn't a sparse state, then the return value is unspecified.
///
/// Do note that this is only legal to call on a sparse state. So for
/// example, "one transition" state is not a sparse state, so it would not
/// be legal to call this method on such a state.
#[inline(always)]
fn sparse_trans_len(state: &[u32]) -> usize {
(state[State::KIND] & 0xFF).as_usize()
}
/// Returns the total number of matching pattern IDs in this state. Calling
/// this on a state that isn't a match results in unspecified behavior.
/// Thus, the returned number is never 0 for all correct calls.
///
/// `state` should be the the raw binary encoding of a state. (The start
/// of the slice must correspond to the start of the state, but the slice
/// may extend past the end of the encoding of the state.)
#[inline(always)]
fn match_len(alphabet_len: usize, state: &[u32]) -> usize {
// We don't need to handle KIND_ONE here because it can never be a
// match state.
let packed = if State::kind(state) == State::KIND_DENSE {
let start = 2 + alphabet_len;
state[start].as_usize()
} else {
let trans_len = State::sparse_trans_len(state);
let classes_len = u32_len(trans_len);
let start = 2 + classes_len + trans_len;
state[start].as_usize()
};
if packed & (1 << 31) == 0 {
packed
} else {
1
}
}
/// Returns the pattern ID corresponding to the given index for the state
/// given. The `index` provided must be less than the number of pattern IDs
/// in this state.
///
/// `state` should be the the raw binary encoding of a state. (The start of
/// the slice must correspond to the start of the state, but the slice may
/// extend past the end of the encoding of the state.)
///
/// If the given state is not a match state or if the index is out of
/// bounds, then this has unspecified behavior.
#[inline(always)]
fn match_pattern(
alphabet_len: usize,
state: &[u32],
index: usize,
) -> PatternID {
// We don't need to handle KIND_ONE here because it can never be a
// match state.
let start = if State::kind(state) == State::KIND_DENSE {
2 + alphabet_len
} else {
let trans_len = State::sparse_trans_len(state);
let classes_len = u32_len(trans_len);
2 + classes_len + trans_len
};
let packed = state[start];
let pid = if packed & (1 << 31) == 0 {
state[start + 1 + index]
} else {
assert_eq!(0, index);
packed & !(1 << 31)
};
PatternID::from_u32_unchecked(pid)
}
/// Read a state's binary encoding to its in-memory representation.
///
/// `alphabet_len` should be the total number of transitions defined for
/// dense states.
///
/// `is_match` should be true if this state is a match state and false
/// otherwise.
///
/// `state` should be the the raw binary encoding of a state. (The start
/// of the slice must correspond to the start of the state, but the slice
/// may extend past the end of the encoding of the state.)
fn read(
alphabet_len: usize,
is_match: bool,
state: &'a [u32],
) -> State<'a> {
let kind = State::kind(state);
let match_len =
if !is_match { 0 } else { State::match_len(alphabet_len, state) };
let (trans, fail) = if kind == State::KIND_DENSE {
let fail = StateID::from_u32_unchecked(state[1]);
let class_to_next = &state[2..][..alphabet_len];
(StateTrans::Dense { class_to_next }, fail)
} else if kind == State::KIND_ONE {
let fail = StateID::from_u32_unchecked(state[1]);
let class = state[State::KIND].low_u16().high_u8();
let next = state[2];
(StateTrans::One { class, next }, fail)
} else {
let fail = StateID::from_u32_unchecked(state[1]);
let trans_len = State::sparse_trans_len(state);
let classes_len = u32_len(trans_len);
let classes = &state[2..][..classes_len];
let nexts = &state[2 + classes_len..][..trans_len];
(StateTrans::Sparse { classes, nexts }, fail)
};
State { fail, match_len, trans }
}
/// Encode the "old" state from a noncontiguous NFA to its binary
/// representation to the given `dst` slice. `classes` should be the byte
/// classes computed for the noncontiguous NFA that the given state came
/// from.
///
/// This returns an error if `dst` became so big that `StateID`s can no
/// longer be created for new states. Otherwise, it returns the state ID of
/// the new state created.
///
/// When `force_dense` is true, then the encoded state will always use a
/// dense format. Otherwise, the choice between dense and sparse will be
/// automatically chosen based on the old state.
fn write(
nnfa: &noncontiguous::NFA,
oldsid: StateID,
old: &noncontiguous::State,
classes: &ByteClasses,
dst: &mut Vec<u32>,
force_dense: bool,
) -> Result<StateID, BuildError> {
let sid = StateID::new(dst.len()).map_err(|e| {
BuildError::state_id_overflow(StateID::MAX.as_u64(), e.attempted())
})?;
let old_len = nnfa.iter_trans(oldsid).count();
// For states with a lot of transitions, we might as well just make
// them dense. These kinds of hot states tend to be very rare, so we're
// okay with it. This also gives us more sentinels in the state's
// 'kind', which lets us create different state kinds to save on
// space.
let kind = if force_dense || old_len > State::MAX_SPARSE_TRANSITIONS {
State::KIND_DENSE
} else if old_len == 1 && !old.is_match() {
State::KIND_ONE
} else {
// For a sparse state, the kind is just the number of transitions.
u32::try_from(old_len).unwrap()
};
if kind == State::KIND_DENSE {
dst.push(kind);
dst.push(old.fail().as_u32());
State::write_dense_trans(nnfa, oldsid, classes, dst)?;
} else if kind == State::KIND_ONE {
let t = nnfa.iter_trans(oldsid).next().unwrap();
let class = u32::from(classes.get(t.byte()));
dst.push(kind | (class << 8));
dst.push(old.fail().as_u32());
dst.push(t.next().as_u32());
} else {
dst.push(kind);
dst.push(old.fail().as_u32());
State::write_sparse_trans(nnfa, oldsid, classes, dst)?;
}
// Now finally write the number of matches and the matches themselves.
if old.is_match() {
let matches_len = nnfa.iter_matches(oldsid).count();
if matches_len == 1 {
let pid = nnfa.iter_matches(oldsid).next().unwrap().as_u32();
assert_eq!(0, pid & (1 << 31));
dst.push((1 << 31) | pid);
} else {
assert_eq!(0, matches_len & (1 << 31));
dst.push(matches_len.as_u32());
dst.extend(nnfa.iter_matches(oldsid).map(|pid| pid.as_u32()));
}
}
Ok(sid)
}
/// Encode the "old" state transitions from a noncontiguous NFA to its
/// binary sparse representation to the given `dst` slice. `classes` should
/// be the byte classes computed for the noncontiguous NFA that the given
/// state came from.
///
/// This returns an error if `dst` became so big that `StateID`s can no
/// longer be created for new states.
fn write_sparse_trans(
nnfa: &noncontiguous::NFA,
oldsid: StateID,
classes: &ByteClasses,
dst: &mut Vec<u32>,
) -> Result<(), BuildError> {
let (mut chunk, mut len) = ([0; 4], 0);
for t in nnfa.iter_trans(oldsid) {
chunk[len] = classes.get(t.byte());
len += 1;
if len == 4 {
dst.push(u32::from_ne_bytes(chunk));
chunk = [0; 4];
len = 0;
}
}
if len > 0 {
// In the case where the number of transitions isn't divisible
// by 4, the last u32 chunk will have some left over room. In
// this case, we "just" repeat the last equivalence class. By
// doing this, we know the leftover faux transitions will never
// be followed because if they were, it would have been followed
// prior to it in the last equivalence class. This saves us some
// branching in the search time state transition code.
let repeat = chunk[len - 1];
while len < 4 {
chunk[len] = repeat;
len += 1;
}
dst.push(u32::from_ne_bytes(chunk));
}
for t in nnfa.iter_trans(oldsid) {
dst.push(t.next().as_u32());
}
Ok(())
}
/// Encode the "old" state transitions from a noncontiguous NFA to its
/// binary dense representation to the given `dst` slice. `classes` should
/// be the byte classes computed for the noncontiguous NFA that the given
/// state came from.
///
/// This returns an error if `dst` became so big that `StateID`s can no
/// longer be created for new states.
fn write_dense_trans(
nnfa: &noncontiguous::NFA,
oldsid: StateID,
classes: &ByteClasses,
dst: &mut Vec<u32>,
) -> Result<(), BuildError> {
// Our byte classes let us shrink the size of our dense states to the
// number of equivalence classes instead of just fixing it to 256.
// Any non-explicitly defined transition is just a transition to the
// FAIL state, so we fill that in first and then overwrite them with
// explicitly defined transitions. (Most states probably only have one
// or two explicitly defined transitions.)
//
// N.B. Remember that while building the contiguous NFA, we use state
// IDs from the noncontiguous NFA. It isn't until we've added all
// states that we go back and map noncontiguous IDs to contiguous IDs.
let start = dst.len();
dst.extend(
core::iter::repeat(noncontiguous::NFA::FAIL.as_u32())
.take(classes.alphabet_len()),
);
assert!(start < dst.len(), "equivalence classes are never empty");
for t in nnfa.iter_trans(oldsid) {
dst[start + usize::from(classes.get(t.byte()))] =
t.next().as_u32();
}
Ok(())
}
/// Return an iterator over every explicitly defined transition in this
/// state.
fn transitions<'b>(&'b self) -> impl Iterator<Item = (u8, StateID)> + 'b {
let mut i = 0;
core::iter::from_fn(move || match self.trans {
StateTrans::Sparse { classes, nexts } => {
if i >= nexts.len() {
return None;
}
let chunk = classes[i / 4];
let class = chunk.to_ne_bytes()[i % 4];
let next = StateID::from_u32_unchecked(nexts[i]);
i += 1;
Some((class, next))
}
StateTrans::One { class, next } => {
if i == 0 {
i += 1;
Some((class, StateID::from_u32_unchecked(next)))
} else {
None
}
}
StateTrans::Dense { class_to_next } => {
if i >= class_to_next.len() {
return None;
}
let class = i.as_u8();
let next = StateID::from_u32_unchecked(class_to_next[i]);
i += 1;
Some((class, next))
}
})
}
}
impl<'a> core::fmt::Debug for State<'a> {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
use crate::{automaton::sparse_transitions, util::debug::DebugByte};
let it = sparse_transitions(self.transitions())
// Writing out all FAIL transitions is quite noisy. Instead, we
// just require readers of the output to assume anything absent
// maps to the FAIL transition.
.filter(|&(_, _, sid)| sid != NFA::FAIL)
.enumerate();
for (i, (start, end, sid)) in it {
if i > 0 {
write!(f, ", ")?;
}
if start == end {
write!(f, "{:?} => {:?}", DebugByte(start), sid.as_usize())?;
} else {
write!(
f,
"{:?}-{:?} => {:?}",
DebugByte(start),
DebugByte(end),
sid.as_usize()
)?;
}
}
Ok(())
}
}
/// A builder for configuring an Aho-Corasick contiguous NFA.
///
/// This builder has a subset of the options available to a
/// [`AhoCorasickBuilder`](crate::AhoCorasickBuilder). Of the shared options,
/// their behavior is identical.
#[derive(Clone, Debug)]
pub struct Builder {
noncontiguous: noncontiguous::Builder,
dense_depth: usize,
byte_classes: bool,
}
impl Default for Builder {
fn default() -> Builder {
Builder {
noncontiguous: noncontiguous::Builder::new(),
dense_depth: 2,
byte_classes: true,
}
}
}
impl Builder {
/// Create a new builder for configuring an Aho-Corasick contiguous NFA.
pub fn new() -> Builder {
Builder::default()
}
/// Build an Aho-Corasick contiguous NFA from the given iterator of
/// patterns.
///
/// A builder may be reused to create more NFAs.
pub fn build<I, P>(&self, patterns: I) -> Result<NFA, BuildError>
where
I: IntoIterator<Item = P>,
P: AsRef<[u8]>,
{
let nnfa = self.noncontiguous.build(patterns)?;
self.build_from_noncontiguous(&nnfa)
}
/// Build an Aho-Corasick contiguous NFA from the given noncontiguous NFA.
///
/// Note that when this method is used, only the `dense_depth` and
/// `byte_classes` settings on this builder are respected. The other
/// settings only apply to the initial construction of the Aho-Corasick
/// automaton. Since using this method requires that initial construction
/// has already completed, all settings impacting only initial construction
/// are no longer relevant.
pub fn build_from_noncontiguous(
&self,
nnfa: &noncontiguous::NFA,
) -> Result<NFA, BuildError> {
debug!("building contiguous NFA");
let byte_classes = if self.byte_classes {
nnfa.byte_classes().clone()
} else {
ByteClasses::singletons()
};
let mut index_to_state_id = vec![NFA::DEAD; nnfa.states().len()];
let mut nfa = NFA {
repr: vec![],
pattern_lens: nnfa.pattern_lens_raw().to_vec(),
state_len: nnfa.states().len(),
prefilter: nnfa.prefilter().map(|p| p.clone()),
match_kind: nnfa.match_kind(),
alphabet_len: byte_classes.alphabet_len(),
byte_classes,
min_pattern_len: nnfa.min_pattern_len(),
max_pattern_len: nnfa.max_pattern_len(),
// The special state IDs are set later.
special: Special::zero(),
};
for (oldsid, state) in nnfa.states().iter().with_state_ids() {
// We don't actually encode a fail state since it isn't necessary.
// But we still want to make sure any FAIL ids are mapped
// correctly.
if oldsid == noncontiguous::NFA::FAIL {
index_to_state_id[oldsid] = NFA::FAIL;
continue;
}
let force_dense = state.depth().as_usize() < self.dense_depth;
let newsid = State::write(
nnfa,
oldsid,
state,
&nfa.byte_classes,
&mut nfa.repr,
force_dense,
)?;
index_to_state_id[oldsid] = newsid;
}
for &newsid in index_to_state_id.iter() {
if newsid == NFA::FAIL {
continue;
}
let state = &mut nfa.repr[newsid.as_usize()..];
State::remap(nfa.alphabet_len, &index_to_state_id, state)?;
}
// Now that we've remapped all the IDs in our states, all that's left
// is remapping the special state IDs.
let remap = &index_to_state_id;
let old = nnfa.special();
let new = &mut nfa.special;
new.max_special_id = remap[old.max_special_id];
new.max_match_id = remap[old.max_match_id];
new.start_unanchored_id = remap[old.start_unanchored_id];
new.start_anchored_id = remap[old.start_anchored_id];
debug!(
"contiguous NFA built, <states: {:?}, size: {:?}, \
alphabet len: {:?}>",
nfa.state_len,
nfa.memory_usage(),
nfa.byte_classes.alphabet_len(),
);
// The vectors can grow ~twice as big during construction because a
// Vec amortizes growth. But here, let's shrink things back down to
// what we actually need since we're never going to add more to it.
nfa.repr.shrink_to_fit();
nfa.pattern_lens.shrink_to_fit();
Ok(nfa)
}
/// Set the desired match semantics.
///
/// This only applies when using [`Builder::build`] and not
/// [`Builder::build_from_noncontiguous`].
///
/// See
/// [`AhoCorasickBuilder::match_kind`](crate::AhoCorasickBuilder::match_kind)
/// for more documentation and examples.
pub fn match_kind(&mut self, kind: MatchKind) -> &mut Builder {
self.noncontiguous.match_kind(kind);
self
}
/// Enable ASCII-aware case insensitive matching.
///
/// This only applies when using [`Builder::build`] and not
/// [`Builder::build_from_noncontiguous`].
///
/// See
/// [`AhoCorasickBuilder::ascii_case_insensitive`](crate::AhoCorasickBuilder::ascii_case_insensitive)
/// for more documentation and examples.
pub fn ascii_case_insensitive(&mut self, yes: bool) -> &mut Builder {
self.noncontiguous.ascii_case_insensitive(yes);
self
}
/// Enable heuristic prefilter optimizations.
///
/// This only applies when using [`Builder::build`] and not
/// [`Builder::build_from_noncontiguous`].
///
/// See
/// [`AhoCorasickBuilder::prefilter`](crate::AhoCorasickBuilder::prefilter)
/// for more documentation and examples.
pub fn prefilter(&mut self, yes: bool) -> &mut Builder {
self.noncontiguous.prefilter(yes);
self
}
/// Set the limit on how many states use a dense representation for their
/// transitions. Other states will generally use a sparse representation.
///
/// See
/// [`AhoCorasickBuilder::dense_depth`](crate::AhoCorasickBuilder::dense_depth)
/// for more documentation and examples.
pub fn dense_depth(&mut self, depth: usize) -> &mut Builder {
self.dense_depth = depth;
self
}
/// A debug setting for whether to attempt to shrink the size of the
/// automaton's alphabet or not.
///
/// This should never be enabled unless you're debugging an automaton.
/// Namely, disabling byte classes makes transitions easier to reason
/// about, since they use the actual bytes instead of equivalence classes.
/// Disabling this confers no performance benefit at search time.
///
/// See
/// [`AhoCorasickBuilder::byte_classes`](crate::AhoCorasickBuilder::byte_classes)
/// for more documentation and examples.
pub fn byte_classes(&mut self, yes: bool) -> &mut Builder {
self.byte_classes = yes;
self
}
}
/// Computes the number of u32 values needed to represent one byte per the
/// number of transitions given.
fn u32_len(ntrans: usize) -> usize {
if ntrans % 4 == 0 {
ntrans >> 2
} else {
(ntrans >> 2) + 1
}
}
#[cfg(test)]
mod tests {
// This test demonstrates a SWAR technique I tried in the sparse transition
// code inside of 'next_state'. Namely, sparse transitions work by
// iterating over u32 chunks, with each chunk containing up to 4 classes
// corresponding to 4 transitions. This SWAR technique lets us find a
// matching transition without converting the u32 to a [u8; 4].
//
// It turned out to be a little slower unfortunately, which isn't too
// surprising, since this is likely a throughput oriented optimization.
// Loop unrolling doesn't really help us because the vast majority of
// states have very few transitions.
//
// Anyway, this code was a little tricky to write, so I converted it to a
// test in case someone figures out how to use it more effectively than
// I could.
//
// (This also only works on little endian. So big endian would need to be
// accounted for if we ever decided to use this I think.)
#[cfg(target_endian = "little")]
#[test]
fn swar() {
use super::*;
fn has_zero_byte(x: u32) -> u32 {
const LO_U32: u32 = 0x01010101;
const HI_U32: u32 = 0x80808080;
x.wrapping_sub(LO_U32) & !x & HI_U32
}
fn broadcast(b: u8) -> u32 {
(u32::from(b)) * (u32::MAX / 255)
}
fn index_of(x: u32) -> usize {
let o =
(((x - 1) & 0x01010101).wrapping_mul(0x01010101) >> 24) - 1;
o.as_usize()
}
let bytes: [u8; 4] = [b'1', b'A', b'a', b'z'];
let chunk = u32::from_ne_bytes(bytes);
let needle = broadcast(b'1');
assert_eq!(0, index_of(has_zero_byte(needle ^ chunk)));
let needle = broadcast(b'A');
assert_eq!(1, index_of(has_zero_byte(needle ^ chunk)));
let needle = broadcast(b'a');
assert_eq!(2, index_of(has_zero_byte(needle ^ chunk)));
let needle = broadcast(b'z');
assert_eq!(3, index_of(has_zero_byte(needle ^ chunk)));
}
}