view src/diff.c @ 35308:22c03485f222 v9.1.0456

patch 9.1.0456: Left shift is incorrect with vartabstop and shiftwidth=0 Commit: https://github.com/vim/vim/commit/88d4f255b7b7a19bb4f6489e0ad0956e47d51fed Author: Gary Johnson <garyjohn@spocom.com> Date: Sat Jun 1 20:51:33 2024 +0200 patch 9.1.0456: Left shift is incorrect with vartabstop and shiftwidth=0 Problem: Left shift is incorrect with vartabstop and shiftwidth=0 Solution: make tabstop_at() function aware of shift direction (Gary Johnson) The problem was that with 'vartabstop' set and 'shiftwidth' equal 0, left shifts using << were shifting the line to the wrong column. The tabstop to the right of the first character in the line was being used as the shift amount instead of the tabstop to the left of that first character. The reason was that the tabstop_at() function always returned the value of the tabstop to the right of the given column and was not accounting for the direction of the shift. The solution was to make tabstop_at() aware of the direction of the shift and to choose the tabtop accordingly. A test was added to check this behavior and make sure it doesn't regress. While at it, also fix a few indentation/alignment issues. fixes: #14864 closes: #14887 Signed-off-by: Gary Johnson <garyjohn@spocom.com> Signed-off-by: Christian Brabandt <cb@256bit.org>
author Christian Brabandt <cb@256bit.org>
date Sat, 01 Jun 2024 21:00:03 +0200
parents f41e8218775a
children a79acd371fe9
line wrap: on
line source

/* 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;

typedef enum {
    DIO_OUTPUT_INDICES = 0,	// default
    DIO_OUTPUT_UNIFIED = 1	// unified diff format
} dio_outfmt_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
    dio_outfmt_T    dio_outfmt;   // internal diff output format
    int		    dio_ctxlen;   // unified diff context length
} 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_indices(long start_a, long count_a, long start_b, long count_b, void *priv);
static int xdiff_out_unified(void *priv, mmbuffer_t *mb, int nbuf);

#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_CLEAR(din->din_mmfile.ptr);
    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 += ml_get_buf_len(buf, lnum) + 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 = diffio->dio_ctxlen;
    emit_cb.priv = &diffio->dio_diff;
    if (diffio->dio_outfmt == DIO_OUTPUT_INDICES)
	emit_cfg.hunk_func = xdiff_out_indices;
    else
	emit_cb.out_line = xdiff_out_unified;
    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
    {
	if (check_restricted())
	    goto theend;

	// 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;
	wp->w_skipcol = 0;
    }
# 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_save)
		    {
			wp->w_p_wrap = TRUE;
			wp->w_leftcol = 0;
		    }
		}
#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 (SAFE_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 (!SAFE_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)
    {
	// Note: Keep this in sync with p_dip_values
	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)
	{
	    // Note: Keep this in sync with p_dip_algorithm_values.
	    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_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
	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 (indices) in a grow array.
 */
    static int
xdiff_out_indices(
	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;
}

/*
 * Callback function for the xdl_diff() function.
 * Stores the unified diff output in a grow array.
 */
    static int
xdiff_out_unified(
	void *priv,
	mmbuffer_t *mb,
	int nbuf)
{
    diffout_T	*dout = (diffout_T *)priv;
    int		i;

    for (i = 0; i < nbuf; i++)
	ga_concat_len(&dout->dout_ga, (char_u *)mb[i].ptr, mb[i].size);

    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
}

# ifdef FEAT_DIFF
/*
 * Parse the diff options passed in "optarg" to the diff() function and return
 * the options in "diffopts" and the diff algorithm in "diffalgo".
 */
    static int
parse_diff_optarg(
    typval_T	    *opts,
    int		    *diffopts,
    long	    *diffalgo,
    dio_outfmt_T    *diff_output_fmt,
    int		    *diff_ctxlen)
{
    dict_T *d = opts->vval.v_dict;

    char_u  *algo = dict_get_string(d, "algorithm", FALSE);
    if (algo != NULL)
    {
	if (STRNCMP(algo, "myers", 5) == 0)
	    *diffalgo = 0;
	else if (STRNCMP(algo, "minimal", 7) == 0)
	    *diffalgo = XDF_NEED_MINIMAL;
	else if (STRNCMP(algo, "patience", 8) == 0)
	    *diffalgo = XDF_PATIENCE_DIFF;
	else if (STRNCMP(algo, "histogram", 9) == 0)
	    *diffalgo = XDF_HISTOGRAM_DIFF;
    }

    char_u  *output_fmt = dict_get_string(d, "output", FALSE);
    if (output_fmt != NULL)
    {
	if (STRNCMP(output_fmt, "unified", 7) == 0)
	    *diff_output_fmt = DIO_OUTPUT_UNIFIED;
	else if (STRNCMP(output_fmt, "indices", 7) == 0)
	    *diff_output_fmt = DIO_OUTPUT_INDICES;
	else
	{
	    semsg(_(e_unsupported_diff_output_format_str), output_fmt);
	    return FAIL;
	}
    }

    *diff_ctxlen = dict_get_number_def(d, "context", 0);
    if (*diff_ctxlen < 0)
	*diff_ctxlen = 0;

    if (dict_get_bool(d, "iblank", FALSE))
	*diffopts |= DIFF_IBLANK;
    if (dict_get_bool(d, "icase", FALSE))
	*diffopts |= DIFF_ICASE;
    if (dict_get_bool(d, "iwhite", FALSE))
	*diffopts |= DIFF_IWHITE;
    if (dict_get_bool(d, "iwhiteall", FALSE))
	*diffopts |= DIFF_IWHITEALL;
    if (dict_get_bool(d, "iwhiteeol", FALSE))
	*diffopts |= DIFF_IWHITEEOL;
    if (dict_get_bool(d, "indent-heuristic", FALSE))
	*diffalgo |= XDF_INDENT_HEURISTIC;

    return OK;
}

/*
 * Concatenate the List of strings in "l" and store the result in
 * "din->din_mmfile.ptr" and the length in "din->din_mmfile.size".
 */
    static void
list_to_diffin(list_T *l, diffin_T *din, int icase)
{
    garray_T	ga;
    listitem_T	*li;
    char_u	*str;

    ga_init2(&ga, 512, 4);

    FOR_ALL_LIST_ITEMS(l, li)
    {
	str = tv_get_string(&li->li_tv);
	if (icase)
	{
	    str = strlow_save(str);
	    if (str == NULL)
		continue;
	}
	ga_concat(&ga, str);
	ga_concat(&ga, (char_u *)NL_STR);
	if (icase)
	    vim_free(str);
    }
    if (ga.ga_len > 0)
	((char *)ga.ga_data)[ga.ga_len] = NUL;

    din->din_mmfile.ptr = (char *)ga.ga_data;
    din->din_mmfile.size = ga.ga_len;
}

/*
 * Get the start and end indices from the diff "hunk".
 */
    static dict_T *
get_diff_hunk_indices(diffhunk_T *hunk)
{
    dict_T	*hunk_dict;

    hunk_dict = dict_alloc();
    if (hunk_dict == NULL)
	return NULL;

    dict_add_number(hunk_dict, "from_idx", hunk->lnum_orig - 1);
    dict_add_number(hunk_dict, "from_count", hunk->count_orig);
    dict_add_number(hunk_dict, "to_idx", hunk->lnum_new  - 1);
    dict_add_number(hunk_dict, "to_count", hunk->count_new);

    return hunk_dict;
}
# endif

/*
 * "diff()" function
 */
    void
f_diff(typval_T *argvars UNUSED, typval_T *rettv UNUSED)
{
# ifdef FEAT_DIFF
    diffio_T dio;

    if (check_for_nonnull_list_arg(argvars, 0) == FAIL
	    || check_for_nonnull_list_arg(argvars, 1) == FAIL
	    || check_for_opt_nonnull_dict_arg(argvars, 2) == FAIL)
	return;

    CLEAR_FIELD(dio);
    dio.dio_internal = TRUE;
    ga_init2(&dio.dio_diff.dout_ga, sizeof(char *), 1000);

    list_T *orig_list = argvars[0].vval.v_list;
    list_T *new_list = argvars[1].vval.v_list;

    // Save the 'diffopt' option value and restore it after getting the diff.
    int		save_diff_flags = diff_flags;
    long	save_diff_algorithm = diff_algorithm;
    diff_flags = DIFF_INTERNAL;
    diff_algorithm = 0;
    dio.dio_outfmt = DIO_OUTPUT_UNIFIED;
    if (argvars[2].v_type != VAR_UNKNOWN)
	if (parse_diff_optarg(&argvars[2], &diff_flags, &diff_algorithm,
			&dio.dio_outfmt, &dio.dio_ctxlen) == FAIL)
	    return;

    // Concatenate the List of strings into a single string using newline
    // separator.  Internal diff library expects a single string.
    list_to_diffin(orig_list, &dio.dio_orig, diff_flags & DIFF_ICASE);
    list_to_diffin(new_list, &dio.dio_new, diff_flags & DIFF_ICASE);

    // If 'diffexpr' is set, then the internal diff is not used.  Set
    // 'diffexpr' to an empty string temporarily.
    int	    restore_diffexpr = FALSE;
    char_u  cc = *p_dex;
    if (*p_dex != NUL)
    {
	restore_diffexpr = TRUE;
	*p_dex = NUL;
    }

    // Compute the diff
    int diff_status = diff_file(&dio);

    // restore 'diffexpr'
    if (restore_diffexpr)
	*p_dex = cc;

    if (diff_status == FAIL)
	goto done;

    int		hunk_idx = 0;
    dict_T	*hunk_dict;

    if (dio.dio_outfmt == DIO_OUTPUT_INDICES)
    {
	if (rettv_list_alloc(rettv) != OK)
	    goto done;
	list_T	*l = rettv->vval.v_list;

	// Process each diff hunk
	diffhunk_T	*hunk = NULL;
	while (hunk_idx < dio.dio_diff.dout_ga.ga_len)
	{
	    hunk = ((diffhunk_T **)dio.dio_diff.dout_ga.ga_data)[hunk_idx++];

	    hunk_dict = get_diff_hunk_indices(hunk);
	    if (hunk_dict == NULL)
		goto done;

	    list_append_dict(l, hunk_dict);
	}
    }
    else
    {
	ga_append(&dio.dio_diff.dout_ga, NUL);
	rettv->v_type = VAR_STRING;
	rettv->vval.v_string =
			vim_strsave((char_u *)dio.dio_diff.dout_ga.ga_data);
    }

done:
    clear_diffin(&dio.dio_new);
    if (dio.dio_outfmt == DIO_OUTPUT_INDICES)
	clear_diffout(&dio.dio_diff);
    else
	ga_clear(&dio.dio_diff.dout_ga);
    clear_diffin(&dio.dio_orig);
    // Restore the 'diffopt' option value.
    diff_flags = save_diff_flags;
    diff_algorithm = save_diff_algorithm;
# endif
}

#endif