/*

* 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"

static size_t get_hash(xdfile_t *xdf, long index)

{

return xdf->recs[xdf->reference_index[index]].minimal_perfect_hash;

}

#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(xdfile_t *xdf1, long off1, long lim1,

xdfile_t *xdf2, 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 && get_hash(xdf1, i1) == get_hash(xdf2, 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 && get_hash(xdf1, i1 - 1) == get_hash(xdf2, 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; get_hash(xdf1, i1 - k) == get_hash(xdf2, 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; get_hash(xdf1, i1 + k) == get_hash(xdf2, 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(xdfile_t *xdf1, long off1, long lim1,

xdfile_t *xdf2, long off2, long lim2,

long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv) {

/*

* Shrink the box by walking through each diagonal snake (SW and NE).

*/

for (; off1 < lim1 && off2 < lim2 && get_hash(xdf1, off1) == get_hash(xdf2, off2); off1++, off2++);

for (; off1 < lim1 && off2 < lim2 && get_hash(xdf1, lim1 - 1) == get_hash(xdf2, lim2 - 1); lim1--, lim2--);

/*

* If one dimension is empty, then all records on the other one must

* be obviously changed.

*/

if (off1 == lim1) {

for (; off2 < lim2; off2++)

xdf2->changed[xdf2->reference_index[off2]] = true;

} else if (off2 == lim2) {

for (; off1 < lim1; off1++)

xdf1->changed[xdf1->reference_index[off1]] = true;

} else {

xdpsplit_t spl;

spl.i1 = spl.i2 = 0;

/*

* Divide ...

*/

if (xdl_split(xdf1, off1, lim1, xdf2, off2, lim2, kvdf, kvdb,

need_min, &spl, xenv) < 0) {

return -1;

}

/*

* ... et Impera.

*/

if (xdl_recs_cmp(xdf1, off1, spl.i1, xdf2, off2, spl.i2,

kvdf, kvdb, spl.min_lo, xenv) < 0 ||

xdl_recs_cmp(xdf1, spl.i1, lim1, xdf2, 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;

int res;

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

return -1;

if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF) {

res = xdl_do_patience_diff(xpp, xe);

goto out;

}

if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF) {

res = xdl_do_histogram_diff(xpp, xe);

goto out;

}

/*

* 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 (!XDL_ALLOC_ARRAY(kvd, 2 * ndiags + 2)) {

xdl_free_env(xe);

return -1;

}

kvdf = kvd;

kvdb = kvdf + ndiags;

kvdf += xe->xdf2.nreff + 1;

kvdb += xe->xdf2.nreff + 1;

xenv.mxcost = (long)xdl_bogosqrt((uint64_t)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;

res = xdl_recs_cmp(&xe->xdf1, 0, xe->xdf1.nreff, &xe->xdf2, 0, xe->xdf2.nreff,

kvdf, kvdb, (xpp->flags & XDF_NEED_MINIMAL) != 0,

&xenv);

xdl_free(kvd);

out:

if (res < 0)

xdl_free_env(xe);

return res;

}

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)

{

return rec1->minimal_perfect_hash == rec2->minimal_perfect_hash;

}

/*

* If a line is indented more than this, get_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 get_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 get_indent(xrecord_t *rec)

{

int ret = 0;

for (size_t i = 0; i < rec->size; i++) {

char c = (char) 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 >= (long)xdf->nrec) {

m->end_of_file = 1;

m->indent = -1;

} else {

m->end_of_file = 0;

m->indent = get_indent(&xdf->recs[split]);

}

m->pre_blank = 0;

m->pre_indent = -1;

for (i = split - 1; i >= 0; i--) {

m->pre_indent = get_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 < (long)xdf->nrec; i++) {

m->post_indent = get_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->changed[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 == (long)xdf->nrec)

return -1;

g->start = g->end + 1;

for (g->end = g->start; xdf->changed[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->changed[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)

{

if (g->end < (long)xdf->nrec &&

recs_match(&xdf->recs[g->start], &xdf->recs[g->end])) {

xdf->changed[g->start++] = false;

xdf->changed[g->end++] = true;

while (xdf->changed[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)

{

if (g->start > 0 &&

recs_match(&xdf->recs[g->start - 1], &xdf->recs[g->end - 1])) {

xdf->changed[--g->start] = true;

xdf->changed[--g->end] = false;

while (xdf->changed[g->start - 1])

g->start--;

return 0;

} else {

return -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;

struct xdlgroup g_orig;

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;

g_orig = g;

/*

* Now shift the change up and then down as far as possible in

* each direction. If it bumps into any other changes, merge

* them and restart the process.

*/

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))

if (group_previous(xdfo, &go))

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))

break;

if (group_next(xdfo, &go))

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. This avoids breaking

* a single change into a separate addition/deletion.

*/

while (go.end == go.start) {

if (group_slide_up(xdf, &g))

BUG("match disappeared");

if (group_previous(xdfo, &go))

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))

BUG("best shift unreached");

if (group_previous(xdfo, &go))

BUG("group sync broken sliding to blank line");

}

}

/*

* If we merged change groups during shifting, the new

* combined group could now have matching lines in both files,

* even if the original separate groups did not. Re-diff the

* new group to find these matching lines to mark them as

* unchanged.

*

* Only do this if the corresponding group in the other file is

* non-empty, as it's trivial otherwise.

*

* Only do this for histogram diff as its LCS algorithm allows

* for this scenario. In contrast, patience diff finds LCS

* of unique lines that groups cannot be shifted across.

* Myer's diff (standalone or used as fall-back in patience

* diff) already finds minimal edits so it is not possible for

* shifted groups to result in a smaller diff. (Without

* XDF_NEED_MINIMAL, Myer's isn't technically guaranteed to be

* minimal, but it should be so most of the time)

*/

if (go.end != go.start &&

XDF_DIFF_ALG(flags) == XDF_HISTOGRAM_DIFF &&

(g.start != g_orig.start ||

g.end != g_orig.end)) {

xpparam_t xpp;

xdfenv_t xe;

memset(&xpp, 0, sizeof(xpp));

xpp.flags = flags & ~XDF_DIFF_ALGORITHM_MASK;

xe.xdf1 = *xdf;

xe.xdf2 = *xdfo;

if (xdl_fall_back_diff(&xe, &xpp,

g.start + 1, g.end - g.start,

go.start + 1, go.end - go.start)) {

return -1;

}

}

next:

/* Move past the just-processed group: */

if (group_next(xdf, &g))

break;

if (group_next(xdfo, &go))

BUG("group sync broken moving to next group");

}

if (!group_next(xdfo, &go))

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;

bool *changed1 = xe->xdf1.changed, *changed2 = xe->xdf2.changed;

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 (changed1[i1 - 1] || changed2[i2 - 1]) {

for (l1 = i1; changed1[i1 - 1]; i1--);

for (l2 = i2; changed2[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;

}