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- aho-corasick
- ==
-
- Aho-Corasick parallel string search, using interleaved arrays.
-
- Mischa Sandberg mischasan@gmail.com
-
- ACISM is an implementation of Aho-Corasick parallel string search,
- using an Interleaved State-transition Matrix.
- It combines the fastest possible Aho-Corasick implementation,
- with the smallest possible data structure (!).
-
- FEATURES
- --------
-
- * Fast. No hashing, no tree traversal; just a straight look-up equivalent to
- matrix[state, input-byte] per input character.
-
- * Tiny. On average, the whole data structure (mostly the array) takes about 2-3 bytes per
- input pattern byte. The original set of pattern strings can be reverse-generated from the machine.
-
- * Shareable. The state machine contains no pointers, so it can be compiled once,
- then memory-mapped by many processes.
-
- * Searches byte vectors, not null-terminated strings.
- Suitable for searching machine code as much as searching text.
-
- * DOS-proof. Well, that's an attribute of Aho-Corasick,
- so no real points for that.
-
- * Stream-ready. The state can be saved between calls to search data.
-
- DOCUMENTATION
- -------------
-
- The GoogleDocs description is at http://goo.gl/lE6zG
- I originally called it "psearch", but found that name was overused by other authors.
-
- LICENSE
- -------
-
- Though I've had strong suggestions to go with BSD license, I'm going with GPL2 until I figure out
- how to keep in touch with people who download and use the code. Hence the "CONTACT ME IF..." line in the license.
-
- GETTING STARTED
- ---------------
-
- Download the source, type "gmake".
- "gmake install" exports lib/libacism.a, include/acism.h and bin/acism_x.
- "acism_x.c" is a good example of calling acism_create and acism_scan/acism_more.
-
- (If you're interested in the GNUmakefile and rules.mk,
- check my blog posts on non-recursive make, at mischasan.wordpress.com.)
-
- HISTORY
- -------
-
- The interleaved-array approach was tried and discarded in the late 70's, because the compile time was O(n^2).
- acism_create beats the problem with a "hint" array that tracks the restart points for searches.
- That, plus discarding the original idea of how to get maximal density, resulted in the tiny-fast win-win.
-
- ACKNOWLEDGEMENTS
- ----------------
-
- I'd like to thank Mike Shannon, who wanted to see a machine built to make best use of L1/L2 cache.
- The change to do that doubled performance on hardware with a much larger cache than the matrix.
- Go figure.
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