https://github.com/sirwumpus/ioccc-npdif
Most Different (diff) - IOCCC 2015 Winner
https://github.com/sirwumpus/ioccc-npdif
c diff file-comparison ioccc posix
Last synced: over 1 year ago
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Most Different (diff) - IOCCC 2015 Winner
- Host: GitHub
- URL: https://github.com/sirwumpus/ioccc-npdif
- Owner: SirWumpus
- License: 0bsd
- Created: 2017-05-10T21:28:16.000Z (about 9 years ago)
- Default Branch: master
- Last Pushed: 2023-01-03T20:05:27.000Z (over 3 years ago)
- Last Synced: 2025-01-28T02:26:49.733Z (over 1 year ago)
- Topics: c, diff, file-comparison, ioccc, posix
- Language: C
- Homepage:
- Size: 60.5 KB
- Stars: 2
- Watchers: 2
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE.md
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README
README
------
To Build
--------
$ cc -o prog prog.c
Usage Examples
--------------
$ ./prog file1 file2
$ ./prog -d file1 file2
$ ./prog-test.sh
Features
--------
* "An O(NP) Sequence Comparison Algorithm" by Wu, Manber, Myers, Miller.
* Output compatible with patch(1).
* Strokes one of the judge's ego (I couldn't email chocolate or curry).
Description
-----------
This is a functioning micro diff tool using an [O(NP) algorithm][Wu+89], compared to the older [O(ND) difference algorithm][Mye86] used by some versions of diff. Its output is based on the default diff(1) output described by POSIX and [The Open Group Base Specifications][SUSV7]. The output is suitable for use with patch(1).
The -d option simply writes the edit distance between file1 and file2.
Observations
------------
The FNV1a hash is a little slow compared to the trival hash GNU Diff uses. I downloaded a plain text copy of "War And Peace" from Project Gutenberg, used ``makeholes.c`` to make 1000 random changes, then profiled and timed the program verses GNU Diff. The bottle neck appears to be in the file I/O and line hashing with an average +0.05s slower. Using a huge file like "War And Peace" for testing offsets the diff(1) optimised file I/O.
There is no hash collision checking, partly because FNV1a appears to generate very [few collisions][HshCmp] and an assumption that localised collisions within a region of edits are highly unlikely.
Support Files
-------------
* ``prog-test.sh``
Basic test program verifies known test edit distances and patch support.
* ``avgtime.sh``
* ``makeholes.c``
Random edits (holes) made to a file in-place.
References
----------
Wu, Manber, Myers, and Miller; August 1989;
"An O(NP) Sequence Comparison Algorithm";
Fowler, Noll, Vo; 1994
Fowler, Noll, Vo on Wikipedia
"diff", The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Eugene W. Myers; "An O(ND) Difference Algorithm and Its Variations";
Algorithmica, 1986, pages. 251-266
Webb Miller and Eugene W. Myers; "A File Comparison Program";
Software-Practice And Experience, Vol. 15(11). 1025-1040 (November 1985)
D.S. Hirschberg, "A linear space algorithm for computing maximal common subsequence problem";
Comm. of ACM, Vol. 18, June 1975, pages 341-343
Which hashing algorithm is best for uniqueness and speed?
[Wu+89]: http://myerslab.mpi-cbg.de/wp-content/uploads/2014/06/np_diff.pdf
[FNV94]: http://www.isthe.com/chongo/tech/comp/fnv/index.html
[FNVWi]: https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
[Mye86]: http://www.xmailserver.org/diff2.pdf
[SUSV7]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html
[Mil85]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.189.70&rep=rep1&type=pdf
[Hir75]: http://www.mathcs.emory.edu/~cheung/Courses/323/Syllabus/DynProg/Docs/Hirschberg-LCS-1975.pdf
[HshCmp]: http://programmers.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed