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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*	$OpenBSD: diff3.c,v 1.28 2009/10/27 23:59:42 deraadt Exp $	*/

/*
 * Copyright (C) Caldera International Inc.  2001-2002.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code and documentation must retain the above
 *    copyright notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed or owned by Caldera
 *	International, Inc.
 * 4. Neither the name of Caldera International, Inc. nor the names of other
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * USE OF THE SOFTWARE PROVIDED FOR UNDER THIS LICENSE BY CALDERA
 * INTERNATIONAL, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL CALDERA INTERNATIONAL, INC. BE LIABLE FOR ANY DIRECT,
 * INDIRECT INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)diff3.c	8.1 (Berkeley) 6/6/93
 */

#include <ctype.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "diff.h"
#include "rcsprog.h"

/* diff3 - 3-way differential file comparison */

/* diff3 [-ex3EX] d13 d23 f1 f2 f3 [m1 m3]
 *
 * d13 = diff report on f1 vs f3
 * d23 = diff report on f2 vs f3
 * f1, f2, f3 the 3 files
 * if changes in f1 overlap with changes in f3, m1 and m3 are used
 * to mark the overlaps; otherwise, the file names f1 and f3 are used
 * (only for options E and X).
 */

/*
 * "from" is first in range of changed lines; "to" is last+1
 * from=to=line after point of insertion for added lines.
 */
struct range {
	int from;
	int to;
};

struct diff {
	struct range old;
	struct range new;
};

static size_t szchanges;

static struct diff *d13;
static struct diff *d23;

/*
 * "de" is used to gather editing scripts.  These are later spewed out in
 * reverse order.  Its first element must be all zero, the "new" component
 * of "de" contains line positions or byte positions depending on when you
 * look (!?).  Array overlap indicates which sections in "de" correspond to
 * lines that are different in all three files.
 */
static struct diff *de;
static char *overlap;
static int overlapcnt = 0;
static FILE *fp[3];
static int cline[3];		/* # of the last-read line in each file (0-2) */

/*
 * the latest known correspondence between line numbers of the 3 files
 * is stored in last[1-3];
 */
static int last[4];
static int eflag = 3;	/* default -E for compatibility with former RCS */
static int oflag = 1;	/* default -E for compatibility with former RCS */
static int debug  = 0;
static char f1mark[256], f3mark[256];	/* markers for -E and -X */

static int duplicate(struct range *, struct range *);
static int edit(struct diff *, int, int);
static char *getchange(FILE *);
static char *getline(FILE *, size_t *);
static int number(char **);
static ssize_t readin(char *, struct diff **);
static int skip(int, int, char *);
static int edscript(int);
static int merge(size_t, size_t);
static void change(int, struct range *, int);
static void keep(int, struct range *);
static void prange(struct range *);
static void repos(int);
static void separate(const char *);
static void increase(void);
static int diff3_internal(int, char **, const char *, const char *);

int diff3_conflicts = 0;

/*
 * For merge(1).
 */
BUF *
merge_diff3(char **av, int flags)
{
	int argc;
	char *argv[5], *dp13, *dp23, *path1, *path2, *path3;
	BUF *b1, *b2, *b3, *d1, *d2, *diffb;
	u_char *data, *patch;
	size_t dlen, plen;

	b1 = b2 = b3 = d1 = d2 = diffb = NULL;
	dp13 = dp23 = path1 = path2 = path3 = NULL;
	data = patch = NULL;

	if ((flags & MERGE_EFLAG) && !(flags & MERGE_OFLAG))
		oflag = 0;

	if ((b1 = rcs_buf_load(av[0], BUF_AUTOEXT)) == NULL)
		goto out;
	if ((b2 = rcs_buf_load(av[1], BUF_AUTOEXT)) == NULL)
		goto out;
	if ((b3 = rcs_buf_load(av[2], BUF_AUTOEXT)) == NULL)
		goto out;

	d1 = rcs_buf_alloc(128, BUF_AUTOEXT);
	d2 = rcs_buf_alloc(128, BUF_AUTOEXT);
	diffb = rcs_buf_alloc(128, BUF_AUTOEXT);

	(void)xasprintf(&path1, "%s/diff1.XXXXXXXXXX", rcs_tmpdir);
	(void)xasprintf(&path2, "%s/diff2.XXXXXXXXXX", rcs_tmpdir);
	(void)xasprintf(&path3, "%s/diff3.XXXXXXXXXX", rcs_tmpdir);

	rcs_buf_write_stmp(b1, path1);
	rcs_buf_write_stmp(b2, path2);
	rcs_buf_write_stmp(b3, path3);

	rcs_buf_free(b2);
	b2 = NULL;

	if ((diffreg(path1, path3, d1, D_FORCEASCII) == D_ERROR) ||
	    (diffreg(path2, path3, d2, D_FORCEASCII) == D_ERROR)) {
		rcs_buf_free(diffb);
		diffb = NULL;
		goto out;
	}

	(void)xasprintf(&dp13, "%s/d13.XXXXXXXXXX", rcs_tmpdir);
	rcs_buf_write_stmp(d1, dp13);

	rcs_buf_free(d1);
	d1 = NULL;

	(void)xasprintf(&dp23, "%s/d23.XXXXXXXXXX", rcs_tmpdir);
	rcs_buf_write_stmp(d2, dp23);

	rcs_buf_free(d2);
	d2 = NULL;

	argc = 0;
	diffbuf = diffb;
	argv[argc++] = dp13;
	argv[argc++] = dp23;
	argv[argc++] = path1;
	argv[argc++] = path2;
	argv[argc++] = path3;

	diff3_conflicts = diff3_internal(argc, argv, av[0], av[2]);
	if (diff3_conflicts < 0) {
		rcs_buf_free(diffb);
		diffb = NULL;
		goto out;
	}

	plen = rcs_buf_len(diffb);
	patch = rcs_buf_release(diffb);
	dlen = rcs_buf_len(b1);
	data = rcs_buf_release(b1);

	if ((diffb = rcs_patchfile(data, dlen, patch, plen, ed_patch_lines)) == NULL)
		goto out;

	if (!(flags & QUIET) && diff3_conflicts != 0)
		warnx("warning: overlaps or other problems during merge");

out:
	if (b2 != NULL)
		rcs_buf_free(b2);
	if (b3 != NULL)
		rcs_buf_free(b3);
	if (d1 != NULL)
		rcs_buf_free(d1);
	if (d2 != NULL)
		rcs_buf_free(d2);

	(void)unlink(path1);
	(void)unlink(path2);
	(void)unlink(path3);
	(void)unlink(dp13);
	(void)unlink(dp23);

	if (path1 != NULL)
		xfree(path1);
	if (path2 != NULL)
		xfree(path2);
	if (path3 != NULL)
		xfree(path3);
	if (dp13 != NULL)
		xfree(dp13);
	if (dp23 != NULL)
		xfree(dp23);
	if (data != NULL)
		xfree(data);
	if (patch != NULL)
		xfree(patch);

	return (diffb);
}

BUF *
rcs_diff3(RCSFILE *rf, char *workfile, RCSNUM *rev1, RCSNUM *rev2, int flags)
{
	int argc;
	char *argv[5], r1[RCS_REV_BUFSZ], r2[RCS_REV_BUFSZ];
	char *dp13, *dp23, *path1, *path2, *path3;
	BUF *b1, *b2, *b3, *d1, *d2, *diffb;
	size_t dlen, plen;
	u_char *data, *patch;

	b1 = b2 = b3 = d1 = d2 = diffb = NULL;
	dp13 = dp23 = path1 = path2 = path3 = NULL;
	data = patch = NULL;

	if ((flags & MERGE_EFLAG) && !(flags & MERGE_OFLAG))
		oflag = 0;

	rcsnum_tostr(rev1, r1, sizeof(r1));
	rcsnum_tostr(rev2, r2, sizeof(r2));

	if ((b1 = rcs_buf_load(workfile, BUF_AUTOEXT)) == NULL)
		goto out;

	if (!(flags & QUIET))
		(void)fprintf(stderr, "retrieving revision %s\n", r1);
	if ((b2 = rcs_getrev(rf, rev1)) == NULL)
		goto out;

	if (!(flags & QUIET))
		(void)fprintf(stderr, "retrieving revision %s\n", r2);
	if ((b3 = rcs_getrev(rf, rev2)) == NULL)
		goto out;

	d1 = rcs_buf_alloc(128, BUF_AUTOEXT);
	d2 = rcs_buf_alloc(128, BUF_AUTOEXT);
	diffb = rcs_buf_alloc(128, BUF_AUTOEXT);

	(void)xasprintf(&path1, "%s/diff1.XXXXXXXXXX", rcs_tmpdir);
	(void)xasprintf(&path2, "%s/diff2.XXXXXXXXXX", rcs_tmpdir);
	(void)xasprintf(&path3, "%s/diff3.XXXXXXXXXX", rcs_tmpdir);

	rcs_buf_write_stmp(b1, path1);
	rcs_buf_write_stmp(b2, path2);
	rcs_buf_write_stmp(b3, path3);

	rcs_buf_free(b2);
	b2 = NULL;

	if ((diffreg(path1, path3, d1, D_FORCEASCII) == D_ERROR) ||
	    (diffreg(path2, path3, d2, D_FORCEASCII) == D_ERROR)) {
		rcs_buf_free(diffb);
		diffb = NULL;
		goto out;
	}

	(void)xasprintf(&dp13, "%s/d13.XXXXXXXXXX", rcs_tmpdir);
	rcs_buf_write_stmp(d1, dp13);

	rcs_buf_free(d1);
	d1 = NULL;

	(void)xasprintf(&dp23, "%s/d23.XXXXXXXXXX", rcs_tmpdir);
	rcs_buf_write_stmp(d2, dp23);

	rcs_buf_free(d2);
	d2 = NULL;

	argc = 0;
	diffbuf = diffb;
	argv[argc++] = dp13;
	argv[argc++] = dp23;
	argv[argc++] = path1;
	argv[argc++] = path2;
	argv[argc++] = path3;

	diff3_conflicts = diff3_internal(argc, argv, workfile, r2);
	if (diff3_conflicts < 0) {
		rcs_buf_free(diffb);
		diffb = NULL;
		goto out;
	}

	plen = rcs_buf_len(diffb);
	patch = rcs_buf_release(diffb);
	dlen = rcs_buf_len(b1);
	data = rcs_buf_release(b1);

	if ((diffb = rcs_patchfile(data, dlen, patch, plen, ed_patch_lines)) == NULL)
		goto out;

	if (!(flags & QUIET) && diff3_conflicts != 0)
		warnx("warning: overlaps or other problems during merge");

out:
	if (b2 != NULL)
		rcs_buf_free(b2);
	if (b3 != NULL)
		rcs_buf_free(b3);
	if (d1 != NULL)
		rcs_buf_free(d1);
	if (d2 != NULL)
		rcs_buf_free(d2);

	(void)unlink(path1);
	(void)unlink(path2);
	(void)unlink(path3);
	(void)unlink(dp13);
	(void)unlink(dp23);

	if (path1 != NULL)
		xfree(path1);
	if (path2 != NULL)
		xfree(path2);
	if (path3 != NULL)
		xfree(path3);
	if (dp13 != NULL)
		xfree(dp13);
	if (dp23 != NULL)
		xfree(dp23);
	if (data != NULL)
		xfree(data);
	if (patch != NULL)
		xfree(patch);

	return (diffb);
}

static int
diff3_internal(int argc, char **argv, const char *fmark, const char *rmark)
{
	ssize_t m, n;
	int i;

	if (argc < 5)
		return (-1);

	if (oflag) {
		i = snprintf(f1mark, sizeof(f1mark), "<<<<<<< %s", fmark);
		if (i < 0 || i >= (int)sizeof(f1mark))
			errx(1, "diff3_internal: string truncated");

		i = snprintf(f3mark, sizeof(f3mark), ">>>>>>> %s", rmark);
		if (i < 0 || i >= (int)sizeof(f3mark))
			errx(1, "diff3_internal: string truncated");
	}

	increase();
	if ((m = readin(argv[0], &d13)) < 0) {
		warn("%s", argv[0]);
		return (-1);
	}
	if ((n = readin(argv[1], &d23)) < 0) {
		warn("%s", argv[1]);
		return (-1);
	}

	for (i = 0; i <= 2; i++)
		if ((fp[i] = fopen(argv[i + 2], "r")) == NULL) {
			warn("%s", argv[i + 2]);
			return (-1);
		}

	return (merge(m, n));
}

int
ed_patch_lines(struct rcs_lines *dlines, struct rcs_lines *plines)
{
	char op, *ep;
	struct rcs_line *sort, *lp, *dlp, *ndlp, *insert_after;
	int start, end, i, lineno;
	u_char tmp;

	dlp = TAILQ_FIRST(&(dlines->l_lines));
	lp = TAILQ_FIRST(&(plines->l_lines));

	end = 0;
	for (lp = TAILQ_NEXT(lp, l_list); lp != NULL;
	    lp = TAILQ_NEXT(lp, l_list)) {
		/* Skip blank lines */
		if (lp->l_len < 2)
			continue;
		/* NUL-terminate line buffer for strtol() safety. */
		tmp = lp->l_line[lp->l_len - 1];
		lp->l_line[lp->l_len - 1] = '\0';
		/* len - 1 is NUL terminator so we use len - 2 for 'op' */
		op = lp->l_line[lp->l_len - 2];
		start = (int)strtol(lp->l_line, &ep, 10);
		/* Restore the last byte of the buffer */
		lp->l_line[lp->l_len - 1] = tmp;
		if (op == 'a') {
			if (start > dlines->l_nblines ||
			    start < 0 || *ep != 'a')
				errx(1, "ed_patch_lines");
		} else if (op == 'c') {
			if (start > dlines->l_nblines ||
			    start < 0 || (*ep != ',' && *ep != 'c'))
				errx(1, "ed_patch_lines");

			if (*ep == ',') {
				ep++;
				end = (int)strtol(ep, &ep, 10);
				if (end < 0 || *ep != 'c')
					errx(1, "ed_patch_lines");
			} else {
				end = start;
			}
		}


		for (;;) {
			if (dlp == NULL)
				break;
			if (dlp->l_lineno == start)
				break;
			if (dlp->l_lineno > start) {
				dlp = TAILQ_PREV(dlp, rcs_tqh, l_list);
			} else if (dlp->l_lineno < start) {
				ndlp = TAILQ_NEXT(dlp, l_list);
				if (ndlp->l_lineno > start)
					break;
				dlp = ndlp;
			}
		}

		if (dlp == NULL)
			errx(1, "ed_patch_lines");


		if (op == 'c') {
			insert_after = TAILQ_PREV(dlp, rcs_tqh, l_list);
			for (i = 0; i <= (end - start); i++) {
				ndlp = TAILQ_NEXT(dlp, l_list);
				TAILQ_REMOVE(&(dlines->l_lines), dlp, l_list);
				dlp = ndlp;
			}
			dlp = insert_after;
		}

		if (op == 'a' || op == 'c') {
			for (;;) {
				ndlp = lp;
				lp = TAILQ_NEXT(lp, l_list);
				if (lp == NULL)
					errx(1, "ed_patch_lines");

				if (!memcmp(lp->l_line, ".", 1))
					break;

				TAILQ_REMOVE(&(plines->l_lines), lp, l_list);
				TAILQ_INSERT_AFTER(&(dlines->l_lines), dlp,
				    lp, l_list);
				dlp = lp;

				lp->l_lineno = start;
				lp = ndlp;
			}
		}

		/*
		 * always resort lines as the markers might be put at the
		 * same line as we first started editing.
		 */
		lineno = 0;
		TAILQ_FOREACH(sort, &(dlines->l_lines), l_list)
			sort->l_lineno = lineno++;
		dlines->l_nblines = lineno - 1;
	}

	return (0);
}

/*
 * Pick up the line numbers of all changes from one change file.
 * (This puts the numbers in a vector, which is not strictly necessary,
 * since the vector is processed in one sequential pass.
 * The vector could be optimized out of existence)
 */
static ssize_t
readin(char *name, struct diff **dd)
{
	int a, b, c, d;
	char kind, *p;
	size_t i;

	fp[0] = fopen(name, "r");
	if (fp[0] == NULL)
		return (-1);
	for (i = 0; (p = getchange(fp[0])); i++) {
		if (i >= szchanges - 1)
			increase();
		a = b = number(&p);
		if (*p == ',') {
			p++;
			b = number(&p);
		}
		kind = *p++;
		c = d = number(&p);
		if (*p==',') {
			p++;
			d = number(&p);
		}
		if (kind == 'a')
			a++;
		if (kind == 'd')
			c++;
		b++;
		d++;
		(*dd)[i].old.from = a;
		(*dd)[i].old.to = b;
		(*dd)[i].new.from = c;
		(*dd)[i].new.to = d;
	}

	if (i) {
		(*dd)[i].old.from = (*dd)[i-1].old.to;
		(*dd)[i].new.from = (*dd)[i-1].new.to;
	}
	(void)fclose(fp[0]);

	return (i);
}

static int
number(char **lc)
{
	int nn;

	nn = 0;
	while (isdigit((unsigned char)(**lc)))
		nn = nn*10 + *(*lc)++ - '0';

	return (nn);
}

static char *
getchange(FILE *b)
{
	char *line;

	while ((line = getline(b, NULL))) {
		if (isdigit((unsigned char)line[0]))
			return (line);
	}

	return (NULL);
}

static char *
getline(FILE *b, size_t *n)
{
	char *cp;
	size_t len;
	static char *buf;
	static size_t bufsize;

	if ((cp = fgetln(b, &len)) == NULL)
		return (NULL);

	if (cp[len - 1] != '\n')
		len++;
	if (len + 1 > bufsize) {
		do {
			bufsize += 1024;
		} while (len + 1 > bufsize);
		buf = xrealloc(buf, 1, bufsize);
	}
	memcpy(buf, cp, len - 1);
	buf[len - 1] = '\n';
	buf[len] = '\0';
	if (n != NULL)
		*n = len;

	return (buf);
}

static int
merge(size_t m1, size_t m2)
{
	struct diff *d1, *d2, *d3;
	int dpl, j, t1, t2;

	d1 = d13;
	d2 = d23;
	j = 0;
	while ((t1 = d1 < d13 + m1) | (t2 = d2 < d23 + m2)) {
		if (debug) {
			printf("%d,%d=%d,%d %d,%d=%d,%d\n",
			d1->old.from, d1->old.to,
			d1->new.from, d1->new.to,
			d2->old.from, d2->old.to,
			d2->new.from, d2->new.to);
		}

		/* first file is different from others */
		if (!t2 || (t1 && d1->new.to < d2->new.from)) {
			/* stuff peculiar to 1st file */
			if (eflag==0) {
				separate("1");
				change(1, &d1->old, 0);
				keep(2, &d1->new);
				change(3, &d1->new, 0);
			}
			d1++;
			continue;
		}

		/* second file is different from others */
		if (!t1 || (t2 && d2->new.to < d1->new.from)) {
			if (eflag==0) {
				separate("2");
				keep(1, &d2->new);
				change(2, &d2->old, 0);
				change(3, &d2->new, 0);
			}
			d2++;
			continue;
		}

		/*
		 * Merge overlapping changes in first file
		 * this happens after extension (see below).
		 */
		if (d1 + 1 < d13 + m1 && d1->new.to >= d1[1].new.from) {
			d1[1].old.from = d1->old.from;
			d1[1].new.from = d1->new.from;
			d1++;
			continue;
		}

		/* merge overlapping changes in second */
		if (d2 + 1 < d23 + m2 && d2->new.to >= d2[1].new.from) {
			d2[1].old.from = d2->old.from;
			d2[1].new.from = d2->new.from;
			d2++;
			continue;
		}
		/* stuff peculiar to third file or different in all */
		if (d1->new.from == d2->new.from && d1->new.to == d2->new.to) {
			dpl = duplicate(&d1->old,&d2->old);
			if (dpl == -1)
				return (-1);

			/*
			 * dpl = 0 means all files differ
			 * dpl = 1 means files 1 and 2 identical
			 */
			if (eflag==0) {
				separate(dpl ? "3" : "");
				change(1, &d1->old, dpl);
				change(2, &d2->old, 0);
				d3 = d1->old.to > d1->old.from ? d1 : d2;
				change(3, &d3->new, 0);
			} else
				j = edit(d1, dpl, j);
			d1++;
			d2++;
			continue;
		}

		/*
		 * Overlapping changes from file 1 and 2; extend changes
		 * appropriately to make them coincide.
		 */
		if (d1->new.from < d2->new.from) {
			d2->old.from -= d2->new.from-d1->new.from;
			d2->new.from = d1->new.from;
		} else if (d2->new.from < d1->new.from) {
			d1->old.from -= d1->new.from-d2->new.from;
			d1->new.from = d2->new.from;
		}
		if (d1->new.to > d2->new.to) {
			d2->old.to += d1->new.to - d2->new.to;
			d2->new.to = d1->new.to;
		} else if (d2->new.to > d1->new.to) {
			d1->old.to += d2->new.to - d1->new.to;
			d1->new.to = d2->new.to;
		}
	}

	return (edscript(j));
}

static void
separate(const char *s)
{
	diff_output("====%s\n", s);
}

/*
 * The range of lines rold.from thru rold.to in file i is to be changed.
 * It is to be printed only if it does not duplicate something to be
 * printed later.
 */
static void
change(int i, struct range *rold, int fdup)
{
	diff_output("%d:", i);
	last[i] = rold->to;
	prange(rold);
	if (fdup || debug)
		return;
	i--;
	(void)skip(i, rold->from, NULL);
	(void)skip(i, rold->to, "  ");
}

/*
 * print the range of line numbers, rold.from thru rold.to, as n1,n2 or n1
 */
static void
prange(struct range *rold)
{
	if (rold->to <= rold->from)
		diff_output("%da\n", rold->from - 1);
	else {
		diff_output("%d", rold->from);
		if (rold->to > rold->from+1)
			diff_output(",%d", rold->to - 1);
		diff_output("c\n");
	}
}

/*
 * No difference was reported by diff between file 1 (or 2) and file 3,
 * and an artificial dummy difference (trange) must be ginned up to
 * correspond to the change reported in the other file.
 */
static void
keep(int i, struct range *rnew)
{
	int delta;
	struct range trange;

	delta = last[3] - last[i];
	trange.from = rnew->from - delta;
	trange.to = rnew->to - delta;
	change(i, &trange, 1);
}

/*
 * skip to just before line number from in file "i".  If "pr" is non-NULL,
 * print all skipped stuff with string pr as a prefix.
 */
static int
skip(int i, int from, char *pr)
{
	size_t j, n;
	char *line;

	for (n = 0; cline[i] < from - 1; n += j) {
		if ((line = getline(fp[i], &j)) == NULL)
			return (-1);
		if (pr != NULL)
			diff_output("%s%s", pr, line);
		cline[i]++;
	}
	return ((int) n);
}

/*
 * Return 1 or 0 according as the old range (in file 1) contains exactly
 * the same data as the new range (in file 2).
 */
static int
duplicate(struct range *r1, struct range *r2)
{
	int c,d;
	int nchar;
	int nline;

	if (r1->to-r1->from != r2->to-r2->from)
		return (0);
	(void)skip(0, r1->from, NULL);
	(void)skip(1, r2->from, NULL);
	nchar = 0;
	for (nline=0; nline < r1->to - r1->from; nline++) {
		do {
			c = getc(fp[0]);
			d = getc(fp[1]);
			if (c == -1 || d== -1)
				return (-1);
			nchar++;
			if (c != d) {
				repos(nchar);
				return (0);
			}
		} while (c != '\n');
	}
	repos(nchar);
	return (1);
}

static void
repos(int nchar)
{
	int i;

	for (i = 0; i < 2; i++)
		(void)fseek(fp[i], (long)-nchar, SEEK_CUR);
}

/*
 * collect an editing script for later regurgitation
 */
static int
edit(struct diff *diff, int fdup, int j)
{
	if (((fdup + 1) & eflag) == 0)
		return (j);
	j++;
	overlap[j] = !fdup;
	if (!fdup)
		overlapcnt++;
	de[j].old.from = diff->old.from;
	de[j].old.to = diff->old.to;
	de[j].new.from = de[j-1].new.to + skip(2, diff->new.from, NULL);
	de[j].new.to = de[j].new.from + skip(2, diff->new.to, NULL);
	return (j);
}

/* regurgitate */
static int
edscript(int n)
{
	int j, k;
	char block[BUFSIZ+1];

	for (n = n; n > 0; n--) {
		if (!oflag || !overlap[n])
			prange(&de[n].old);
		else
			diff_output("%da\n=======\n", de[n].old.to -1);
		(void)fseek(fp[2], (long)de[n].new.from, SEEK_SET);
		for (k = de[n].new.to-de[n].new.from; k > 0; k-= j) {
			j = k > BUFSIZ ? BUFSIZ : k;
			if (fread(block, 1, (size_t)j,
			    fp[2]) != (size_t)j)
				return (-1);
			block[j] = '\0';
			diff_output("%s", block);
		}

		if (!oflag || !overlap[n])
			diff_output(".\n");
		else {
			diff_output("%s\n.\n", f3mark);
			diff_output("%da\n%s\n.\n", de[n].old.from - 1, f1mark);
		}
	}

	return (overlapcnt);
}

static void
increase(void)
{
	size_t newsz, incr;

	/* are the memset(3) calls needed? */
	newsz = szchanges == 0 ? 64 : 2 * szchanges;
	incr = newsz - szchanges;

	d13 = xrealloc(d13, newsz, sizeof(*d13));
	memset(d13 + szchanges, 0, incr * sizeof(*d13));
	d23 = xrealloc(d23, newsz, sizeof(*d23));
	memset(d23 + szchanges, 0, incr * sizeof(*d23));
	de = xrealloc(de, newsz, sizeof(*de));
	memset(de + szchanges, 0, incr * sizeof(*de));
	overlap = xrealloc(overlap, newsz, sizeof(*overlap));
	memset(overlap + szchanges, 0, incr * sizeof(*overlap));
	szchanges = newsz;
}