neovim

xdiffi.c (28743B)

---

/*
*  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 <davidel@xmailserver.org>
*
*/

#include "xinclude.h"

#define XDL_MAX_COST_MIN 256
#define XDL_HEUR_MIN_COST 256
#define XDL_LINE_MAX (long)((1UL << (CHAR_BIT * sizeof(long) - 1)) - 1)
#define XDL_SNAKE_CNT 20
#define XDL_K_HEUR 4

typedef struct s_xdpsplit {
long i1, i2;
int min_lo, min_hi;
} xdpsplit_t;

/*
* See "An O(ND) Difference Algorithm and its Variations", by Eugene Myers.
* Basically considers a "box" (off1, off2, lim1, lim2) and scan from both
* the forward diagonal starting from (off1, off2) and the backward diagonal
* starting from (lim1, lim2). If the K values on the same diagonal crosses
* returns the furthest point of reach. We might encounter expensive edge cases
* using this algorithm, so a little bit of heuristic is needed to cut the
* search and to return a suboptimal point.
*/
static long xdl_split(unsigned long const *ha1, long off1, long lim1,
	      unsigned long const *ha2, long off2, long lim2,
	      long *kvdf, long *kvdb, int need_min, xdpsplit_t *spl,
	      xdalgoenv_t *xenv) {
long dmin = off1 - lim2, dmax = lim1 - off2;
long fmid = off1 - off2, bmid = lim1 - lim2;
long odd = (fmid - bmid) & 1;
long fmin = fmid, fmax = fmid;
long bmin = bmid, bmax = bmid;
long ec, d, i1, i2, prev1, best, dd, v, k;

/*
 * Set initial diagonal values for both forward and backward path.
 */
kvdf[fmid] = off1;
kvdb[bmid] = lim1;

for (ec = 1;; ec++) {
	int got_snake = 0;

	/*
	 * We need to extend the diagonal "domain" by one. If the next
	 * values exits the box boundaries we need to change it in the
	 * opposite direction because (max - min) must be a power of
	 * two.
	 *
	 * Also we initialize the external K value to -1 so that we can
	 * avoid extra conditions in the check inside the core loop.
	 */
	if (fmin > dmin)
		kvdf[--fmin - 1] = -1;
	else
		++fmin;
	if (fmax < dmax)
		kvdf[++fmax + 1] = -1;
	else
		--fmax;

	for (d = fmax; d >= fmin; d -= 2) {
		if (kvdf[d - 1] >= kvdf[d + 1])
			i1 = kvdf[d - 1] + 1;
		else
			i1 = kvdf[d + 1];
		prev1 = i1;
		i2 = i1 - d;
		for (; i1 < lim1 && i2 < lim2 && ha1[i1] == ha2[i2]; i1++, i2++);
		if (i1 - prev1 > xenv->snake_cnt)
			got_snake = 1;
		kvdf[d] = i1;
		if (odd && bmin <= d && d <= bmax && kvdb[d] <= i1) {
			spl->i1 = i1;
			spl->i2 = i2;
			spl->min_lo = spl->min_hi = 1;
			return ec;
		}
	}

	/*
	 * We need to extend the diagonal "domain" by one. If the next
	 * values exits the box boundaries we need to change it in the
	 * opposite direction because (max - min) must be a power of
	 * two.
	 *
	 * Also we initialize the external K value to -1 so that we can
	 * avoid extra conditions in the check inside the core loop.
	 */
	if (bmin > dmin)
		kvdb[--bmin - 1] = XDL_LINE_MAX;
	else
		++bmin;
	if (bmax < dmax)
		kvdb[++bmax + 1] = XDL_LINE_MAX;
	else
		--bmax;

	for (d = bmax; d >= bmin; d -= 2) {
		if (kvdb[d - 1] < kvdb[d + 1])
			i1 = kvdb[d - 1];
		else
			i1 = kvdb[d + 1] - 1;
		prev1 = i1;
		i2 = i1 - d;
		for (; i1 > off1 && i2 > off2 && ha1[i1 - 1] == ha2[i2 - 1]; i1--, i2--);
		if (prev1 - i1 > xenv->snake_cnt)
			got_snake = 1;
		kvdb[d] = i1;
		if (!odd && fmin <= d && d <= fmax && i1 <= kvdf[d]) {
			spl->i1 = i1;
			spl->i2 = i2;
			spl->min_lo = spl->min_hi = 1;
			return ec;
		}
	}

	if (need_min)
		continue;

	/*
	 * If the edit cost is above the heuristic trigger and if
	 * we got a good snake, we sample current diagonals to see
	 * if some of them have reached an "interesting" path. Our
	 * measure is a function of the distance from the diagonal
	 * corner (i1 + i2) penalized with the distance from the
	 * mid diagonal itself. If this value is above the current
	 * edit cost times a magic factor (XDL_K_HEUR) we consider
	 * it interesting.
	 */
	if (got_snake && ec > xenv->heur_min) {
		for (best = 0, d = fmax; d >= fmin; d -= 2) {
			dd = d > fmid ? d - fmid: fmid - d;
			i1 = kvdf[d];
			i2 = i1 - d;
			v = (i1 - off1) + (i2 - off2) - dd;

			if (v > XDL_K_HEUR * ec && v > best &&
			    off1 + xenv->snake_cnt <= i1 && i1 < lim1 &&
			    off2 + xenv->snake_cnt <= i2 && i2 < lim2) {
				for (k = 1; ha1[i1 - k] == ha2[i2 - k]; k++)
					if (k == xenv->snake_cnt) {
						best = v;
						spl->i1 = i1;
						spl->i2 = i2;
						break;
					}
			}
		}
		if (best > 0) {
			spl->min_lo = 1;
			spl->min_hi = 0;
			return ec;
		}

		for (best = 0, d = bmax; d >= bmin; d -= 2) {
			dd = d > bmid ? d - bmid: bmid - d;
			i1 = kvdb[d];
			i2 = i1 - d;
			v = (lim1 - i1) + (lim2 - i2) - dd;

			if (v > XDL_K_HEUR * ec && v > best &&
			    off1 < i1 && i1 <= lim1 - xenv->snake_cnt &&
			    off2 < i2 && i2 <= lim2 - xenv->snake_cnt) {
				for (k = 0; ha1[i1 + k] == ha2[i2 + k]; k++)
					if (k == xenv->snake_cnt - 1) {
						best = v;
						spl->i1 = i1;
						spl->i2 = i2;
						break;
					}
			}
		}
		if (best > 0) {
			spl->min_lo = 0;
			spl->min_hi = 1;
			return ec;
		}
	}

	/*
	 * Enough is enough. We spent too much time here and now we
	 * collect the furthest reaching path using the (i1 + i2)
	 * measure.
	 */
	if (ec >= xenv->mxcost) {
		long fbest, fbest1, bbest, bbest1;

		fbest = fbest1 = -1;
		for (d = fmax; d >= fmin; d -= 2) {
			i1 = XDL_MIN(kvdf[d], lim1);
			i2 = i1 - d;
			if (lim2 < i2)
				i1 = lim2 + d, i2 = lim2;
			if (fbest < i1 + i2) {
				fbest = i1 + i2;
				fbest1 = i1;
			}
		}

		bbest = bbest1 = XDL_LINE_MAX;
		for (d = bmax; d >= bmin; d -= 2) {
			i1 = XDL_MAX(off1, kvdb[d]);
			i2 = i1 - d;
			if (i2 < off2)
				i1 = off2 + d, i2 = off2;
			if (i1 + i2 < bbest) {
				bbest = i1 + i2;
				bbest1 = i1;
			}
		}

		if ((lim1 + lim2) - bbest < fbest - (off1 + off2)) {
			spl->i1 = fbest1;
			spl->i2 = fbest - fbest1;
			spl->min_lo = 1;
			spl->min_hi = 0;
		} else {
			spl->i1 = bbest1;
			spl->i2 = bbest - bbest1;
			spl->min_lo = 0;
			spl->min_hi = 1;
		}
		return ec;
	}
}
}


/*
* Rule: "Divide et Impera" (divide & conquer). Recursively split the box in
* sub-boxes by calling the box splitting function. Note that the real job
* (marking changed lines) is done in the two boundary reaching checks.
*/
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) {
unsigned long const *ha1 = dd1->ha, *ha2 = dd2->ha;

/*
 * Shrink the box by walking through each diagonal snake (SW and NE).
 */
for (; off1 < lim1 && off2 < lim2 && ha1[off1] == ha2[off2]; off1++, off2++);
for (; off1 < lim1 && off2 < lim2 && ha1[lim1 - 1] == ha2[lim2 - 1]; lim1--, lim2--);

/*
 * If one dimension is empty, then all records on the other one must
 * be obviously changed.
 */
if (off1 == lim1) {
	char *rchg2 = dd2->rchg;
	long *rindex2 = dd2->rindex;

	for (; off2 < lim2; off2++)
		rchg2[rindex2[off2]] = 1;
} else if (off2 == lim2) {
	char *rchg1 = dd1->rchg;
	long *rindex1 = dd1->rindex;

	for (; off1 < lim1; off1++)
		rchg1[rindex1[off1]] = 1;
} else {
	xdpsplit_t spl;
	spl.i1 = spl.i2 = 0;

	/*
	 * Divide ...
	 */
	if (xdl_split(ha1, off1, lim1, ha2, off2, lim2, kvdf, kvdb,
		      need_min, &spl, xenv) < 0) {

		return -1;
	}

	/*
	 * ... et Impera.
	 */
	if (xdl_recs_cmp(dd1, off1, spl.i1, dd2, off2, spl.i2,
			 kvdf, kvdb, spl.min_lo, xenv) < 0 ||
	    xdl_recs_cmp(dd1, spl.i1, lim1, dd2, spl.i2, lim2,
			 kvdf, kvdb, spl.min_hi, xenv) < 0) {

		return -1;
	}
}

return 0;
}


int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
	xdfenv_t *xe) {
long ndiags;
long *kvd, *kvdf, *kvdb;
xdalgoenv_t xenv;
diffdata_t dd1, dd2;

if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF)
	return xdl_do_patience_diff(mf1, mf2, xpp, xe);

if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
	return xdl_do_histogram_diff(mf1, mf2, xpp, xe);

if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0) {

	return -1;
}

/*
 * Allocate and setup K vectors to be used by the differential
 * algorithm.
 *
 * One is to store the forward path and one to store the backward path.
 */
ndiags = xe->xdf1.nreff + xe->xdf2.nreff + 3;
if (!(kvd = (long *) xdl_malloc((2 * ndiags + 2) * sizeof(long)))) {

	xdl_free_env(xe);
	return -1;
}
kvdf = kvd;
kvdb = kvdf + ndiags;
kvdf += xe->xdf2.nreff + 1;
kvdb += xe->xdf2.nreff + 1;

xenv.mxcost = xdl_bogosqrt(ndiags);
if (xenv.mxcost < XDL_MAX_COST_MIN)
	xenv.mxcost = XDL_MAX_COST_MIN;
xenv.snake_cnt = XDL_SNAKE_CNT;
xenv.heur_min = XDL_HEUR_MIN_COST;

dd1.nrec = xe->xdf1.nreff;
dd1.ha = xe->xdf1.ha;
dd1.rchg = xe->xdf1.rchg;
dd1.rindex = xe->xdf1.rindex;
dd2.nrec = xe->xdf2.nreff;
dd2.ha = xe->xdf2.ha;
dd2.rchg = xe->xdf2.rchg;
dd2.rindex = xe->xdf2.rindex;

if (xdl_recs_cmp(&dd1, 0, dd1.nrec, &dd2, 0, dd2.nrec,
		 kvdf, kvdb, (xpp->flags & XDF_NEED_MINIMAL) != 0, &xenv) < 0) {

	xdl_free(kvd);
	xdl_free_env(xe);
	return -1;
}

xdl_free(kvd);

return 0;
}


static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2) {
xdchange_t *xch;

if (!(xch = (xdchange_t *) xdl_malloc(sizeof(xdchange_t))))
	return NULL;

xch->next = xscr;
xch->i1 = i1;
xch->i2 = i2;
xch->chg1 = chg1;
xch->chg2 = chg2;
xch->ignore = 0;

return xch;
}


static int recs_match(xrecord_t *rec1, xrecord_t *rec2, long flags)
{
return (rec1->ha == rec2->ha &&
	xdl_recmatch(rec1->ptr, rec1->size,
		     rec2->ptr, rec2->size,
		     flags));
}

/*
* If a line is indented more than this, xget_indent() just returns this value.
* This avoids having to do absurd amounts of work for data that are not
* human-readable text, and also ensures that the output of xget_indent fits within
* an int.
*/
#define MAX_INDENT 200

/*
* Return the amount of indentation of the specified line, treating TAB as 8
* columns. Return -1 if line is empty or contains only whitespace. Clamp the
* output value at MAX_INDENT.
*/
static int xget_indent(xrecord_t *rec)
{
long i;
int ret = 0;

for (i = 0; i < rec->size; i++) {
	char c = rec->ptr[i];

	if (!XDL_ISSPACE(c))
		return ret;
	else if (c == ' ')
		ret += 1;
	else if (c == '\t')
		ret += 8 - ret % 8;
	/* ignore other whitespace characters */

	if (ret >= MAX_INDENT)
		return MAX_INDENT;
}

/* The line contains only whitespace. */
return -1;
}

/*
* If more than this number of consecutive blank rows are found, just return
* this value. This avoids requiring O(N^2) work for pathological cases, and
* also ensures that the output of score_split fits in an int.
*/
#define MAX_BLANKS 20

/* Characteristics measured about a hypothetical split position. */
struct split_measurement {
/*
 * Is the split at the end of the file (aside from any blank lines)?
 */
int end_of_file;

/*
 * How much is the line immediately following the split indented (or -1
 * if the line is blank):
 */
int indent;

/*
 * How many consecutive lines above the split are blank?
 */
int pre_blank;

/*
 * How much is the nearest non-blank line above the split indented (or
 * -1 if there is no such line)?
 */
int pre_indent;

/*
 * How many lines after the line following the split are blank?
 */
int post_blank;

/*
 * How much is the nearest non-blank line after the line following the
 * split indented (or -1 if there is no such line)?
 */
int post_indent;
};

struct split_score {
/* The effective indent of this split (smaller is preferred). */
int effective_indent;

/* Penalty for this split (smaller is preferred). */
int penalty;
};

/*
* Fill m with information about a hypothetical split of xdf above line split.
*/
static void measure_split(const xdfile_t *xdf, long split,
		  struct split_measurement *m)
{
long i;

if (split >= xdf->nrec) {
	m->end_of_file = 1;
	m->indent = -1;
} else {
	m->end_of_file = 0;
	m->indent = xget_indent(xdf->recs[split]);
}

m->pre_blank = 0;
m->pre_indent = -1;
for (i = split - 1; i >= 0; i--) {
	m->pre_indent = xget_indent(xdf->recs[i]);
	if (m->pre_indent != -1)
		break;
	m->pre_blank += 1;
	if (m->pre_blank == MAX_BLANKS) {
		m->pre_indent = 0;
		break;
	}
}

m->post_blank = 0;
m->post_indent = -1;
for (i = split + 1; i < xdf->nrec; i++) {
	m->post_indent = xget_indent(xdf->recs[i]);
	if (m->post_indent != -1)
		break;
	m->post_blank += 1;
	if (m->post_blank == MAX_BLANKS) {
		m->post_indent = 0;
		break;
	}
}
}

/*
* The empirically-determined weight factors used by score_split() below.
* Larger values means that the position is a less favorable place to split.
*
* Note that scores are only ever compared against each other, so multiplying
* all of these weight/penalty values by the same factor wouldn't change the
* heuristic's behavior. Still, we need to set that arbitrary scale *somehow*.
* In practice, these numbers are chosen to be large enough that they can be
* adjusted relative to each other with sufficient precision despite using
* integer math.
*/

/* Penalty if there are no non-blank lines before the split */
#define START_OF_FILE_PENALTY 1

/* Penalty if there are no non-blank lines after the split */
#define END_OF_FILE_PENALTY 21

/* Multiplier for the number of blank lines around the split */
#define TOTAL_BLANK_WEIGHT (-30)

/* Multiplier for the number of blank lines after the split */
#define POST_BLANK_WEIGHT 6

/*
* Penalties applied if the line is indented more than its predecessor
*/
#define RELATIVE_INDENT_PENALTY (-4)
#define RELATIVE_INDENT_WITH_BLANK_PENALTY 10

/*
* Penalties applied if the line is indented less than both its predecessor and
* its successor
*/
#define RELATIVE_OUTDENT_PENALTY 24
#define RELATIVE_OUTDENT_WITH_BLANK_PENALTY 17

/*
* Penalties applied if the line is indented less than its predecessor but not
* less than its successor
*/
#define RELATIVE_DEDENT_PENALTY 23
#define RELATIVE_DEDENT_WITH_BLANK_PENALTY 17

/*
* We only consider whether the sum of the effective indents for splits are
* less than (-1), equal to (0), or greater than (+1) each other. The resulting
* value is multiplied by the following weight and combined with the penalty to
* determine the better of two scores.
*/
#define INDENT_WEIGHT 60

/*
* How far do we slide a hunk at most?
*/
#define INDENT_HEURISTIC_MAX_SLIDING 100

/*
* Compute a badness score for the hypothetical split whose measurements are
* stored in m. The weight factors were determined empirically using the tools
* and corpus described in
*
*     https://github.com/mhagger/diff-slider-tools
*
* Also see that project if you want to improve the weights based on, for
* example, a larger or more diverse corpus.
*/
static void score_add_split(const struct split_measurement *m, struct split_score *s)
{
/*
 * A place to accumulate penalty factors (positive makes this index more
 * favored):
 */
int post_blank, total_blank, indent, any_blanks;

if (m->pre_indent == -1 && m->pre_blank == 0)
	s->penalty += START_OF_FILE_PENALTY;

if (m->end_of_file)
	s->penalty += END_OF_FILE_PENALTY;

/*
 * Set post_blank to the number of blank lines following the split,
 * including the line immediately after the split:
 */
post_blank = (m->indent == -1) ? 1 + m->post_blank : 0;
total_blank = m->pre_blank + post_blank;

/* Penalties based on nearby blank lines: */
s->penalty += TOTAL_BLANK_WEIGHT * total_blank;
s->penalty += POST_BLANK_WEIGHT * post_blank;

if (m->indent != -1)
	indent = m->indent;
else
	indent = m->post_indent;

any_blanks = (total_blank != 0);

/* Note that the effective indent is -1 at the end of the file: */
s->effective_indent += indent;

if (indent == -1) {
	/* No additional adjustments needed. */
} else if (m->pre_indent == -1) {
	/* No additional adjustments needed. */
} else if (indent > m->pre_indent) {
	/*
	 * The line is indented more than its predecessor.
	 */
	s->penalty += any_blanks ?
		RELATIVE_INDENT_WITH_BLANK_PENALTY :
		RELATIVE_INDENT_PENALTY;
} else if (indent == m->pre_indent) {
	/*
	 * The line has the same indentation level as its predecessor.
	 * No additional adjustments needed.
	 */
} else {
	/*
	 * The line is indented less than its predecessor. It could be
	 * the block terminator of the previous block, but it could
	 * also be the start of a new block (e.g., an "else" block, or
	 * maybe the previous block didn't have a block terminator).
	 * Try to distinguish those cases based on what comes next:
	 */
	if (m->post_indent != -1 && m->post_indent > indent) {
		/*
		 * The following line is indented more. So it is likely
		 * that this line is the start of a block.
		 */
		s->penalty += any_blanks ?
			RELATIVE_OUTDENT_WITH_BLANK_PENALTY :
			RELATIVE_OUTDENT_PENALTY;
	} else {
		/*
		 * That was probably the end of a block.
		 */
		s->penalty += any_blanks ?
			RELATIVE_DEDENT_WITH_BLANK_PENALTY :
			RELATIVE_DEDENT_PENALTY;
	}
}
}

static int score_cmp(struct split_score *s1, struct split_score *s2)
{
/* -1 if s1.effective_indent < s2->effective_indent, etc. */
int cmp_indents = ((s1->effective_indent > s2->effective_indent) -
		   (s1->effective_indent < s2->effective_indent));

return INDENT_WEIGHT * cmp_indents + (s1->penalty - s2->penalty);
}

/*
* Represent a group of changed lines in an xdfile_t (i.e., a contiguous group
* of lines that was inserted or deleted from the corresponding version of the
* file). We consider there to be such a group at the beginning of the file, at
* the end of the file, and between any two unchanged lines, though most such
* groups will usually be empty.
*
* If the first line in a group is equal to the line following the group, then
* the group can be slid down. Similarly, if the last line in a group is equal
* to the line preceding the group, then the group can be slid up. See
* group_slide_down() and group_slide_up().
*
* Note that loops that are testing for changed lines in xdf->rchg do not need
* index bounding since the array is prepared with a zero at position -1 and N.
*/
struct xdlgroup {
/*
 * The index of the first changed line in the group, or the index of
 * the unchanged line above which the (empty) group is located.
 */
long start;

/*
 * The index of the first unchanged line after the group. For an empty
 * group, end is equal to start.
 */
long end;
};

/*
* Initialize g to point at the first group in xdf.
*/
static void group_init(xdfile_t *xdf, struct xdlgroup *g)
{
g->start = g->end = 0;
while (xdf->rchg[g->end])
	g->end++;
}

/*
* Move g to describe the next (possibly empty) group in xdf and return 0. If g
* is already at the end of the file, do nothing and return -1.
*/
static inline int group_next(xdfile_t *xdf, struct xdlgroup *g)
{
if (g->end == xdf->nrec)
	return -1;

g->start = g->end + 1;
for (g->end = g->start; xdf->rchg[g->end]; g->end++)
	;

return 0;
}

/*
* Move g to describe the previous (possibly empty) group in xdf and return 0.
* If g is already at the beginning of the file, do nothing and return -1.
*/
static inline int group_previous(xdfile_t *xdf, struct xdlgroup *g)
{
if (g->start == 0)
	return -1;

g->end = g->start - 1;
for (g->start = g->end; xdf->rchg[g->start - 1]; g->start--)
	;

return 0;
}

/*
* If g can be slid toward the end of the file, do so, and if it bumps into a
* following group, expand this group to include it. Return 0 on success or -1
* if g cannot be slid down.
*/
static int group_slide_down(xdfile_t *xdf, struct xdlgroup *g, long flags)
{
if (g->end < xdf->nrec &&
    recs_match(xdf->recs[g->start], xdf->recs[g->end], flags)) {
	xdf->rchg[g->start++] = 0;
	xdf->rchg[g->end++] = 1;

	while (xdf->rchg[g->end])
		g->end++;

	return 0;
} else {
	return -1;
}
}

/*
* If g can be slid toward the beginning of the file, do so, and if it bumps
* into a previous group, expand this group to include it. Return 0 on success
* or -1 if g cannot be slid up.
*/
static int group_slide_up(xdfile_t *xdf, struct xdlgroup *g, long flags)
{
if (g->start > 0 &&
    recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1], flags)) {
	xdf->rchg[--g->start] = 1;
	xdf->rchg[--g->end] = 0;

	while (xdf->rchg[g->start - 1])
		g->start--;

	return 0;
} else {
	return -1;
}
}

static void xdl_bug(const char *msg)
{
fprintf(stderr, "BUG: %s\n", msg);
exit(1);
}

/*
* Move back and forward change groups for a consistent and pretty diff output.
* This also helps in finding joinable change groups and reducing the diff
* size.
*/
int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
struct xdlgroup g, go;
long earliest_end, end_matching_other;
long groupsize;

group_init(xdf, &g);
group_init(xdfo, &go);

while (1) {
	/*
	 * If the group is empty in the to-be-compacted file, skip it:
	 */
	if (g.end == g.start)
		goto next;

	/*
	 * Now shift the change up and then down as far as possible in
	 * each direction. If it bumps into any other changes, merge
	 * them.
	 */
	do {
		groupsize = g.end - g.start;

		/*
		 * Keep track of the last "end" index that causes this
		 * group to align with a group of changed lines in the
		 * other file. -1 indicates that we haven't found such
		 * a match yet:
		 */
		end_matching_other = -1;

		/* Shift the group backward as much as possible: */
		while (!group_slide_up(xdf, &g, flags))
			if (group_previous(xdfo, &go))
				xdl_bug("group sync broken sliding up");

		/*
		 * This is this highest that this group can be shifted.
		 * Record its end index:
		 */
		earliest_end = g.end;

		if (go.end > go.start)
			end_matching_other = g.end;

		/* Now shift the group forward as far as possible: */
		while (1) {
			if (group_slide_down(xdf, &g, flags))
				break;
			if (group_next(xdfo, &go))
				xdl_bug("group sync broken sliding down");

			if (go.end > go.start)
				end_matching_other = g.end;
		}
	} while (groupsize != g.end - g.start);

	/*
	 * If the group can be shifted, then we can possibly use this
	 * freedom to produce a more intuitive diff.
	 *
	 * The group is currently shifted as far down as possible, so
	 * the heuristics below only have to handle upwards shifts.
	 */

	if (g.end == earliest_end) {
		/* no shifting was possible */
	} else if (end_matching_other != -1) {
		/*
		 * Move the possibly merged group of changes back to
		 * line up with the last group of changes from the
		 * other file that it can align with.
		 */
		while (go.end == go.start) {
			if (group_slide_up(xdf, &g, flags))
				xdl_bug("match disappeared");
			if (group_previous(xdfo, &go))
				xdl_bug("group sync broken sliding to match");
		}
	} else if (flags & XDF_INDENT_HEURISTIC) {
		/*
		 * Indent heuristic: a group of pure add/delete lines
		 * implies two splits, one between the end of the
		 * "before" context and the start of the group, and
		 * another between the end of the group and the
		 * beginning of the "after" context. Some splits are
		 * aesthetically better and some are worse. We compute
		 * a badness "score" for each split, and add the scores
		 * for the two splits to define a "score" for each
		 * position that the group can be shifted to. Then we
		 * pick the shift with the lowest score.
		 */
		long shift, best_shift = -1;
		struct split_score best_score;

		shift = earliest_end;
		if (g.end - groupsize - 1 > shift)
			shift = g.end - groupsize - 1;
		if (g.end - INDENT_HEURISTIC_MAX_SLIDING > shift)
			shift = g.end - INDENT_HEURISTIC_MAX_SLIDING;
		for (; shift <= g.end; shift++) {
			struct split_measurement m;
			struct split_score score = {0, 0};

			measure_split(xdf, shift, &m);
			score_add_split(&m, &score);
			measure_split(xdf, shift - groupsize, &m);
			score_add_split(&m, &score);
			if (best_shift == -1 ||
			    score_cmp(&score, &best_score) <= 0) {
				best_score.effective_indent = score.effective_indent;
				best_score.penalty = score.penalty;
				best_shift = shift;
			}
		}

		while (g.end > best_shift) {
			if (group_slide_up(xdf, &g, flags))
				xdl_bug("best shift unreached");
			if (group_previous(xdfo, &go))
				xdl_bug("group sync broken sliding to blank line");
		}
	}

next:
	/* Move past the just-processed group: */
	if (group_next(xdf, &g))
		break;
	if (group_next(xdfo, &go))
		xdl_bug("group sync broken moving to next group");
}

if (!group_next(xdfo, &go))
	xdl_bug("group sync broken at end of file");

return 0;
}


int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr) {
xdchange_t *cscr = NULL, *xch;
char *rchg1 = xe->xdf1.rchg, *rchg2 = xe->xdf2.rchg;
long i1, i2, l1, l2;

/*
 * Trivial. Collects "groups" of changes and creates an edit script.
 */
for (i1 = xe->xdf1.nrec, i2 = xe->xdf2.nrec; i1 >= 0 || i2 >= 0; i1--, i2--)
	if (rchg1[i1 - 1] || rchg2[i2 - 1]) {
		for (l1 = i1; rchg1[i1 - 1]; i1--);
		for (l2 = i2; rchg2[i2 - 1]; i2--);

		if (!(xch = xdl_add_change(cscr, i1, i2, l1 - i1, l2 - i2))) {
			xdl_free_script(cscr);
			return -1;
		}
		cscr = xch;
	}

*xscr = cscr;

return 0;
}


void xdl_free_script(xdchange_t *xscr) {
xdchange_t *xch;

while ((xch = xscr) != NULL) {
	xscr = xscr->next;
	xdl_free(xch);
}
}

static int xdl_call_hunk_func(xdfenv_t *xe UNUSED, xdchange_t *xscr, xdemitcb_t *ecb,
		      xdemitconf_t const *xecfg)
{
xdchange_t *xch, *xche;

for (xch = xscr; xch; xch = xche->next) {
	xche = xdl_get_hunk(&xch, xecfg);
	if (!xch)
		break;
	if (xecfg->hunk_func(xch->i1, xche->i1 + xche->chg1 - xch->i1,
			     xch->i2, xche->i2 + xche->chg2 - xch->i2,
			     ecb->priv) < 0)
		return -1;
}
return 0;
}

static void xdl_mark_ignorable_lines(xdchange_t *xscr, xdfenv_t *xe, long flags)
{
xdchange_t *xch;

for (xch = xscr; xch; xch = xch->next) {
	int ignore = 1;
	xrecord_t **rec;
	long i;

	rec = &xe->xdf1.recs[xch->i1];
	for (i = 0; i < xch->chg1 && ignore; i++)
		ignore = xdl_blankline(rec[i]->ptr, rec[i]->size, flags);

	rec = &xe->xdf2.recs[xch->i2];
	for (i = 0; i < xch->chg2 && ignore; i++)
		ignore = xdl_blankline(rec[i]->ptr, rec[i]->size, flags);

	xch->ignore = ignore;
}
}

#if 0 // unused by Vim
static int record_matches_regex(xrecord_t *rec, xpparam_t const *xpp) {
regmatch_t regmatch;
int i;

for (i = 0; i < xpp->ignore_regex_nr; i++)
	if (!regexec_buf(xpp->ignore_regex[i], rec->ptr, rec->size, 1,
			 &regmatch, 0))
		return 1;

return 0;
}

static void xdl_mark_ignorable_regex(xdchange_t *xscr, const xdfenv_t *xe,
			     xpparam_t const *xpp)
{
xdchange_t *xch;

for (xch = xscr; xch; xch = xch->next) {
	xrecord_t **rec;
	int ignore = 1;
	long i;

	/*
	 * Do not override --ignore-blank-lines.
	 */
	if (xch->ignore)
		continue;

	rec = &xe->xdf1.recs[xch->i1];
	for (i = 0; i < xch->chg1 && ignore; i++)
		ignore = record_matches_regex(rec[i], xpp);

	rec = &xe->xdf2.recs[xch->i2];
	for (i = 0; i < xch->chg2 && ignore; i++)
		ignore = record_matches_regex(rec[i], xpp);

	xch->ignore = ignore;
}
}
#endif

int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
     xdemitconf_t const *xecfg, xdemitcb_t *ecb) {
xdchange_t *xscr;
xdfenv_t xe;
emit_func_t ef = xecfg->hunk_func ? xdl_call_hunk_func : xdl_emit_diff;

if (xdl_do_diff(mf1, mf2, xpp, &xe) < 0) {

	return -1;
}
if (xdl_change_compact(&xe.xdf1, &xe.xdf2, xpp->flags) < 0 ||
    xdl_change_compact(&xe.xdf2, &xe.xdf1, xpp->flags) < 0 ||
    xdl_build_script(&xe, &xscr) < 0) {

	xdl_free_env(&xe);
	return -1;
}
if (xscr) {
	if (xpp->flags & XDF_IGNORE_BLANK_LINES)
		xdl_mark_ignorable_lines(xscr, &xe, xpp->flags);

#if 0
	if (xpp->ignore_regex)
		xdl_mark_ignorable_regex(xscr, &xe, xpp);
#endif

	if (ef(&xe, xscr, ecb, xecfg) < 0) {

		xdl_free_script(xscr);
		xdl_free_env(&xe);
		return -1;
	}
	xdl_free_script(xscr);
}
xdl_free_env(&xe);

return 0;
}