new file mode 100644
--- /dev/null
+++ b/src/diff.c
@@ -0,0 +1,2208 @@
+/* vim:set ts=8 sts=4 sw=4:
+ *
+ * VIM - Vi IMproved	by Bram Moolenaar
+ *
+ * Do ":help uganda"  in Vim to read copying and usage conditions.
+ * Do ":help credits" in Vim to see a list of people who contributed.
+ * See README.txt for an overview of the Vim source code.
+ */
+
+/*
+ * diff.c: code for diff'ing two or three buffers.
+ */
+
+#include "vim.h"
+
+#if defined(FEAT_DIFF) || defined(PROTO)
+
+#define DB_COUNT 4	/* up to four buffers can be diff'ed */
+
+/*
+ * Each diffblock defines where a block of lines starts in each of the buffers
+ * and how many lines it occupies in that buffer.  When the lines are missing
+ * in the buffer the df_count[] is zero.  This is all counted in
+ * buffer lines.
+ * There is always at least one unchanged line in between the diffs.
+ * Otherwise it would have been included in the diff above or below it.
+ * df_lnum[] + df_count[] is the lnum below the change.  When in one buffer
+ * lines have been inserted, in the other buffer df_lnum[] is the line below
+ * the insertion and df_count[] is zero.  When appending lines at the end of
+ * the buffer, df_lnum[] is one beyond the end!
+ * This is using a linked list, because the number of differences is expected
+ * to be reasonable small.  The list is sorted on lnum.
+ */
+typedef struct diffblock diff_T;
+struct diffblock
+{
+    diff_T	*df_next;
+    linenr_T	df_lnum[DB_COUNT];	/* line number in buffer */
+    linenr_T	df_count[DB_COUNT];	/* nr of inserted/changed lines */
+};
+
+static diff_T	*first_diff = NULL;
+
+static buf_T	*(diffbuf[DB_COUNT]);
+
+static int	diff_invalid = TRUE;	/* list of diffs is outdated */
+
+static int	diff_busy = FALSE;	/* ex_diffgetput() is busy */
+
+/* flags obtained from the 'diffopt' option */
+#define DIFF_FILLER	1	/* display filler lines */
+#define DIFF_ICASE	2	/* ignore case */
+#define DIFF_IWHITE	4	/* ignore change in white space */
+static int	diff_flags = DIFF_FILLER;
+
+#define LBUFLEN 50		/* length of line in diff file */
+
+static int diff_a_works = MAYBE; /* TRUE when "diff -a" works, FALSE when it
+				    doesn't work, MAYBE when not checked yet */
+#if defined(MSWIN) || defined(MSDOS)
+static int diff_bin_works = MAYBE; /* TRUE when "diff --binary" works, FALSE
+				      when it doesn't work, MAYBE when not
+				      checked yet */
+#endif
+
+static int diff_buf_idx __ARGS((buf_T *buf));
+static void diff_check_unchanged __ARGS((diff_T *dp));
+static int diff_check_sanity __ARGS((diff_T *dp));
+static void diff_redraw __ARGS((int dofold));
+static int diff_write __ARGS((buf_T *buf, char_u *fname));
+static void diff_file __ARGS((char_u *tmp_orig, char_u *tmp_new, char_u *tmp_diff));
+static void diff_clear __ARGS((void));
+static int diff_equal_entry __ARGS((diff_T *dp, int idx1, int idx2));
+static int diff_cmp __ARGS((char_u *s1, char_u *s2));
+#ifdef FEAT_FOLDING
+static void diff_fold_update __ARGS((diff_T *dp, int skip_idx));
+#endif
+static void diff_read __ARGS((int idx_orig, int idx_new, char_u *fname));
+static void diff_copy_entry __ARGS((diff_T *dprev, diff_T *dp, int idx_orig, int idx_new));
+static diff_T *diff_alloc_new __ARGS((diff_T *dprev, diff_T *dp));
+
+#ifndef USE_CR
+# define tag_fgets vim_fgets
+#endif
+
+/*
+ * Call this when a new buffer is being edited in the current window.  curbuf
+ * must already have been set.
+ * Marks the current buffer as being part of the diff and requireing updating.
+ * This must be done before any autocmd, because a command the uses info
+ * about the screen contents.
+ */
+    void
+diff_new_buffer()
+{
+    if (curwin->w_p_diff)
+	diff_buf_add(curbuf);
+}
+
+/*
+ * Called when deleting or unloading a buffer: No longer make a diff with it.
+ * Also called when 'diff' is reset in the last window showing a diff for a
+ * buffer.
+ */
+    void
+diff_buf_delete(buf)
+    buf_T	*buf;
+{
+    int		i;
+
+    i = diff_buf_idx(buf);
+    if (i != DB_COUNT)
+    {
+	diffbuf[i] = NULL;
+	diff_invalid = TRUE;
+    }
+}
+
+/*
+ * Add a buffer to make diffs for.
+ */
+    void
+diff_buf_add(buf)
+    buf_T	*buf;
+{
+    int		i;
+
+    if (diff_buf_idx(buf) != DB_COUNT)
+	return;		/* It's already there. */
+
+    for (i = 0; i < DB_COUNT; ++i)
+	if (diffbuf[i] == NULL)
+	{
+	    diffbuf[i] = buf;
+	    diff_invalid = TRUE;
+	    return;
+	}
+
+    EMSGN(_("E96: Can not diff more than %ld buffers"), DB_COUNT);
+}
+
+/*
+ * Find buffer "buf" in the list of diff buffers.
+ * Return its index or DB_COUNT if not found.
+ */
+    static int
+diff_buf_idx(buf)
+    buf_T	*buf;
+{
+    int		idx;
+
+    for (idx = 0; idx < DB_COUNT; ++idx)
+	if (diffbuf[idx] == buf)
+	    break;
+    return idx;
+}
+
+/*
+ * Mark the diff info as invalid, it will be updated when info is requested.
+ */
+    void
+diff_invalidate()
+{
+    if (curwin->w_p_diff)
+    {
+	diff_invalid = TRUE;
+	diff_redraw(TRUE);
+    }
+}
+
+/*
+ * Called by mark_adjust(): update line numbers.
+ * This attempts to update the changes as much as possible:
+ * When inserting/deleting lines outside of existing change blocks, create a
+ * new change block and update the line numbers in following blocks.
+ * When inserting/deleting lines in existing change blocks, update them.
+ */
+    void
+diff_mark_adjust(line1, line2, amount, amount_after)
+    linenr_T	line1;
+    linenr_T	line2;
+    long	amount;
+    long	amount_after;
+{
+    diff_T	*dp;
+    diff_T	*dprev;
+    diff_T	*dnext;
+    int		idx;
+    int		i;
+    int		inserted, deleted;
+    int		n, off;
+    linenr_T	last;
+    linenr_T	lnum_deleted = line1;	/* lnum of remaining deletion */
+    int		check_unchanged;
+
+    /* Find the index for the current buffer. */
+    idx = diff_buf_idx(curbuf);
+    if (idx == DB_COUNT)
+	return;		/* This buffer doesn't have diffs. */
+
+    if (line2 == MAXLNUM)
+    {
+	/* mark_adjust(99, MAXLNUM, 9, 0): insert lines */
+	inserted = amount;
+	deleted = 0;
+    }
+    else if (amount_after > 0)
+    {
+	/* mark_adjust(99, 98, MAXLNUM, 9): a change that inserts lines*/
+	inserted = amount_after;
+	deleted = 0;
+    }
+    else
+    {
+	/* mark_adjust(98, 99, MAXLNUM, -2): delete lines */
+	inserted = 0;
+	deleted = -amount_after;
+    }
+
+    dprev = NULL;
+    dp = first_diff;
+    for (;;)
+    {
+	/* If the change is after the previous diff block and before the next
+	 * diff block, thus not touching an existing change, create a new diff
+	 * block.  Don't do this when ex_diffgetput() is busy. */
+	if ((dp == NULL || dp->df_lnum[idx] - 1 > line2
+		    || (line2 == MAXLNUM && dp->df_lnum[idx] > line1))
+		&& (dprev == NULL
+		    || dprev->df_lnum[idx] + dprev->df_count[idx] < line1)
+		&& !diff_busy)
+	{
+	    dnext = diff_alloc_new(dprev, dp);
+	    if (dnext == NULL)
+		return;
+
+	    dnext->df_lnum[idx] = line1;
+	    dnext->df_count[idx] = inserted;
+	    for (i = 0; i < DB_COUNT; ++i)
+		if (diffbuf[i] != NULL && i != idx)
+		{
+		    if (dprev == NULL)
+			dnext->df_lnum[i] = line1;
+		    else
+			dnext->df_lnum[i] = line1
+			    + (dprev->df_lnum[i] + dprev->df_count[i])
+			    - (dprev->df_lnum[idx] + dprev->df_count[idx]);
+		    dnext->df_count[i] = deleted;
+		}
+	}
+
+	/* if at end of the list, quit */
+	if (dp == NULL)
+	    break;
+
+	/*
+	 * Check for these situations:
+	 *	  1  2	3
+	 *	  1  2	3
+	 * line1     2	3  4  5
+	 *	     2	3  4  5
+	 *	     2	3  4  5
+	 * line2     2	3  4  5
+	 *		3     5  6
+	 *		3     5  6
+	 */
+	/* compute last line of this change */
+	last = dp->df_lnum[idx] + dp->df_count[idx] - 1;
+
+	/* 1. change completely above line1: nothing to do */
+	if (last >= line1 - 1)
+	{
+	    /* 6. change below line2: only adjust for amount_after; also when
+	     * "deleted" became zero when deleted all lines between two diffs */
+	    if (dp->df_lnum[idx] - (deleted + inserted != 0) > line2)
+	    {
+		if (amount_after == 0)
+		    break;	/* nothing left to change */
+		dp->df_lnum[idx] += amount_after;
+	    }
+	    else
+	    {
+		check_unchanged = FALSE;
+
+		/* 2. 3. 4. 5.: inserted/deleted lines touching this diff. */
+		if (deleted > 0)
+		{
+		    if (dp->df_lnum[idx] >= line1)
+		    {
+			off = dp->df_lnum[idx] - lnum_deleted;
+			if (last <= line2)
+			{
+			    /* 4. delete all lines of diff */
+			    if (dp->df_next != NULL
+				    && dp->df_next->df_lnum[idx] - 1 <= line2)
+			    {
+				/* delete continues in next diff, only do
+				 * lines until that one */
+				n = dp->df_next->df_lnum[idx] - lnum_deleted;
+				deleted -= n;
+				n -= dp->df_count[idx];
+				lnum_deleted = dp->df_next->df_lnum[idx];
+			    }
+			    else
+				n = deleted - dp->df_count[idx];
+			    dp->df_count[idx] = 0;
+			}
+			else
+			{
+			    /* 5. delete lines at or just before top of diff */
+			    n = off;
+			    dp->df_count[idx] -= line2 - dp->df_lnum[idx] + 1;
+			    check_unchanged = TRUE;
+			}
+			dp->df_lnum[idx] = line1;
+		    }
+		    else
+		    {
+			off = 0;
+			if (last < line2)
+			{
+			    /* 2. delete at end of of diff */
+			    dp->df_count[idx] -= last - lnum_deleted + 1;
+			    if (dp->df_next != NULL
+				    && dp->df_next->df_lnum[idx] - 1 <= line2)
+			    {
+				/* delete continues in next diff, only do
+				 * lines until that one */
+				n = dp->df_next->df_lnum[idx] - 1 - last;
+				deleted -= dp->df_next->df_lnum[idx]
+							       - lnum_deleted;
+				lnum_deleted = dp->df_next->df_lnum[idx];
+			    }
+			    else
+				n = line2 - last;
+			    check_unchanged = TRUE;
+			}
+			else
+			{
+			    /* 3. delete lines inside the diff */
+			    n = 0;
+			    dp->df_count[idx] -= deleted;
+			}
+		    }
+
+		    for (i = 0; i < DB_COUNT; ++i)
+			if (diffbuf[i] != NULL && i != idx)
+			{
+			    dp->df_lnum[i] -= off;
+			    dp->df_count[i] += n;
+			}
+		}
+		else
+		{
+		    if (dp->df_lnum[idx] <= line1)
+		    {
+			/* inserted lines somewhere in this diff */
+			dp->df_count[idx] += inserted;
+			check_unchanged = TRUE;
+		    }
+		    else
+			/* inserted lines somewhere above this diff */
+			dp->df_lnum[idx] += inserted;
+		}
+
+		if (check_unchanged)
+		    /* Check if inserted lines are equal, may reduce the
+		     * size of the diff.  TODO: also check for equal lines
+		     * in the middle and perhaps split the block. */
+		    diff_check_unchanged(dp);
+	    }
+	}
+
+	/* check if this block touches the previous one, may merge them. */
+	if (dprev != NULL && dprev->df_lnum[idx] + dprev->df_count[idx]
+							  == dp->df_lnum[idx])
+	{
+	    for (i = 0; i < DB_COUNT; ++i)
+		if (diffbuf[i] != NULL)
+		    dprev->df_count[i] += dp->df_count[i];
+	    dprev->df_next = dp->df_next;
+	    vim_free(dp);
+	    dp = dprev->df_next;
+	}
+	else
+	{
+	    /* Advance to next entry. */
+	    dprev = dp;
+	    dp = dp->df_next;
+	}
+    }
+
+    dprev = NULL;
+    dp = first_diff;
+    while (dp != NULL)
+    {
+	/* All counts are zero, remove this entry. */
+	for (i = 0; i < DB_COUNT; ++i)
+	    if (diffbuf[i] != NULL && dp->df_count[i] != 0)
+		break;
+	if (i == DB_COUNT)
+	{
+	    dnext = dp->df_next;
+	    vim_free(dp);
+	    dp = dnext;
+	    if (dprev == NULL)
+		first_diff = dnext;
+	    else
+		dprev->df_next = dnext;
+	}
+	else
+	{
+	    /* Advance to next entry. */
+	    dprev = dp;
+	    dp = dp->df_next;
+	}
+
+    }
+    diff_redraw(TRUE);
+
+    /* Recompute the scroll binding, may remove or add filler lines (e.g.,
+     * when adding lines above w_topline). */
+    check_scrollbind((linenr_T)0, 0L);
+}
+
+/*
+ * Allocate a new diff block and link it between "dprev" and "dp".
+ */
+    static diff_T *
+diff_alloc_new(dprev, dp)
+    diff_T	*dprev;
+    diff_T	*dp;
+{
+    diff_T	*dnew;
+
+    dnew = (diff_T *)alloc((unsigned)sizeof(diff_T));
+    if (dnew != NULL)
+    {
+	dnew->df_next = dp;
+	if (dprev == NULL)
+	    first_diff = dnew;
+	else
+	    dprev->df_next = dnew;
+    }
+    return dnew;
+}
+
+/*
+ * Check if the diff block "dp" can be made smaller for lines at the start and
+ * end that are equal.  Called after inserting lines.
+ * This may result in a change where all buffers have zero lines, the caller
+ * must take care of removing it.
+ */
+    static void
+diff_check_unchanged(dp)
+    diff_T	*dp;
+{
+    int		i_org;
+    int		i_new;
+    int		off_org, off_new;
+    char_u	*line_org;
+    int		dir = FORWARD;
+
+    /* Find the first buffers, use it as the original, compare the other
+     * buffer lines against this one. */
+    for (i_org = 0; i_org < DB_COUNT; ++i_org)
+	if (diffbuf[i_org] != NULL)
+	    break;
+    if (i_org == DB_COUNT)	/* safety check */
+	return;
+
+    if (diff_check_sanity(dp) == FAIL)
+	return;
+
+    /* First check lines at the top, then at the bottom. */
+    off_org = 0;
+    off_new = 0;
+    for (;;)
+    {
+	/* Repeat until a line is found which is different or the number of
+	 * lines has become zero. */
+	while (dp->df_count[i_org] > 0)
+	{
+	    /* Copy the line, the next ml_get() will invalidate it.  */
+	    if (dir == BACKWARD)
+		off_org = dp->df_count[i_org] - 1;
+	    line_org = vim_strsave(ml_get_buf(diffbuf[i_org],
+					dp->df_lnum[i_org] + off_org, FALSE));
+	    if (line_org == NULL)
+		return;
+	    for (i_new = i_org + 1; i_new < DB_COUNT; ++i_new)
+	    {
+		if (diffbuf[i_new] == NULL)
+		    continue;
+		if (dir == BACKWARD)
+		    off_new = dp->df_count[i_new] - 1;
+		/* if other buffer doesn't have this line, it was inserted */
+		if (off_new < 0 || off_new >= dp->df_count[i_new])
+		    break;
+		if (diff_cmp(line_org, ml_get_buf(diffbuf[i_new],
+				   dp->df_lnum[i_new] + off_new, FALSE)) != 0)
+		    break;
+	    }
+	    vim_free(line_org);
+
+	    /* Stop when a line isn't equal in all diff buffers. */
+	    if (i_new != DB_COUNT)
+		break;
+
+	    /* Line matched in all buffers, remove it from the diff. */
+	    for (i_new = i_org; i_new < DB_COUNT; ++i_new)
+		if (diffbuf[i_new] != NULL)
+		{
+		    if (dir == FORWARD)
+			++dp->df_lnum[i_new];
+		    --dp->df_count[i_new];
+		}
+	}
+	if (dir == BACKWARD)
+	    break;
+	dir = BACKWARD;
+    }
+}
+
+/*
+ * Check if a diff block doesn't contain invalid line numbers.
+ * This can happen when the diff program returns invalid results.
+ */
+    static int
+diff_check_sanity(dp)
+    diff_T	*dp;
+{
+    int		i;
+
+    for (i = 0; i < DB_COUNT; ++i)
+	if (diffbuf[i] != NULL)
+	    if (dp->df_lnum[i] + dp->df_count[i] - 1
+					     > diffbuf[i]->b_ml.ml_line_count)
+		return FAIL;
+    return OK;
+}
+
+/*
+ * Mark all diff buffers for redraw.
+ */
+    static void
+diff_redraw(dofold)
+    int		dofold;	    /* also recompute the folds */
+{
+    win_T	*wp;
+    int		n;
+
+    for (wp = firstwin; wp != NULL; wp = wp->w_next)
+	if (wp->w_p_diff)
+	{
+	    redraw_win_later(wp, NOT_VALID);
+#ifdef FEAT_FOLDING
+	    if (dofold && foldmethodIsDiff(wp))
+		foldUpdateAll(wp);
+#endif
+	    /* A change may have made filler lines invalid, need to take care
+	     * of that for other windows. */
+	    if (wp != curwin && wp->w_topfill > 0)
+	    {
+		n = diff_check(wp, wp->w_topline);
+		if (wp->w_topfill > n)
+		    wp->w_topfill = (n < 0 ? 0 : n);
+	    }
+	}
+}
+
+/*
+ * Write buffer "buf" to file "name".
+ * Always use 'fileformat' set to "unix".
+ * Return FAIL for failure
+ */
+    static int
+diff_write(buf, fname)
+    buf_T	*buf;
+    char_u	*fname;
+{
+    int		r;
+    char_u	*save_ff;
+
+    save_ff = buf->b_p_ff;
+    buf->b_p_ff = vim_strsave((char_u *)FF_UNIX);
+    r = buf_write(buf, fname, NULL, (linenr_T)1, buf->b_ml.ml_line_count,
+					     NULL, FALSE, FALSE, FALSE, TRUE);
+    free_string_option(buf->b_p_ff);
+    buf->b_p_ff = save_ff;
+    return r;
+}
+
+/*
+ * Completely update the diffs for the buffers involved.
+ * This uses the ordinary "diff" command.
+ * The buffers are written to a file, also for unmodified buffers (the file
+ * could have been produced by autocommands, e.g. the netrw plugin).
+ */
+/*ARGSUSED*/
+    void
+ex_diffupdate(eap)
+    exarg_T	*eap;
+{
+    buf_T	*buf;
+    int		idx_orig;
+    int		idx_new;
+    char_u	*tmp_orig;
+    char_u	*tmp_new;
+    char_u	*tmp_diff;
+    FILE	*fd;
+    int		ok;
+
+    /* Delete all diffblocks. */
+    diff_clear();
+    diff_invalid = FALSE;
+
+    /* Use the first buffer as the original text. */
+    for (idx_orig = 0; idx_orig < DB_COUNT; ++idx_orig)
+	if (diffbuf[idx_orig] != NULL)
+	    break;
+    if (idx_orig == DB_COUNT)
+	return;
+
+    /* Only need to do something when there is another buffer. */
+    for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new)
+	if (diffbuf[idx_new] != NULL)
+	    break;
+    if (idx_new == DB_COUNT)
+	return;
+
+    /* We need three temp file names. */
+    tmp_orig = vim_tempname('o');
+    tmp_new = vim_tempname('n');
+    tmp_diff = vim_tempname('d');
+    if (tmp_orig == NULL || tmp_new == NULL || tmp_diff == NULL)
+	goto theend;
+
+    /*
+     * Do a quick test if "diff" really works.  Otherwise it looks like there
+     * are no differences.  Can't use the return value, it's non-zero when
+     * there are differences.
+     * May try twice, first with "-a" and then without.
+     */
+    for (;;)
+    {
+	ok = FALSE;
+	fd = fopen((char *)tmp_orig, "w");
+	if (fd != NULL)
+	{
+	    fwrite("line1\n", (size_t)6, (size_t)1, fd);
+	    fclose(fd);
+	    fd = fopen((char *)tmp_new, "w");
+	    if (fd != NULL)
+	    {
+		fwrite("line2\n", (size_t)6, (size_t)1, fd);
+		fclose(fd);
+		diff_file(tmp_orig, tmp_new, tmp_diff);
+		fd = fopen((char *)tmp_diff, "r");
+		if (fd != NULL)
+		{
+		    char_u	linebuf[LBUFLEN];
+
+		    for (;;)
+		    {
+			/* There must be a line that contains "1c1". */
+			if (tag_fgets(linebuf, LBUFLEN, fd))
+			    break;
+			if (STRNCMP(linebuf, "1c1", 3) == 0)
+			    ok = TRUE;
+		    }
+		    fclose(fd);
+		}
+		mch_remove(tmp_diff);
+		mch_remove(tmp_new);
+	    }
+	    mch_remove(tmp_orig);
+	}
+
+#ifdef FEAT_EVAL
+	/* When using 'diffexpr' break here. */
+	if (*p_dex != NUL)
+	    break;
+#endif
+
+#if defined(MSWIN) || defined(MSDOS)
+	/* If the "-a" argument works, also check if "--binary" works. */
+	if (ok && diff_a_works == MAYBE && diff_bin_works == MAYBE)
+	{
+	    diff_a_works = TRUE;
+	    diff_bin_works = TRUE;
+	    continue;
+	}
+	if (!ok && diff_a_works == TRUE && diff_bin_works == TRUE)
+	{
+	    /* Tried --binary, but it failed. "-a" works though. */
+	    diff_bin_works = FALSE;
+	    ok = TRUE;
+	}
+#endif
+
+	/* If we checked if "-a" works already, break here. */
+	if (diff_a_works != MAYBE)
+	    break;
+	diff_a_works = ok;
+
+	/* If "-a" works break here, otherwise retry without "-a". */
+	if (ok)
+	    break;
+    }
+    if (!ok)
+    {
+	EMSG(_("E97: Cannot create diffs"));
+	diff_a_works = MAYBE;
+#if defined(MSWIN) || defined(MSDOS)
+	diff_bin_works = MAYBE;
+#endif
+	goto theend;
+    }
+
+    /* Write the first buffer to a tempfile. */
+    buf = diffbuf[idx_orig];
+    if (diff_write(buf, tmp_orig) == FAIL)
+	goto theend;
+
+    /* Make a difference between the first buffer and every other. */
+    for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new)
+    {
+	buf = diffbuf[idx_new];
+	if (buf == NULL)
+	    continue;
+	if (diff_write(buf, tmp_new) == FAIL)
+	    continue;
+	diff_file(tmp_orig, tmp_new, tmp_diff);
+
+	/* Read the diff output and add each entry to the diff list. */
+	diff_read(idx_orig, idx_new, tmp_diff);
+	mch_remove(tmp_diff);
+	mch_remove(tmp_new);
+    }
+    mch_remove(tmp_orig);
+
+    diff_redraw(TRUE);
+
+theend:
+    vim_free(tmp_orig);
+    vim_free(tmp_new);
+    vim_free(tmp_diff);
+}
+
+/*
+ * Make a diff between files "tmp_orig" and "tmp_new", results in "tmp_diff".
+ */
+    static void
+diff_file(tmp_orig, tmp_new, tmp_diff)
+    char_u	*tmp_orig;
+    char_u	*tmp_new;
+    char_u	*tmp_diff;
+{
+    char_u	*cmd;
+
+#ifdef FEAT_EVAL
+    if (*p_dex != NUL)
+	/* Use 'diffexpr' to generate the diff file. */
+	eval_diff(tmp_orig, tmp_new, tmp_diff);
+    else
+#endif
+    {
+	cmd = alloc((unsigned)(STRLEN(tmp_orig) + STRLEN(tmp_new)
+				+ STRLEN(tmp_diff) + STRLEN(p_srr) + 27));
+	if (cmd != NULL)
+	{
+	    /* Build the diff command and execute it.  Always use -a, binary
+	     * differences are of no use.  Ignore errors, diff returns
+	     * non-zero when differences have been found. */
+	    sprintf((char *)cmd, "diff %s%s%s%s%s %s",
+		    diff_a_works == FALSE ? "" : "-a ",
+#if defined(MSWIN) || defined(MSDOS)
+		    diff_bin_works == TRUE ? "--binary " : "",
+#else
+		    "",
+#endif
+		    (diff_flags & DIFF_IWHITE) ? "-b " : "",
+		    (diff_flags & DIFF_ICASE) ? "-i " : "",
+		    tmp_orig, tmp_new);
+	    append_redir(cmd, p_srr, tmp_diff);
+	    (void)call_shell(cmd, SHELL_FILTER|SHELL_SILENT|SHELL_DOOUT);
+	    vim_free(cmd);
+	}
+    }
+}
+
+/*
+ * Create a new version of a file from the current buffer and a diff file.
+ * The buffer is written to a file, also for unmodified buffers (the file
+ * could have been produced by autocommands, e.g. the netrw plugin).
+ */
+    void
+ex_diffpatch(eap)
+    exarg_T	*eap;
+{
+    char_u	*tmp_orig;	/* name of original temp file */
+    char_u	*tmp_new;	/* name of patched temp file */
+    char_u	*buf = NULL;
+    win_T	*old_curwin = curwin;
+    char_u	*newname = NULL;	/* name of patched file buffer */
+#ifdef UNIX
+    char_u	dirbuf[MAXPATHL];
+    char_u	*fullname = NULL;
+#endif
+#ifdef FEAT_BROWSE
+    char_u	*browseFile = NULL;
+    int		browse_flag = cmdmod.browse;
+#endif
+
+#ifdef FEAT_BROWSE
+    if (cmdmod.browse)
+    {
+	browseFile = do_browse(FALSE, (char_u *)_("Patch file"),
+			 eap->arg, NULL, NULL, BROWSE_FILTER_ALL_FILES, NULL);
+	if (browseFile == NULL)
+	    return;		/* operation cancelled */
+	eap->arg = browseFile;
+	cmdmod.browse = FALSE;	/* don't let do_ecmd() browse again */
+    }
+#endif
+
+    /* We need two temp file names. */
+    tmp_orig = vim_tempname('o');
+    tmp_new = vim_tempname('n');
+    if (tmp_orig == NULL || tmp_new == NULL)
+	goto theend;
+
+    /* Write the current buffer to "tmp_orig". */
+    if (buf_write(curbuf, tmp_orig, NULL,
+		(linenr_T)1, curbuf->b_ml.ml_line_count,
+				     NULL, FALSE, FALSE, FALSE, TRUE) == FAIL)
+	goto theend;
+
+#ifdef UNIX
+    /* Get the absolute path of the patchfile, changing directory below. */
+    fullname = FullName_save(eap->arg, FALSE);
+#endif
+    buf = alloc((unsigned)(STRLEN(tmp_orig) + (
+# ifdef UNIX
+		    fullname != NULL ? STRLEN(fullname) :
+# endif
+		    STRLEN(eap->arg)) + STRLEN(tmp_new) + 16));
+    if (buf == NULL)
+	goto theend;
+
+#ifdef UNIX
+    /* Temporaraly chdir to /tmp, to avoid patching files in the current
+     * directory when the patch file contains more than one patch.  When we
+     * have our own temp dir use that instead, it will be cleaned up when we
+     * exit (any .rej files created).  Don't change directory if we can't
+     * return to the current. */
+    if (mch_dirname(dirbuf, MAXPATHL) != OK || mch_chdir((char *)dirbuf) != 0)
+	dirbuf[0] = NUL;
+    else
+    {
+# ifdef TEMPDIRNAMES
+	if (vim_tempdir != NULL)
+	    mch_chdir((char *)vim_tempdir);
+	else
+# endif
+	    mch_chdir("/tmp");
+	shorten_fnames(TRUE);
+    }
+#endif
+
+#ifdef FEAT_EVAL
+    if (*p_pex != NUL)
+	/* Use 'patchexpr' to generate the new file. */
+	eval_patch(tmp_orig,
+# ifdef UNIX
+		fullname != NULL ? fullname :
+# endif
+		eap->arg, tmp_new);
+    else
+#endif
+    {
+	/* Build the patch command and execute it.  Ignore errors.  Switch to
+	 * cooked mode to allow the user to respond to prompts. */
+	sprintf((char *)buf, "patch -o %s %s < \"%s\"", tmp_new, tmp_orig,
+# ifdef UNIX
+		fullname != NULL ? fullname :
+# endif
+		eap->arg);
+	(void)call_shell(buf, SHELL_FILTER | SHELL_COOKED);
+    }
+
+#ifdef UNIX
+    if (dirbuf[0] != NUL)
+    {
+	if (mch_chdir((char *)dirbuf) != 0)
+	    EMSG(_(e_prev_dir));
+	shorten_fnames(TRUE);
+    }
+#endif
+
+    /* patch probably has written over the screen */
+    redraw_later(CLEAR);
+
+    /* Delete any .orig or .rej file created. */
+    STRCPY(buf, tmp_new);
+    STRCAT(buf, ".orig");
+    mch_remove(buf);
+    STRCPY(buf, tmp_new);
+    STRCAT(buf, ".rej");
+    mch_remove(buf);
+
+    if (curbuf->b_fname != NULL)
+    {
+	newname = vim_strnsave(curbuf->b_fname,
+					  (int)(STRLEN(curbuf->b_fname) + 4));
+	if (newname != NULL)
+	    STRCAT(newname, ".new");
+    }
+
+#ifdef FEAT_GUI
+    need_mouse_correct = TRUE;
+#endif
+    if (win_split(0, 0) != FAIL)
+    {
+	/* Pretend it was a ":split fname" command */
+	eap->cmdidx = CMD_split;
+	eap->arg = tmp_new;
+	do_exedit(eap, old_curwin);
+
+	if (curwin != old_curwin)		/* split must have worked */
+	{
+	    /* Set 'diff', 'scrollbind' on and 'wrap' off. */
+	    diff_win_options(curwin, TRUE);
+	    diff_win_options(old_curwin, TRUE);
+
+	    if (newname != NULL)
+	    {
+		/* do a ":file filename.new" on the patched buffer */
+		eap->arg = newname;
+		ex_file(eap);
+
+#ifdef FEAT_AUTOCMD
+		/* Do filetype detection with the new name. */
+		do_cmdline_cmd((char_u *)":doau filetypedetect BufRead");
+#endif
+	    }
+	}
+    }
+
+theend:
+    if (tmp_orig != NULL)
+	mch_remove(tmp_orig);
+    vim_free(tmp_orig);
+    if (tmp_new != NULL)
+	mch_remove(tmp_new);
+    vim_free(tmp_new);
+    vim_free(newname);
+    vim_free(buf);
+#ifdef UNIX
+    vim_free(fullname);
+#endif
+#ifdef FEAT_BROWSE
+    vim_free(browseFile);
+    cmdmod.browse = browse_flag;
+#endif
+}
+
+/*
+ * Split the window and edit another file, setting options to show the diffs.
+ */
+    void
+ex_diffsplit(eap)
+    exarg_T	*eap;
+{
+    win_T	*old_curwin = curwin;
+
+#ifdef FEAT_GUI
+    need_mouse_correct = TRUE;
+#endif
+    if (win_split(0, 0) != FAIL)
+    {
+	/* Pretend it was a ":split fname" command */
+	eap->cmdidx = CMD_split;
+	do_exedit(eap, old_curwin);
+
+	if (curwin != old_curwin)		/* split must have worked */
+	{
+	    /* Set 'diff', 'scrollbind' on and 'wrap' off. */
+	    diff_win_options(curwin, TRUE);
+	    diff_win_options(old_curwin, TRUE);
+	}
+    }
+}
+
+/*
+ * Set options to show difs for the current window.
+ */
+/*ARGSUSED*/
+    void
+ex_diffthis(eap)
+    exarg_T	*eap;
+{
+    /* Set 'diff', 'scrollbind' on and 'wrap' off. */
+    diff_win_options(curwin, TRUE);
+}
+
+/*
+ * Set options in window "wp" for diff mode.
+ */
+    void
+diff_win_options(wp, addbuf)
+    win_T	*wp;
+    int		addbuf;		/* Add buffer to diff. */
+{
+    wp->w_p_diff = TRUE;
+    wp->w_p_scb = TRUE;
+    wp->w_p_wrap = FALSE;
+# ifdef FEAT_FOLDING
+    {
+	win_T	    *old_curwin = curwin;
+
+	curwin = wp;
+	curbuf = curwin->w_buffer;
+	set_string_option_direct((char_u *)"fdm", -1, (char_u *)"diff",
+							  OPT_LOCAL|OPT_FREE);
+	curwin = old_curwin;
+	curbuf = curwin->w_buffer;
+	wp->w_p_fdc = 2;
+	wp->w_p_fen = TRUE;
+	wp->w_p_fdl = 0;
+	foldUpdateAll(wp);
+	changed_window_setting(); /* make sure topline is not halfway a fold */
+    }
+# endif
+#ifdef FEAT_SCROLLBIND
+    if (vim_strchr(p_sbo, 'h') == NULL)
+	do_cmdline_cmd((char_u *)"set sbo+=hor");
+#endif
+
+    if (addbuf)
+	diff_buf_add(wp->w_buffer);
+    redraw_win_later(wp, NOT_VALID);
+}
+
+/*
+ * Read the diff output and add each entry to the diff list.
+ */
+    static void
+diff_read(idx_orig, idx_new, fname)
+    int		idx_orig;	/* idx of original file */
+    int		idx_new;	/* idx of new file */
+    char_u	*fname;		/* name of diff output file */
+{
+    FILE	*fd;
+    diff_T	*dprev = NULL;
+    diff_T	*dp = first_diff;
+    diff_T	*dn, *dpl;
+    long	f1, l1, f2, l2;
+    char_u	linebuf[LBUFLEN];   /* only need to hold the diff line */
+    int		difftype;
+    char_u	*p;
+    long	off;
+    int		i;
+    linenr_T	lnum_orig, lnum_new;
+    long	count_orig, count_new;
+    int		notset = TRUE;	    /* block "*dp" not set yet */
+
+    fd = fopen((char *)fname, "r");
+    if (fd == NULL)
+    {
+	EMSG(_("E98: Cannot read diff output"));
+	return;
+    }
+
+    for (;;)
+    {
+	if (tag_fgets(linebuf, LBUFLEN, fd))
+	    break;		/* end of file */
+	if (!isdigit(*linebuf))
+	    continue;		/* not the start of a diff block */
+
+	/* This line must be one of three formats:
+	 * {first}[,{last}]c{first}[,{last}]
+	 * {first}a{first}[,{last}]
+	 * {first}[,{last}]d{first}
+	 */
+	p = linebuf;
+	f1 = getdigits(&p);
+	if (*p == ',')
+	{
+	    ++p;
+	    l1 = getdigits(&p);
+	}
+	else
+	    l1 = f1;
+	if (*p != 'a' && *p != 'c' && *p != 'd')
+	    continue;		/* invalid diff format */
+	difftype = *p++;
+	f2 = getdigits(&p);
+	if (*p == ',')
+	{
+	    ++p;
+	    l2 = getdigits(&p);
+	}
+	else
+	    l2 = f2;
+	if (l1 < f1 || l2 < f2)
+	    continue;		/* invalid line range */
+
+	if (difftype == 'a')
+	{
+	    lnum_orig = f1 + 1;
+	    count_orig = 0;
+	}
+	else
+	{
+	    lnum_orig = f1;
+	    count_orig = l1 - f1 + 1;
+	}
+	if (difftype == 'd')
+	{
+	    lnum_new = f2 + 1;
+	    count_new = 0;
+	}
+	else
+	{
+	    lnum_new = f2;
+	    count_new = l2 - f2 + 1;
+	}
+
+	/* Go over blocks before the change, for which orig and new are equal.
+	 * Copy blocks from orig to new. */
+	while (dp != NULL
+		&& lnum_orig > dp->df_lnum[idx_orig] + dp->df_count[idx_orig])
+	{
+	    if (notset)
+		diff_copy_entry(dprev, dp, idx_orig, idx_new);
+	    dprev = dp;
+	    dp = dp->df_next;
+	    notset = TRUE;
+	}
+
+	if (dp != NULL
+		&& lnum_orig <= dp->df_lnum[idx_orig] + dp->df_count[idx_orig]
+		&& lnum_orig + count_orig >= dp->df_lnum[idx_orig])
+	{
+	    /* New block overlaps with existing block(s).
+	     * First find last block that overlaps. */
+	    for (dpl = dp; dpl->df_next != NULL; dpl = dpl->df_next)
+		if (lnum_orig + count_orig < dpl->df_next->df_lnum[idx_orig])
+		    break;
+
+	    /* If the newly found block starts before the old one, set the
+	     * start back a number of lines. */
+	    off = dp->df_lnum[idx_orig] - lnum_orig;
+	    if (off > 0)
+	    {
+		for (i = idx_orig; i < idx_new; ++i)
+		    if (diffbuf[i] != NULL)
+			dp->df_lnum[i] -= off;
+		dp->df_lnum[idx_new] = lnum_new;
+		dp->df_count[idx_new] = count_new;
+	    }
+	    else if (notset)
+	    {
+		/* new block inside existing one, adjust new block */
+		dp->df_lnum[idx_new] = lnum_new + off;
+		dp->df_count[idx_new] = count_new - off;
+	    }
+	    else
+		/* second overlap of new block with existing block */
+		dp->df_count[idx_new] += count_new - count_orig;
+
+	    /* Adjust the size of the block to include all the lines to the
+	     * end of the existing block or the new diff, whatever ends last. */
+	    off = (lnum_orig + count_orig)
+			 - (dpl->df_lnum[idx_orig] + dpl->df_count[idx_orig]);
+	    if (off < 0)
+	    {
+		/* new change ends in existing block, adjust the end if not
+		 * done already */
+		if (notset)
+		    dp->df_count[idx_new] += -off;
+		off = 0;
+	    }
+	    for (i = idx_orig; i < idx_new + !notset; ++i)
+		if (diffbuf[i] != NULL)
+		    dp->df_count[i] = dpl->df_lnum[i] + dpl->df_count[i]
+						       - dp->df_lnum[i] + off;
+
+	    /* Delete the diff blocks that have been merged into one. */
+	    dn = dp->df_next;
+	    dp->df_next = dpl->df_next;
+	    while (dn != dp->df_next)
+	    {
+		dpl = dn->df_next;
+		vim_free(dn);
+		dn = dpl;
+	    }
+	}
+	else
+	{
+	    /* Allocate a new diffblock. */
+	    dp = diff_alloc_new(dprev, dp);
+	    if (dp == NULL)
+		return;
+
+	    dp->df_lnum[idx_orig] = lnum_orig;
+	    dp->df_count[idx_orig] = count_orig;
+	    dp->df_lnum[idx_new] = lnum_new;
+	    dp->df_count[idx_new] = count_new;
+
+	    /* Set values for other buffers, these must be equal to the
+	     * original buffer, otherwise there would have been a change
+	     * already. */
+	    for (i = idx_orig + 1; i < idx_new; ++i)
+		if (diffbuf[i] != NULL)
+		    diff_copy_entry(dprev, dp, idx_orig, i);
+	}
+	notset = FALSE;		/* "*dp" has been set */
+    }
+
+    /* for remaining diff blocks orig and new are equal */
+    while (dp != NULL)
+    {
+	if (notset)
+	    diff_copy_entry(dprev, dp, idx_orig, idx_new);
+	dprev = dp;
+	dp = dp->df_next;
+	notset = TRUE;
+    }
+
+    fclose(fd);
+}
+
+/*
+ * Copy an entry at "dp" from "idx_orig" to "idx_new".
+ */
+    static void
+diff_copy_entry(dprev, dp, idx_orig, idx_new)
+    diff_T	*dprev;
+    diff_T	*dp;
+    int		idx_orig;
+    int		idx_new;
+{
+    long	off;
+
+    if (dprev == NULL)
+	off = 0;
+    else
+	off = (dprev->df_lnum[idx_orig] + dprev->df_count[idx_orig])
+	    - (dprev->df_lnum[idx_new] + dprev->df_count[idx_new]);
+    dp->df_lnum[idx_new] = dp->df_lnum[idx_orig] - off;
+    dp->df_count[idx_new] = dp->df_count[idx_orig];
+}
+
+/*
+ * Clear the list of diffblocks.
+ */
+    static void
+diff_clear()
+{
+    diff_T	*p, *next_p;
+
+    for (p = first_diff; p != NULL; p = next_p)
+    {
+	next_p = p->df_next;
+	vim_free(p);
+    }
+    first_diff = NULL;
+}
+
+/*
+ * Check diff status for line "lnum" in buffer "buf":
+ * Returns 0 for nothing special
+ * Returns -1 for a line that should be highlighted as changed.
+ * Returns -2 for a line that should be highlighted as added/deleted.
+ * Returns > 0 for inserting that many filler lines above it (never happens
+ * when 'diffopt' doesn't contain "filler").
+ * This should only be used for windows where 'diff' is set.
+ */
+    int
+diff_check(wp, lnum)
+    win_T	*wp;
+    linenr_T	lnum;
+{
+    int		idx;		/* index in diffbuf[] for this buffer */
+    diff_T	*dp;
+    int		maxcount;
+    int		i;
+    buf_T	*buf = wp->w_buffer;
+    int		cmp;
+
+    if (diff_invalid)
+	ex_diffupdate(NULL);		/* update after a big change */
+
+    if (first_diff == NULL || !wp->w_p_diff)	/* no diffs at all */
+	return 0;
+
+    /* safety check: "lnum" must be a buffer line */
+    if (lnum < 1 || lnum > buf->b_ml.ml_line_count + 1)
+	return 0;
+
+    idx = diff_buf_idx(buf);
+    if (idx == DB_COUNT)
+	return 0;		/* no diffs for buffer "buf" */
+
+#ifdef FEAT_FOLDING
+    /* A closed fold never has filler lines. */
+    if (hasFoldingWin(wp, lnum, NULL, NULL, TRUE, NULL))
+	return 0;
+#endif
+
+    /* search for a change that includes "lnum" in the list of diffblocks. */
+    for (dp = first_diff; dp != NULL; dp = dp->df_next)
+	if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
+	    break;
+    if (dp == NULL || lnum < dp->df_lnum[idx])
+	return 0;
+
+    if (lnum < dp->df_lnum[idx] + dp->df_count[idx])
+    {
+	int	zero = FALSE;
+
+	/* Changed or inserted line.  If the other buffers have a count of
+	 * zero, the lines were inserted.  If the other buffers have the same
+	 * count, check if the lines are identical. */
+	cmp = FALSE;
+	for (i = 0; i < DB_COUNT; ++i)
+	    if (i != idx && diffbuf[i] != NULL)
+	    {
+		if (dp->df_count[i] == 0)
+		    zero = TRUE;
+		else
+		{
+		    if (dp->df_count[i] != dp->df_count[idx])
+			return -1;	    /* nr of lines changed. */
+		    cmp = TRUE;
+		}
+	    }
+	if (cmp)
+	{
+	    /* Compare all lines.  If they are equal the lines were inserted
+	     * in some buffers, deleted in others, but not changed. */
+	    for (i = 0; i < DB_COUNT; ++i)
+		if (i != idx && diffbuf[i] != NULL && dp->df_count[i] != 0)
+		    if (!diff_equal_entry(dp, idx, i))
+			return -1;
+	}
+	/* If there is no buffer with zero lines then there is no difference
+	 * any longer.  Happens when making a change (or undo) that removes
+	 * the difference.  Can't remove the entry here, we might be halfway
+	 * updating the window.  Just report the text as unchanged.  Other
+	 * windows might still show the change though. */
+	if (zero == FALSE)
+	    return 0;
+	return -2;
+    }
+
+    /* If 'diffopt' doesn't contain "filler", return 0. */
+    if (!(diff_flags & DIFF_FILLER))
+	return 0;
+
+    /* Insert filler lines above the line just below the change.  Will return
+     * 0 when this buf had the max count. */
+    maxcount = 0;
+    for (i = 0; i < DB_COUNT; ++i)
+	if (diffbuf[i] != NULL && dp->df_count[i] > maxcount)
+	    maxcount = dp->df_count[i];
+    return maxcount - dp->df_count[idx];
+}
+
+/*
+ * Compare two entries in diff "*dp" and return TRUE if they are equal.
+ */
+    static int
+diff_equal_entry(dp, idx1, idx2)
+    diff_T	*dp;
+    int		idx1;
+    int		idx2;
+{
+    int		i;
+    char_u	*line;
+    int		cmp;
+
+    if (dp->df_count[idx1] != dp->df_count[idx2])
+	return FALSE;
+    if (diff_check_sanity(dp) == FAIL)
+	return FALSE;
+    for (i = 0; i < dp->df_count[idx1]; ++i)
+    {
+	line = vim_strsave(ml_get_buf(diffbuf[idx1],
+					       dp->df_lnum[idx1] + i, FALSE));
+	if (line == NULL)
+	    return FALSE;
+	cmp = diff_cmp(line, ml_get_buf(diffbuf[idx2],
+					       dp->df_lnum[idx2] + i, FALSE));
+	vim_free(line);
+	if (cmp != 0)
+	    return FALSE;
+    }
+    return TRUE;
+}
+
+/*
+ * Compare strings "s1" and "s2" according to 'diffopt'.
+ * Return non-zero when they are different.
+ */
+    static int
+diff_cmp(s1, s2)
+    char_u	*s1;
+    char_u	*s2;
+{
+    char_u	*p1, *p2;
+#ifdef FEAT_MBYTE
+    int		l;
+#endif
+
+    if ((diff_flags & (DIFF_ICASE | DIFF_IWHITE)) == 0)
+	return STRCMP(s1, s2);
+    if ((diff_flags & DIFF_ICASE) && !(diff_flags & DIFF_IWHITE))
+	return MB_STRICMP(s1, s2);
+
+    /* Ignore white space changes and possibly ignore case. */
+    p1 = s1;
+    p2 = s2;
+    while (*p1 != NUL && *p2 != NUL)
+    {
+	if (vim_iswhite(*p1) && vim_iswhite(*p2))
+	{
+	    p1 = skipwhite(p1);
+	    p2 = skipwhite(p2);
+	}
+	else
+	{
+#ifdef FEAT_MBYTE
+	    l  = (*mb_ptr2len_check)(p1);
+	    if (l != (*mb_ptr2len_check)(p2))
+		break;
+	    if (l > 1)
+	    {
+		if (STRNCMP(p1, p2, l) != 0
+			&& (!enc_utf8
+			    || !(diff_flags & DIFF_ICASE)
+			    || utf_fold(utf_ptr2char(p1))
+					       != utf_fold(utf_ptr2char(p2))))
+		    break;
+		p1 += l;
+		p2 += l;
+	    }
+	    else
+#endif
+	    {
+		if (*p1 != *p2 && (!(diff_flags & DIFF_ICASE)
+				     || TOLOWER_LOC(*p1) != TOLOWER_LOC(*p2)))
+		    break;
+		++p1;
+		++p2;
+	    }
+	}
+    }
+
+    /* Ignore trailing white space. */
+    p1 = skipwhite(p1);
+    p2 = skipwhite(p2);
+    if (*p1 != NUL || *p2 != NUL)
+	return 1;
+    return 0;
+}
+
+/*
+ * Return the number of filler lines above "lnum".
+ */
+    int
+diff_check_fill(wp, lnum)
+    win_T	*wp;
+    linenr_T	lnum;
+{
+    int		n;
+
+    /* be quick when there are no filler lines */
+    if (!(diff_flags & DIFF_FILLER))
+	return 0;
+    n = diff_check(wp, lnum);
+    if (n <= 0)
+	return 0;
+    return n;
+}
+
+/*
+ * Set the topline of "towin" to match the position in "fromwin", so that they
+ * show the same diff'ed lines.
+ */
+    void
+diff_set_topline(fromwin, towin)
+    win_T	*fromwin;
+    win_T	*towin;
+{
+    buf_T	*buf = fromwin->w_buffer;
+    linenr_T	lnum = fromwin->w_topline;
+    int		idx;
+    diff_T	*dp;
+    int		i;
+
+    idx = diff_buf_idx(buf);
+    if (idx == DB_COUNT)
+	return;		/* safety check */
+
+    if (diff_invalid)
+	ex_diffupdate(NULL);		/* update after a big change */
+
+    towin->w_topfill = 0;
+
+    /* search for a change that includes "lnum" in the list of diffblocks. */
+    for (dp = first_diff; dp != NULL; dp = dp->df_next)
+	if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
+	    break;
+    if (dp == NULL)
+    {
+	/* After last change, compute topline relative to end of file; no
+	 * filler lines. */
+	towin->w_topline = towin->w_buffer->b_ml.ml_line_count
+					   - (buf->b_ml.ml_line_count - lnum);
+    }
+    else
+    {
+	/* Find index for "towin". */
+	i = diff_buf_idx(towin->w_buffer);
+	if (i == DB_COUNT)
+	    return;		/* safety check */
+
+	towin->w_topline = lnum + (dp->df_lnum[i] - dp->df_lnum[idx]);
+	if (lnum >= dp->df_lnum[idx])
+	{
+	    /* Inside a change: compute filler lines. */
+	    if (dp->df_count[i] == dp->df_count[idx])
+		towin->w_topfill = fromwin->w_topfill;
+	    else if (dp->df_count[i] > dp->df_count[idx])
+	    {
+		if (lnum == dp->df_lnum[idx] + dp->df_count[idx])
+		    towin->w_topline = dp->df_lnum[i] + dp->df_count[i]
+							 - fromwin->w_topfill;
+	    }
+	    else
+	    {
+		if (towin->w_topline >= dp->df_lnum[i] + dp->df_count[i])
+		{
+		    if (diff_flags & DIFF_FILLER)
+			towin->w_topfill = dp->df_lnum[idx]
+						   + dp->df_count[idx] - lnum;
+		    towin->w_topline = dp->df_lnum[i] + dp->df_count[i];
+		}
+	    }
+	}
+    }
+
+    /* safety check (if diff info gets outdated strange things may happen) */
+    towin->w_botfill = FALSE;
+    if (towin->w_topline > towin->w_buffer->b_ml.ml_line_count)
+    {
+	towin->w_topline = towin->w_buffer->b_ml.ml_line_count;
+	towin->w_botfill = TRUE;
+    }
+    if (towin->w_topline < 1)
+    {
+	towin->w_topline = 1;
+	towin->w_topfill = 0;
+    }
+
+    /* When w_topline changes need to recompute w_botline and cursor position */
+    invalidate_botline_win(towin);
+    changed_line_abv_curs_win(towin);
+
+    check_topfill(towin, FALSE);
+#ifdef FEAT_FOLDING
+    (void)hasFoldingWin(towin, towin->w_topline, &towin->w_topline,
+							    NULL, TRUE, NULL);
+#endif
+}
+
+/*
+ * This is called when 'diffopt' is changed.
+ */
+    int
+diffopt_changed()
+{
+    char_u	*p;
+    int		diff_context_new = 6;
+    int		diff_flags_new = 0;
+
+    p = p_dip;
+    while (*p != NUL)
+    {
+	if (STRNCMP(p, "filler", 6) == 0)
+	{
+	    p += 6;
+	    diff_flags_new |= DIFF_FILLER;
+	}
+	else if (STRNCMP(p, "context:", 8) == 0 && VIM_ISDIGIT(p[8]))
+	{
+	    p += 8;
+	    diff_context_new = getdigits(&p);
+	}
+	else if (STRNCMP(p, "icase", 5) == 0)
+	{
+	    p += 5;
+	    diff_flags_new |= DIFF_ICASE;
+	}
+	else if (STRNCMP(p, "iwhite", 6) == 0)
+	{
+	    p += 6;
+	    diff_flags_new |= DIFF_IWHITE;
+	}
+	if (*p != ',' && *p != NUL)
+	    return FAIL;
+	if (*p == ',')
+	    ++p;
+    }
+
+    /* If "icase" or "iwhite" was added or removed, need to update the diff. */
+    if (diff_flags != diff_flags_new)
+	diff_invalid = TRUE;
+
+    diff_flags = diff_flags_new;
+    diff_context = diff_context_new;
+
+    diff_redraw(TRUE);
+
+    /* recompute the scroll binding with the new option value, may
+     * remove or add filler lines */
+    check_scrollbind((linenr_T)0, 0L);
+
+    return OK;
+}
+
+/*
+ * Find the difference within a changed line.
+ * Returns TRUE if the line was added, no other buffer has it.
+ */
+    int
+diff_find_change(wp, lnum, startp, endp)
+    win_T	*wp;
+    linenr_T	lnum;
+    int		*startp;	/* first char of the change */
+    int		*endp;		/* last char of the change */
+{
+    char_u	*line_org;
+    char_u	*line_new;
+    int		i;
+    int		si, ei_org, ei_new;
+    diff_T	*dp;
+    int		idx;
+    int		off;
+    int		added = TRUE;
+
+    /* Make a copy of the line, the next ml_get() will invalidate it. */
+    line_org = vim_strsave(ml_get_buf(wp->w_buffer, lnum, FALSE));
+    if (line_org == NULL)
+	return FALSE;
+
+    idx = diff_buf_idx(wp->w_buffer);
+    if (idx == DB_COUNT)	/* cannot happen */
+	return FALSE;
+
+    /* search for a change that includes "lnum" in the list of diffblocks. */
+    for (dp = first_diff; dp != NULL; dp = dp->df_next)
+	if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
+	    break;
+    if (dp == NULL || diff_check_sanity(dp) == FAIL)
+	return FALSE;
+
+    off = lnum - dp->df_lnum[idx];
+
+    for (i = 0; i < DB_COUNT; ++i)
+	if (diffbuf[i] != NULL && i != idx)
+	{
+	    /* Skip lines that are not in the other change (filler lines). */
+	    if (off >= dp->df_count[i])
+		continue;
+	    added = FALSE;
+	    line_new = ml_get_buf(diffbuf[i], dp->df_lnum[i] + off, FALSE);
+
+	    /* Search for start of difference */
+	    for (si = 0; line_org[si] != NUL && line_org[si] == line_new[si]; )
+		++si;
+#ifdef FEAT_MBYTE
+	    if (has_mbyte)
+	    {
+		/* Move back to first byte of character in both lines (may
+		 * have "nn^" in line_org and "n^ in line_new). */
+		si -= (*mb_head_off)(line_org, line_org + si);
+		si -= (*mb_head_off)(line_new, line_new + si);
+	    }
+#endif
+	    if (*startp > si)
+		*startp = si;
+
+	    /* Search for end of difference, if any. */
+	    if (line_org[si] != NUL || line_new[si] != NUL)
+	    {
+		ei_org = (int)STRLEN(line_org);
+		ei_new = (int)STRLEN(line_new);
+		while (ei_org >= *startp && ei_new >= *startp
+			&& ei_org >= 0 && ei_new >= 0
+			&& line_org[ei_org] == line_new[ei_new])
+		{
+		    --ei_org;
+		    --ei_new;
+		}
+		if (*endp < ei_org)
+		    *endp = ei_org;
+	    }
+	}
+
+    vim_free(line_org);
+    return added;
+}
+
+#if defined(FEAT_FOLDING) || defined(PROTO)
+/*
+ * Return TRUE if line "lnum" is not close to a diff block, this line should
+ * be in a fold.
+ * Return FALSE if there are no diff blocks at all in this window.
+ */
+    int
+diff_infold(wp, lnum)
+    win_T	*wp;
+    linenr_T	lnum;
+{
+    int		i;
+    int		idx = -1;
+    int		other = FALSE;
+    diff_T	*dp;
+
+    /* Return if 'diff' isn't set. */
+    if (!wp->w_p_diff)
+	return FALSE;
+
+    for (i = 0; i < DB_COUNT; ++i)
+    {
+	if (diffbuf[i] == wp->w_buffer)
+	    idx = i;
+	else if (diffbuf[i] != NULL)
+	    other = TRUE;
+    }
+
+    /* return here if there are no diffs in the window */
+    if (idx == -1 || !other)
+	return FALSE;
+
+    if (diff_invalid)
+	ex_diffupdate(NULL);		/* update after a big change */
+
+    /* Return if there are no diff blocks.  All lines will be folded. */
+    if (first_diff == NULL)
+	return TRUE;
+
+    for (dp = first_diff; dp != NULL; dp = dp->df_next)
+    {
+	/* If this change is below the line there can't be any further match. */
+	if (dp->df_lnum[idx] - diff_context > lnum)
+	    break;
+	/* If this change ends before the line we have a match. */
+	if (dp->df_lnum[idx] + dp->df_count[idx] + diff_context > lnum)
+	    return FALSE;
+    }
+    return TRUE;
+}
+#endif
+
+/*
+ * "dp" and "do" commands.
+ */
+    void
+nv_diffgetput(put)
+    int		put;
+{
+    exarg_T	ea;
+
+    ea.arg = (char_u *)"";
+    if (put)
+	ea.cmdidx = CMD_diffput;
+    else
+	ea.cmdidx = CMD_diffget;
+    ea.addr_count = 0;
+    ea.line1 = curwin->w_cursor.lnum;
+    ea.line2 = curwin->w_cursor.lnum;
+    ex_diffgetput(&ea);
+}
+
+/*
+ * ":diffget"
+ * ":diffput"
+ */
+    void
+ex_diffgetput(eap)
+    exarg_T	*eap;
+{
+    linenr_T	lnum;
+    int		count;
+    linenr_T	off = 0;
+    diff_T	*dp;
+    diff_T	*dprev;
+    diff_T	*dfree;
+    int		idx_cur;
+    int		idx_other;
+    int		idx_from;
+    int		idx_to;
+    int		i;
+    int		added;
+    char_u	*p;
+    aco_save_T	aco;
+    buf_T	*buf;
+    int		start_skip, end_skip;
+    int		new_count;
+
+    /* Find the current buffer in the list of diff buffers. */
+    idx_cur = diff_buf_idx(curbuf);
+    if (idx_cur == DB_COUNT)
+    {
+	EMSG(_("E99: Current buffer is not in diff mode"));
+	return;
+    }
+
+    if (*eap->arg == NUL)
+    {
+	/* No argument: Find the other buffer in the list of diff buffers. */
+	for (idx_other = 0; idx_other < DB_COUNT; ++idx_other)
+	    if (diffbuf[idx_other] != curbuf && diffbuf[idx_other] != NULL)
+		break;
+	if (idx_other == DB_COUNT)
+	{
+	    EMSG(_("E100: No other buffer in diff mode"));
+	    return;
+	}
+
+	/* Check that there isn't a third buffer in the list */
+	for (i = idx_other + 1; i < DB_COUNT; ++i)
+	    if (diffbuf[i] != curbuf && diffbuf[i] != NULL)
+	    {
+		EMSG(_("E101: More than two buffers in diff mode, don't know which one to use"));
+		return;
+	    }
+    }
+    else
+    {
+	/* Buffer number or pattern given.  Ignore trailing white space. */
+	p = eap->arg + STRLEN(eap->arg);
+	while (p > eap->arg && vim_iswhite(p[-1]))
+	    --p;
+	for (i = 0; vim_isdigit(eap->arg[i]) && eap->arg + i < p; ++i)
+	    ;
+	if (eap->arg + i == p)	    /* digits only */
+	    i = atol((char *)eap->arg);
+	else
+	{
+	    i = buflist_findpat(eap->arg, p, FALSE, TRUE);
+	    if (i < 0)
+		return;		/* error message already given */
+	}
+	buf = buflist_findnr(i);
+	if (buf == NULL)
+	{
+	    EMSG2(_("E102: Can't find buffer \"%s\""), eap->arg);
+	    return;
+	}
+	idx_other = diff_buf_idx(buf);
+	if (idx_other == DB_COUNT)
+	{
+	    EMSG2(_("E103: Buffer \"%s\" is not in diff mode"), eap->arg);
+	    return;
+	}
+    }
+
+    diff_busy = TRUE;
+
+    /* When no range given include the line above or below the cursor. */
+    if (eap->addr_count == 0)
+    {
+	/* Make it possible that ":diffget" on the last line gets line below
+	 * the cursor line when there is no difference above the cursor. */
+	if (eap->cmdidx == CMD_diffget
+		&& eap->line1 == curbuf->b_ml.ml_line_count
+		&& diff_check(curwin, eap->line1) == 0
+		&& (eap->line1 == 1 || diff_check(curwin, eap->line1 - 1) == 0))
+	    ++eap->line2;
+	else if (eap->line1 > 0)
+	    --eap->line1;
+    }
+
+    if (eap->cmdidx == CMD_diffget)
+    {
+	idx_from = idx_other;
+	idx_to = idx_cur;
+    }
+    else
+    {
+	idx_from = idx_cur;
+	idx_to = idx_other;
+	/* Need to make the other buffer the current buffer to be able to make
+	 * changes in it. */
+	/* set curwin/curbuf to buf and save a few things */
+	aucmd_prepbuf(&aco, diffbuf[idx_other]);
+    }
+
+    dprev = NULL;
+    for (dp = first_diff; dp != NULL; )
+    {
+	if (dp->df_lnum[idx_cur] > eap->line2 + off)
+	    break;	/* past the range that was specified */
+
+	dfree = NULL;
+	lnum = dp->df_lnum[idx_to];
+	count = dp->df_count[idx_to];
+	if (dp->df_lnum[idx_cur] + dp->df_count[idx_cur] > eap->line1 + off
+		&& u_save(lnum - 1, lnum + count) != FAIL)
+	{
+	    /* Inside the specified range and saving for undo worked. */
+	    start_skip = 0;
+	    end_skip = 0;
+	    if (eap->addr_count > 0)
+	    {
+		/* A range was specified: check if lines need to be skipped. */
+		start_skip = eap->line1 + off - dp->df_lnum[idx_cur];
+		if (start_skip > 0)
+		{
+		    /* range starts below start of current diff block */
+		    if (start_skip > count)
+		    {
+			lnum += count;
+			count = 0;
+		    }
+		    else
+		    {
+			count -= start_skip;
+			lnum += start_skip;
+		    }
+		}
+		else
+		    start_skip = 0;
+
+		end_skip = dp->df_lnum[idx_cur] + dp->df_count[idx_cur] - 1
+							 - (eap->line2 + off);
+		if (end_skip > 0)
+		{
+		    /* range ends above end of current/from diff block */
+		    if (idx_cur == idx_from)	/* :diffput */
+		    {
+			i = dp->df_count[idx_cur] - start_skip - end_skip;
+			if (count > i)
+			    count = i;
+		    }
+		    else			/* :diffget */
+		    {
+			count -= end_skip;
+			end_skip = dp->df_count[idx_from] - start_skip - count;
+			if (end_skip < 0)
+			    end_skip = 0;
+		    }
+		}
+		else
+		    end_skip = 0;
+	    }
+
+	    added = 0;
+	    for (i = 0; i < count; ++i)
+	    {
+		ml_delete(lnum, FALSE);
+		--added;
+	    }
+	    for (i = 0; i < dp->df_count[idx_from] - start_skip - end_skip; ++i)
+	    {
+		linenr_T nr;
+
+		nr = dp->df_lnum[idx_from] + start_skip + i;
+		if (nr > diffbuf[idx_from]->b_ml.ml_line_count)
+		    break;
+		p = vim_strsave(ml_get_buf(diffbuf[idx_from], nr, FALSE));
+		if (p != NULL)
+		{
+		    ml_append(lnum + i - 1, p, 0, FALSE);
+		    vim_free(p);
+		    ++added;
+		}
+	    }
+	    new_count = dp->df_count[idx_to] + added;
+	    dp->df_count[idx_to] = new_count;
+
+	    if (start_skip == 0 && end_skip == 0)
+	    {
+		/* Check if there are any other buffers and if the diff is
+		 * equal in them. */
+		for (i = 0; i < DB_COUNT; ++i)
+		    if (diffbuf[i] != NULL && i != idx_from && i != idx_to
+			    && !diff_equal_entry(dp, idx_from, i))
+			break;
+		if (i == DB_COUNT)
+		{
+		    /* delete the diff entry, the buffers are now equal here */
+		    dfree = dp;
+		    dp = dp->df_next;
+		    if (dprev == NULL)
+			first_diff = dp;
+		    else
+			dprev->df_next = dp;
+		}
+	    }
+
+	    /* Adjust marks.  This will change the following entries! */
+	    if (added != 0)
+	    {
+		mark_adjust(lnum, lnum + count - 1, (long)MAXLNUM, (long)added);
+		if (curwin->w_cursor.lnum >= lnum)
+		{
+		    /* Adjust the cursor position if it's in/after the changed
+		     * lines. */
+		    if (curwin->w_cursor.lnum >= lnum + count)
+			curwin->w_cursor.lnum += added;
+		    else if (added < 0)
+			curwin->w_cursor.lnum = lnum;
+		}
+	    }
+	    changed_lines(lnum, 0, lnum + count, (long)added);
+
+	    if (dfree != NULL)
+	    {
+		/* Diff is deleted, update folds in other windows. */
+#ifdef FEAT_FOLDING
+		diff_fold_update(dfree, idx_to);
+#endif
+		vim_free(dfree);
+	    }
+	    else
+		/* mark_adjust() may have changed the count in a wrong way */
+		dp->df_count[idx_to] = new_count;
+
+	    /* When changing the current buffer, keep track of line numbers */
+	    if (idx_cur == idx_to)
+		off += added;
+	}
+
+	/* If before the range or not deleted, go to next diff. */
+	if (dfree == NULL)
+	{
+	    dprev = dp;
+	    dp = dp->df_next;
+	}
+    }
+
+    /* restore curwin/curbuf and a few other things */
+    if (idx_other == idx_to)
+    {
+	/* Syncing undo only works for the current buffer, but we change
+	 * another buffer.  Sync undo if the command was typed.  This isn't
+	 * 100% right when ":diffput" is used in a function or mapping. */
+	if (KeyTyped)
+	    u_sync();
+	aucmd_restbuf(&aco);
+    }
+
+    diff_busy = FALSE;
+
+    /* Check that the cursor is on a valid character and update it's position.
+     * When there were filler lines the topline has become invalid. */
+    check_cursor();
+    changed_line_abv_curs();
+
+    /* Also need to redraw the other buffers. */
+    diff_redraw(FALSE);
+}
+
+#ifdef FEAT_FOLDING
+/*
+ * Update folds for all diff buffers for entry "dp".
+ * Skip buffer with index "skip_idx".
+ * When there are no diffs, all folds are removed.
+ */
+    static void
+diff_fold_update(dp, skip_idx)
+    diff_T	*dp;
+    int		skip_idx;
+{
+    int		i;
+    win_T	*wp;
+
+    for (wp = firstwin; wp != NULL; wp = wp->w_next)
+	for (i = 0; i < DB_COUNT; ++i)
+	    if (diffbuf[i] == wp->w_buffer && i != skip_idx)
+		foldUpdate(wp, dp->df_lnum[i],
+					    dp->df_lnum[i] + dp->df_count[i]);
+}
+#endif
+
+/*
+ * Return TRUE if buffer "buf" is in diff-mode.
+ */
+    int
+diff_mode_buf(buf)
+    buf_T	*buf;
+{
+    return diff_buf_idx(buf) != DB_COUNT;
+}
+
+/*
+ * Move "count" times in direction "dir" to the next diff block.
+ * Return FAIL if there isn't such a diff block.
+ */
+    int
+diff_move_to(dir, count)
+    int		dir;
+    long	count;
+{
+    int		idx;
+    linenr_T	lnum = curwin->w_cursor.lnum;
+    diff_T	*dp;
+
+    idx = diff_buf_idx(curbuf);
+    if (idx == DB_COUNT || first_diff == NULL)
+	return FAIL;
+
+    if (diff_invalid)
+	ex_diffupdate(NULL);		/* update after a big change */
+
+    if (first_diff == NULL)		/* no diffs today */
+	return FAIL;
+
+    while (--count >= 0)
+    {
+	/* Check if already before first diff. */
+	if (dir == BACKWARD && lnum <= first_diff->df_lnum[idx])
+	    break;
+
+	for (dp = first_diff; ; dp = dp->df_next)
+	{
+	    if (dp == NULL)
+		break;
+	    if ((dir == FORWARD && lnum < dp->df_lnum[idx])
+		    || (dir == BACKWARD
+			&& (dp->df_next == NULL
+			    || lnum <= dp->df_next->df_lnum[idx])))
+	    {
+		lnum = dp->df_lnum[idx];
+		break;
+	    }
+	}
+    }
+
+    /* don't end up past the end of the file */
+    if (lnum > curbuf->b_ml.ml_line_count)
+	lnum = curbuf->b_ml.ml_line_count;
+
+    /* When the cursor didn't move at all we fail. */
+    if (lnum == curwin->w_cursor.lnum)
+	return FAIL;
+
+    setpcmark();
+    curwin->w_cursor.lnum = lnum;
+    curwin->w_cursor.col = 0;
+
+    return OK;
+}
+
+#if defined(FEAT_FOLDING) || defined(PROTO)
+/*
+ * For line "lnum" in the current window find the equivalent lnum in window
+ * "wp", compensating for inserted/deleted lines.
+ */
+    linenr_T
+diff_lnum_win(lnum, wp)
+    linenr_T	lnum;
+    win_T	*wp;
+{
+    diff_T	*dp;
+    int		idx;
+    int		i;
+    linenr_T	n;
+
+    idx = diff_buf_idx(curbuf);
+    if (idx == DB_COUNT)		/* safety check */
+	return (linenr_T)0;
+
+    if (diff_invalid)
+	ex_diffupdate(NULL);		/* update after a big change */
+
+    /* search for a change that includes "lnum" in the list of diffblocks. */
+    for (dp = first_diff; dp != NULL; dp = dp->df_next)
+	if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
+	    break;
+
+    /* When after the last change, compute relative to the last line number. */
+    if (dp == NULL)
+	return wp->w_buffer->b_ml.ml_line_count
+					- (curbuf->b_ml.ml_line_count - lnum);
+
+    /* Find index for "wp". */
+    i = diff_buf_idx(wp->w_buffer);
+    if (i == DB_COUNT)			/* safety check */
+	return (linenr_T)0;
+
+    n = lnum + (dp->df_lnum[i] - dp->df_lnum[idx]);
+    if (n > dp->df_lnum[i] + dp->df_count[i])
+	n = dp->df_lnum[i] + dp->df_count[i];
+    return n;
+}
+#endif
+
+#endif	/* FEAT_DIFF */