| ## Edit Distance Match Finder |
| |
| ``` |
| /* This match finder leverages techniques used in file comparison algorithms |
| * to find matches between a dictionary and a source file. |
| * |
| * The original motivation for studying this approach was to try and optimize |
| * Zstandard for the use case of patching: the most common scenario being |
| * updating an existing software package with the next version. When patching, |
| * the difference between the old version of the package and the new version |
| * is generally tiny (most of the new file will be identical to |
| * the old one). In more technical terms, the edit distance (the minimal number |
| * of changes required to take one sequence of bytes to another) between the |
| * files would be small relative to the size of the file. |
| * |
| * Various 'diffing' algorithms utilize this notion of edit distance and |
| * the corresponding concept of a minimal edit script between two |
| * sequences to identify the regions within two files where they differ. |
| * The core algorithm used in this match finder is described in: |
| * |
| * "An O(ND) Difference Algorithm and its Variations", Eugene W. Myers, |
| * Algorithmica Vol. 1, 1986, pp. 251-266, |
| * <https://doi.org/10.1007/BF01840446>. |
| * |
| * Additional algorithmic heuristics for speed improvement have also been included. |
| * These we inspired from implementations of various regular and binary diffing |
| * algorithms such as GNU diff, bsdiff, and Xdelta. |
| * |
| * Note: after some experimentation, this approach proved to not provide enough |
| * utility to justify the additional CPU used in finding matches. The one area |
| * where this approach consistently outperforms Zstandard even on level 19 is |
| * when compressing small files (<10 KB) using an equally small dictionary that |
| * is very similar to the source file. For the use case that this was intended, |
| * (large similar files) this approach by itself took 5-10X longer than zstd-19 and |
| * generally resulted in 2-3X larger files. The core advantage that zstd-19 has |
| * over this approach for match finding is the overlapping matches. This approach |
| * cannot find any. |
| * |
| * I'm leaving this in the contrib section in case this ever becomes interesting |
| * to explore again. |
| * */ |
| ``` |
