git/xdiff/xdiffi.c

/*
 *  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);
static int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo);





/*
 * 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 extenal 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 extenal 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;
}


static int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo) {
	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 joineable 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], recs[ix - 1])) {
				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], recs[ix])) {
				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) < 0 ||
	    xdl_change_compact(&xe.xdf2, &xe.xdf1) < 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;
}