mod.rs - Codebrowser

1	/!*
2	Provides packed multiple substring search, principally for a small number of
3	patterns.
4
5	This sub-module provides vectorized routines for quickly finding
6	matches of a small number of patterns. In general, users of this crate
7	shouldn't need to interface with this module directly, as the primary
8	[`AhoCorasick`](crate::AhoCorasick) searcher will use these routines
9	automatically as a prefilter when applicable. However, in some cases, callers
10	may want to bypass the Aho-Corasick machinery entirely and use this vectorized
11	searcher directly.
12
13	# Overview
14
15	The primary types in this sub-module are:
16
17	* [`Searcher`] executes the actual search algorithm to report matches in a
18	haystack.
19	* [`Builder`] accumulates patterns incrementally and can construct a
20	`Searcher`.
21	* [`Config`] permits tuning the searcher, and itself will produce a `Builder`
22	(which can then be used to build a `Searcher`). Currently, the only tuneable
23	knob are the match semantics, but this may be expanded in the future.
24
25	# Examples
26
27	This example shows how to create a searcher from an iterator of patterns.
28	By default, leftmost-first match semantics are used. (See the top-level
29	[`MatchKind`] type for more details about match semantics, which apply
30	similarly to packed substring search.)
31
32	```
33	use aho_corasick::{packed::{MatchKind, Searcher}, PatternID};
34
35	# fn example() -> Option<()> {
36	let searcher = Searcher::new(["foobar", "foo"].iter().cloned())?;
37	let matches: Vec<PatternID> = searcher
38	.find_iter("foobar")
39	.map(\|mat\| mat.pattern())
40	.collect();
41	assert_eq!(vec![PatternID::ZERO], matches);
42	# Some(()) }
43	# if cfg!(all(feature = "std", any(
44	# target_arch = "x86_64", target_arch = "aarch64",
45	# ))) {
46	# example().unwrap()
47	# } else {
48	# assert!(example().is_none());
49	# }
50	```
51
52	This example shows how to use [`Config`] to change the match semantics to
53	leftmost-longest:
54
55	```
56	use aho_corasick::{packed::{Config, MatchKind}, PatternID};
57
58	# fn example() -> Option<()> {
59	let searcher = Config::new()
60	.match_kind(MatchKind::LeftmostLongest)
61	.builder()
62	.add("foo")
63	.add("foobar")
64	.build()?;
65	let matches: Vec<PatternID> = searcher
66	.find_iter("foobar")
67	.map(\|mat\| mat.pattern())
68	.collect();
69	assert_eq!(vec![PatternID::must(`1`)], matches);
70	# Some(()) }
71	# if cfg!(all(feature = "std", any(
72	# target_arch = "x86_64", target_arch = "aarch64",
73	# ))) {
74	# example().unwrap()
75	# } else {
76	# assert!(example().is_none());
77	# }
78	```
79
80	# Packed substring searching
81
82	Packed substring searching refers to the use of SIMD (Single Instruction,
83	Multiple Data) to accelerate the detection of matches in a haystack. Unlike
84	conventional algorithms, such as Aho-Corasick, SIMD algorithms for substring
85	search tend to do better with a small number of patterns, where as Aho-Corasick
86	generally maintains reasonably consistent performance regardless of the number
87	of patterns you give it. Because of this, the vectorized searcher in this
88	sub-module cannot be used as a general purpose searcher, since building the
89	searcher may fail even when given a small number of patterns. However, in
90	exchange, when searching for a small number of patterns, searching can be quite
91	a bit faster than Aho-Corasick (sometimes by an order of magnitude).
92
93	The key take away here is that constructing a searcher from a list of patterns
94	is a fallible operation with no clear rules for when it will fail. While the
95	precise conditions under which building a searcher can fail is specifically an
96	implementation detail, here are some common reasons:
97
98	* Too many patterns were given. Typically, the limit is on the order of 100 or
99	so, but this limit may fluctuate based on available CPU features.
100	* The available packed algorithms require CPU features that aren't available.
101	For example, currently, this crate only provides packed algorithms for
102	`x86_64` and `aarch64`. Therefore, constructing a packed searcher on any
103	other target will always fail.
104	* Zero patterns were given, or one of the patterns given was empty. Packed
105	searchers require at least one pattern and that all patterns are non-empty.
106	* Something else about the nature of the patterns (typically based on
107	heuristics) suggests that a packed searcher would perform very poorly, so
108	no searcher is built.
109	*/
110
111	pub use crate::packed::api::{Builder, Config, FindIter, MatchKind, Searcher};
112
113	mod api;
114	mod ext;
115	mod pattern;
116	mod rabinkarp;
117	mod teddy;
118	#[cfg(all(feature = "std", test))]
119	mod tests;
120	mod vector;
121