[7.2.350] Win32: When changing font the window may jump from the secondary

[vim_mainline.git] / src / diff.c

/* vim:set ts=8 sts=4 sw=4:
 *
 * VIM - Vi IMproved    by Bram Moolenaar
 *
 * Do ":help uganda"  in Vim to read copying and usage conditions.
 * Do ":help credits" in Vim to see a list of people who contributed.
 * See README.txt for an overview of the Vim source code.
 */

/*
 * diff.c: code for diff'ing two, three or four buffers.
 */

#include "vim.h"

#if defined(FEAT_DIFF) || defined(PROTO)

static int      diff_busy = FALSE;      /* ex_diffgetput() is busy */

/* flags obtained from the 'diffopt' option */
#define DIFF_FILLER     1       /* display filler lines */
#define DIFF_ICASE      2       /* ignore case */
#define DIFF_IWHITE     4       /* ignore change in white space */
#define DIFF_HORIZONTAL 8       /* horizontal splits */
#define DIFF_VERTICAL   16      /* vertical splits */
static int      diff_flags = DIFF_FILLER;

#define LBUFLEN 50              /* length of line in diff file */

static int diff_a_works = MAYBE; /* TRUE when "diff -a" works, FALSE when it
                                    doesn't work, MAYBE when not checked yet */
#if defined(MSWIN) || defined(MSDOS)
static int diff_bin_works = MAYBE; /* TRUE when "diff --binary" works, FALSE
                                      when it doesn't work, MAYBE when not
                                      checked yet */
#endif

static int diff_buf_idx __ARGS((buf_T *buf));
static int diff_buf_idx_tp __ARGS((buf_T *buf, tabpage_T *tp));
static void diff_mark_adjust_tp __ARGS((tabpage_T *tp, int idx, linenr_T line1, linenr_T line2, long amount, long amount_after));
static void diff_check_unchanged __ARGS((tabpage_T *tp, diff_T *dp));
static int diff_check_sanity __ARGS((tabpage_T *tp, diff_T *dp));
static void diff_redraw __ARGS((int dofold));
static int diff_write __ARGS((buf_T *buf, char_u *fname));
static void diff_file __ARGS((char_u *tmp_orig, char_u *tmp_new, char_u *tmp_diff));
static int diff_equal_entry __ARGS((diff_T *dp, int idx1, int idx2));
static int diff_cmp __ARGS((char_u *s1, char_u *s2));
#ifdef FEAT_FOLDING
static void diff_fold_update __ARGS((diff_T *dp, int skip_idx));
#endif
static void diff_read __ARGS((int idx_orig, int idx_new, char_u *fname));
static void diff_copy_entry __ARGS((diff_T *dprev, diff_T *dp, int idx_orig, int idx_new));
static diff_T *diff_alloc_new __ARGS((tabpage_T *tp, diff_T *dprev, diff_T *dp));

#ifndef USE_CR
# define tag_fgets vim_fgets
#endif

/*
 * Called when deleting or unloading a buffer: No longer make a diff with it.
 */
    void
diff_buf_delete(buf)
    buf_T       *buf;
{
    int         i;
    tabpage_T   *tp;

    for (tp = first_tabpage; tp != NULL; tp = tp->tp_next)
    {
        i = diff_buf_idx_tp(buf, tp);
        if (i != DB_COUNT)
        {
            tp->tp_diffbuf[i] = NULL;
            tp->tp_diff_invalid = TRUE;
            if (tp == curtab)
                diff_redraw(TRUE);
        }
    }
}

/*
 * Check if the current buffer should be added to or removed from the list of
 * diff buffers.
 */
    void
diff_buf_adjust(win)
    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 (wp = firstwin; wp != NULL; wp = wp->w_next)
            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)
    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;
        }

    EMSGN(_("E96: Can not diff more than %ld buffers"), DB_COUNT);
}

/*
 * 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)
    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, 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)
    buf_T       *buf;
{
    tabpage_T   *tp;
    int         i;

    for (tp = first_tabpage; tp != NULL; tp = tp->tp_next)
    {
        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(line1, line2, amount, amount_after)
    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 (tp = first_tabpage; tp != NULL; tp = tp->tp_next)
    {
        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(tp, idx, line1, line2, amount, amount_after)
    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 (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)
                {
                    if (dp->df_lnum[idx] >= line1)
                    {
                        off = dp->df_lnum[idx] - lnum_deleted;
                        if (last <= line2)
                        {
                            /* 4. delete all lines of diff */
                            if (dp->df_next != NULL
                                    && dp->df_next->df_lnum[idx] - 1 <= line2)
                            {
                                /* delete continues in next diff, only do
                                 * lines until that one */
                                n = dp->df_next->df_lnum[idx] - lnum_deleted;
                                deleted -= n;
                                n -= dp->df_count[idx];
                                lnum_deleted = dp->df_next->df_lnum[idx];
                            }
                            else
                                n = deleted - dp->df_count[idx];
                            dp->df_count[idx] = 0;
                        }
                        else
                        {
                            /* 5. delete lines at or just before top of diff */
                            n = off;
                            dp->df_count[idx] -= line2 - dp->df_lnum[idx] + 1;
                            check_unchanged = TRUE;
                        }
                        dp->df_lnum[idx] = line1;
                    }
                    else
                    {
                        off = 0;
                        if (last < line2)
                        {
                            /* 2. delete at end of of diff */
                            dp->df_count[idx] -= last - lnum_deleted + 1;
                            if (dp->df_next != NULL
                                    && dp->df_next->df_lnum[idx] - 1 <= line2)
                            {
                                /* delete continues in next diff, only do
                                 * lines until that one */
                                n = dp->df_next->df_lnum[idx] - 1 - last;
                                deleted -= dp->df_next->df_lnum[idx]
                                                               - lnum_deleted;
                                lnum_deleted = dp->df_next->df_lnum[idx];
                            }
                            else
                                n = line2 - last;
                            check_unchanged = TRUE;
                        }
                        else
                        {
                            /* 3. delete lines inside the diff */
                            n = 0;
                            dp->df_count[idx] -= deleted;
                        }
                    }

                    for (i = 0; i < DB_COUNT; ++i)
                        if (tp->tp_diffbuf[i] != NULL && i != idx)
                        {
                            dp->df_lnum[i] -= off;
                            dp->df_count[i] += n;
                        }
                }
                else
                {
                    if (dp->df_lnum[idx] <= line1)
                    {
                        /* inserted lines somewhere in this diff */
                        dp->df_count[idx] += inserted;
                        check_unchanged = TRUE;
                    }
                    else
                        /* inserted lines somewhere above this diff */
                        dp->df_lnum[idx] += inserted;
                }

                if (check_unchanged)
                    /* Check if inserted lines are equal, may reduce the
                     * size of the diff.  TODO: also check for equal lines
                     * in the middle and perhaps split the block. */
                    diff_check_unchanged(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)
    {
        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(tp, dprev, dp)
    tabpage_T   *tp;
    diff_T      *dprev;
    diff_T      *dp;
{
    diff_T      *dnew;

    dnew = (diff_T *)alloc((unsigned)sizeof(diff_T));
    if (dnew != NULL)
    {
        dnew->df_next = dp;
        if (dprev == NULL)
            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(tp, dp)
    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(tp, dp)
    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.
 */
    static void
diff_redraw(dofold)
    int         dofold;     /* also recompute the folds */
{
    win_T       *wp;
    int         n;

    for (wp = firstwin; wp != NULL; wp = wp->w_next)
        if (wp->w_p_diff)
        {
            redraw_win_later(wp, SOME_VALID);
#ifdef FEAT_FOLDING
            if (dofold && foldmethodIsDiff(wp))
                foldUpdateAll(wp);
#endif
            /* A change may have made filler lines invalid, need to take care
             * of that for other windows. */
            if (wp != curwin && wp->w_topfill > 0)
            {
                n = diff_check(wp, wp->w_topline);
                if (wp->w_topfill > n)
                    wp->w_topfill = (n < 0 ? 0 : n);
            }
        }
}

/*
 * Write buffer "buf" to file "name".
 * Always use 'fileformat' set to "unix".
 * Return FAIL for failure
 */
    static int
diff_write(buf, fname)
    buf_T       *buf;
    char_u      *fname;
{
    int         r;
    char_u      *save_ff;

    save_ff = buf->b_p_ff;
    buf->b_p_ff = vim_strsave((char_u *)FF_UNIX);
    r = buf_write(buf, fname, NULL, (linenr_T)1, buf->b_ml.ml_line_count,
                                             NULL, FALSE, FALSE, FALSE, TRUE);
    free_string_option(buf->b_p_ff);
    buf->b_p_ff = save_ff;
    return r;
}

/*
 * Completely update the diffs for the buffers involved.
 * This uses the ordinary "diff" command.
 * The buffers are written to a file, also for unmodified buffers (the file
 * could have been produced by autocommands, e.g. the netrw plugin).
 */
    void
ex_diffupdate(eap)
    exarg_T     *eap UNUSED;        /* can be NULL */
{
    buf_T       *buf;
    int         idx_orig;
    int         idx_new;
    char_u      *tmp_orig;
    char_u      *tmp_new;
    char_u      *tmp_diff;
    FILE        *fd;
    int         ok;
    int         io_error = FALSE;

    /* 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)
        return;

    /* 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)
        return;

    /* We need three temp file names. */
    tmp_orig = vim_tempname('o');
    tmp_new = vim_tempname('n');
    tmp_diff = vim_tempname('d');
    if (tmp_orig == NULL || tmp_new == NULL || tmp_diff == NULL)
        goto theend;

    /*
     * Do a quick test if "diff" really works.  Otherwise it looks like there
     * are no differences.  Can't use the return value, it's non-zero when
     * there are differences.
     * May try twice, first with "-a" and then without.
     */
    for (;;)
    {
        ok = FALSE;
        fd = mch_fopen((char *)tmp_orig, "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 *)tmp_new, "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);
                diff_file(tmp_orig, tmp_new, tmp_diff);
                fd = mch_fopen((char *)tmp_diff, "r");
                if (fd == NULL)
                    io_error = TRUE;
                else
                {
                    char_u      linebuf[LBUFLEN];

                    for (;;)
                    {
                        /* There must be a line that contains "1c1". */
                        if (tag_fgets(linebuf, LBUFLEN, fd))
                            break;
                        if (STRNCMP(linebuf, "1c1", 3) == 0)
                            ok = TRUE;
                    }
                    fclose(fd);
                }
                mch_remove(tmp_diff);
                mch_remove(tmp_new);
            }
            mch_remove(tmp_orig);
        }

#ifdef FEAT_EVAL
        /* When using 'diffexpr' break here. */
        if (*p_dex != NUL)
            break;
#endif

#if defined(MSWIN) || defined(MSDOS)
        /* If the "-a" argument works, also check if "--binary" works. */
        if (ok && diff_a_works == MAYBE && diff_bin_works == MAYBE)
        {
            diff_a_works = TRUE;
            diff_bin_works = TRUE;
            continue;
        }
        if (!ok && diff_a_works == TRUE && diff_bin_works == TRUE)
        {
            /* Tried --binary, but it failed. "-a" works though. */
            diff_bin_works = FALSE;
            ok = TRUE;
        }
#endif

        /* If we checked if "-a" works already, break here. */
        if (diff_a_works != MAYBE)
            break;
        diff_a_works = ok;

        /* If "-a" works break here, otherwise retry without "-a". */
        if (ok)
            break;
    }
    if (!ok)
    {
        if (io_error)
            EMSG(_("E810: Cannot read or write temp files"));
        EMSG(_("E97: Cannot create diffs"));
        diff_a_works = MAYBE;
#if defined(MSWIN) || defined(MSDOS)
        diff_bin_works = MAYBE;
#endif
        goto theend;
    }

    /* Write the first buffer to a tempfile. */
    buf = curtab->tp_diffbuf[idx_orig];
    if (diff_write(buf, tmp_orig) == FAIL)
        goto theend;

    /* Make a difference between the first buffer and every other. */
    for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new)
    {
        buf = curtab->tp_diffbuf[idx_new];
        if (buf == NULL)
            continue;
        if (diff_write(buf, tmp_new) == FAIL)
            continue;
        diff_file(tmp_orig, tmp_new, tmp_diff);

        /* Read the diff output and add each entry to the diff list. */
        diff_read(idx_orig, idx_new, tmp_diff);
        mch_remove(tmp_diff);
        mch_remove(tmp_new);
    }
    mch_remove(tmp_orig);

    /* force updating cursor position on screen */
    curwin->w_valid_cursor.lnum = 0;

    diff_redraw(TRUE);

theend:
    vim_free(tmp_orig);
    vim_free(tmp_new);
    vim_free(tmp_diff);
}

/*
 * Make a diff between files "tmp_orig" and "tmp_new", results in "tmp_diff".
 */
    static void
diff_file(tmp_orig, tmp_new, tmp_diff)
    char_u      *tmp_orig;
    char_u      *tmp_new;
    char_u      *tmp_diff;
{
    char_u      *cmd;
    size_t      len;

#ifdef FEAT_EVAL
    if (*p_dex != NUL)
        /* Use 'diffexpr' to generate the diff file. */
        eval_diff(tmp_orig, tmp_new, tmp_diff);
    else
#endif
    {
        len = STRLEN(tmp_orig) + STRLEN(tmp_new)
                                      + STRLEN(tmp_diff) + STRLEN(p_srr) + 27;
        cmd = alloc((unsigned)len);
        if (cmd != NULL)
        {
            /* 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",
                    diff_a_works == FALSE ? "" : "-a ",
#if defined(MSWIN) || defined(MSDOS)
                    diff_bin_works == TRUE ? "--binary " : "",
#else
                    "",
#endif
                    (diff_flags & DIFF_IWHITE) ? "-b " : "",
                    (diff_flags & DIFF_ICASE) ? "-i " : "",
                    tmp_orig, tmp_new);
            append_redir(cmd, (int)len, p_srr, tmp_diff);
#ifdef FEAT_AUTOCMD
            block_autocmds();   /* Avoid ShellCmdPost stuff */
#endif
            (void)call_shell(cmd, SHELL_FILTER|SHELL_SILENT|SHELL_DOOUT);
#ifdef FEAT_AUTOCMD
            unblock_autocmds();
#endif
            vim_free(cmd);
        }
    }
}

/*
 * Create a new version of a file from the current buffer and a diff file.
 * The buffer is written to a file, also for unmodified buffers (the file
 * could have been produced by autocommands, e.g. the netrw plugin).
 */
    void
ex_diffpatch(eap)
    exarg_T     *eap;
{
    char_u      *tmp_orig;      /* name of original temp file */
    char_u      *tmp_new;       /* name of patched temp file */
    char_u      *buf = NULL;
    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         browse_flag = cmdmod.browse;
#endif
    struct stat st;

#ifdef FEAT_BROWSE
    if (cmdmod.browse)
    {
        browseFile = do_browse(0, (char_u *)_("Patch file"),
                         eap->arg, NULL, NULL, BROWSE_FILTER_ALL_FILES, NULL);
        if (browseFile == NULL)
            return;             /* operation cancelled */
        eap->arg = browseFile;
        cmdmod.browse = FALSE;  /* don't let do_ecmd() browse again */
    }
#endif

    /* We need two temp file names. */
    tmp_orig = vim_tempname('o');
    tmp_new = vim_tempname('n');
    if (tmp_orig == NULL || tmp_new == NULL)
        goto theend;

    /* Write the current buffer to "tmp_orig". */
    if (buf_write(curbuf, tmp_orig, NULL,
                (linenr_T)1, curbuf->b_ml.ml_line_count,
                                     NULL, FALSE, FALSE, FALSE, TRUE) == FAIL)
        goto theend;

#ifdef UNIX
    /* Get the absolute path of the patchfile, changing directory below. */
    fullname = FullName_save(eap->arg, FALSE);
#endif
    buflen = STRLEN(tmp_orig) + (
# ifdef UNIX
                    fullname != NULL ? STRLEN(fullname) :
# endif
                    STRLEN(eap->arg)) + STRLEN(tmp_new) + 16;
    buf = alloc((unsigned)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)
            ignored = mch_chdir((char *)vim_tempdir);
        else
# endif
            ignored = mch_chdir("/tmp");
        shorten_fnames(TRUE);
    }
#endif

#ifdef FEAT_EVAL
    if (*p_pex != NUL)
        /* Use 'patchexpr' to generate the new file. */
        eval_patch(tmp_orig,
# ifdef UNIX
                fullname != NULL ? fullname :
# endif
                eap->arg, tmp_new);
    else
#endif
    {
        /* Build the patch command and execute it.  Ignore errors.  Switch to
         * cooked mode to allow the user to respond to prompts. */
        vim_snprintf((char *)buf, buflen, "patch -o %s %s < \"%s\"",
                tmp_new, tmp_orig,
# ifdef UNIX
                fullname != NULL ? fullname :
# endif
                eap->arg);
#ifdef FEAT_AUTOCMD
        block_autocmds();       /* Avoid ShellCmdPost stuff */
#endif
        (void)call_shell(buf, SHELL_FILTER | SHELL_COOKED);
#ifdef FEAT_AUTOCMD
        unblock_autocmds();
#endif
    }

#ifdef UNIX
    if (dirbuf[0] != NUL)
    {
        if (mch_chdir((char *)dirbuf) != 0)
            EMSG(_(e_prev_dir));
        shorten_fnames(TRUE);
    }
#endif

    /* patch probably has written over the screen */
    redraw_later(CLEAR);

    /* Delete any .orig or .rej file created. */
    STRCPY(buf, tmp_new);
    STRCAT(buf, ".orig");
    mch_remove(buf);
    STRCPY(buf, tmp_new);
    STRCAT(buf, ".rej");
    mch_remove(buf);

    /* Only continue if the output file was created. */
    if (mch_stat((char *)tmp_new, &st) < 0 || st.st_size == 0)
        EMSG(_("E816: Cannot read patch output"));
    else
    {
        if (curbuf->b_fname != NULL)
        {
            newname = vim_strnsave(curbuf->b_fname,
                                          (int)(STRLEN(curbuf->b_fname) + 4));
            if (newname != NULL)
                STRCAT(newname, ".new");
        }

#ifdef FEAT_GUI
        need_mouse_correct = TRUE;
#endif
        /* don't use a new tab page, each tab page has its own diffs */
        cmdmod.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);

#ifdef FEAT_AUTOCMD
                    /* Do filetype detection with the new name. */
                    if (au_has_group((char_u *)"filetypedetect"))
                        do_cmdline_cmd((char_u *)":doau filetypedetect BufRead");
#endif
                }
            }
        }
    }

theend:
    if (tmp_orig != NULL)
        mch_remove(tmp_orig);
    vim_free(tmp_orig);
    if (tmp_new != NULL)
        mch_remove(tmp_new);
    vim_free(tmp_new);
    vim_free(newname);
    vim_free(buf);
#ifdef UNIX
    vim_free(fullname);
#endif
#ifdef FEAT_BROWSE
    vim_free(browseFile);
    cmdmod.browse = browse_flag;
#endif
}

/*
 * Split the window and edit another file, setting options to show the diffs.
 */
    void
ex_diffsplit(eap)
    exarg_T     *eap;
{
    win_T       *old_curwin = curwin;

#ifdef FEAT_GUI
    need_mouse_correct = TRUE;
#endif
    /* don't use a new tab page, each tab page has its own diffs */
    cmdmod.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;
        curwin->w_p_diff = TRUE;
        do_exedit(eap, old_curwin);

        if (curwin != old_curwin)               /* split must have worked */
        {
            /* Set 'diff', 'scrollbind' on and 'wrap' off. */
            diff_win_options(curwin, TRUE);
            diff_win_options(old_curwin, TRUE);
        }
    }
}

/*
 * Set options to show difs for the current window.
 */
    void
ex_diffthis(eap)
    exarg_T     *eap UNUSED;
{
    /* Set 'diff', 'scrollbind' on and 'wrap' off. */
    diff_win_options(curwin, TRUE);
}

/*
 * Set options in window "wp" for diff mode.
 */
    void
diff_win_options(wp, addbuf)
    win_T       *wp;
    int         addbuf;         /* Add buffer to diff. */
{
    wp->w_p_diff = TRUE;
    wp->w_p_scb = TRUE;
    wp->w_p_wrap = FALSE;
# ifdef FEAT_FOLDING
    {
        win_T       *old_curwin = curwin;

        curwin = wp;
        curbuf = curwin->w_buffer;
        set_string_option_direct((char_u *)"fdm", -1, (char_u *)"diff",
                                                       OPT_LOCAL|OPT_FREE, 0);
        curwin = old_curwin;
        curbuf = curwin->w_buffer;
        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
#ifdef FEAT_SCROLLBIND
    if (vim_strchr(p_sbo, 'h') == NULL)
        do_cmdline_cmd((char_u *)"set sbo+=hor");
#endif

    if (addbuf)
        diff_buf_add(wp->w_buffer);
    redraw_win_later(wp, NOT_VALID);
}

/*
 * Set options not to show diffs.  For the current window or all windows.
 * Only in the current tab page.
 */
    void
ex_diffoff(eap)
    exarg_T     *eap;
{
    win_T       *wp;
    win_T       *old_curwin = curwin;
#ifdef FEAT_SCROLLBIND
    int         diffwin = FALSE;
#endif

    for (wp = firstwin; wp != NULL; wp = wp->w_next)
    {
        if (wp == curwin || (eap->forceit && wp->w_p_diff))
        {
            /* Set 'diff', 'scrollbind' off and 'wrap' on. */
            wp->w_p_diff = FALSE;
            wp->w_p_scb = FALSE;
            wp->w_p_wrap = TRUE;
#ifdef FEAT_FOLDING
            curwin = wp;
            curbuf = curwin->w_buffer;
            set_string_option_direct((char_u *)"fdm", -1,
                                   (char_u *)"manual", OPT_LOCAL|OPT_FREE, 0);
            curwin = old_curwin;
            curbuf = curwin->w_buffer;
            wp->w_p_fdc = 0;
            wp->w_p_fen = FALSE;
            wp->w_p_fdl = 0;
            foldUpdateAll(wp);
            /* make sure topline is not halfway a fold */
            changed_window_setting_win(wp);
#endif
            diff_buf_adjust(wp);
        }
#ifdef FEAT_SCROLLBIND
        diffwin |= wp->w_p_diff;
#endif
    }

#ifdef FEAT_SCROLLBIND
    /* Remove "hor" from 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");
#endif
}

/*
 * Read the diff output and add each entry to the diff list.
 */
    static void
diff_read(idx_orig, idx_new, fname)
    int         idx_orig;       /* idx of original file */
    int         idx_new;        /* idx of new file */
    char_u      *fname;         /* name of diff output file */
{
    FILE        *fd;
    diff_T      *dprev = NULL;
    diff_T      *dp = curtab->tp_first_diff;
    diff_T      *dn, *dpl;
    long        f1, l1, f2, l2;
    char_u      linebuf[LBUFLEN];   /* only need to hold the diff line */
    int         difftype;
    char_u      *p;
    long        off;
    int         i;
    linenr_T    lnum_orig, lnum_new;
    long        count_orig, count_new;
    int         notset = TRUE;      /* block "*dp" not set yet */

    fd = mch_fopen((char *)fname, "r");
    if (fd == NULL)
    {
        EMSG(_("E98: Cannot read diff output"));
        return;
    }

    for (;;)
    {
        if (tag_fgets(linebuf, LBUFLEN, fd))
            break;              /* end of file */
        if (!isdigit(*linebuf))
            continue;           /* not the start of a diff block */

        /* This line must be one of three formats:
         * {first}[,{last}]c{first}[,{last}]
         * {first}a{first}[,{last}]
         * {first}[,{last}]d{first}
         */
        p = linebuf;
        f1 = getdigits(&p);
        if (*p == ',')
        {
            ++p;
            l1 = getdigits(&p);
        }
        else
            l1 = f1;
        if (*p != 'a' && *p != 'c' && *p != 'd')
            continue;           /* invalid diff format */
        difftype = *p++;
        f2 = getdigits(&p);
        if (*p == ',')
        {
            ++p;
            l2 = getdigits(&p);
        }
        else
            l2 = f2;
        if (l1 < f1 || l2 < f2)
            continue;           /* invalid line range */

        if (difftype == 'a')
        {
            lnum_orig = f1 + 1;
            count_orig = 0;
        }
        else
        {
            lnum_orig = f1;
            count_orig = l1 - f1 + 1;
        }
        if (difftype == 'd')
        {
            lnum_new = f2 + 1;
            count_new = 0;
        }
        else
        {
            lnum_new = f2;
            count_new = l2 - f2 + 1;
        }

        /* Go over blocks before the change, for which orig and new are equal.
         * Copy blocks from orig to new. */
        while (dp != NULL
                && lnum_orig > dp->df_lnum[idx_orig] + dp->df_count[idx_orig])
        {
            if (notset)
                diff_copy_entry(dprev, dp, idx_orig, idx_new);
            dprev = dp;
            dp = dp->df_next;
            notset = TRUE;
        }

        if (dp != NULL
                && lnum_orig <= dp->df_lnum[idx_orig] + dp->df_count[idx_orig]
                && lnum_orig + count_orig >= dp->df_lnum[idx_orig])
        {
            /* New block overlaps with existing block(s).
             * First find last block that overlaps. */
            for (dpl = dp; dpl->df_next != NULL; dpl = dpl->df_next)
                if (lnum_orig + count_orig < dpl->df_next->df_lnum[idx_orig])
                    break;

            /* If the newly found block starts before the old one, set the
             * start back a number of lines. */
            off = dp->df_lnum[idx_orig] - lnum_orig;
            if (off > 0)
            {
                for (i = idx_orig; i < idx_new; ++i)
                    if (curtab->tp_diffbuf[i] != NULL)
                        dp->df_lnum[i] -= off;
                dp->df_lnum[idx_new] = lnum_new;
                dp->df_count[idx_new] = count_new;
            }
            else if (notset)
            {
                /* new block inside existing one, adjust new block */
                dp->df_lnum[idx_new] = lnum_new + off;
                dp->df_count[idx_new] = count_new - off;
            }
            else
                /* second overlap of new block with existing block */
                dp->df_count[idx_new] += count_new - count_orig
                    + 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 = (lnum_orig + count_orig)
                         - (dpl->df_lnum[idx_orig] + dpl->df_count[idx_orig]);
            if (off < 0)
            {
                /* new change ends in existing block, adjust the end if not
                 * done already */
                if (notset)
                    dp->df_count[idx_new] += -off;
                off = 0;
            }
            for (i = idx_orig; i < idx_new; ++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] = lnum_orig;
            dp->df_count[idx_orig] = count_orig;
            dp->df_lnum[idx_new] = lnum_new;
            dp->df_count[idx_new] = count_new;

            /* Set values for other buffers, these must be equal to the
             * original buffer, otherwise there would have been a change
             * already. */
            for (i = idx_orig + 1; i < idx_new; ++i)
                if (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:
    fclose(fd);
}

/*
 * Copy an entry at "dp" from "idx_orig" to "idx_new".
 */
    static void
diff_copy_entry(dprev, dp, idx_orig, idx_new)
    diff_T      *dprev;
    diff_T      *dp;
    int         idx_orig;
    int         idx_new;
{
    long        off;

    if (dprev == NULL)
        off = 0;
    else
        off = (dprev->df_lnum[idx_orig] + dprev->df_count[idx_orig])
            - (dprev->df_lnum[idx_new] + dprev->df_count[idx_new]);
    dp->df_lnum[idx_new] = dp->df_lnum[idx_orig] - off;
    dp->df_count[idx_new] = dp->df_count[idx_orig];
}

/*
 * Clear the list of diffblocks for tab page "tp".
 */
    void
diff_clear(tp)
    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(wp, lnum)
    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 (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)
        if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
            break;
    if (dp == NULL || lnum < dp->df_lnum[idx])
        return 0;

    if (lnum < dp->df_lnum[idx] + dp->df_count[idx])
    {
        int     zero = FALSE;

        /* Changed or inserted line.  If the other buffers have a count of
         * zero, the lines were inserted.  If the other buffers have the same
         * count, check if the lines are identical. */
        cmp = FALSE;
        for (i = 0; i < DB_COUNT; ++i)
            if (i != idx && 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(dp, idx1, idx2)
    diff_T      *dp;
    int         idx1;
    int         idx2;
{
    int         i;
    char_u      *line;
    int         cmp;

    if (dp->df_count[idx1] != dp->df_count[idx2])
        return FALSE;
    if (diff_check_sanity(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 strings "s1" and "s2" according to 'diffopt'.
 * Return non-zero when they are different.
 */
    static int
diff_cmp(s1, s2)
    char_u      *s1;
    char_u      *s2;
{
    char_u      *p1, *p2;
#ifdef FEAT_MBYTE
    int         l;
#endif

    if ((diff_flags & (DIFF_ICASE | DIFF_IWHITE)) == 0)
        return STRCMP(s1, s2);
    if ((diff_flags & DIFF_ICASE) && !(diff_flags & DIFF_IWHITE))
        return MB_STRICMP(s1, s2);

    /* Ignore white space changes and possibly ignore case. */
    p1 = s1;
    p2 = s2;
    while (*p1 != NUL && *p2 != NUL)
    {
        if (vim_iswhite(*p1) && vim_iswhite(*p2))
        {
            p1 = skipwhite(p1);
            p2 = skipwhite(p2);
        }
        else
        {
#ifdef FEAT_MBYTE
            l  = (*mb_ptr2len)(p1);
            if (l != (*mb_ptr2len)(p2))
                break;
            if (l > 1)
            {
                if (STRNCMP(p1, p2, l) != 0
                        && (!enc_utf8
                            || !(diff_flags & DIFF_ICASE)
                            || utf_fold(utf_ptr2char(p1))
                                               != utf_fold(utf_ptr2char(p2))))
                    break;
                p1 += l;
                p2 += l;
            }
            else
#endif
            {
                if (*p1 != *p2 && (!(diff_flags & DIFF_ICASE)
                                     || TOLOWER_LOC(*p1) != TOLOWER_LOC(*p2)))
                    break;
                ++p1;
                ++p2;
            }
        }
    }

    /* Ignore trailing white space. */
    p1 = skipwhite(p1);
    p2 = skipwhite(p2);
    if (*p1 != NUL || *p2 != NUL)
        return 1;
    return 0;
}

/*
 * Return the number of filler lines above "lnum".
 */
    int
diff_check_fill(wp, lnum)
    win_T       *wp;
    linenr_T    lnum;
{
    int         n;

    /* be quick when there are no filler lines */
    if (!(diff_flags & DIFF_FILLER))
        return 0;
    n = diff_check(wp, lnum);
    if (n <= 0)
        return 0;
    return n;
}

/*
 * Set the topline of "towin" to match the position in "fromwin", so that they
 * show the same diff'ed lines.
 */
    void
diff_set_topline(fromwin, towin)
    win_T       *fromwin;
    win_T       *towin;
{
    buf_T       *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 (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)
        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()
{
    char_u      *p;
    int         diff_context_new = 6;
    int         diff_flags_new = 0;
    int         diff_foldcolumn_new = 2;
    tabpage_T   *tp;

    p = p_dip;
    while (*p != NUL)
    {
        if (STRNCMP(p, "filler", 6) == 0)
        {
            p += 6;
            diff_flags_new |= DIFF_FILLER;
        }
        else if (STRNCMP(p, "context:", 8) == 0 && VIM_ISDIGIT(p[8]))
        {
            p += 8;
            diff_context_new = getdigits(&p);
        }
        else if (STRNCMP(p, "icase", 5) == 0)
        {
            p += 5;
            diff_flags_new |= DIFF_ICASE;
        }
        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);
        }
        if (*p != ',' && *p != NUL)
            return FAIL;
        if (*p == ',')
            ++p;
    }

    /* Can't have both "horizontal" and "vertical". */
    if ((diff_flags_new & DIFF_HORIZONTAL) && (diff_flags_new & DIFF_VERTICAL))
        return FAIL;

    /* If "icase" or "iwhite" was added or removed, need to update the diff. */
    if (diff_flags != diff_flags_new)
        for (tp = first_tabpage; tp != NULL; tp = tp->tp_next)
            tp->tp_diff_invalid = TRUE;

    diff_flags = diff_flags_new;
    diff_context = diff_context_new;
    diff_foldcolumn = diff_foldcolumn_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()
{
    return (diff_flags & DIFF_HORIZONTAL) != 0;
}

/*
 * Find the difference within a changed line.
 * Returns TRUE if the line was added, no other buffer has it.
 */
    int
diff_find_change(wp, lnum, startp, endp)
    win_T       *wp;
    linenr_T    lnum;
    int         *startp;        /* first char of the change */
    int         *endp;          /* last char of the change */
{
    char_u      *line_org;
    char_u      *line_new;
    int         i;
    int         si_org, si_new;
    int         ei_org, ei_new;
    diff_T      *dp;
    int         idx;
    int         off;
    int         added = TRUE;

    /* Make a copy of the line, the next ml_get() will invalidate it. */
    line_org = vim_strsave(ml_get_buf(wp->w_buffer, lnum, FALSE));
    if (line_org == NULL)
        return FALSE;

    idx = diff_buf_idx(wp->w_buffer);
    if (idx == DB_COUNT)        /* cannot happen */
    {
        vim_free(line_org);
        return FALSE;
    }

    /* search for a change that includes "lnum" in the list of diffblocks. */
    for (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)
        if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
            break;
    if (dp == NULL || diff_check_sanity(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]))
                {
                    si_org = (int)(skipwhite(line_org + si_org) - line_org);
                    si_new = (int)(skipwhite(line_new + si_new) - line_new);
                }
                else
                {
                    if (line_org[si_org] != line_new[si_new])
                        break;
                    ++si_org;
                    ++si_new;
                }
            }
#ifdef FEAT_MBYTE
            if (has_mbyte)
            {
                /* Move back to first byte of character in both lines (may
                 * have "nn^" in line_org and "n^ in line_new). */
                si_org -= (*mb_head_off)(line_org, line_org + si_org);
                si_new -= (*mb_head_off)(line_new, line_new + si_new);
            }
#endif
            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]))
                    {
                        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
                    {
                        if (line_org[ei_org] != line_new[ei_new])
                            break;
                        --ei_org;
                        --ei_new;
                    }
                }
                if (*endp < ei_org)
                    *endp = ei_org;
            }
        }

    vim_free(line_org);
    return added;
}

#if defined(FEAT_FOLDING) || defined(PROTO)
/*
 * Return TRUE if line "lnum" is not close to a diff block, this line should
 * be in a fold.
 * Return FALSE if there are no diff blocks at all in this window.
 */
    int
diff_infold(wp, lnum)
    win_T       *wp;
    linenr_T    lnum;
{
    int         i;
    int         idx = -1;
    int         other = FALSE;
    diff_T      *dp;

    /* Return if 'diff' isn't set. */
    if (!wp->w_p_diff)
        return FALSE;

    for (i = 0; i < DB_COUNT; ++i)
    {
        if (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 (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)
    {
        /* If this change is below the line there can't be any further match. */
        if (dp->df_lnum[idx] - diff_context > lnum)
            break;
        /* If this change ends before the line we have a match. */
        if (dp->df_lnum[idx] + dp->df_count[idx] + diff_context > lnum)
            return FALSE;
    }
    return TRUE;
}
#endif

/*
 * "dp" and "do" commands.
 */
    void
nv_diffgetput(put)
    int         put;
{
    exarg_T     ea;

    ea.arg = (char_u *)"";
    if (put)
        ea.cmdidx = CMD_diffput;
    else
        ea.cmdidx = CMD_diffget;
    ea.addr_count = 0;
    ea.line1 = curwin->w_cursor.lnum;
    ea.line2 = curwin->w_cursor.lnum;
    ex_diffgetput(&ea);
}

/*
 * ":diffget"
 * ":diffput"
 */
    void
ex_diffgetput(eap)
    exarg_T     *eap;
{
    linenr_T    lnum;
    int         count;
    linenr_T    off = 0;
    diff_T      *dp;
    diff_T      *dprev;
    diff_T      *dfree;
    int         idx_cur;
    int         idx_other;
    int         idx_from;
    int         idx_to;
    int         i;
    int         added;
    char_u      *p;
    aco_save_T  aco;
    buf_T       *buf;
    int         start_skip, end_skip;
    int         new_count;
    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(_("E99: Current buffer is not in diff mode"));
        return;
    }

    if (*eap->arg == NUL)
    {
        /* No argument: Find the other buffer in the list of diff buffers. */
        for (idx_other = 0; idx_other < DB_COUNT; ++idx_other)
            if (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(_("E793: No other buffer in diff mode is modifiable"));
            else
                EMSG(_("E100: No other buffer in diff mode"));
            return;
        }

        /* Check that there isn't a third buffer in the list */
        for (i = idx_other + 1; i < DB_COUNT; ++i)
            if (curtab->tp_diffbuf[i] != curbuf
                    && curtab->tp_diffbuf[i] != NULL
                    && (eap->cmdidx != CMD_diffput || curtab->tp_diffbuf[i]->b_p_ma))
            {
                EMSG(_("E101: More than two buffers in diff mode, don't know which one to use"));
                return;
            }
    }
    else
    {
        /* Buffer number or pattern given.  Ignore trailing white space. */
        p = eap->arg + STRLEN(eap->arg);
        while (p > eap->arg && vim_iswhite(p[-1]))
            --p;
        for (i = 0; vim_isdigit(eap->arg[i]) && eap->arg + i < p; ++i)
            ;
        if (eap->arg + i == p)      /* digits only */
            i = atol((char *)eap->arg);
        else
        {
            i = buflist_findpat(eap->arg, p, FALSE, TRUE);
            if (i < 0)
                return;         /* error message already given */
        }
        buf = buflist_findnr(i);
        if (buf == NULL)
        {
            EMSG2(_("E102: Can't find buffer \"%s\""), eap->arg);
            return;
        }
        if (buf == curbuf)
            return;             /* nothing to do */
        idx_other = diff_buf_idx(buf);
        if (idx_other == DB_COUNT)
        {
            EMSG2(_("E103: Buffer \"%s\" is not in diff mode"), eap->arg);
            return;
        }
    }

    diff_busy = TRUE;

    /* When no range given include the line above or below the cursor. */
    if (eap->addr_count == 0)
    {
        /* Make it possible that ":diffget" on the last line gets line below
         * the cursor line when there is no difference above the cursor. */
        if (eap->cmdidx == CMD_diffget
                && eap->line1 == curbuf->b_ml.ml_line_count
                && diff_check(curwin, eap->line1) == 0
                && (eap->line1 == 1 || diff_check(curwin, eap->line1 - 1) == 0))
            ++eap->line2;
        else if (eap->line1 > 0)
            --eap->line1;
    }

    if (eap->cmdidx == CMD_diffget)
    {
        idx_from = idx_other;
        idx_to = idx_cur;
    }
    else
    {
        idx_from = idx_cur;
        idx_to = idx_other;
        /* Need to make the other buffer the current buffer to be able to make
         * changes in it. */
        /* set curwin/curbuf to buf and save a few things */
        aucmd_prepbuf(&aco, curtab->tp_diffbuf[idx_other]);
    }

    /* 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(_("E787: Buffer changed unexpectedly"));
            return;
        }
    }

    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 = FALSE;
            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;
                ml_delete(lnum, FALSE);
                --added;
            }
            for (i = 0; i < dp->df_count[idx_from] - start_skip - end_skip; ++i)
            {
                linenr_T nr;

                nr = dp->df_lnum[idx_from] + start_skip + i;
                if (nr > 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, FALSE);
                    }
                }
            }
            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;
                }
            }

            /* Adjust marks.  This will change the following entries! */
            if (added != 0)
            {
                mark_adjust(lnum, lnum + count - 1, (long)MAXLNUM, (long)added);
                if (curwin->w_cursor.lnum >= lnum)
                {
                    /* Adjust the cursor position if it's in/after the changed
                     * lines. */
                    if (curwin->w_cursor.lnum >= lnum + count)
                        curwin->w_cursor.lnum += added;
                    else if (added < 0)
                        curwin->w_cursor.lnum = lnum;
                }
            }
            changed_lines(lnum, 0, lnum + count, (long)added);

            if (dfree != NULL)
            {
                /* Diff is deleted, update folds in other windows. */
#ifdef FEAT_FOLDING
                diff_fold_update(dfree, idx_to);
#endif
                vim_free(dfree);
            }
            else
                /* mark_adjust() may have changed the count in a wrong way */
                dp->df_count[idx_to] = new_count;

            /* When changing the current buffer, keep track of line numbers */
            if (idx_cur == idx_to)
                off += added;
        }

        /* If before the range or not deleted, go to next diff. */
        if (dfree == NULL)
        {
            dprev = dp;
            dp = dp->df_next;
        }
    }

    /* restore curwin/curbuf and a few other things */
    if (idx_other == idx_to)
    {
        /* Syncing undo only works for the current buffer, but we change
         * another buffer.  Sync undo if the command was typed.  This isn't
         * 100% right when ":diffput" is used in a function or mapping. */
        if (KeyTyped)
            u_sync(FALSE);
        aucmd_restbuf(&aco);
    }

    diff_busy = FALSE;

    /* Check that the cursor is on a valid character and update it's position.
     * When there were filler lines the topline has become invalid. */
    check_cursor();
    changed_line_abv_curs();

    /* Also need to redraw the other buffers. */
    diff_redraw(FALSE);
}

#ifdef FEAT_FOLDING
/*
 * Update folds for all diff buffers for entry "dp".
 * Skip buffer with index "skip_idx".
 * When there are no diffs, all folds are removed.
 */
    static void
diff_fold_update(dp, skip_idx)
    diff_T      *dp;
    int         skip_idx;
{
    int         i;
    win_T       *wp;

    for (wp = firstwin; wp != NULL; wp = wp->w_next)
        for (i = 0; i < DB_COUNT; ++i)
            if (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)
    buf_T       *buf;
{
    tabpage_T   *tp;

    for (tp = first_tabpage; tp != NULL; tp = tp->tp_next)
        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(dir, count)
    int         dir;
    long        count;
{
    int         idx;
    linenr_T    lnum = curwin->w_cursor.lnum;
    diff_T      *dp;

    idx = diff_buf_idx(curbuf);
    if (idx == DB_COUNT || 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;
}

#if defined(FEAT_FOLDING) || defined(PROTO)
/*
 * For line "lnum" in the current window find the equivalent lnum in window
 * "wp", compensating for inserted/deleted lines.
 */
    linenr_T
diff_lnum_win(lnum, wp)
    linenr_T    lnum;
    win_T       *wp;
{
    diff_T      *dp;
    int         idx;
    int         i;
    linenr_T    n;

    idx = diff_buf_idx(curbuf);
    if (idx == DB_COUNT)                /* safety check */
        return (linenr_T)0;

    if (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 (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)
        if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
            break;

    /* When after the last change, compute relative to the last line number. */
    if (dp == NULL)
        return wp->w_buffer->b_ml.ml_line_count
                                        - (curbuf->b_ml.ml_line_count - lnum);

    /* Find index for "wp". */
    i = diff_buf_idx(wp->w_buffer);
    if (i == DB_COUNT)                  /* safety check */
        return (linenr_T)0;

    n = lnum + (dp->df_lnum[i] - dp->df_lnum[idx]);
    if (n > dp->df_lnum[i] + dp->df_count[i])
        n = dp->df_lnum[i] + dp->df_count[i];
    return n;
}
#endif

#endif  /* FEAT_DIFF */