Adding upstream version 2:9.0.1378.upstream/2%9.0.1378upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3439 insertions, 0 deletions

diff --git a/src/diff.c b/src/diff.c
new file mode 100644
index 0000000..a155c5e
--- /dev/null
+++ b/src/diff.c
@@ -0,0 +1,3439 @@
+/* vi:set ts=8 sts=4 sw=4 noet:
+ *
+ * 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, three or four buffers.
+ *
+ * There are three ways to diff:
+ * - Shell out to an external diff program, using files.
+ * - Use the compiled-in xdiff library.
+ * - Let 'diffexpr' do the work, using files.
+ */
+
+#include "vim.h"
+#include "xdiff/xdiff.h"
+
+#if defined(FEAT_DIFF) || defined(PROTO)
+
+static int diff_busy = FALSE;	    // using diff structs, don't change them
+static int diff_need_update = FALSE; // ex_diffupdate needs to be called
+
+// flags obtained from the 'diffopt' option
+#define DIFF_FILLER	0x001	// display filler lines
+#define DIFF_IBLANK	0x002	// ignore empty lines
+#define DIFF_ICASE	0x004	// ignore case
+#define DIFF_IWHITE	0x008	// ignore change in white space
+#define DIFF_IWHITEALL	0x010	// ignore all white space changes
+#define DIFF_IWHITEEOL	0x020	// ignore change in white space at EOL
+#define DIFF_HORIZONTAL	0x040	// horizontal splits
+#define DIFF_VERTICAL	0x080	// vertical splits
+#define DIFF_HIDDEN_OFF	0x100	// diffoff when hidden
+#define DIFF_INTERNAL	0x200	// use internal xdiff algorithm
+#define DIFF_CLOSE_OFF	0x400	// diffoff when closing window
+#define DIFF_FOLLOWWRAP	0x800	// follow the wrap option
+#define ALL_WHITE_DIFF (DIFF_IWHITE | DIFF_IWHITEALL | DIFF_IWHITEEOL)
+static int	diff_flags = DIFF_INTERNAL | DIFF_FILLER | DIFF_CLOSE_OFF;
+
+static long diff_algorithm = 0;
+
+#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)
+static int diff_bin_works = MAYBE; // TRUE when "diff --binary" works, FALSE
+				   // when it doesn't work, MAYBE when not
+				   // checked yet
+#endif
+
+// used for diff input
+typedef struct {
+    char_u	*din_fname;  // used for external diff
+    mmfile_t	din_mmfile;  // used for internal diff
+} diffin_T;
+
+// used for diff result
+typedef struct {
+    char_u	*dout_fname;  // used for external diff
+    garray_T	dout_ga;      // used for internal diff
+} diffout_T;
+
+// used for recording hunks from xdiff
+typedef struct {
+    linenr_T lnum_orig;
+    long     count_orig;
+    linenr_T lnum_new;
+    long     count_new;
+} diffhunk_T;
+
+// two diff inputs and one result
+typedef struct {
+    diffin_T	dio_orig;     // original file input
+    diffin_T	dio_new;      // new file input
+    diffout_T	dio_diff;     // diff result
+    int		dio_internal; // using internal diff
+} diffio_T;
+
+static int diff_buf_idx(buf_T *buf);
+static int diff_buf_idx_tp(buf_T *buf, tabpage_T *tp);
+static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1, linenr_T line2, long amount, long amount_after);
+static void diff_check_unchanged(tabpage_T *tp, diff_T *dp);
+static int diff_check_sanity(tabpage_T *tp, diff_T *dp);
+static int check_external_diff(diffio_T *diffio);
+static int diff_file(diffio_T *diffio);
+static int diff_equal_entry(diff_T *dp, int idx1, int idx2);
+static int diff_cmp(char_u *s1, char_u *s2);
+#ifdef FEAT_FOLDING
+static void diff_fold_update(diff_T *dp, int skip_idx);
+#endif
+static void diff_read(int idx_orig, int idx_new, diffio_T *dio);
+static void diff_copy_entry(diff_T *dprev, diff_T *dp, int idx_orig, int idx_new);
+static diff_T *diff_alloc_new(tabpage_T *tp, diff_T *dprev, diff_T *dp);
+static int parse_diff_ed(char_u *line, diffhunk_T *hunk);
+static int parse_diff_unified(char_u *line, diffhunk_T *hunk);
+static int xdiff_out(long start_a, long count_a, long start_b, long count_b, void *priv);
+
+#define FOR_ALL_DIFFBLOCKS_IN_TAB(tp, dp) \
+    for ((dp) = (tp)->tp_first_diff; (dp) != NULL; (dp) = (dp)->df_next)
+
+/*
+ * Called when deleting or unloading a buffer: No longer make a diff with it.
+ */
+    void
+diff_buf_delete(buf_T *buf)
+{
+    int		i;
+    tabpage_T	*tp;
+
+    FOR_ALL_TABPAGES(tp)
+    {
+	i = diff_buf_idx_tp(buf, tp);
+	if (i != DB_COUNT)
+	{
+	    tp->tp_diffbuf[i] = NULL;
+	    tp->tp_diff_invalid = TRUE;
+	    if (tp == curtab)
+	    {
+		// don't redraw right away, more might change or buffer state
+		// is invalid right now
+		need_diff_redraw = TRUE;
+		redraw_later(UPD_VALID);
+	    }
+	}
+    }
+}
+
+/*
+ * Check if the current buffer should be added to or removed from the list of
+ * diff buffers.
+ */
+    void
+diff_buf_adjust(win_T *win)
+{
+    win_T	*wp;
+    int		i;
+
+    if (!win->w_p_diff)
+    {
+	// When there is no window showing a diff for this buffer, remove
+	// it from the diffs.
+	FOR_ALL_WINDOWS(wp)
+	    if (wp->w_buffer == win->w_buffer && wp->w_p_diff)
+		break;
+	if (wp == NULL)
+	{
+	    i = diff_buf_idx(win->w_buffer);
+	    if (i != DB_COUNT)
+	    {
+		curtab->tp_diffbuf[i] = NULL;
+		curtab->tp_diff_invalid = TRUE;
+		diff_redraw(TRUE);
+	    }
+	}
+    }
+    else
+	diff_buf_add(win->w_buffer);
+}
+
+/*
+ * Add a buffer to make diffs for.
+ * Call this when a new buffer is being edited in the current window where
+ * 'diff' is set.
+ * Marks the current buffer as being part of the diff and requiring updating.
+ * This must be done before any autocmd, because a command may use info
+ * about the screen contents.
+ */
+    void
+diff_buf_add(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 (curtab->tp_diffbuf[i] == NULL)
+	{
+	    curtab->tp_diffbuf[i] = buf;
+	    curtab->tp_diff_invalid = TRUE;
+	    diff_redraw(TRUE);
+	    return;
+	}
+
+    semsg(_(e_cannot_diff_more_than_nr_buffers), DB_COUNT);
+}
+
+/*
+ * Remove all buffers to make diffs for.
+ */
+    static void
+diff_buf_clear(void)
+{
+    int		i;
+
+    for (i = 0; i < DB_COUNT; ++i)
+	if (curtab->tp_diffbuf[i] != NULL)
+	{
+	    curtab->tp_diffbuf[i] = NULL;
+	    curtab->tp_diff_invalid = TRUE;
+	    diff_redraw(TRUE);
+	}
+}
+
+/*
+ * Find buffer "buf" in the list of diff buffers for the current tab page.
+ * Return its index or DB_COUNT if not found.
+ */
+    static int
+diff_buf_idx(buf_T *buf)
+{
+    int		idx;
+
+    for (idx = 0; idx < DB_COUNT; ++idx)
+	if (curtab->tp_diffbuf[idx] == buf)
+	    break;
+    return idx;
+}
+
+/*
+ * Find buffer "buf" in the list of diff buffers for tab page "tp".
+ * Return its index or DB_COUNT if not found.
+ */
+    static int
+diff_buf_idx_tp(buf_T *buf, tabpage_T *tp)
+{
+    int		idx;
+
+    for (idx = 0; idx < DB_COUNT; ++idx)
+	if (tp->tp_diffbuf[idx] == buf)
+	    break;
+    return idx;
+}
+
+/*
+ * Mark the diff info involving buffer "buf" as invalid, it will be updated
+ * when info is requested.
+ */
+    void
+diff_invalidate(buf_T *buf)
+{
+    tabpage_T	*tp;
+    int		i;
+
+    FOR_ALL_TABPAGES(tp)
+    {
+	i = diff_buf_idx_tp(buf, tp);
+	if (i != DB_COUNT)
+	{
+	    tp->tp_diff_invalid = TRUE;
+	    if (tp == curtab)
+		diff_redraw(TRUE);
+	}
+    }
+}
+
+/*
+ * Called by mark_adjust(): update line numbers in "curbuf".
+ */
+    void
+diff_mark_adjust(
+    linenr_T	line1,
+    linenr_T	line2,
+    long	amount,
+    long	amount_after)
+{
+    int		idx;
+    tabpage_T	*tp;
+
+    // Handle all tab pages that use the current buffer in a diff.
+    FOR_ALL_TABPAGES(tp)
+    {
+	idx = diff_buf_idx_tp(curbuf, tp);
+	if (idx != DB_COUNT)
+	    diff_mark_adjust_tp(tp, idx, line1, line2, amount, amount_after);
+    }
+}
+
+/*
+ * Update line numbers in tab page "tp" for "curbuf" with index "idx".
+ * 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.
+ */
+    static void
+diff_mark_adjust_tp(
+    tabpage_T	*tp,
+    int		idx,
+    linenr_T	line1,
+    linenr_T	line2,
+    long	amount,
+    long	amount_after)
+{
+    diff_T	*dp;
+    diff_T	*dprev;
+    diff_T	*dnext;
+    int		i;
+    int		inserted, deleted;
+    int		n, off;
+    linenr_T	last;
+    linenr_T	lnum_deleted = line1;	// lnum of remaining deletion
+    int		check_unchanged;
+
+    if (diff_internal())
+    {
+	// Will update diffs before redrawing.  Set _invalid to update the
+	// diffs themselves, set _update to also update folds properly just
+	// before redrawing.
+	// Do update marks here, it is needed for :%diffput.
+	tp->tp_diff_invalid = TRUE;
+	tp->tp_diff_update = TRUE;
+    }
+
+    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 = tp->tp_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(tp, dprev, dp);
+	    if (dnext == NULL)
+		return;
+
+	    dnext->df_lnum[idx] = line1;
+	    dnext->df_count[idx] = inserted;
+	    for (i = 0; i < DB_COUNT; ++i)
+		if (tp->tp_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)
+		{
+		    off = 0;
+		    if (dp->df_lnum[idx] >= line1)
+		    {
+			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
+			    off = dp->df_lnum[idx] - lnum_deleted;
+			    n = off;
+			    dp->df_count[idx] -= line2 - dp->df_lnum[idx] + 1;
+			    check_unchanged = TRUE;
+			}
+			dp->df_lnum[idx] = line1;
+		    }
+		    else
+		    {
+			if (last < line2)
+			{
+			    // 2. delete at end 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 (tp->tp_diffbuf[i] != NULL && i != idx)
+			{
+			    if (dp->df_lnum[i] > off)
+				dp->df_lnum[i] -= off;
+			    else
+				dp->df_lnum[i] = 1;
+			    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(tp, 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 (tp->tp_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 = tp->tp_first_diff;
+    while (dp != NULL)
+    {
+	// All counts are zero, remove this entry.
+	for (i = 0; i < DB_COUNT; ++i)
+	    if (tp->tp_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)
+		tp->tp_first_diff = dnext;
+	    else
+		dprev->df_next = dnext;
+	}
+	else
+	{
+	    // Advance to next entry.
+	    dprev = dp;
+	    dp = dp->df_next;
+	}
+
+    }
+
+    if (tp == curtab)
+    {
+	// Don't redraw right away, this updates the diffs, which can be slow.
+	need_diff_redraw = TRUE;
+
+	// Need to recompute the scroll binding, may remove or add filler
+	// lines (e.g., when adding lines above w_topline). But it's slow when
+	// making many changes, postpone until redrawing.
+	diff_need_scrollbind = TRUE;
+    }
+}
+
+/*
+ * Allocate a new diff block and link it between "dprev" and "dp".
+ */
+    static diff_T *
+diff_alloc_new(tabpage_T *tp, diff_T *dprev, diff_T *dp)
+{
+    diff_T	*dnew;
+
+    dnew = ALLOC_ONE(diff_T);
+    if (dnew == NULL)
+	return NULL;
+
+    dnew->df_next = dp;
+    if (dprev == NULL)
+	tp->tp_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(tabpage_T *tp, 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 (tp->tp_diffbuf[i_org] != NULL)
+	    break;
+    if (i_org == DB_COUNT)	// safety check
+	return;
+
+    if (diff_check_sanity(tp, 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(tp->tp_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 (tp->tp_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(tp->tp_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 (tp->tp_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(tabpage_T *tp, diff_T *dp)
+{
+    int		i;
+
+    for (i = 0; i < DB_COUNT; ++i)
+	if (tp->tp_diffbuf[i] != NULL)
+	    if (dp->df_lnum[i] + dp->df_count[i] - 1
+				      > tp->tp_diffbuf[i]->b_ml.ml_line_count)
+		return FAIL;
+    return OK;
+}
+
+/*
+ * Mark all diff buffers in the current tab page for redraw.
+ */
+    void
+diff_redraw(
+    int		dofold)	    // also recompute the folds
+{
+    win_T	*wp;
+    win_T	*wp_other = NULL;
+    int		used_max_fill_other = FALSE;
+    int		used_max_fill_curwin = FALSE;
+    int		n;
+
+    need_diff_redraw = FALSE;
+    FOR_ALL_WINDOWS(wp)
+    {
+	// when closing windows or wiping buffers skip invalid window
+	if (!wp->w_p_diff || !buf_valid(wp->w_buffer))
+	    continue;
+
+	redraw_win_later(wp, UPD_SOME_VALID);
+	if (wp != curwin)
+	    wp_other = wp;
+#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.
+	n = diff_check(wp, wp->w_topline);
+	if ((wp != curwin && wp->w_topfill > 0) || n > 0)
+	{
+	    if (wp->w_topfill > n)
+		wp->w_topfill = (n < 0 ? 0 : n);
+	    else if (n > 0 && n > wp->w_topfill)
+	    {
+		wp->w_topfill = n;
+		if (wp == curwin)
+		    used_max_fill_curwin = TRUE;
+		else if (wp_other != NULL)
+		    used_max_fill_other = TRUE;
+	    }
+	    check_topfill(wp, FALSE);
+	}
+    }
+
+    if (wp_other != NULL && curwin->w_p_scb)
+    {
+	if (used_max_fill_curwin)
+	    // The current window was set to use the maximum number of filler
+	    // lines, may need to reduce them.
+	    diff_set_topline(wp_other, curwin);
+	else if (used_max_fill_other)
+	    // The other window was set to use the maximum number of filler
+	    // lines, may need to reduce them.
+	    diff_set_topline(curwin, wp_other);
+    }
+}
+
+    static void
+clear_diffin(diffin_T *din)
+{
+    if (din->din_fname == NULL)
+    {
+	vim_free(din->din_mmfile.ptr);
+	din->din_mmfile.ptr = NULL;
+    }
+    else
+	mch_remove(din->din_fname);
+}
+
+    static void
+clear_diffout(diffout_T *dout)
+{
+    if (dout->dout_fname == NULL)
+	ga_clear_strings(&dout->dout_ga);
+    else
+	mch_remove(dout->dout_fname);
+}
+
+/*
+ * Write buffer "buf" to a memory buffer.
+ * Return FAIL for failure.
+ */
+    static int
+diff_write_buffer(buf_T *buf, diffin_T *din)
+{
+    linenr_T	lnum;
+    char_u	*s;
+    long	len = 0;
+    char_u	*ptr;
+
+    // xdiff requires one big block of memory with all the text.
+    for (lnum = 1; lnum <= buf->b_ml.ml_line_count; ++lnum)
+	len += (long)STRLEN(ml_get_buf(buf, lnum, FALSE)) + 1;
+    ptr = alloc(len);
+    if (ptr == NULL)
+    {
+	// Allocating memory failed.  This can happen, because we try to read
+	// the whole buffer text into memory.  Set the failed flag, the diff
+	// will be retried with external diff.  The flag is never reset.
+	buf->b_diff_failed = TRUE;
+	if (p_verbose > 0)
+	{
+	    verbose_enter();
+	    smsg(_("Not enough memory to use internal diff for buffer \"%s\""),
+								 buf->b_fname);
+	    verbose_leave();
+	}
+	return FAIL;
+    }
+    din->din_mmfile.ptr = (char *)ptr;
+    din->din_mmfile.size = len;
+
+    len = 0;
+    for (lnum = 1; lnum <= buf->b_ml.ml_line_count; ++lnum)
+    {
+	for (s = ml_get_buf(buf, lnum, FALSE); *s != NUL; )
+	{
+	    if (diff_flags & DIFF_ICASE)
+	    {
+		int c;
+		int	orig_len;
+		char_u	cbuf[MB_MAXBYTES + 1];
+
+		if (*s == NL)
+		    c = NUL;
+		else
+		{
+		    // xdiff doesn't support ignoring case, fold-case the text.
+		    c = PTR2CHAR(s);
+		    c = MB_CASEFOLD(c);
+		}
+		orig_len = mb_ptr2len(s);
+		if (mb_char2bytes(c, cbuf) != orig_len)
+		    // TODO: handle byte length difference
+		    mch_memmove(ptr + len, s, orig_len);
+		else
+		    mch_memmove(ptr + len, cbuf, orig_len);
+
+		s += orig_len;
+		len += orig_len;
+	    }
+	    else
+	    {
+		ptr[len++] = *s == NL ? NUL : *s;
+		s++;
+	    }
+	}
+	ptr[len++] = NL;
+    }
+    return OK;
+}
+
+/*
+ * Write buffer "buf" to file or memory buffer.
+ * Return FAIL for failure.
+ */
+    static int
+diff_write(buf_T *buf, diffin_T *din)
+{
+    int		r;
+    char_u	*save_ff;
+    int		save_cmod_flags;
+
+    if (din->din_fname == NULL)
+	return diff_write_buffer(buf, din);
+
+    // Always use 'fileformat' set to "unix".
+    save_ff = buf->b_p_ff;
+    buf->b_p_ff = vim_strsave((char_u *)FF_UNIX);
+    save_cmod_flags = cmdmod.cmod_flags;
+    // Writing the buffer is an implementation detail of performing the diff,
+    // so it shouldn't update the '[ and '] marks.
+    cmdmod.cmod_flags |= CMOD_LOCKMARKS;
+    r = buf_write(buf, din->din_fname, NULL,
+			(linenr_T)1, buf->b_ml.ml_line_count,
+			NULL, FALSE, FALSE, FALSE, TRUE);
+    cmdmod.cmod_flags = save_cmod_flags;
+    free_string_option(buf->b_p_ff);
+    buf->b_p_ff = save_ff;
+    return r;
+}
+
+/*
+ * Update the diffs for all buffers involved.
+ */
+    static void
+diff_try_update(
+	diffio_T    *dio,
+	int	    idx_orig,
+	exarg_T	    *eap)	// "eap" can be NULL
+{
+    buf_T	*buf;
+    int		idx_new;
+
+    if (dio->dio_internal)
+    {
+	ga_init2(&dio->dio_diff.dout_ga, sizeof(char *), 1000);
+    }
+    else
+    {
+	// We need three temp file names.
+	dio->dio_orig.din_fname = vim_tempname('o', TRUE);
+	dio->dio_new.din_fname = vim_tempname('n', TRUE);
+	dio->dio_diff.dout_fname = vim_tempname('d', TRUE);
+	if (dio->dio_orig.din_fname == NULL
+		|| dio->dio_new.din_fname == NULL
+		|| dio->dio_diff.dout_fname == NULL)
+	    goto theend;
+    }
+
+    // Check external diff is actually working.
+    if (!dio->dio_internal && check_external_diff(dio) == FAIL)
+	goto theend;
+
+    // :diffupdate!
+    if (eap != NULL && eap->forceit)
+	for (idx_new = idx_orig; idx_new < DB_COUNT; ++idx_new)
+	{
+	    buf = curtab->tp_diffbuf[idx_new];
+	    if (buf_valid(buf))
+		buf_check_timestamp(buf, FALSE);
+	}
+
+    // Write the first buffer to a tempfile or mmfile_t.
+    buf = curtab->tp_diffbuf[idx_orig];
+    if (diff_write(buf, &dio->dio_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 = curtab->tp_diffbuf[idx_new];
+	if (buf == NULL || buf->b_ml.ml_mfp == NULL)
+	    continue; // skip buffer that isn't loaded
+
+	// Write the other buffer and diff with the first one.
+	if (diff_write(buf, &dio->dio_new) == FAIL)
+	    continue;
+	if (diff_file(dio) == FAIL)
+	    continue;
+
+	// Read the diff output and add each entry to the diff list.
+	diff_read(idx_orig, idx_new, dio);
+
+	clear_diffin(&dio->dio_new);
+	clear_diffout(&dio->dio_diff);
+    }
+    clear_diffin(&dio->dio_orig);
+
+theend:
+    vim_free(dio->dio_orig.din_fname);
+    vim_free(dio->dio_new.din_fname);
+    vim_free(dio->dio_diff.dout_fname);
+}
+
+/*
+ * Return TRUE if the options are set to use the internal diff library.
+ * Note that if the internal diff failed for one of the buffers, the external
+ * diff will be used anyway.
+ */
+    int
+diff_internal(void)
+{
+    return (diff_flags & DIFF_INTERNAL) != 0
+#ifdef FEAT_EVAL
+	&& *p_dex == NUL
+#endif
+	;
+}
+
+/*
+ * Return TRUE if the internal diff failed for one of the diff buffers.
+ */
+    static int
+diff_internal_failed(void)
+{
+    int idx;
+
+    // Only need to do something when there is another buffer.
+    for (idx = 0; idx < DB_COUNT; ++idx)
+	if (curtab->tp_diffbuf[idx] != NULL
+		&& curtab->tp_diffbuf[idx]->b_diff_failed)
+	    return TRUE;
+    return FALSE;
+}
+
+/*
+ * Completely update the diffs for the buffers involved.
+ * When using the external "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).
+ */
+    void
+ex_diffupdate(exarg_T *eap)	// "eap" can be NULL
+{
+    int		idx_orig;
+    int		idx_new;
+    diffio_T	diffio;
+    int		had_diffs = curtab->tp_first_diff != NULL;
+
+    if (diff_busy)
+    {
+	diff_need_update = TRUE;
+	return;
+    }
+
+    // Delete all diffblocks.
+    diff_clear(curtab);
+    curtab->tp_diff_invalid = FALSE;
+
+    // Use the first buffer as the original text.
+    for (idx_orig = 0; idx_orig < DB_COUNT; ++idx_orig)
+	if (curtab->tp_diffbuf[idx_orig] != NULL)
+	    break;
+    if (idx_orig == DB_COUNT)
+	goto theend;
+
+    // Only need to do something when there is another buffer.
+    for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new)
+	if (curtab->tp_diffbuf[idx_new] != NULL)
+	    break;
+    if (idx_new == DB_COUNT)
+	goto theend;
+
+    // Only use the internal method if it did not fail for one of the buffers.
+    CLEAR_FIELD(diffio);
+    diffio.dio_internal = diff_internal() && !diff_internal_failed();
+
+    diff_try_update(&diffio, idx_orig, eap);
+    if (diffio.dio_internal && diff_internal_failed())
+    {
+	// Internal diff failed, use external diff instead.
+	CLEAR_FIELD(diffio);
+	diff_try_update(&diffio, idx_orig, eap);
+    }
+
+    // force updating cursor position on screen
+    curwin->w_valid_cursor.lnum = 0;
+
+theend:
+    // A redraw is needed if there were diffs and they were cleared, or there
+    // are diffs now, which means they got updated.
+    if (had_diffs || curtab->tp_first_diff != NULL)
+    {
+	diff_redraw(TRUE);
+	apply_autocmds(EVENT_DIFFUPDATED, NULL, NULL, FALSE, curbuf);
+    }
+}
+
+/*
+ * 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.
+ */
+    static int
+check_external_diff(diffio_T *diffio)
+{
+    FILE	*fd;
+    int		ok;
+    int		io_error = FALSE;
+
+    // May try twice, first with "-a" and then without.
+    for (;;)
+    {
+	ok = FALSE;
+	fd = mch_fopen((char *)diffio->dio_orig.din_fname, "w");
+	if (fd == NULL)
+	    io_error = TRUE;
+	else
+	{
+	    if (fwrite("line1\n", (size_t)6, (size_t)1, fd) != 1)
+		io_error = TRUE;
+	    fclose(fd);
+	    fd = mch_fopen((char *)diffio->dio_new.din_fname, "w");
+	    if (fd == NULL)
+		io_error = TRUE;
+	    else
+	    {
+		if (fwrite("line2\n", (size_t)6, (size_t)1, fd) != 1)
+		    io_error = TRUE;
+		fclose(fd);
+		fd = NULL;
+		if (diff_file(diffio) == OK)
+		    fd = mch_fopen((char *)diffio->dio_diff.dout_fname, "r");
+		if (fd == NULL)
+		    io_error = TRUE;
+		else
+		{
+		    char_u	linebuf[LBUFLEN];
+
+		    for (;;)
+		    {
+			// For normal diff there must be a line that contains
+			// "1c1".  For unified diff "@@ -1 +1 @@".
+			if (vim_fgets(linebuf, LBUFLEN, fd))
+			    break;
+			if (STRNCMP(linebuf, "1c1", 3) == 0
+				|| STRNCMP(linebuf, "@@ -1 +1 @@", 11) == 0)
+			    ok = TRUE;
+		    }
+		    fclose(fd);
+		}
+		mch_remove(diffio->dio_diff.dout_fname);
+		mch_remove(diffio->dio_new.din_fname);
+	    }
+	    mch_remove(diffio->dio_orig.din_fname);
+	}
+
+#ifdef FEAT_EVAL
+	// When using 'diffexpr' break here.
+	if (*p_dex != NUL)
+	    break;
+#endif
+
+#if defined(MSWIN)
+	// 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)
+    {
+	if (io_error)
+	    emsg(_(e_cannot_read_or_write_temp_files));
+	emsg(_(e_cannot_create_diffs));
+	diff_a_works = MAYBE;
+#if defined(MSWIN)
+	diff_bin_works = MAYBE;
+#endif
+	return FAIL;
+    }
+    return OK;
+}
+
+/*
+ * Invoke the xdiff function.
+ */
+    static int
+diff_file_internal(diffio_T *diffio)
+{
+    xpparam_t	    param;
+    xdemitconf_t    emit_cfg;
+    xdemitcb_t	    emit_cb;
+
+    CLEAR_FIELD(param);
+    CLEAR_FIELD(emit_cfg);
+    CLEAR_FIELD(emit_cb);
+
+    param.flags = diff_algorithm;
+
+    if (diff_flags & DIFF_IWHITE)
+	param.flags |= XDF_IGNORE_WHITESPACE_CHANGE;
+    if (diff_flags & DIFF_IWHITEALL)
+	param.flags |= XDF_IGNORE_WHITESPACE;
+    if (diff_flags & DIFF_IWHITEEOL)
+	param.flags |= XDF_IGNORE_WHITESPACE_AT_EOL;
+    if (diff_flags & DIFF_IBLANK)
+	param.flags |= XDF_IGNORE_BLANK_LINES;
+
+    emit_cfg.ctxlen = 0; // don't need any diff_context here
+    emit_cb.priv = &diffio->dio_diff;
+    emit_cfg.hunk_func = xdiff_out;
+    if (xdl_diff(&diffio->dio_orig.din_mmfile,
+		&diffio->dio_new.din_mmfile,
+		&param, &emit_cfg, &emit_cb) < 0)
+    {
+	emsg(_(e_problem_creating_internal_diff));
+	return FAIL;
+    }
+    return OK;
+}
+
+/*
+ * Make a diff between files "tmp_orig" and "tmp_new", results in "tmp_diff".
+ * return OK or FAIL;
+ */
+    static int
+diff_file(diffio_T *dio)
+{
+    char_u	*cmd;
+    size_t	len;
+    char_u	*tmp_orig = dio->dio_orig.din_fname;
+    char_u	*tmp_new = dio->dio_new.din_fname;
+    char_u	*tmp_diff = dio->dio_diff.dout_fname;
+
+#ifdef FEAT_EVAL
+    if (*p_dex != NUL)
+    {
+	// Use 'diffexpr' to generate the diff file.
+	eval_diff(tmp_orig, tmp_new, tmp_diff);
+	return OK;
+    }
+    else
+#endif
+    // Use xdiff for generating the diff.
+    if (dio->dio_internal)
+	return diff_file_internal(dio);
+
+    len = STRLEN(tmp_orig) + STRLEN(tmp_new)
+				+ STRLEN(tmp_diff) + STRLEN(p_srr) + 27;
+    cmd = alloc(len);
+    if (cmd == NULL)
+	return FAIL;
+
+    // We don't want $DIFF_OPTIONS to get in the way.
+    if (getenv("DIFF_OPTIONS"))
+	vim_setenv((char_u *)"DIFF_OPTIONS", (char_u *)"");
+
+    // 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.
+    vim_snprintf((char *)cmd, len, "diff %s%s%s%s%s%s%s%s %s",
+	    diff_a_works == FALSE ? "" : "-a ",
+#if defined(MSWIN)
+	    diff_bin_works == TRUE ? "--binary " : "",
+#else
+	    "",
+#endif
+	    (diff_flags & DIFF_IWHITE) ? "-b " : "",
+	    (diff_flags & DIFF_IWHITEALL) ? "-w " : "",
+	    (diff_flags & DIFF_IWHITEEOL) ? "-Z " : "",
+	    (diff_flags & DIFF_IBLANK) ? "-B " : "",
+	    (diff_flags & DIFF_ICASE) ? "-i " : "",
+	    tmp_orig, tmp_new);
+    append_redir(cmd, (int)len, p_srr, tmp_diff);
+    block_autocmds();	// avoid ShellCmdPost stuff
+    (void)call_shell(cmd, SHELL_FILTER|SHELL_SILENT|SHELL_DOOUT);
+    unblock_autocmds();
+    vim_free(cmd);
+    return OK;
+}
+
+/*
+ * 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(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;
+    size_t	buflen;
+    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		save_cmod_flags = cmdmod.cmod_flags;
+#endif
+    stat_T	st;
+    char_u	*esc_name = NULL;
+
+#ifdef FEAT_BROWSE
+    if (cmdmod.cmod_flags & CMOD_BROWSE)
+    {
+	browseFile = do_browse(0, (char_u *)_("Patch file"),
+			 eap->arg, NULL, NULL,
+			 (char_u *)_(BROWSE_FILTER_ALL_FILES), NULL);
+	if (browseFile == NULL)
+	    return;		// operation cancelled
+	eap->arg = browseFile;
+	cmdmod.cmod_flags &= ~CMOD_BROWSE; // don't let do_ecmd() browse again
+    }
+#endif
+
+    // We need two temp file names.
+    tmp_orig = vim_tempname('o', FALSE);
+    tmp_new = vim_tempname('n', FALSE);
+    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
+    esc_name = vim_strsave_shellescape(
+# ifdef UNIX
+		    fullname != NULL ? fullname :
+# endif
+		    eap->arg, TRUE, TRUE);
+    if (esc_name == NULL)
+	goto theend;
+    buflen = STRLEN(tmp_orig) + STRLEN(esc_name) + STRLEN(tmp_new) + 16;
+    buf = alloc(buflen);
+    if (buf == NULL)
+	goto theend;
+
+#ifdef UNIX
+    // Temporarily 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)
+	    vim_ignored = mch_chdir((char *)vim_tempdir);
+	else
+# endif
+	    vim_ignored = 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.
+	vim_snprintf((char *)buf, buflen, "patch -o %s %s < %s",
+						  tmp_new, tmp_orig, esc_name);
+	block_autocmds();	// Avoid ShellCmdPost stuff
+	(void)call_shell(buf, SHELL_FILTER | SHELL_COOKED);
+	unblock_autocmds();
+    }
+
+#ifdef UNIX
+    if (dirbuf[0] != NUL)
+    {
+	if (mch_chdir((char *)dirbuf) != 0)
+	    emsg(_(e_cannot_go_back_to_previous_directory));
+	shorten_fnames(TRUE);
+    }
+#endif
+
+    // patch probably has written over the screen
+    redraw_later(UPD_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);
+
+    // Only continue if the output file was created.
+    if (mch_stat((char *)tmp_new, &st) < 0 || st.st_size == 0)
+	emsg(_(e_cannot_read_patch_output));
+    else
+    {
+	if (curbuf->b_fname != NULL)
+	{
+	    newname = vim_strnsave(curbuf->b_fname,
+						  STRLEN(curbuf->b_fname) + 4);
+	    if (newname != NULL)
+		STRCAT(newname, ".new");
+	}
+
+#ifdef FEAT_GUI
+	need_mouse_correct = TRUE;
+#endif
+	// don't use a new tab page, each tab page has its own diffs
+	cmdmod.cmod_tab = 0;
+
+	if (win_split(0, (diff_flags & DIFF_VERTICAL) ? WSP_VERT : 0) != FAIL)
+	{
+	    // Pretend it was a ":split fname" command
+	    eap->cmdidx = CMD_split;
+	    eap->arg = tmp_new;
+	    do_exedit(eap, old_curwin);
+
+	    // check that split worked and editing tmp_new
+	    if (curwin != old_curwin && win_valid(old_curwin))
+	    {
+		// 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);
+
+		    // Do filetype detection with the new name.
+		    if (au_has_group((char_u *)"filetypedetect"))
+			do_cmdline_cmd((char_u *)":doau filetypedetect BufRead");
+		}
+	    }
+	}
+    }
+
+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
+    vim_free(esc_name);
+#ifdef FEAT_BROWSE
+    vim_free(browseFile);
+    cmdmod.cmod_flags = save_cmod_flags;
+#endif
+}
+
+/*
+ * Split the window and edit another file, setting options to show the diffs.
+ */
+    void
+ex_diffsplit(exarg_T *eap)
+{
+    win_T	*old_curwin = curwin;
+    bufref_T	old_curbuf;
+
+    set_bufref(&old_curbuf, curbuf);
+#ifdef FEAT_GUI
+    need_mouse_correct = TRUE;
+#endif
+    // Need to compute w_fraction when no redraw happened yet.
+    validate_cursor();
+    set_fraction(curwin);
+
+    // don't use a new tab page, each tab page has its own diffs
+    cmdmod.cmod_tab = 0;
+
+    if (win_split(0, (diff_flags & DIFF_VERTICAL) ? WSP_VERT : 0) == FAIL)
+	return;
+
+    // Pretend it was a ":split fname" command
+    eap->cmdidx = CMD_split;
+    curwin->w_p_diff = TRUE;
+    do_exedit(eap, old_curwin);
+
+    if (curwin == old_curwin)		// split didn't work
+	return;
+
+    // Set 'diff', 'scrollbind' on and 'wrap' off.
+    diff_win_options(curwin, TRUE);
+    if (win_valid(old_curwin))
+    {
+	diff_win_options(old_curwin, TRUE);
+
+	if (bufref_valid(&old_curbuf))
+	    // Move the cursor position to that of the old window.
+	    curwin->w_cursor.lnum = diff_get_corresponding_line(
+		    old_curbuf.br_buf, old_curwin->w_cursor.lnum);
+    }
+    // Now that lines are folded scroll to show the cursor at the same
+    // relative position.
+    scroll_to_fraction(curwin, curwin->w_height);
+}
+
+/*
+ * Set options to show diffs for the current window.
+ */
+    void
+ex_diffthis(exarg_T *eap UNUSED)
+{
+    // Set 'diff', 'scrollbind' on and 'wrap' off.
+    diff_win_options(curwin, TRUE);
+}
+
+    static void
+set_diff_option(win_T *wp, int value)
+{
+    win_T *old_curwin = curwin;
+
+    curwin = wp;
+    curbuf = curwin->w_buffer;
+    ++curbuf_lock;
+    set_option_value_give_err((char_u *)"diff", (long)value, NULL, OPT_LOCAL);
+    --curbuf_lock;
+    curwin = old_curwin;
+    curbuf = curwin->w_buffer;
+}
+
+/*
+ * Set options in window "wp" for diff mode.
+ */
+    void
+diff_win_options(
+    win_T	*wp,
+    int		addbuf)		// Add buffer to diff.
+{
+# ifdef FEAT_FOLDING
+    win_T *old_curwin = curwin;
+
+    // close the manually opened folds
+    curwin = wp;
+    newFoldLevel();
+    curwin = old_curwin;
+# endif
+
+    // Use 'scrollbind' and 'cursorbind' when available
+    if (!wp->w_p_diff)
+	wp->w_p_scb_save = wp->w_p_scb;
+    wp->w_p_scb = TRUE;
+    if (!wp->w_p_diff)
+	wp->w_p_crb_save = wp->w_p_crb;
+    wp->w_p_crb = TRUE;
+    if (!(diff_flags & DIFF_FOLLOWWRAP))
+    {
+	if (!wp->w_p_diff)
+	    wp->w_p_wrap_save = wp->w_p_wrap;
+	wp->w_p_wrap = FALSE;
+    }
+# ifdef FEAT_FOLDING
+    if (!wp->w_p_diff)
+    {
+	if (wp->w_p_diff_saved)
+	    free_string_option(wp->w_p_fdm_save);
+	wp->w_p_fdm_save = vim_strsave(wp->w_p_fdm);
+    }
+    set_string_option_direct_in_win(wp, (char_u *)"fdm", -1, (char_u *)"diff",
+						       OPT_LOCAL|OPT_FREE, 0);
+    if (!wp->w_p_diff)
+    {
+	wp->w_p_fdc_save = wp->w_p_fdc;
+	wp->w_p_fen_save = wp->w_p_fen;
+	wp->w_p_fdl_save = wp->w_p_fdl;
+    }
+    wp->w_p_fdc = diff_foldcolumn;
+    wp->w_p_fen = TRUE;
+    wp->w_p_fdl = 0;
+    foldUpdateAll(wp);
+    // make sure topline is not halfway a fold
+    changed_window_setting_win(wp);
+# endif
+    if (vim_strchr(p_sbo, 'h') == NULL)
+	do_cmdline_cmd((char_u *)"set sbo+=hor");
+    // Save the current values, to be restored in ex_diffoff().
+    wp->w_p_diff_saved = TRUE;
+
+    set_diff_option(wp, TRUE);
+
+    if (addbuf)
+	diff_buf_add(wp->w_buffer);
+    redraw_win_later(wp, UPD_NOT_VALID);
+}
+
+/*
+ * Set options not to show diffs.  For the current window or all windows.
+ * Only in the current tab page.
+ */
+    void
+ex_diffoff(exarg_T *eap)
+{
+    win_T	*wp;
+    int		diffwin = FALSE;
+
+    FOR_ALL_WINDOWS(wp)
+    {
+	if (eap->forceit ? wp->w_p_diff : wp == curwin)
+	{
+	    // Set 'diff' off. If option values were saved in
+	    // diff_win_options(), restore the ones whose settings seem to have
+	    // been left over from diff mode.
+	    set_diff_option(wp, FALSE);
+
+	    if (wp->w_p_diff_saved)
+	    {
+
+		if (wp->w_p_scb)
+		    wp->w_p_scb = wp->w_p_scb_save;
+		if (wp->w_p_crb)
+		    wp->w_p_crb = wp->w_p_crb_save;
+		if (!(diff_flags & DIFF_FOLLOWWRAP))
+		{
+		    if (!wp->w_p_wrap)
+			wp->w_p_wrap = wp->w_p_wrap_save;
+		}
+#ifdef FEAT_FOLDING
+		free_string_option(wp->w_p_fdm);
+		wp->w_p_fdm = vim_strsave(
+		    *wp->w_p_fdm_save ? wp->w_p_fdm_save : (char_u*)"manual");
+
+		if (wp->w_p_fdc == diff_foldcolumn)
+		    wp->w_p_fdc = wp->w_p_fdc_save;
+		if (wp->w_p_fdl == 0)
+		    wp->w_p_fdl = wp->w_p_fdl_save;
+
+		// Only restore 'foldenable' when 'foldmethod' is not
+		// "manual", otherwise we continue to show the diff folds.
+		if (wp->w_p_fen)
+		    wp->w_p_fen = foldmethodIsManual(wp) ? FALSE
+							 : wp->w_p_fen_save;
+
+		foldUpdateAll(wp);
+#endif
+	    }
+	    // remove filler lines
+	    wp->w_topfill = 0;
+
+	    // make sure topline is not halfway a fold and cursor is
+	    // invalidated
+	    changed_window_setting_win(wp);
+
+	    // Note: 'sbo' is not restored, it's a global option.
+	    diff_buf_adjust(wp);
+	}
+	diffwin |= wp->w_p_diff;
+    }
+
+    // Also remove hidden buffers from the list.
+    if (eap->forceit)
+	diff_buf_clear();
+
+    if (!diffwin)
+    {
+	diff_need_update = FALSE;
+	curtab->tp_diff_invalid = FALSE;
+	curtab->tp_diff_update = FALSE;
+	diff_clear(curtab);
+    }
+
+    // Remove "hor" from 'scrollopt' if there are no diff windows left.
+    if (!diffwin && vim_strchr(p_sbo, 'h') != NULL)
+	do_cmdline_cmd((char_u *)"set sbo-=hor");
+}
+
+/*
+ * Read the diff output and add each entry to the diff list.
+ */
+    static void
+diff_read(
+    int		idx_orig,	// idx of original file
+    int		idx_new,	// idx of new file
+    diffio_T   *dio)		// diff output
+{
+    FILE	*fd = NULL;
+    int		line_idx = 0;
+    diff_T	*dprev = NULL;
+    diff_T	*dp = curtab->tp_first_diff;
+    diff_T	*dn, *dpl;
+    diffout_T   *dout = &dio->dio_diff;
+    char_u	linebuf[LBUFLEN];   // only need to hold the diff line
+    char_u	*line;
+    long	off;
+    int		i;
+    int		notset = TRUE;	    // block "*dp" not set yet
+    diffhunk_T	*hunk = NULL;	    // init to avoid gcc warning
+
+    enum {
+	DIFF_ED,
+	DIFF_UNIFIED,
+	DIFF_NONE
+    } diffstyle = DIFF_NONE;
+
+    if (dout->dout_fname == NULL)
+    {
+	diffstyle = DIFF_UNIFIED;
+    }
+    else
+    {
+	fd = mch_fopen((char *)dout->dout_fname, "r");
+	if (fd == NULL)
+	{
+	    emsg(_(e_cannot_read_diff_output));
+	    return;
+	}
+    }
+
+    if (!dio->dio_internal)
+    {
+	hunk = ALLOC_ONE(diffhunk_T);
+	if (hunk == NULL)
+	{
+	    if (fd != NULL)
+		fclose(fd);
+	    return;
+	}
+    }
+
+    for (;;)
+    {
+	if (dio->dio_internal)
+	{
+	    if (line_idx >= dout->dout_ga.ga_len)
+		break;      // did last line
+	    hunk = ((diffhunk_T **)dout->dout_ga.ga_data)[line_idx++];
+	}
+	else
+	{
+	    if (fd == NULL)
+	    {
+		if (line_idx >= dout->dout_ga.ga_len)
+		    break;	    // did last line
+		line = ((char_u **)dout->dout_ga.ga_data)[line_idx++];
+	    }
+	    else
+	    {
+		if (vim_fgets(linebuf, LBUFLEN, fd))
+		    break;		// end of file
+		line = linebuf;
+	    }
+
+	    if (diffstyle == DIFF_NONE)
+	    {
+		// Determine diff style.
+		// ed like diff looks like this:
+		// {first}[,{last}]c{first}[,{last}]
+		// {first}a{first}[,{last}]
+		// {first}[,{last}]d{first}
+		//
+		// unified diff looks like this:
+		// --- file1       2018-03-20 13:23:35.783153140 +0100
+		// +++ file2       2018-03-20 13:23:41.183156066 +0100
+		// @@ -1,3 +1,5 @@
+		if (isdigit(*line))
+		    diffstyle = DIFF_ED;
+		else if ((STRNCMP(line, "@@ ", 3) == 0))
+		    diffstyle = DIFF_UNIFIED;
+		else if ((STRNCMP(line, "--- ", 4) == 0)
+			&& (vim_fgets(linebuf, LBUFLEN, fd) == 0)
+			&& (STRNCMP(line, "+++ ", 4) == 0)
+			&& (vim_fgets(linebuf, LBUFLEN, fd) == 0)
+			&& (STRNCMP(line, "@@ ", 3) == 0))
+		    diffstyle = DIFF_UNIFIED;
+		else
+		    // Format not recognized yet, skip over this line.  Cygwin
+		    // diff may put a warning at the start of the file.
+		    continue;
+	    }
+
+	    if (diffstyle == DIFF_ED)
+	    {
+		if (!isdigit(*line))
+		    continue;	// not the start of a diff block
+		if (parse_diff_ed(line, hunk) == FAIL)
+		    continue;
+	    }
+	    else if (diffstyle == DIFF_UNIFIED)
+	    {
+		if (STRNCMP(line, "@@ ", 3)  != 0)
+		    continue;	// not the start of a diff block
+		if (parse_diff_unified(line, hunk) == FAIL)
+		    continue;
+	    }
+	    else
+	    {
+		emsg(_(e_invalid_diff_format));
+		break;
+	    }
+	}
+
+	// Go over blocks before the change, for which orig and new are equal.
+	// Copy blocks from orig to new.
+	while (dp != NULL
+		&& hunk->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
+		&& hunk->lnum_orig <= dp->df_lnum[idx_orig]
+						       + dp->df_count[idx_orig]
+		&& hunk->lnum_orig + hunk->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 (hunk->lnum_orig + hunk->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] - hunk->lnum_orig;
+	    if (off > 0)
+	    {
+		for (i = idx_orig; i < idx_new; ++i)
+		    if (curtab->tp_diffbuf[i] != NULL)
+			dp->df_lnum[i] -= off;
+		dp->df_lnum[idx_new] = hunk->lnum_new;
+		dp->df_count[idx_new] = hunk->count_new;
+	    }
+	    else if (notset)
+	    {
+		// new block inside existing one, adjust new block
+		dp->df_lnum[idx_new] = hunk->lnum_new + off;
+		dp->df_count[idx_new] = hunk->count_new - off;
+	    }
+	    else
+		// second overlap of new block with existing block
+		dp->df_count[idx_new] += hunk->count_new - hunk->count_orig
+		    + dpl->df_lnum[idx_orig] + dpl->df_count[idx_orig]
+		    - (dp->df_lnum[idx_orig] + dp->df_count[idx_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 = (hunk->lnum_orig + hunk->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; ++i)
+		if (curtab->tp_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(curtab, dprev, dp);
+	    if (dp == NULL)
+		goto done;
+
+	    dp->df_lnum[idx_orig] = hunk->lnum_orig;
+	    dp->df_count[idx_orig] = hunk->count_orig;
+	    dp->df_lnum[idx_new] = hunk->lnum_new;
+	    dp->df_count[idx_new] = hunk->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 (curtab->tp_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;
+    }
+
+done:
+    if (!dio->dio_internal)
+	vim_free(hunk);
+
+    if (fd != NULL)
+	fclose(fd);
+}
+
+/*
+ * Copy an entry at "dp" from "idx_orig" to "idx_new".
+ */
+    static void
+diff_copy_entry(
+    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 for tab page "tp".
+ */
+    void
+diff_clear(tabpage_T *tp)
+{
+    diff_T	*p, *next_p;
+
+    for (p = tp->tp_first_diff; p != NULL; p = next_p)
+    {
+	next_p = p->df_next;
+	vim_free(p);
+    }
+    tp->tp_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(win_T *wp, linenr_T lnum)
+{
+    int		idx;		// index in tp_diffbuf[] for this buffer
+    diff_T	*dp;
+    int		maxcount;
+    int		i;
+    buf_T	*buf = wp->w_buffer;
+    int		cmp;
+
+    if (curtab->tp_diff_invalid)
+	ex_diffupdate(NULL);		// update after a big change
+
+    if (curtab->tp_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_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
+	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 && curtab->tp_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 && curtab->tp_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 (curtab->tp_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(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(curtab, dp) == FAIL)
+	return FALSE;
+    for (i = 0; i < dp->df_count[idx1]; ++i)
+    {
+	line = vim_strsave(ml_get_buf(curtab->tp_diffbuf[idx1],
+					       dp->df_lnum[idx1] + i, FALSE));
+	if (line == NULL)
+	    return FALSE;
+	cmp = diff_cmp(line, ml_get_buf(curtab->tp_diffbuf[idx2],
+					       dp->df_lnum[idx2] + i, FALSE));
+	vim_free(line);
+	if (cmp != 0)
+	    return FALSE;
+    }
+    return TRUE;
+}
+
+/*
+ * Compare the characters at "p1" and "p2".  If they are equal (possibly
+ * ignoring case) return TRUE and set "len" to the number of bytes.
+ */
+    static int
+diff_equal_char(char_u *p1, char_u *p2, int *len)
+{
+    int l  = (*mb_ptr2len)(p1);
+
+    if (l != (*mb_ptr2len)(p2))
+	return FALSE;
+    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))))
+	    return FALSE;
+	*len = l;
+    }
+    else
+    {
+	if ((*p1 != *p2)
+		&& (!(diff_flags & DIFF_ICASE)
+		    || TOLOWER_LOC(*p1) != TOLOWER_LOC(*p2)))
+	    return FALSE;
+	*len = 1;
+    }
+    return TRUE;
+}
+
+/*
+ * Compare strings "s1" and "s2" according to 'diffopt'.
+ * Return non-zero when they are different.
+ */
+    static int
+diff_cmp(char_u *s1, char_u *s2)
+{
+    char_u	*p1, *p2;
+    int		l;
+
+    if ((diff_flags & DIFF_IBLANK)
+	    && (*skipwhite(s1) == NUL || *skipwhite(s2) == NUL))
+	return 0;
+
+    if ((diff_flags & (DIFF_ICASE | ALL_WHITE_DIFF)) == 0)
+	return STRCMP(s1, s2);
+    if ((diff_flags & DIFF_ICASE) && !(diff_flags & ALL_WHITE_DIFF))
+	return MB_STRICMP(s1, s2);
+
+    p1 = s1;
+    p2 = s2;
+
+    // Ignore white space changes and possibly ignore case.
+    while (*p1 != NUL && *p2 != NUL)
+    {
+	if (((diff_flags & DIFF_IWHITE)
+		    && VIM_ISWHITE(*p1) && VIM_ISWHITE(*p2))
+		|| ((diff_flags & DIFF_IWHITEALL)
+		    && (VIM_ISWHITE(*p1) || VIM_ISWHITE(*p2))))
+	{
+	    p1 = skipwhite(p1);
+	    p2 = skipwhite(p2);
+	}
+	else
+	{
+	    if (!diff_equal_char(p1, p2, &l))
+		break;
+	    p1 += l;
+	    p2 += l;
+	}
+    }
+
+    // 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(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(win_T *fromwin, win_T *towin)
+{
+    buf_T	*frombuf = fromwin->w_buffer;
+    linenr_T	lnum = fromwin->w_topline;
+    int		fromidx;
+    int		toidx;
+    diff_T	*dp;
+    int		max_count;
+    int		i;
+
+    fromidx = diff_buf_idx(frombuf);
+    if (fromidx == DB_COUNT)
+	return;		// safety check
+
+    if (curtab->tp_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_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
+	if (lnum <= dp->df_lnum[fromidx] + dp->df_count[fromidx])
+	    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
+				       - (frombuf->b_ml.ml_line_count - lnum);
+    }
+    else
+    {
+	// Find index for "towin".
+	toidx = diff_buf_idx(towin->w_buffer);
+	if (toidx == DB_COUNT)
+	    return;		// safety check
+
+	towin->w_topline = lnum + (dp->df_lnum[toidx] - dp->df_lnum[fromidx]);
+	if (lnum >= dp->df_lnum[fromidx])
+	{
+	    // Inside a change: compute filler lines. With three or more
+	    // buffers we need to know the largest count.
+	    max_count = 0;
+	    for (i = 0; i < DB_COUNT; ++i)
+		if (curtab->tp_diffbuf[i] != NULL
+					       && max_count < dp->df_count[i])
+		    max_count = dp->df_count[i];
+
+	    if (dp->df_count[toidx] == dp->df_count[fromidx])
+	    {
+		// same number of lines: use same filler count
+		towin->w_topfill = fromwin->w_topfill;
+	    }
+	    else if (dp->df_count[toidx] > dp->df_count[fromidx])
+	    {
+		if (lnum == dp->df_lnum[fromidx] + dp->df_count[fromidx])
+		{
+		    // more lines in towin and fromwin doesn't show diff
+		    // lines, only filler lines
+		    if (max_count - fromwin->w_topfill >= dp->df_count[toidx])
+		    {
+			// towin also only shows filler lines
+			towin->w_topline = dp->df_lnum[toidx]
+						       + dp->df_count[toidx];
+			towin->w_topfill = fromwin->w_topfill;
+		    }
+		    else
+			// towin still has some diff lines to show
+			towin->w_topline = dp->df_lnum[toidx]
+					     + max_count - fromwin->w_topfill;
+		}
+	    }
+	    else if (towin->w_topline >= dp->df_lnum[toidx]
+							+ dp->df_count[toidx])
+	    {
+		// less lines in towin and no diff lines to show: compute
+		// filler lines
+		towin->w_topline = dp->df_lnum[toidx] + dp->df_count[toidx];
+		if (diff_flags & DIFF_FILLER)
+		{
+		    if (lnum == dp->df_lnum[fromidx] + dp->df_count[fromidx])
+			// fromwin is also out of diff lines
+			towin->w_topfill = fromwin->w_topfill;
+		    else
+			// fromwin has some diff lines
+			towin->w_topfill = dp->df_lnum[fromidx]
+							   + max_count - lnum;
+		}
+	    }
+	}
+    }
+
+    // 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(void)
+{
+    char_u	*p;
+    int		diff_context_new = 6;
+    int		diff_flags_new = 0;
+    int		diff_foldcolumn_new = 2;
+    long	diff_algorithm_new = 0;
+    long	diff_indent_heuristic = 0;
+    tabpage_T	*tp;
+
+    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, "iblank", 6) == 0)
+	{
+	    p += 6;
+	    diff_flags_new |= DIFF_IBLANK;
+	}
+	else if (STRNCMP(p, "icase", 5) == 0)
+	{
+	    p += 5;
+	    diff_flags_new |= DIFF_ICASE;
+	}
+	else if (STRNCMP(p, "iwhiteall", 9) == 0)
+	{
+	    p += 9;
+	    diff_flags_new |= DIFF_IWHITEALL;
+	}
+	else if (STRNCMP(p, "iwhiteeol", 9) == 0)
+	{
+	    p += 9;
+	    diff_flags_new |= DIFF_IWHITEEOL;
+	}
+	else if (STRNCMP(p, "iwhite", 6) == 0)
+	{
+	    p += 6;
+	    diff_flags_new |= DIFF_IWHITE;
+	}
+	else if (STRNCMP(p, "horizontal", 10) == 0)
+	{
+	    p += 10;
+	    diff_flags_new |= DIFF_HORIZONTAL;
+	}
+	else if (STRNCMP(p, "vertical", 8) == 0)
+	{
+	    p += 8;
+	    diff_flags_new |= DIFF_VERTICAL;
+	}
+	else if (STRNCMP(p, "foldcolumn:", 11) == 0 && VIM_ISDIGIT(p[11]))
+	{
+	    p += 11;
+	    diff_foldcolumn_new = getdigits(&p);
+	}
+	else if (STRNCMP(p, "hiddenoff", 9) == 0)
+	{
+	    p += 9;
+	    diff_flags_new |= DIFF_HIDDEN_OFF;
+	}
+	else if (STRNCMP(p, "closeoff", 8) == 0)
+	{
+	    p += 8;
+	    diff_flags_new |= DIFF_CLOSE_OFF;
+	}
+	else if (STRNCMP(p, "followwrap", 10) == 0)
+	{
+	    p += 10;
+	    diff_flags_new |= DIFF_FOLLOWWRAP;
+	}
+	else if (STRNCMP(p, "indent-heuristic", 16) == 0)
+	{
+	    p += 16;
+	    diff_indent_heuristic = XDF_INDENT_HEURISTIC;
+	}
+	else if (STRNCMP(p, "internal", 8) == 0)
+	{
+	    p += 8;
+	    diff_flags_new |= DIFF_INTERNAL;
+	}
+	else if (STRNCMP(p, "algorithm:", 10) == 0)
+	{
+	    p += 10;
+	    if (STRNCMP(p, "myers", 5) == 0)
+	    {
+		p += 5;
+		diff_algorithm_new = 0;
+	    }
+	    else if (STRNCMP(p, "minimal", 7) == 0)
+	    {
+		p += 7;
+		diff_algorithm_new = XDF_NEED_MINIMAL;
+	    }
+	    else if (STRNCMP(p, "patience", 8) == 0)
+	    {
+		p += 8;
+		diff_algorithm_new = XDF_PATIENCE_DIFF;
+	    }
+	    else if (STRNCMP(p, "histogram", 9) == 0)
+	    {
+		p += 9;
+		diff_algorithm_new = XDF_HISTOGRAM_DIFF;
+	    }
+	    else
+		return FAIL;
+	}
+
+	if (*p != ',' && *p != NUL)
+	    return FAIL;
+	if (*p == ',')
+	    ++p;
+    }
+
+    diff_algorithm_new |= diff_indent_heuristic;
+
+    // Can't have both "horizontal" and "vertical".
+    if ((diff_flags_new & DIFF_HORIZONTAL) && (diff_flags_new & DIFF_VERTICAL))
+	return FAIL;
+
+    // If flags were added or removed, or the algorithm was changed, need to
+    // update the diff.
+    if (diff_flags != diff_flags_new || diff_algorithm != diff_algorithm_new)
+	FOR_ALL_TABPAGES(tp)
+	    tp->tp_diff_invalid = TRUE;
+
+    diff_flags = diff_flags_new;
+    diff_context = diff_context_new == 0 ? 1 : diff_context_new;
+    diff_foldcolumn = diff_foldcolumn_new;
+    diff_algorithm = diff_algorithm_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;
+}
+
+/*
+ * Return TRUE if 'diffopt' contains "horizontal".
+ */
+    int
+diffopt_horizontal(void)
+{
+    return (diff_flags & DIFF_HORIZONTAL) != 0;
+}
+
+/*
+ * Return TRUE if 'diffopt' contains "hiddenoff".
+ */
+    int
+diffopt_hiddenoff(void)
+{
+    return (diff_flags & DIFF_HIDDEN_OFF) != 0;
+}
+
+/*
+ * Return TRUE if 'diffopt' contains "closeoff".
+ */
+    int
+diffopt_closeoff(void)
+{
+    return (diff_flags & DIFF_CLOSE_OFF) != 0;
+}
+
+/*
+ * Find the difference within a changed line.
+ * Returns TRUE if the line was added, no other buffer has it.
+ */
+    int
+diff_find_change(
+    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_org, si_new;
+    int		ei_org, ei_new;
+    diff_T	*dp;
+    int		idx;
+    int		off;
+    int		added = TRUE;
+    char_u	*p1, *p2;
+    int		l;
+
+    // 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
+    {
+	vim_free(line_org);
+	return FALSE;
+    }
+
+    // search for a change that includes "lnum" in the list of diffblocks.
+    FOR_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
+	if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
+	    break;
+    if (dp == NULL || diff_check_sanity(curtab, dp) == FAIL)
+    {
+	vim_free(line_org);
+	return FALSE;
+    }
+
+    off = lnum - dp->df_lnum[idx];
+
+    for (i = 0; i < DB_COUNT; ++i)
+	if (curtab->tp_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(curtab->tp_diffbuf[i],
+						 dp->df_lnum[i] + off, FALSE);
+
+	    // Search for start of difference
+	    si_org = si_new = 0;
+	    while (line_org[si_org] != NUL)
+	    {
+		if (((diff_flags & DIFF_IWHITE)
+			    && VIM_ISWHITE(line_org[si_org])
+					      && VIM_ISWHITE(line_new[si_new]))
+			|| ((diff_flags & DIFF_IWHITEALL)
+			    && (VIM_ISWHITE(line_org[si_org])
+					    || VIM_ISWHITE(line_new[si_new]))))
+		{
+		    si_org = (int)(skipwhite(line_org + si_org) - line_org);
+		    si_new = (int)(skipwhite(line_new + si_new) - line_new);
+		}
+		else
+		{
+		    if (!diff_equal_char(line_org + si_org, line_new + si_new,
+									   &l))
+			break;
+		    si_org += l;
+		    si_new += l;
+		}
+	    }
+	    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_org -= (*mb_head_off)(line_org, line_org + si_org);
+		si_new -= (*mb_head_off)(line_new, line_new + si_new);
+	    }
+	    if (*startp > si_org)
+		*startp = si_org;
+
+	    // Search for end of difference, if any.
+	    if (line_org[si_org] != NUL || line_new[si_new] != NUL)
+	    {
+		ei_org = (int)STRLEN(line_org);
+		ei_new = (int)STRLEN(line_new);
+		while (ei_org >= *startp && ei_new >= si_new
+						&& ei_org >= 0 && ei_new >= 0)
+		{
+		    if (((diff_flags & DIFF_IWHITE)
+				&& VIM_ISWHITE(line_org[ei_org])
+					      && VIM_ISWHITE(line_new[ei_new]))
+			    || ((diff_flags & DIFF_IWHITEALL)
+				&& (VIM_ISWHITE(line_org[ei_org])
+					    || VIM_ISWHITE(line_new[ei_new]))))
+		    {
+			while (ei_org >= *startp
+					     && VIM_ISWHITE(line_org[ei_org]))
+			    --ei_org;
+			while (ei_new >= si_new
+					     && VIM_ISWHITE(line_new[ei_new]))
+			    --ei_new;
+		    }
+		    else
+		    {
+			p1 = line_org + ei_org;
+			p2 = line_new + ei_new;
+			p1 -= (*mb_head_off)(line_org, p1);
+			p2 -= (*mb_head_off)(line_new, p2);
+			if (!diff_equal_char(p1, p2, &l))
+			    break;
+			ei_org -= l;
+			ei_new -= l;
+		    }
+		}
+		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(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 (curtab->tp_diffbuf[i] == wp->w_buffer)
+	    idx = i;
+	else if (curtab->tp_diffbuf[i] != NULL)
+	    other = TRUE;
+    }
+
+    // return here if there are no diffs in the window
+    if (idx == -1 || !other)
+	return FALSE;
+
+    if (curtab->tp_diff_invalid)
+	ex_diffupdate(NULL);		// update after a big change
+
+    // Return if there are no diff blocks.  All lines will be folded.
+    if (curtab->tp_first_diff == NULL)
+	return TRUE;
+
+    FOR_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
+    {
+	// 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(int put, long count)
+{
+    exarg_T	ea;
+    char_u	buf[30];
+
+#ifdef FEAT_JOB_CHANNEL
+    if (bt_prompt(curbuf))
+    {
+	vim_beep(BO_OPER);
+	return;
+    }
+#endif
+    if (count == 0)
+	ea.arg = (char_u *)"";
+    else
+    {
+	vim_snprintf((char *)buf, 30, "%ld", count);
+	ea.arg = buf;
+    }
+    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);
+}
+
+/*
+ * Return TRUE if "diff" appears in the list of diff blocks of the current tab.
+ */
+    static int
+valid_diff(diff_T *diff)
+{
+    diff_T	*dp;
+
+    for (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)
+	if (dp == diff)
+	    return TRUE;
+    return FALSE;
+}
+
+/*
+ * ":diffget"
+ * ":diffput"
+ */
+    void
+ex_diffgetput(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;
+    int		buf_empty;
+    int		found_not_ma = FALSE;
+
+    // Find the current buffer in the list of diff buffers.
+    idx_cur = diff_buf_idx(curbuf);
+    if (idx_cur == DB_COUNT)
+    {
+	emsg(_(e_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 (curtab->tp_diffbuf[idx_other] != curbuf
+		    && curtab->tp_diffbuf[idx_other] != NULL)
+	    {
+		if (eap->cmdidx != CMD_diffput
+				     || curtab->tp_diffbuf[idx_other]->b_p_ma)
+		    break;
+		found_not_ma = TRUE;
+	    }
+	if (idx_other == DB_COUNT)
+	{
+	    if (found_not_ma)
+		emsg(_(e_no_other_buffer_in_diff_mode_is_modifiable));
+	    else
+		emsg(_(e_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 (curtab->tp_diffbuf[i] != curbuf
+		    && curtab->tp_diffbuf[i] != NULL
+		    && (eap->cmdidx != CMD_diffput || curtab->tp_diffbuf[i]->b_p_ma))
+	    {
+		emsg(_(e_more_than_two_buffers_in_diff_mode_dont_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, FALSE);
+	    if (i < 0)
+		return;		// error message already given
+	}
+	buf = buflist_findnr(i);
+	if (buf == NULL)
+	{
+	    semsg(_(e_cant_find_buffer_str), eap->arg);
+	    return;
+	}
+	if (buf == curbuf)
+	    return;		// nothing to do
+	idx_other = diff_buf_idx(buf);
+	if (idx_other == DB_COUNT)
+	{
+	    semsg(_(e_buffer_str_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, curtab->tp_diffbuf[idx_other]);
+	if (curbuf != curtab->tp_diffbuf[idx_other])
+	    // Could not find a window for this buffer, the rest is likely to
+	    // fail.
+	    goto theend;
+    }
+
+    // May give the warning for a changed buffer here, which can trigger the
+    // FileChangedRO autocommand, which may do nasty things and mess
+    // everything up.
+    if (!curbuf->b_changed)
+    {
+	change_warning(0);
+	if (diff_buf_idx(curbuf) != idx_to)
+	{
+	    emsg(_(e_buffer_changed_unexpectedly));
+	    goto theend;
+	}
+    }
+
+    dprev = NULL;
+    for (dp = curtab->tp_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;
+	    }
+
+	    buf_empty = BUFEMPTY();
+	    added = 0;
+	    for (i = 0; i < count; ++i)
+	    {
+		// remember deleting the last line of the buffer
+		buf_empty = curbuf->b_ml.ml_line_count == 1;
+		if (ml_delete(lnum) == OK)
+		    --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 > curtab->tp_diffbuf[idx_from]->b_ml.ml_line_count)
+		    break;
+		p = vim_strsave(ml_get_buf(curtab->tp_diffbuf[idx_from],
+								  nr, FALSE));
+		if (p != NULL)
+		{
+		    ml_append(lnum + i - 1, p, 0, FALSE);
+		    vim_free(p);
+		    ++added;
+		    if (buf_empty && curbuf->b_ml.ml_line_count == 2)
+		    {
+			// Added the first line into an empty buffer, need to
+			// delete the dummy empty line.
+			buf_empty = FALSE;
+			ml_delete((linenr_T)2);
+		    }
+		}
+	    }
+	    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 (curtab->tp_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)
+			curtab->tp_first_diff = dp;
+		    else
+			dprev->df_next = dp;
+		}
+	    }
+
+	    if (added != 0)
+	    {
+		// Adjust marks.  This will change the following entries!
+		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);
+	    }
+
+	    // mark_adjust() may have made "dp" invalid.  We don't know where
+	    // to continue then, bail out.
+	    if (added != 0 && !valid_diff(dp))
+		break;
+
+	    if (dfree == NULL)
+		// 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 (eap->cmdidx != CMD_diffget)
+    {
+	// 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(FALSE);
+	aucmd_restbuf(&aco);
+    }
+
+theend:
+    diff_busy = FALSE;
+    if (diff_need_update)
+	ex_diffupdate(NULL);
+
+    // Check that the cursor is on a valid character and update its
+    // position.  When there were filler lines the topline has become
+    // invalid.
+    check_cursor();
+    changed_line_abv_curs();
+
+    if (diff_need_update)
+	// redraw already done by ex_diffupdate()
+	diff_need_update = FALSE;
+    else
+    {
+	// Also need to redraw the other buffers.
+	diff_redraw(FALSE);
+	apply_autocmds(EVENT_DIFFUPDATED, NULL, NULL, FALSE, curbuf);
+    }
+}
+
+#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(diff_T *dp, int skip_idx)
+{
+    int		i;
+    win_T	*wp;
+
+    FOR_ALL_WINDOWS(wp)
+	for (i = 0; i < DB_COUNT; ++i)
+	    if (curtab->tp_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_T *buf)
+{
+    tabpage_T	*tp;
+
+    FOR_ALL_TABPAGES(tp)
+	if (diff_buf_idx_tp(buf, tp) != DB_COUNT)
+	    return TRUE;
+    return FALSE;
+}
+
+/*
+ * 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(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 || curtab->tp_first_diff == NULL)
+	return FAIL;
+
+    if (curtab->tp_diff_invalid)
+	ex_diffupdate(NULL);		// update after a big change
+
+    if (curtab->tp_first_diff == NULL)		// no diffs today
+	return FAIL;
+
+    while (--count >= 0)
+    {
+	// Check if already before first diff.
+	if (dir == BACKWARD && lnum <= curtab->tp_first_diff->df_lnum[idx])
+	    break;
+
+	for (dp = curtab->tp_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;
+}
+
+/*
+ * Return the line number in the current window that is closest to "lnum1" in
+ * "buf1" in diff mode.
+ */
+    static linenr_T
+diff_get_corresponding_line_int(
+    buf_T	*buf1,
+    linenr_T	lnum1)
+{
+    int		idx1;
+    int		idx2;
+    diff_T	*dp;
+    int		baseline = 0;
+
+    idx1 = diff_buf_idx(buf1);
+    idx2 = diff_buf_idx(curbuf);
+    if (idx1 == DB_COUNT || idx2 == DB_COUNT || curtab->tp_first_diff == NULL)
+	return lnum1;
+
+    if (curtab->tp_diff_invalid)
+	ex_diffupdate(NULL);		// update after a big change
+
+    if (curtab->tp_first_diff == NULL)		// no diffs today
+	return lnum1;
+
+    FOR_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
+    {
+	if (dp->df_lnum[idx1] > lnum1)
+	    return lnum1 - baseline;
+	if ((dp->df_lnum[idx1] + dp->df_count[idx1]) > lnum1)
+	{
+	    // Inside the diffblock
+	    baseline = lnum1 - dp->df_lnum[idx1];
+	    if (baseline > dp->df_count[idx2])
+		baseline = dp->df_count[idx2];
+
+	    return dp->df_lnum[idx2] + baseline;
+	}
+	if (    (dp->df_lnum[idx1] == lnum1)
+	     && (dp->df_count[idx1] == 0)
+	     && (dp->df_lnum[idx2] <= curwin->w_cursor.lnum)
+	     && ((dp->df_lnum[idx2] + dp->df_count[idx2])
+						      > curwin->w_cursor.lnum))
+	    /*
+	     * Special case: if the cursor is just after a zero-count
+	     * block (i.e. all filler) and the target cursor is already
+	     * inside the corresponding block, leave the target cursor
+	     * unmoved. This makes repeated CTRL-W W operations work
+	     * as expected.
+	     */
+	    return curwin->w_cursor.lnum;
+	baseline = (dp->df_lnum[idx1] + dp->df_count[idx1])
+				   - (dp->df_lnum[idx2] + dp->df_count[idx2]);
+    }
+
+    // If we get here then the cursor is after the last diff
+    return lnum1 - baseline;
+}
+
+/*
+ * Return the line number in the current window that is closest to "lnum1" in
+ * "buf1" in diff mode.  Checks the line number to be valid.
+ */
+    linenr_T
+diff_get_corresponding_line(buf_T *buf1, linenr_T lnum1)
+{
+    linenr_T lnum = diff_get_corresponding_line_int(buf1, lnum1);
+
+    // don't end up past the end of the file
+    if (lnum > curbuf->b_ml.ml_line_count)
+	return curbuf->b_ml.ml_line_count;
+    return lnum;
+}
+
+/*
+ * For line "lnum" in the current window find the equivalent lnum in window
+ * "wp", compensating for inserted/deleted lines.
+ */
+    linenr_T
+diff_lnum_win(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 (curtab->tp_diff_invalid)
+	ex_diffupdate(NULL);		// update after a big change
+
+    // search for a change that includes "lnum" in the list of diffblocks.
+    FOR_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
+	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;
+}
+
+/*
+ * Handle an ED style diff line.
+ * Return FAIL if the line does not contain diff info.
+ */
+    static int
+parse_diff_ed(
+	char_u	    *line,
+	diffhunk_T  *hunk)
+{
+    char_u *p;
+    long    f1, l1, f2, l2;
+    int	    difftype;
+
+    // The line must be one of three formats:
+    // change: {first}[,{last}]c{first}[,{last}]
+    // append: {first}a{first}[,{last}]
+    // delete: {first}[,{last}]d{first}
+    p = line;
+    f1 = getdigits(&p);
+    if (*p == ',')
+    {
+	++p;
+	l1 = getdigits(&p);
+    }
+    else
+	l1 = f1;
+    if (*p != 'a' && *p != 'c' && *p != 'd')
+	return FAIL;		// invalid diff format
+    difftype = *p++;
+    f2 = getdigits(&p);
+    if (*p == ',')
+    {
+	++p;
+	l2 = getdigits(&p);
+    }
+    else
+	l2 = f2;
+    if (l1 < f1 || l2 < f2)
+	return FAIL;
+
+    if (difftype == 'a')
+    {
+	hunk->lnum_orig = f1 + 1;
+	hunk->count_orig = 0;
+    }
+    else
+    {
+	hunk->lnum_orig = f1;
+	hunk->count_orig = l1 - f1 + 1;
+    }
+    if (difftype == 'd')
+    {
+	hunk->lnum_new = f2 + 1;
+	hunk->count_new = 0;
+    }
+    else
+    {
+	hunk->lnum_new = f2;
+	hunk->count_new = l2 - f2 + 1;
+    }
+    return OK;
+}
+
+/*
+ * Parses unified diff with zero(!) context lines.
+ * Return FAIL if there is no diff information in "line".
+ */
+    static int
+parse_diff_unified(
+	char_u	    *line,
+	diffhunk_T  *hunk)
+{
+    char_u *p;
+    long    oldline, oldcount, newline, newcount;
+
+    // Parse unified diff hunk header:
+    // @@ -oldline,oldcount +newline,newcount @@
+    p = line;
+    if (*p++ == '@' && *p++ == '@' && *p++ == ' ' && *p++ == '-')
+    {
+	oldline = getdigits(&p);
+	if (*p == ',')
+	{
+	    ++p;
+	    oldcount = getdigits(&p);
+	}
+	else
+	    oldcount = 1;
+	if (*p++ == ' ' && *p++ == '+')
+	{
+	    newline = getdigits(&p);
+	    if (*p == ',')
+	    {
+		++p;
+		newcount = getdigits(&p);
+	    }
+	    else
+		newcount = 1;
+	}
+	else
+	    return FAIL;	// invalid diff format
+
+	if (oldcount == 0)
+	    oldline += 1;
+	if (newcount == 0)
+	    newline += 1;
+	if (newline == 0)
+	    newline = 1;
+
+	hunk->lnum_orig = oldline;
+	hunk->count_orig = oldcount;
+	hunk->lnum_new = newline;
+	hunk->count_new = newcount;
+
+	return OK;
+    }
+
+    return FAIL;
+}
+
+/*
+ * Callback function for the xdl_diff() function.
+ * Stores the diff output in a grow array.
+ */
+    static int
+xdiff_out(
+	long start_a,
+	long count_a,
+	long start_b,
+	long count_b,
+	void *priv)
+{
+    diffout_T	*dout = (diffout_T *)priv;
+    diffhunk_T *p = ALLOC_ONE(diffhunk_T);
+
+    if (p == NULL)
+	return -1;
+
+    if (ga_grow(&dout->dout_ga, 1) == FAIL)
+    {
+	vim_free(p);
+	return -1;
+    }
+
+    p->lnum_orig  = start_a + 1;
+    p->count_orig = count_a;
+    p->lnum_new   = start_b + 1;
+    p->count_new  = count_b;
+    ((diffhunk_T **)dout->dout_ga.ga_data)[dout->dout_ga.ga_len++] = p;
+    return 0;
+}
+
+#endif	// FEAT_DIFF
+
+#if defined(FEAT_EVAL) || defined(PROTO)
+
+/*
+ * "diff_filler()" function
+ */
+    void
+f_diff_filler(typval_T *argvars UNUSED, typval_T *rettv UNUSED)
+{
+#ifdef FEAT_DIFF
+    if (in_vim9script() && check_for_lnum_arg(argvars, 0) == FAIL)
+	return;
+
+    rettv->vval.v_number = diff_check_fill(curwin, tv_get_lnum(argvars));
+#endif
+}
+
+/*
+ * "diff_hlID()" function
+ */
+    void
+f_diff_hlID(typval_T *argvars UNUSED, typval_T *rettv UNUSED)
+{
+#ifdef FEAT_DIFF
+    linenr_T		lnum;
+    static linenr_T	prev_lnum = 0;
+    static varnumber_T	changedtick = 0;
+    static int		fnum = 0;
+    static int		change_start = 0;
+    static int		change_end = 0;
+    static hlf_T	hlID = (hlf_T)0;
+    int			filler_lines;
+    int			col;
+
+    if (in_vim9script()
+	    && (check_for_lnum_arg(argvars,0) == FAIL
+		|| check_for_number_arg(argvars, 1) == FAIL))
+	return;
+
+    lnum = tv_get_lnum(argvars);
+    if (lnum < 0)	// ignore type error in {lnum} arg
+	lnum = 0;
+    if (lnum != prev_lnum
+	    || changedtick != CHANGEDTICK(curbuf)
+	    || fnum != curbuf->b_fnum)
+    {
+	// New line, buffer, change: need to get the values.
+	filler_lines = diff_check(curwin, lnum);
+	if (filler_lines < 0)
+	{
+	    if (filler_lines == -1)
+	    {
+		change_start = MAXCOL;
+		change_end = -1;
+		if (diff_find_change(curwin, lnum, &change_start, &change_end))
+		    hlID = HLF_ADD;	// added line
+		else
+		    hlID = HLF_CHD;	// changed line
+	    }
+	    else
+		hlID = HLF_ADD;	// added line
+	}
+	else
+	    hlID = (hlf_T)0;
+	prev_lnum = lnum;
+	changedtick = CHANGEDTICK(curbuf);
+	fnum = curbuf->b_fnum;
+    }
+
+    if (hlID == HLF_CHD || hlID == HLF_TXD)
+    {
+	col = tv_get_number(&argvars[1]) - 1; // ignore type error in {col}
+	if (col >= change_start && col <= change_end)
+	    hlID = HLF_TXD;			// changed text
+	else
+	    hlID = HLF_CHD;			// changed line
+    }
+    rettv->vval.v_number = hlID == (hlf_T)0 ? 0 : (int)hlID;
+#endif
+}
+
+#endif