annotate mercurial/thirdparty/xdiff/xdiffi.h @ 36671:34e2ff1f9cd8

xdiff: vendor xdiff library from git

Vendor git's xdiff library from git commit
d7c6c2369d7c6c2369ac21141b7c6cceaebc6414ec3da14ad using GPL2+ license.

There is another recent user report that hg diff generates suboptimal
result. It seems the fix to issue4074 isn't good enough. I crafted some
other interesting cases, and hg diff barely has any advantage compared with
gnu diffutils or git diff.

| testcase | gnu diffutils |      hg diff |   git diff |
|          |    lines time |   lines time | lines time |
| patience |        6 0.00 |     602 0.08 |     6 0.00 |
|   random |    91772 0.90 |  109462 0.70 | 91772 0.24 |
|     json |        2 0.03 | 1264814 1.81 |     2 0.29 |

"lines" means the size of the output, i.e. the count of "+/-" lines. "time"
means seconds needed to do the calculation. Both are the smaller the better.
"hg diff" counts Python startup overhead.

Git and GNU diffutils generate optimal results. For the "json" case, git can
have an optimization that does a scan for common prefix and suffix first,
and match them if the length is greater than half of the text. See
https://neil.fraser.name/news/2006/03/12/. That would make git the fastest
for all above cases.

About testcases:

patience:
Aiming for the weakness of the greedy "patience diff" algorithm.  Using
git's patience diff option would also get suboptimal result. Generated using
the Python script:

```
open('a', 'w').write('\n'.join(list('a' + 'x' * 300 + 'u' + 'x' * 700 + 'a\n')))
open('b', 'w').write('\n'.join(list('b' + 'x' * 700 + 'u' + 'x' * 300 + 'b\n')))
```

random:
Generated using the script in `test-issue4074.t`. It practically makes the
algorithm suffer. Impressively, git wins in both performance and diff
quality.

json:
The recent user reported case. It's a single line movement near the end of a
very large (800K lines) JSON file.

Test Plan:
Code taken as-is.

Differential Revision: https://phab.mercurial-scm.org/D2572

# no-check-commit for vendored code

/*
 *  LibXDiff by Davide Libenzi ( File Differential Library )
 *  Copyright (C) 2003  Davide Libenzi
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, see
 *  <http://www.gnu.org/licenses/>.
 *
 *  Davide Libenzi <[e-mail]>
 *
 */

#if !defined(XDIFFI_H)
#define XDIFFI_H


typedef struct s_diffdata {
	long nrec;
	unsigned long const *ha;
	long *rindex;
	char *rchg;
} diffdata_t;

typedef struct s_xdalgoenv {
	long mxcost;
	long snake_cnt;
	long heur_min;
} xdalgoenv_t;

typedef struct s_xdchange {
	struct s_xdchange *next;
	long i1, i2;
	long chg1, chg2;
	int ignore;
} xdchange_t;



int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
		 diffdata_t *dd2, long off2, long lim2,
		 long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv);
int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
		xdfenv_t *xe);
int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags);
int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr);
void xdl_free_script(xdchange_t *xscr);
int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
		  xdemitconf_t const *xecfg);
int xdl_do_patience_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
		xdfenv_t *env);
int xdl_do_histogram_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
		xdfenv_t *env);

#endif /* #if !defined(XDIFFI_H) */