1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141
/*!
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)));
}
}