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git/xdiff/xdiffi.c
Johannes Schindelin 857b933e04 xdiff: add xdl_merge() 
This new function implements the functionality of RCS merge, but
in-memory. It returns < 0 on error, otherwise the number of conflicts.

Finding the conflicting lines can be a very expensive task. You can
control the eagerness of this algorithm:

- a level value of 0 means that all overlapping changes are treated
  as conflicts,
- a value of 1 means that if the overlapping changes are identical,
  it is not treated as a conflict.
- If you set level to 2, overlapping changes will be analyzed, so that
  almost identical changes will not result in huge conflicts. Rather,
  only the conflicting lines will be shown inside conflict markers.

With each increasing level, the algorithm gets slower, but more accurate.
Note that the code for level 2 depends on the simple definition of
mmfile_t specific to git, and therefore it will be harder to port that
to LibXDiff.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>
2006-12-02 17:28:19 -08:00

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/*
* 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, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* 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 << (8 * 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;
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);
static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2);
/*
* 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 end up having to expensive
* cases using this algorithm is full, 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 extent 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 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 extent 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 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 the, 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;
}
}
return -1;
}
/*
* Rule: "Divide et Impera". 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 {
long ec;
xdpsplit_t spl;
spl.i1 = spl.i2 = 0;
/*
* Divide ...
*/
if ((ec = 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 (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;
return xch;
}
int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
long ix, ixo, ixs, ixref, grpsiz, nrec = xdf->nrec;
char *rchg = xdf->rchg, *rchgo = xdfo->rchg;
xrecord_t **recs = xdf->recs;
/*
* This is the same of what GNU diff does. Move back and forward
* change groups for a consistent and pretty diff output. This also
* helps in finding joinable change groups and reduce the diff size.
*/
for (ix = ixo = 0;;) {
/*
* Find the first changed line in the to-be-compacted file.
* We need to keep track of both indexes, so if we find a
* changed lines group on the other file, while scanning the
* to-be-compacted file, we need to skip it properly. Note
* that loops that are testing for changed lines on rchg* do
* not need index bounding since the array is prepared with
* a zero at position -1 and N.
*/
for (; ix < nrec && !rchg[ix]; ix++)
while (rchgo[ixo++]);
if (ix == nrec)
break;
/*
* Record the start of a changed-group in the to-be-compacted file
* and find the end of it, on both to-be-compacted and other file
* indexes (ix and ixo).
*/
ixs = ix;
for (ix++; rchg[ix]; ix++);
for (; rchgo[ixo]; ixo++);
do {
grpsiz = ix - ixs;
/*
* If the line before the current change group, is equal to
* the last line of the current change group, shift backward
* the group.
*/
while (ixs > 0 && recs[ixs - 1]->ha == recs[ix - 1]->ha &&
xdl_recmatch(recs[ixs - 1]->ptr, recs[ixs - 1]->size, recs[ix - 1]->ptr, recs[ix - 1]->size, flags)) {
rchg[--ixs] = 1;
rchg[--ix] = 0;
/*
* This change might have joined two change groups,
* so we try to take this scenario in account by moving
* the start index accordingly (and so the other-file
* end-of-group index).
*/
for (; rchg[ixs - 1]; ixs--);
while (rchgo[--ixo]);
}
/*
* Record the end-of-group position in case we are matched
* with a group of changes in the other file (that is, the
* change record before the enf-of-group index in the other
* file is set).
*/
ixref = rchgo[ixo - 1] ? ix: nrec;
/*
* If the first line of the current change group, is equal to
* the line next of the current change group, shift forward
* the group.
*/
while (ix < nrec && recs[ixs]->ha == recs[ix]->ha &&
xdl_recmatch(recs[ixs]->ptr, recs[ixs]->size, recs[ix]->ptr, recs[ix]->size, flags)) {
rchg[ixs++] = 0;
rchg[ix++] = 1;
/*
* This change might have joined two change groups,
* so we try to take this scenario in account by moving
* the start index accordingly (and so the other-file
* end-of-group index). Keep tracking the reference
* index in case we are shifting together with a
* corresponding group of changes in the other file.
*/
for (; rchg[ix]; ix++);
while (rchgo[++ixo])
ixref = ix;
}
} while (grpsiz != ix - ixs);
/*
* Try to move back the possibly merged group of changes, to match
* the recorded postion in the other file.
*/
while (ixref < ix) {
rchg[--ixs] = 1;
rchg[--ix] = 0;
while (rchgo[--ixo]);
}
}
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);
}
}
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;
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 (xdl_emit_diff(&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;
}
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