xref: /vim-8.2.3635/src/undo.c (revision bb76f24a)
1 /* vi:set ts=8 sts=4 sw=4 noet:
2  *
3  * VIM - Vi IMproved	by Bram Moolenaar
4  *
5  * Do ":help uganda"  in Vim to read copying and usage conditions.
6  * Do ":help credits" in Vim to see a list of people who contributed.
7  * See README.txt for an overview of the Vim source code.
8  */
9 
10 /*
11  * undo.c: multi level undo facility
12  *
13  * The saved lines are stored in a list of lists (one for each buffer):
14  *
15  * b_u_oldhead------------------------------------------------+
16  *							      |
17  *							      V
18  *		  +--------------+    +--------------+	  +--------------+
19  * b_u_newhead--->| u_header	 |    | u_header     |	  | u_header	 |
20  *		  |	uh_next------>|     uh_next------>|	uh_next---->NULL
21  *	   NULL<--------uh_prev  |<---------uh_prev  |<---------uh_prev  |
22  *		  |	uh_entry |    |     uh_entry |	  |	uh_entry |
23  *		  +--------|-----+    +--------|-----+	  +--------|-----+
24  *			   |		       |		   |
25  *			   V		       V		   V
26  *		  +--------------+    +--------------+	  +--------------+
27  *		  | u_entry	 |    | u_entry      |	  | u_entry	 |
28  *		  |	ue_next  |    |     ue_next  |	  |	ue_next  |
29  *		  +--------|-----+    +--------|-----+	  +--------|-----+
30  *			   |		       |		   |
31  *			   V		       V		   V
32  *		  +--------------+	      NULL		  NULL
33  *		  | u_entry	 |
34  *		  |	ue_next  |
35  *		  +--------|-----+
36  *			   |
37  *			   V
38  *			  etc.
39  *
40  * Each u_entry list contains the information for one undo or redo.
41  * curbuf->b_u_curhead points to the header of the last undo (the next redo),
42  * or is NULL if nothing has been undone (end of the branch).
43  *
44  * For keeping alternate undo/redo branches the uh_alt field is used.  Thus at
45  * each point in the list a branch may appear for an alternate to redo.  The
46  * uh_seq field is numbered sequentially to be able to find a newer or older
47  * branch.
48  *
49  *		   +---------------+	+---------------+
50  * b_u_oldhead --->| u_header	   |	| u_header	|
51  *		   |   uh_alt_next ---->|   uh_alt_next ----> NULL
52  *	   NULL <----- uh_alt_prev |<------ uh_alt_prev |
53  *		   |   uh_prev	   |	|   uh_prev	|
54  *		   +-----|---------+	+-----|---------+
55  *			 |		      |
56  *			 V		      V
57  *		   +---------------+	+---------------+
58  *		   | u_header	   |	| u_header	|
59  *		   |   uh_alt_next |	|   uh_alt_next |
60  * b_u_newhead --->|   uh_alt_prev |	|   uh_alt_prev |
61  *		   |   uh_prev	   |	|   uh_prev	|
62  *		   +-----|---------+	+-----|---------+
63  *			 |		      |
64  *			 V		      V
65  *		       NULL		+---------------+    +---------------+
66  *					| u_header	|    | u_header      |
67  *					|   uh_alt_next ---->|	 uh_alt_next |
68  *					|   uh_alt_prev |<------ uh_alt_prev |
69  *					|   uh_prev	|    |	 uh_prev     |
70  *					+-----|---------+    +-----|---------+
71  *					      |			   |
72  *					     etc.		  etc.
73  *
74  *
75  * All data is allocated and will all be freed when the buffer is unloaded.
76  */
77 
78 /* Uncomment the next line for including the u_check() function.  This warns
79  * for errors in the debug information. */
80 /* #define U_DEBUG 1 */
81 #define UH_MAGIC 0x18dade	/* value for uh_magic when in use */
82 #define UE_MAGIC 0xabc123	/* value for ue_magic when in use */
83 
84 /* Size of buffer used for encryption. */
85 #define CRYPT_BUF_SIZE 8192
86 
87 #include "vim.h"
88 
89 /* Structure passed around between functions.
90  * Avoids passing cryptstate_T when encryption not available. */
91 typedef struct {
92     buf_T	*bi_buf;
93     FILE	*bi_fp;
94 #ifdef FEAT_CRYPT
95     cryptstate_T *bi_state;
96     char_u	*bi_buffer; /* CRYPT_BUF_SIZE, NULL when not buffering */
97     size_t	bi_used;    /* bytes written to/read from bi_buffer */
98     size_t	bi_avail;   /* bytes available in bi_buffer */
99 #endif
100 } bufinfo_T;
101 
102 
103 static long get_undolevel(void);
104 static void u_unch_branch(u_header_T *uhp);
105 static u_entry_T *u_get_headentry(void);
106 static void u_getbot(void);
107 static void u_doit(int count);
108 static void u_undoredo(int undo);
109 static void u_undo_end(int did_undo, int absolute);
110 static void u_add_time(char_u *buf, size_t buflen, time_t tt);
111 static void u_freeheader(buf_T *buf, u_header_T *uhp, u_header_T **uhpp);
112 static void u_freebranch(buf_T *buf, u_header_T *uhp, u_header_T **uhpp);
113 static void u_freeentries(buf_T *buf, u_header_T *uhp, u_header_T **uhpp);
114 static void u_freeentry(u_entry_T *, long);
115 #ifdef FEAT_PERSISTENT_UNDO
116 static void corruption_error(char *mesg, char_u *file_name);
117 static void u_free_uhp(u_header_T *uhp);
118 static int undo_write(bufinfo_T *bi, char_u *ptr, size_t len);
119 # ifdef FEAT_CRYPT
120 static int undo_flush(bufinfo_T *bi);
121 # endif
122 static int fwrite_crypt(bufinfo_T *bi, char_u *ptr, size_t len);
123 static int undo_write_bytes(bufinfo_T *bi, long_u nr, int len);
124 static void put_header_ptr(bufinfo_T *bi, u_header_T *uhp);
125 static int undo_read_4c(bufinfo_T *bi);
126 static int undo_read_2c(bufinfo_T *bi);
127 static int undo_read_byte(bufinfo_T *bi);
128 static time_t undo_read_time(bufinfo_T *bi);
129 static int undo_read(bufinfo_T *bi, char_u *buffer, size_t size);
130 static char_u *read_string_decrypt(bufinfo_T *bi, int len);
131 static int serialize_header(bufinfo_T *bi, char_u *hash);
132 static int serialize_uhp(bufinfo_T *bi, u_header_T *uhp);
133 static u_header_T *unserialize_uhp(bufinfo_T *bi, char_u *file_name);
134 static int serialize_uep(bufinfo_T *bi, u_entry_T *uep);
135 static u_entry_T *unserialize_uep(bufinfo_T *bi, int *error, char_u *file_name);
136 static void serialize_pos(bufinfo_T *bi, pos_T pos);
137 static void unserialize_pos(bufinfo_T *bi, pos_T *pos);
138 static void serialize_visualinfo(bufinfo_T *bi, visualinfo_T *info);
139 static void unserialize_visualinfo(bufinfo_T *bi, visualinfo_T *info);
140 #endif
141 
142 #define U_ALLOC_LINE(size) lalloc((long_u)(size), FALSE)
143 static char_u *u_save_line(linenr_T);
144 
145 /* used in undo_end() to report number of added and deleted lines */
146 static long	u_newcount, u_oldcount;
147 
148 /*
149  * When 'u' flag included in 'cpoptions', we behave like vi.  Need to remember
150  * the action that "u" should do.
151  */
152 static int	undo_undoes = FALSE;
153 
154 static int	lastmark = 0;
155 
156 #if defined(U_DEBUG) || defined(PROTO)
157 /*
158  * Check the undo structures for being valid.  Print a warning when something
159  * looks wrong.
160  */
161 static int seen_b_u_curhead;
162 static int seen_b_u_newhead;
163 static int header_count;
164 
165     static void
166 u_check_tree(u_header_T *uhp,
167 	u_header_T *exp_uh_next,
168 	u_header_T *exp_uh_alt_prev)
169 {
170     u_entry_T *uep;
171 
172     if (uhp == NULL)
173 	return;
174     ++header_count;
175     if (uhp == curbuf->b_u_curhead && ++seen_b_u_curhead > 1)
176     {
177 	EMSG("b_u_curhead found twice (looping?)");
178 	return;
179     }
180     if (uhp == curbuf->b_u_newhead && ++seen_b_u_newhead > 1)
181     {
182 	EMSG("b_u_newhead found twice (looping?)");
183 	return;
184     }
185 
186     if (uhp->uh_magic != UH_MAGIC)
187 	EMSG("uh_magic wrong (may be using freed memory)");
188     else
189     {
190 	/* Check pointers back are correct. */
191 	if (uhp->uh_next.ptr != exp_uh_next)
192 	{
193 	    EMSG("uh_next wrong");
194 	    smsg((char_u *)"expected: 0x%x, actual: 0x%x",
195 					       exp_uh_next, uhp->uh_next.ptr);
196 	}
197 	if (uhp->uh_alt_prev.ptr != exp_uh_alt_prev)
198 	{
199 	    EMSG("uh_alt_prev wrong");
200 	    smsg((char_u *)"expected: 0x%x, actual: 0x%x",
201 				       exp_uh_alt_prev, uhp->uh_alt_prev.ptr);
202 	}
203 
204 	/* Check the undo tree at this header. */
205 	for (uep = uhp->uh_entry; uep != NULL; uep = uep->ue_next)
206 	{
207 	    if (uep->ue_magic != UE_MAGIC)
208 	    {
209 		EMSG("ue_magic wrong (may be using freed memory)");
210 		break;
211 	    }
212 	}
213 
214 	/* Check the next alt tree. */
215 	u_check_tree(uhp->uh_alt_next.ptr, uhp->uh_next.ptr, uhp);
216 
217 	/* Check the next header in this branch. */
218 	u_check_tree(uhp->uh_prev.ptr, uhp, NULL);
219     }
220 }
221 
222     static void
223 u_check(int newhead_may_be_NULL)
224 {
225     seen_b_u_newhead = 0;
226     seen_b_u_curhead = 0;
227     header_count = 0;
228 
229     u_check_tree(curbuf->b_u_oldhead, NULL, NULL);
230 
231     if (seen_b_u_newhead == 0 && curbuf->b_u_oldhead != NULL
232 	    && !(newhead_may_be_NULL && curbuf->b_u_newhead == NULL))
233 	EMSGN("b_u_newhead invalid: 0x%x", curbuf->b_u_newhead);
234     if (curbuf->b_u_curhead != NULL && seen_b_u_curhead == 0)
235 	EMSGN("b_u_curhead invalid: 0x%x", curbuf->b_u_curhead);
236     if (header_count != curbuf->b_u_numhead)
237     {
238 	EMSG("b_u_numhead invalid");
239 	smsg((char_u *)"expected: %ld, actual: %ld",
240 			       (long)header_count, (long)curbuf->b_u_numhead);
241     }
242 }
243 #endif
244 
245 /*
246  * Save the current line for both the "u" and "U" command.
247  * Careful: may trigger autocommands that reload the buffer.
248  * Returns OK or FAIL.
249  */
250     int
251 u_save_cursor(void)
252 {
253     return (u_save((linenr_T)(curwin->w_cursor.lnum - 1),
254 				      (linenr_T)(curwin->w_cursor.lnum + 1)));
255 }
256 
257 /*
258  * Save the lines between "top" and "bot" for both the "u" and "U" command.
259  * "top" may be 0 and bot may be curbuf->b_ml.ml_line_count + 1.
260  * Careful: may trigger autocommands that reload the buffer.
261  * Returns FAIL when lines could not be saved, OK otherwise.
262  */
263     int
264 u_save(linenr_T top, linenr_T bot)
265 {
266     if (undo_off)
267 	return OK;
268 
269     if (top > curbuf->b_ml.ml_line_count
270 	    || top >= bot
271 	    || bot > curbuf->b_ml.ml_line_count + 1)
272 	return FALSE;	/* rely on caller to do error messages */
273 
274     if (top + 2 == bot)
275 	u_saveline((linenr_T)(top + 1));
276 
277     return (u_savecommon(top, bot, (linenr_T)0, FALSE));
278 }
279 
280 /*
281  * Save the line "lnum" (used by ":s" and "~" command).
282  * The line is replaced, so the new bottom line is lnum + 1.
283  * Careful: may trigger autocommands that reload the buffer.
284  * Returns FAIL when lines could not be saved, OK otherwise.
285  */
286     int
287 u_savesub(linenr_T lnum)
288 {
289     if (undo_off)
290 	return OK;
291 
292     return (u_savecommon(lnum - 1, lnum + 1, lnum + 1, FALSE));
293 }
294 
295 /*
296  * A new line is inserted before line "lnum" (used by :s command).
297  * The line is inserted, so the new bottom line is lnum + 1.
298  * Careful: may trigger autocommands that reload the buffer.
299  * Returns FAIL when lines could not be saved, OK otherwise.
300  */
301     int
302 u_inssub(linenr_T lnum)
303 {
304     if (undo_off)
305 	return OK;
306 
307     return (u_savecommon(lnum - 1, lnum, lnum + 1, FALSE));
308 }
309 
310 /*
311  * Save the lines "lnum" - "lnum" + nlines (used by delete command).
312  * The lines are deleted, so the new bottom line is lnum, unless the buffer
313  * becomes empty.
314  * Careful: may trigger autocommands that reload the buffer.
315  * Returns FAIL when lines could not be saved, OK otherwise.
316  */
317     int
318 u_savedel(linenr_T lnum, long nlines)
319 {
320     if (undo_off)
321 	return OK;
322 
323     return (u_savecommon(lnum - 1, lnum + nlines,
324 		     nlines == curbuf->b_ml.ml_line_count ? 2 : lnum, FALSE));
325 }
326 
327 /*
328  * Return TRUE when undo is allowed.  Otherwise give an error message and
329  * return FALSE.
330  */
331     int
332 undo_allowed(void)
333 {
334     /* Don't allow changes when 'modifiable' is off.  */
335     if (!curbuf->b_p_ma)
336     {
337 	EMSG(_(e_modifiable));
338 	return FALSE;
339     }
340 
341 #ifdef HAVE_SANDBOX
342     /* In the sandbox it's not allowed to change the text. */
343     if (sandbox != 0)
344     {
345 	EMSG(_(e_sandbox));
346 	return FALSE;
347     }
348 #endif
349 
350     /* Don't allow changes in the buffer while editing the cmdline.  The
351      * caller of getcmdline() may get confused. */
352     if (textlock != 0)
353     {
354 	EMSG(_(e_secure));
355 	return FALSE;
356     }
357 
358     return TRUE;
359 }
360 
361 /*
362  * Get the undolevle value for the current buffer.
363  */
364     static long
365 get_undolevel(void)
366 {
367     if (curbuf->b_p_ul == NO_LOCAL_UNDOLEVEL)
368 	return p_ul;
369     return curbuf->b_p_ul;
370 }
371 
372 /*
373  * Common code for various ways to save text before a change.
374  * "top" is the line above the first changed line.
375  * "bot" is the line below the last changed line.
376  * "newbot" is the new bottom line.  Use zero when not known.
377  * "reload" is TRUE when saving for a buffer reload.
378  * Careful: may trigger autocommands that reload the buffer.
379  * Returns FAIL when lines could not be saved, OK otherwise.
380  */
381     int
382 u_savecommon(
383     linenr_T	top,
384     linenr_T	bot,
385     linenr_T	newbot,
386     int		reload)
387 {
388     linenr_T	lnum;
389     long	i;
390     u_header_T	*uhp;
391     u_header_T	*old_curhead;
392     u_entry_T	*uep;
393     u_entry_T	*prev_uep;
394     long	size;
395 
396     if (!reload)
397     {
398 	/* When making changes is not allowed return FAIL.  It's a crude way
399 	 * to make all change commands fail. */
400 	if (!undo_allowed())
401 	    return FAIL;
402 
403 #ifdef FEAT_NETBEANS_INTG
404 	/*
405 	 * Netbeans defines areas that cannot be modified.  Bail out here when
406 	 * trying to change text in a guarded area.
407 	 */
408 	if (netbeans_active())
409 	{
410 	    if (netbeans_is_guarded(top, bot))
411 	    {
412 		EMSG(_(e_guarded));
413 		return FAIL;
414 	    }
415 	    if (curbuf->b_p_ro)
416 	    {
417 		EMSG(_(e_nbreadonly));
418 		return FAIL;
419 	    }
420 	}
421 #endif
422 
423 #ifdef FEAT_AUTOCMD
424 	/*
425 	 * Saving text for undo means we are going to make a change.  Give a
426 	 * warning for a read-only file before making the change, so that the
427 	 * FileChangedRO event can replace the buffer with a read-write version
428 	 * (e.g., obtained from a source control system).
429 	 */
430 	change_warning(0);
431 	if (bot > curbuf->b_ml.ml_line_count + 1)
432 	{
433 	    /* This happens when the FileChangedRO autocommand changes the
434 	     * file in a way it becomes shorter. */
435 	    EMSG(_("E881: Line count changed unexpectedly"));
436 	    return FAIL;
437 	}
438 #endif
439     }
440 
441 #ifdef U_DEBUG
442     u_check(FALSE);
443 #endif
444 
445     size = bot - top - 1;
446 
447     /*
448      * If curbuf->b_u_synced == TRUE make a new header.
449      */
450     if (curbuf->b_u_synced)
451     {
452 #ifdef FEAT_JUMPLIST
453 	/* Need to create new entry in b_changelist. */
454 	curbuf->b_new_change = TRUE;
455 #endif
456 
457 	if (get_undolevel() >= 0)
458 	{
459 	    /*
460 	     * Make a new header entry.  Do this first so that we don't mess
461 	     * up the undo info when out of memory.
462 	     */
463 	    uhp = (u_header_T *)U_ALLOC_LINE(sizeof(u_header_T));
464 	    if (uhp == NULL)
465 		goto nomem;
466 #ifdef U_DEBUG
467 	    uhp->uh_magic = UH_MAGIC;
468 #endif
469 	}
470 	else
471 	    uhp = NULL;
472 
473 	/*
474 	 * If we undid more than we redid, move the entry lists before and
475 	 * including curbuf->b_u_curhead to an alternate branch.
476 	 */
477 	old_curhead = curbuf->b_u_curhead;
478 	if (old_curhead != NULL)
479 	{
480 	    curbuf->b_u_newhead = old_curhead->uh_next.ptr;
481 	    curbuf->b_u_curhead = NULL;
482 	}
483 
484 	/*
485 	 * free headers to keep the size right
486 	 */
487 	while (curbuf->b_u_numhead > get_undolevel()
488 					       && curbuf->b_u_oldhead != NULL)
489 	{
490 	    u_header_T	    *uhfree = curbuf->b_u_oldhead;
491 
492 	    if (uhfree == old_curhead)
493 		/* Can't reconnect the branch, delete all of it. */
494 		u_freebranch(curbuf, uhfree, &old_curhead);
495 	    else if (uhfree->uh_alt_next.ptr == NULL)
496 		/* There is no branch, only free one header. */
497 		u_freeheader(curbuf, uhfree, &old_curhead);
498 	    else
499 	    {
500 		/* Free the oldest alternate branch as a whole. */
501 		while (uhfree->uh_alt_next.ptr != NULL)
502 		    uhfree = uhfree->uh_alt_next.ptr;
503 		u_freebranch(curbuf, uhfree, &old_curhead);
504 	    }
505 #ifdef U_DEBUG
506 	    u_check(TRUE);
507 #endif
508 	}
509 
510 	if (uhp == NULL)		/* no undo at all */
511 	{
512 	    if (old_curhead != NULL)
513 		u_freebranch(curbuf, old_curhead, NULL);
514 	    curbuf->b_u_synced = FALSE;
515 	    return OK;
516 	}
517 
518 	uhp->uh_prev.ptr = NULL;
519 	uhp->uh_next.ptr = curbuf->b_u_newhead;
520 	uhp->uh_alt_next.ptr = old_curhead;
521 	if (old_curhead != NULL)
522 	{
523 	    uhp->uh_alt_prev.ptr = old_curhead->uh_alt_prev.ptr;
524 	    if (uhp->uh_alt_prev.ptr != NULL)
525 		uhp->uh_alt_prev.ptr->uh_alt_next.ptr = uhp;
526 	    old_curhead->uh_alt_prev.ptr = uhp;
527 	    if (curbuf->b_u_oldhead == old_curhead)
528 		curbuf->b_u_oldhead = uhp;
529 	}
530 	else
531 	    uhp->uh_alt_prev.ptr = NULL;
532 	if (curbuf->b_u_newhead != NULL)
533 	    curbuf->b_u_newhead->uh_prev.ptr = uhp;
534 
535 	uhp->uh_seq = ++curbuf->b_u_seq_last;
536 	curbuf->b_u_seq_cur = uhp->uh_seq;
537 	uhp->uh_time = vim_time();
538 	uhp->uh_save_nr = 0;
539 	curbuf->b_u_time_cur = uhp->uh_time + 1;
540 
541 	uhp->uh_walk = 0;
542 	uhp->uh_entry = NULL;
543 	uhp->uh_getbot_entry = NULL;
544 	uhp->uh_cursor = curwin->w_cursor;	/* save cursor pos. for undo */
545 #ifdef FEAT_VIRTUALEDIT
546 	if (virtual_active() && curwin->w_cursor.coladd > 0)
547 	    uhp->uh_cursor_vcol = getviscol();
548 	else
549 	    uhp->uh_cursor_vcol = -1;
550 #endif
551 
552 	/* save changed and buffer empty flag for undo */
553 	uhp->uh_flags = (curbuf->b_changed ? UH_CHANGED : 0) +
554 		       ((curbuf->b_ml.ml_flags & ML_EMPTY) ? UH_EMPTYBUF : 0);
555 
556 	/* save named marks and Visual marks for undo */
557 	mch_memmove(uhp->uh_namedm, curbuf->b_namedm, sizeof(pos_T) * NMARKS);
558 	uhp->uh_visual = curbuf->b_visual;
559 
560 	curbuf->b_u_newhead = uhp;
561 	if (curbuf->b_u_oldhead == NULL)
562 	    curbuf->b_u_oldhead = uhp;
563 	++curbuf->b_u_numhead;
564     }
565     else
566     {
567 	if (get_undolevel() < 0)	/* no undo at all */
568 	    return OK;
569 
570 	/*
571 	 * When saving a single line, and it has been saved just before, it
572 	 * doesn't make sense saving it again.  Saves a lot of memory when
573 	 * making lots of changes inside the same line.
574 	 * This is only possible if the previous change didn't increase or
575 	 * decrease the number of lines.
576 	 * Check the ten last changes.  More doesn't make sense and takes too
577 	 * long.
578 	 */
579 	if (size == 1)
580 	{
581 	    uep = u_get_headentry();
582 	    prev_uep = NULL;
583 	    for (i = 0; i < 10; ++i)
584 	    {
585 		if (uep == NULL)
586 		    break;
587 
588 		/* If lines have been inserted/deleted we give up.
589 		 * Also when the line was included in a multi-line save. */
590 		if ((curbuf->b_u_newhead->uh_getbot_entry != uep
591 			    ? (uep->ue_top + uep->ue_size + 1
592 				!= (uep->ue_bot == 0
593 				    ? curbuf->b_ml.ml_line_count + 1
594 				    : uep->ue_bot))
595 			    : uep->ue_lcount != curbuf->b_ml.ml_line_count)
596 			|| (uep->ue_size > 1
597 			    && top >= uep->ue_top
598 			    && top + 2 <= uep->ue_top + uep->ue_size + 1))
599 		    break;
600 
601 		/* If it's the same line we can skip saving it again. */
602 		if (uep->ue_size == 1 && uep->ue_top == top)
603 		{
604 		    if (i > 0)
605 		    {
606 			/* It's not the last entry: get ue_bot for the last
607 			 * entry now.  Following deleted/inserted lines go to
608 			 * the re-used entry. */
609 			u_getbot();
610 			curbuf->b_u_synced = FALSE;
611 
612 			/* Move the found entry to become the last entry.  The
613 			 * order of undo/redo doesn't matter for the entries
614 			 * we move it over, since they don't change the line
615 			 * count and don't include this line.  It does matter
616 			 * for the found entry if the line count is changed by
617 			 * the executed command. */
618 			prev_uep->ue_next = uep->ue_next;
619 			uep->ue_next = curbuf->b_u_newhead->uh_entry;
620 			curbuf->b_u_newhead->uh_entry = uep;
621 		    }
622 
623 		    /* The executed command may change the line count. */
624 		    if (newbot != 0)
625 			uep->ue_bot = newbot;
626 		    else if (bot > curbuf->b_ml.ml_line_count)
627 			uep->ue_bot = 0;
628 		    else
629 		    {
630 			uep->ue_lcount = curbuf->b_ml.ml_line_count;
631 			curbuf->b_u_newhead->uh_getbot_entry = uep;
632 		    }
633 		    return OK;
634 		}
635 		prev_uep = uep;
636 		uep = uep->ue_next;
637 	    }
638 	}
639 
640 	/* find line number for ue_bot for previous u_save() */
641 	u_getbot();
642     }
643 
644 #if !defined(UNIX) && !defined(WIN32)
645 	/*
646 	 * With Amiga we can't handle big undo's, because
647 	 * then u_alloc_line would have to allocate a block larger than 32K
648 	 */
649     if (size >= 8000)
650 	goto nomem;
651 #endif
652 
653     /*
654      * add lines in front of entry list
655      */
656     uep = (u_entry_T *)U_ALLOC_LINE(sizeof(u_entry_T));
657     if (uep == NULL)
658 	goto nomem;
659     vim_memset(uep, 0, sizeof(u_entry_T));
660 #ifdef U_DEBUG
661     uep->ue_magic = UE_MAGIC;
662 #endif
663 
664     uep->ue_size = size;
665     uep->ue_top = top;
666     if (newbot != 0)
667 	uep->ue_bot = newbot;
668     /*
669      * Use 0 for ue_bot if bot is below last line.
670      * Otherwise we have to compute ue_bot later.
671      */
672     else if (bot > curbuf->b_ml.ml_line_count)
673 	uep->ue_bot = 0;
674     else
675     {
676 	uep->ue_lcount = curbuf->b_ml.ml_line_count;
677 	curbuf->b_u_newhead->uh_getbot_entry = uep;
678     }
679 
680     if (size > 0)
681     {
682 	if ((uep->ue_array = (char_u **)U_ALLOC_LINE(
683 					    sizeof(char_u *) * size)) == NULL)
684 	{
685 	    u_freeentry(uep, 0L);
686 	    goto nomem;
687 	}
688 	for (i = 0, lnum = top + 1; i < size; ++i)
689 	{
690 	    fast_breakcheck();
691 	    if (got_int)
692 	    {
693 		u_freeentry(uep, i);
694 		return FAIL;
695 	    }
696 	    if ((uep->ue_array[i] = u_save_line(lnum++)) == NULL)
697 	    {
698 		u_freeentry(uep, i);
699 		goto nomem;
700 	    }
701 	}
702     }
703     else
704 	uep->ue_array = NULL;
705     uep->ue_next = curbuf->b_u_newhead->uh_entry;
706     curbuf->b_u_newhead->uh_entry = uep;
707     curbuf->b_u_synced = FALSE;
708     undo_undoes = FALSE;
709 
710 #ifdef U_DEBUG
711     u_check(FALSE);
712 #endif
713     return OK;
714 
715 nomem:
716     msg_silent = 0;	/* must display the prompt */
717     if (ask_yesno((char_u *)_("No undo possible; continue anyway"), TRUE)
718 								       == 'y')
719     {
720 	undo_off = TRUE;	    /* will be reset when character typed */
721 	return OK;
722     }
723     do_outofmem_msg((long_u)0);
724     return FAIL;
725 }
726 
727 #if defined(FEAT_PERSISTENT_UNDO) || defined(PROTO)
728 
729 # define UF_START_MAGIC	    "Vim\237UnDo\345"  /* magic at start of undofile */
730 # define UF_START_MAGIC_LEN	9
731 # define UF_HEADER_MAGIC	0x5fd0	/* magic at start of header */
732 # define UF_HEADER_END_MAGIC	0xe7aa	/* magic after last header */
733 # define UF_ENTRY_MAGIC		0xf518	/* magic at start of entry */
734 # define UF_ENTRY_END_MAGIC	0x3581	/* magic after last entry */
735 # define UF_VERSION		2	/* 2-byte undofile version number */
736 # define UF_VERSION_CRYPT	0x8002	/* idem, encrypted */
737 
738 /* extra fields for header */
739 # define UF_LAST_SAVE_NR	1
740 
741 /* extra fields for uhp */
742 # define UHP_SAVE_NR		1
743 
744 static char_u e_not_open[] = N_("E828: Cannot open undo file for writing: %s");
745 
746 /*
747  * Compute the hash for the current buffer text into hash[UNDO_HASH_SIZE].
748  */
749     void
750 u_compute_hash(char_u *hash)
751 {
752     context_sha256_T	ctx;
753     linenr_T		lnum;
754     char_u		*p;
755 
756     sha256_start(&ctx);
757     for (lnum = 1; lnum <= curbuf->b_ml.ml_line_count; ++lnum)
758     {
759 	p = ml_get(lnum);
760 	sha256_update(&ctx, p, (UINT32_T)(STRLEN(p) + 1));
761     }
762     sha256_finish(&ctx, hash);
763 }
764 
765 /*
766  * Return an allocated string of the full path of the target undofile.
767  * When "reading" is TRUE find the file to read, go over all directories in
768  * 'undodir'.
769  * When "reading" is FALSE use the first name where the directory exists.
770  * Returns NULL when there is no place to write or no file to read.
771  */
772     char_u *
773 u_get_undo_file_name(char_u *buf_ffname, int reading)
774 {
775     char_u	*dirp;
776     char_u	dir_name[IOSIZE + 1];
777     char_u	*munged_name = NULL;
778     char_u	*undo_file_name = NULL;
779     int		dir_len;
780     char_u	*p;
781     stat_T	st;
782     char_u	*ffname = buf_ffname;
783 #ifdef HAVE_READLINK
784     char_u	fname_buf[MAXPATHL];
785 #endif
786 
787     if (ffname == NULL)
788 	return NULL;
789 
790 #ifdef HAVE_READLINK
791     /* Expand symlink in the file name, so that we put the undo file with the
792      * actual file instead of with the symlink. */
793     if (resolve_symlink(ffname, fname_buf) == OK)
794 	ffname = fname_buf;
795 #endif
796 
797     /* Loop over 'undodir'.  When reading find the first file that exists.
798      * When not reading use the first directory that exists or ".". */
799     dirp = p_udir;
800     while (*dirp != NUL)
801     {
802 	dir_len = copy_option_part(&dirp, dir_name, IOSIZE, ",");
803 	if (dir_len == 1 && dir_name[0] == '.')
804 	{
805 	    /* Use same directory as the ffname,
806 	     * "dir/name" -> "dir/.name.un~" */
807 	    undo_file_name = vim_strnsave(ffname, (int)(STRLEN(ffname) + 5));
808 	    if (undo_file_name == NULL)
809 		break;
810 	    p = gettail(undo_file_name);
811 #ifdef VMS
812 	    /* VMS can not handle more than one dot in the filenames
813 	     * use "dir/name" -> "dir/_un_name" - add _un_
814 	     * at the beginning to keep the extension */
815 	    mch_memmove(p + 4,  p, STRLEN(p) + 1);
816 	    mch_memmove(p, "_un_", 4);
817 
818 #else
819 	    /* Use same directory as the ffname,
820 	     * "dir/name" -> "dir/.name.un~" */
821 	    mch_memmove(p + 1, p, STRLEN(p) + 1);
822 	    *p = '.';
823 	    STRCAT(p, ".un~");
824 #endif
825 	}
826 	else
827 	{
828 	    dir_name[dir_len] = NUL;
829 	    if (mch_isdir(dir_name))
830 	    {
831 		if (munged_name == NULL)
832 		{
833 		    munged_name = vim_strsave(ffname);
834 		    if (munged_name == NULL)
835 			return NULL;
836 		    for (p = munged_name; *p != NUL; mb_ptr_adv(p))
837 			if (vim_ispathsep(*p))
838 			    *p = '%';
839 		}
840 		undo_file_name = concat_fnames(dir_name, munged_name, TRUE);
841 	    }
842 	}
843 
844 	/* When reading check if the file exists. */
845 	if (undo_file_name != NULL && (!reading
846 			       || mch_stat((char *)undo_file_name, &st) >= 0))
847 	    break;
848 	vim_free(undo_file_name);
849 	undo_file_name = NULL;
850     }
851 
852     vim_free(munged_name);
853     return undo_file_name;
854 }
855 
856     static void
857 corruption_error(char *mesg, char_u *file_name)
858 {
859     EMSG3(_("E825: Corrupted undo file (%s): %s"), mesg, file_name);
860 }
861 
862     static void
863 u_free_uhp(u_header_T *uhp)
864 {
865     u_entry_T	*nuep;
866     u_entry_T	*uep;
867 
868     uep = uhp->uh_entry;
869     while (uep != NULL)
870     {
871 	nuep = uep->ue_next;
872 	u_freeentry(uep, uep->ue_size);
873 	uep = nuep;
874     }
875     vim_free(uhp);
876 }
877 
878 /*
879  * Write a sequence of bytes to the undo file.
880  * Buffers and encrypts as needed.
881  * Returns OK or FAIL.
882  */
883     static int
884 undo_write(bufinfo_T *bi, char_u *ptr, size_t len)
885 {
886 #ifdef FEAT_CRYPT
887     if (bi->bi_buffer != NULL)
888     {
889 	size_t	len_todo = len;
890 	char_u  *p = ptr;
891 
892 	while (bi->bi_used + len_todo >= CRYPT_BUF_SIZE)
893 	{
894 	    size_t	n = CRYPT_BUF_SIZE - bi->bi_used;
895 
896 	    mch_memmove(bi->bi_buffer + bi->bi_used, p, n);
897 	    len_todo -= n;
898 	    p += n;
899 	    bi->bi_used = CRYPT_BUF_SIZE;
900 	    if (undo_flush(bi) == FAIL)
901 		return FAIL;
902 	}
903 	if (len_todo > 0)
904 	{
905 	    mch_memmove(bi->bi_buffer + bi->bi_used, p, len_todo);
906 	    bi->bi_used += len_todo;
907 	}
908 	return OK;
909     }
910 #endif
911     if (fwrite(ptr, len, (size_t)1, bi->bi_fp) != 1)
912 	return FAIL;
913     return OK;
914 }
915 
916 #ifdef FEAT_CRYPT
917     static int
918 undo_flush(bufinfo_T *bi)
919 {
920     if (bi->bi_buffer != NULL && bi->bi_used > 0)
921     {
922 	crypt_encode_inplace(bi->bi_state, bi->bi_buffer, bi->bi_used);
923 	if (fwrite(bi->bi_buffer, bi->bi_used, (size_t)1, bi->bi_fp) != 1)
924 	    return FAIL;
925 	bi->bi_used = 0;
926     }
927     return OK;
928 }
929 #endif
930 
931 /*
932  * Write "ptr[len]" and crypt the bytes when needed.
933  * Returns OK or FAIL.
934  */
935     static int
936 fwrite_crypt(bufinfo_T *bi, char_u *ptr, size_t len)
937 {
938 #ifdef FEAT_CRYPT
939     char_u  *copy;
940     char_u  small_buf[100];
941     size_t  i;
942 
943     if (bi->bi_state != NULL && bi->bi_buffer == NULL)
944     {
945 	/* crypting every piece of text separately */
946 	if (len < 100)
947 	    copy = small_buf;  /* no malloc()/free() for short strings */
948 	else
949 	{
950 	    copy = lalloc(len, FALSE);
951 	    if (copy == NULL)
952 		return 0;
953 	}
954 	crypt_encode(bi->bi_state, ptr, len, copy);
955 	i = fwrite(copy, len, (size_t)1, bi->bi_fp);
956 	if (copy != small_buf)
957 	    vim_free(copy);
958 	return i == 1 ? OK : FAIL;
959     }
960 #endif
961     return undo_write(bi, ptr, len);
962 }
963 
964 /*
965  * Write a number, MSB first, in "len" bytes.
966  * Must match with undo_read_?c() functions.
967  * Returns OK or FAIL.
968  */
969     static int
970 undo_write_bytes(bufinfo_T *bi, long_u nr, int len)
971 {
972     char_u  buf[8];
973     int	    i;
974     int	    bufi = 0;
975 
976     for (i = len - 1; i >= 0; --i)
977 	buf[bufi++] = (char_u)(nr >> (i * 8));
978     return undo_write(bi, buf, (size_t)len);
979 }
980 
981 /*
982  * Write the pointer to an undo header.  Instead of writing the pointer itself
983  * we use the sequence number of the header.  This is converted back to
984  * pointers when reading. */
985     static void
986 put_header_ptr(bufinfo_T *bi, u_header_T *uhp)
987 {
988     undo_write_bytes(bi, (long_u)(uhp != NULL ? uhp->uh_seq : 0), 4);
989 }
990 
991     static int
992 undo_read_4c(bufinfo_T *bi)
993 {
994 #ifdef FEAT_CRYPT
995     if (bi->bi_buffer != NULL)
996     {
997 	char_u  buf[4];
998 	int	n;
999 
1000 	undo_read(bi, buf, (size_t)4);
1001 	n = ((unsigned)buf[0] << 24) + (buf[1] << 16) + (buf[2] << 8) + buf[3];
1002 	return n;
1003     }
1004 #endif
1005     return get4c(bi->bi_fp);
1006 }
1007 
1008     static int
1009 undo_read_2c(bufinfo_T *bi)
1010 {
1011 #ifdef FEAT_CRYPT
1012     if (bi->bi_buffer != NULL)
1013     {
1014 	char_u  buf[2];
1015 	int	n;
1016 
1017 	undo_read(bi, buf, (size_t)2);
1018 	n = (buf[0] << 8) + buf[1];
1019 	return n;
1020     }
1021 #endif
1022     return get2c(bi->bi_fp);
1023 }
1024 
1025     static int
1026 undo_read_byte(bufinfo_T *bi)
1027 {
1028 #ifdef FEAT_CRYPT
1029     if (bi->bi_buffer != NULL)
1030     {
1031 	char_u  buf[1];
1032 
1033 	undo_read(bi, buf, (size_t)1);
1034 	return buf[0];
1035     }
1036 #endif
1037     return getc(bi->bi_fp);
1038 }
1039 
1040     static time_t
1041 undo_read_time(bufinfo_T *bi)
1042 {
1043 #ifdef FEAT_CRYPT
1044     if (bi->bi_buffer != NULL)
1045     {
1046 	char_u  buf[8];
1047 	time_t	n = 0;
1048 	int	i;
1049 
1050 	undo_read(bi, buf, (size_t)8);
1051 	for (i = 0; i < 8; ++i)
1052 	    n = (n << 8) + buf[i];
1053 	return n;
1054     }
1055 #endif
1056     return get8ctime(bi->bi_fp);
1057 }
1058 
1059 /*
1060  * Read "buffer[size]" from the undo file.
1061  * Return OK or FAIL.
1062  */
1063     static int
1064 undo_read(bufinfo_T *bi, char_u *buffer, size_t size)
1065 {
1066 #ifdef FEAT_CRYPT
1067     if (bi->bi_buffer != NULL)
1068     {
1069 	int	size_todo = (int)size;
1070 	char_u	*p = buffer;
1071 
1072 	while (size_todo > 0)
1073 	{
1074 	    size_t n;
1075 
1076 	    if (bi->bi_used >= bi->bi_avail)
1077 	    {
1078 		n = fread(bi->bi_buffer, 1, (size_t)CRYPT_BUF_SIZE, bi->bi_fp);
1079 		if (n <= 0)
1080 		{
1081 		    /* Error may be checked for only later.  Fill with zeros,
1082 		     * so that the reader won't use garbage. */
1083 		    vim_memset(p, 0, size_todo);
1084 		    return FAIL;
1085 		}
1086 		bi->bi_avail = n;
1087 		bi->bi_used = 0;
1088 		crypt_decode_inplace(bi->bi_state, bi->bi_buffer, bi->bi_avail);
1089 	    }
1090 	    n = size_todo;
1091 	    if (n > bi->bi_avail - bi->bi_used)
1092 		n = bi->bi_avail - bi->bi_used;
1093 	    mch_memmove(p, bi->bi_buffer + bi->bi_used, n);
1094 	    bi->bi_used += n;
1095 	    size_todo -= (int)n;
1096 	    p += n;
1097 	}
1098 	return OK;
1099     }
1100 #endif
1101     if (fread(buffer, (size_t)size, 1, bi->bi_fp) != 1)
1102 	return FAIL;
1103     return OK;
1104 }
1105 
1106 /*
1107  * Read a string of length "len" from "bi->bi_fd".
1108  * "len" can be zero to allocate an empty line.
1109  * Decrypt the bytes if needed.
1110  * Append a NUL.
1111  * Returns a pointer to allocated memory or NULL for failure.
1112  */
1113     static char_u *
1114 read_string_decrypt(bufinfo_T *bi, int len)
1115 {
1116     char_u  *ptr = alloc((unsigned)len + 1);
1117 
1118     if (ptr != NULL)
1119     {
1120 	if (len > 0 && undo_read(bi, ptr, len) == FAIL)
1121 	{
1122 	    vim_free(ptr);
1123 	    return NULL;
1124 	}
1125 	ptr[len] = NUL;
1126 #ifdef FEAT_CRYPT
1127 	if (bi->bi_state != NULL && bi->bi_buffer == NULL)
1128 	    crypt_decode_inplace(bi->bi_state, ptr, len);
1129 #endif
1130     }
1131     return ptr;
1132 }
1133 
1134 /*
1135  * Writes the (not encrypted) header and initializes encryption if needed.
1136  */
1137     static int
1138 serialize_header(bufinfo_T *bi, char_u *hash)
1139 {
1140     int		len;
1141     buf_T	*buf = bi->bi_buf;
1142     FILE	*fp = bi->bi_fp;
1143     char_u	time_buf[8];
1144 
1145     /* Start writing, first the magic marker and undo info version. */
1146     if (fwrite(UF_START_MAGIC, (size_t)UF_START_MAGIC_LEN, (size_t)1, fp) != 1)
1147 	return FAIL;
1148 
1149     /* If the buffer is encrypted then all text bytes following will be
1150      * encrypted.  Numbers and other info is not crypted. */
1151 #ifdef FEAT_CRYPT
1152     if (*buf->b_p_key != NUL)
1153     {
1154 	char_u *header;
1155 	int    header_len;
1156 
1157 	undo_write_bytes(bi, (long_u)UF_VERSION_CRYPT, 2);
1158 	bi->bi_state = crypt_create_for_writing(crypt_get_method_nr(buf),
1159 					  buf->b_p_key, &header, &header_len);
1160 	if (bi->bi_state == NULL)
1161 	    return FAIL;
1162 	len = (int)fwrite(header, (size_t)header_len, (size_t)1, fp);
1163 	vim_free(header);
1164 	if (len != 1)
1165 	{
1166 	    crypt_free_state(bi->bi_state);
1167 	    bi->bi_state = NULL;
1168 	    return FAIL;
1169 	}
1170 
1171 	if (crypt_whole_undofile(crypt_get_method_nr(buf)))
1172 	{
1173 	    bi->bi_buffer = alloc(CRYPT_BUF_SIZE);
1174 	    if (bi->bi_buffer == NULL)
1175 	    {
1176 		crypt_free_state(bi->bi_state);
1177 		bi->bi_state = NULL;
1178 		return FAIL;
1179 	    }
1180 	    bi->bi_used = 0;
1181 	}
1182     }
1183     else
1184 #endif
1185 	undo_write_bytes(bi, (long_u)UF_VERSION, 2);
1186 
1187 
1188     /* Write a hash of the buffer text, so that we can verify it is still the
1189      * same when reading the buffer text. */
1190     if (undo_write(bi, hash, (size_t)UNDO_HASH_SIZE) == FAIL)
1191 	return FAIL;
1192 
1193     /* buffer-specific data */
1194     undo_write_bytes(bi, (long_u)buf->b_ml.ml_line_count, 4);
1195     len = buf->b_u_line_ptr != NULL ? (int)STRLEN(buf->b_u_line_ptr) : 0;
1196     undo_write_bytes(bi, (long_u)len, 4);
1197     if (len > 0 && fwrite_crypt(bi, buf->b_u_line_ptr, (size_t)len) == FAIL)
1198 	return FAIL;
1199     undo_write_bytes(bi, (long_u)buf->b_u_line_lnum, 4);
1200     undo_write_bytes(bi, (long_u)buf->b_u_line_colnr, 4);
1201 
1202     /* Undo structures header data */
1203     put_header_ptr(bi, buf->b_u_oldhead);
1204     put_header_ptr(bi, buf->b_u_newhead);
1205     put_header_ptr(bi, buf->b_u_curhead);
1206 
1207     undo_write_bytes(bi, (long_u)buf->b_u_numhead, 4);
1208     undo_write_bytes(bi, (long_u)buf->b_u_seq_last, 4);
1209     undo_write_bytes(bi, (long_u)buf->b_u_seq_cur, 4);
1210     time_to_bytes(buf->b_u_time_cur, time_buf);
1211     undo_write(bi, time_buf, 8);
1212 
1213     /* Optional fields. */
1214     undo_write_bytes(bi, 4, 1);
1215     undo_write_bytes(bi, UF_LAST_SAVE_NR, 1);
1216     undo_write_bytes(bi, (long_u)buf->b_u_save_nr_last, 4);
1217 
1218     undo_write_bytes(bi, 0, 1);  /* end marker */
1219 
1220     return OK;
1221 }
1222 
1223     static int
1224 serialize_uhp(bufinfo_T *bi, u_header_T *uhp)
1225 {
1226     int		i;
1227     u_entry_T	*uep;
1228     char_u	time_buf[8];
1229 
1230     if (undo_write_bytes(bi, (long_u)UF_HEADER_MAGIC, 2) == FAIL)
1231 	return FAIL;
1232 
1233     put_header_ptr(bi, uhp->uh_next.ptr);
1234     put_header_ptr(bi, uhp->uh_prev.ptr);
1235     put_header_ptr(bi, uhp->uh_alt_next.ptr);
1236     put_header_ptr(bi, uhp->uh_alt_prev.ptr);
1237     undo_write_bytes(bi, uhp->uh_seq, 4);
1238     serialize_pos(bi, uhp->uh_cursor);
1239 #ifdef FEAT_VIRTUALEDIT
1240     undo_write_bytes(bi, (long_u)uhp->uh_cursor_vcol, 4);
1241 #else
1242     undo_write_bytes(bi, (long_u)0, 4);
1243 #endif
1244     undo_write_bytes(bi, (long_u)uhp->uh_flags, 2);
1245     /* Assume NMARKS will stay the same. */
1246     for (i = 0; i < NMARKS; ++i)
1247 	serialize_pos(bi, uhp->uh_namedm[i]);
1248     serialize_visualinfo(bi, &uhp->uh_visual);
1249     time_to_bytes(uhp->uh_time, time_buf);
1250     undo_write(bi, time_buf, 8);
1251 
1252     /* Optional fields. */
1253     undo_write_bytes(bi, 4, 1);
1254     undo_write_bytes(bi, UHP_SAVE_NR, 1);
1255     undo_write_bytes(bi, (long_u)uhp->uh_save_nr, 4);
1256 
1257     undo_write_bytes(bi, 0, 1);  /* end marker */
1258 
1259     /* Write all the entries. */
1260     for (uep = uhp->uh_entry; uep != NULL; uep = uep->ue_next)
1261     {
1262 	undo_write_bytes(bi, (long_u)UF_ENTRY_MAGIC, 2);
1263 	if (serialize_uep(bi, uep) == FAIL)
1264 	    return FAIL;
1265     }
1266     undo_write_bytes(bi, (long_u)UF_ENTRY_END_MAGIC, 2);
1267     return OK;
1268 }
1269 
1270     static u_header_T *
1271 unserialize_uhp(bufinfo_T *bi, char_u *file_name)
1272 {
1273     u_header_T	*uhp;
1274     int		i;
1275     u_entry_T	*uep, *last_uep;
1276     int		c;
1277     int		error;
1278 
1279     uhp = (u_header_T *)U_ALLOC_LINE(sizeof(u_header_T));
1280     if (uhp == NULL)
1281 	return NULL;
1282     vim_memset(uhp, 0, sizeof(u_header_T));
1283 #ifdef U_DEBUG
1284     uhp->uh_magic = UH_MAGIC;
1285 #endif
1286     uhp->uh_next.seq = undo_read_4c(bi);
1287     uhp->uh_prev.seq = undo_read_4c(bi);
1288     uhp->uh_alt_next.seq = undo_read_4c(bi);
1289     uhp->uh_alt_prev.seq = undo_read_4c(bi);
1290     uhp->uh_seq = undo_read_4c(bi);
1291     if (uhp->uh_seq <= 0)
1292     {
1293 	corruption_error("uh_seq", file_name);
1294 	vim_free(uhp);
1295 	return NULL;
1296     }
1297     unserialize_pos(bi, &uhp->uh_cursor);
1298 #ifdef FEAT_VIRTUALEDIT
1299     uhp->uh_cursor_vcol = undo_read_4c(bi);
1300 #else
1301     (void)undo_read_4c(bi);
1302 #endif
1303     uhp->uh_flags = undo_read_2c(bi);
1304     for (i = 0; i < NMARKS; ++i)
1305 	unserialize_pos(bi, &uhp->uh_namedm[i]);
1306     unserialize_visualinfo(bi, &uhp->uh_visual);
1307     uhp->uh_time = undo_read_time(bi);
1308 
1309     /* Optional fields. */
1310     for (;;)
1311     {
1312 	int len = undo_read_byte(bi);
1313 	int what;
1314 
1315 	if (len == 0)
1316 	    break;
1317 	what = undo_read_byte(bi);
1318 	switch (what)
1319 	{
1320 	    case UHP_SAVE_NR:
1321 		uhp->uh_save_nr = undo_read_4c(bi);
1322 		break;
1323 	    default:
1324 		/* field not supported, skip */
1325 		while (--len >= 0)
1326 		    (void)undo_read_byte(bi);
1327 	}
1328     }
1329 
1330     /* Unserialize the uep list. */
1331     last_uep = NULL;
1332     while ((c = undo_read_2c(bi)) == UF_ENTRY_MAGIC)
1333     {
1334 	error = FALSE;
1335 	uep = unserialize_uep(bi, &error, file_name);
1336 	if (last_uep == NULL)
1337 	    uhp->uh_entry = uep;
1338 	else
1339 	    last_uep->ue_next = uep;
1340 	last_uep = uep;
1341 	if (uep == NULL || error)
1342 	{
1343 	    u_free_uhp(uhp);
1344 	    return NULL;
1345 	}
1346     }
1347     if (c != UF_ENTRY_END_MAGIC)
1348     {
1349 	corruption_error("entry end", file_name);
1350 	u_free_uhp(uhp);
1351 	return NULL;
1352     }
1353 
1354     return uhp;
1355 }
1356 
1357 /*
1358  * Serialize "uep".
1359  */
1360     static int
1361 serialize_uep(
1362     bufinfo_T	*bi,
1363     u_entry_T	*uep)
1364 {
1365     int		i;
1366     size_t	len;
1367 
1368     undo_write_bytes(bi, (long_u)uep->ue_top, 4);
1369     undo_write_bytes(bi, (long_u)uep->ue_bot, 4);
1370     undo_write_bytes(bi, (long_u)uep->ue_lcount, 4);
1371     undo_write_bytes(bi, (long_u)uep->ue_size, 4);
1372     for (i = 0; i < uep->ue_size; ++i)
1373     {
1374 	len = STRLEN(uep->ue_array[i]);
1375 	if (undo_write_bytes(bi, (long_u)len, 4) == FAIL)
1376 	    return FAIL;
1377 	if (len > 0 && fwrite_crypt(bi, uep->ue_array[i], len) == FAIL)
1378 	    return FAIL;
1379     }
1380     return OK;
1381 }
1382 
1383     static u_entry_T *
1384 unserialize_uep(bufinfo_T *bi, int *error, char_u *file_name)
1385 {
1386     int		i;
1387     u_entry_T	*uep;
1388     char_u	**array;
1389     char_u	*line;
1390     int		line_len;
1391 
1392     uep = (u_entry_T *)U_ALLOC_LINE(sizeof(u_entry_T));
1393     if (uep == NULL)
1394 	return NULL;
1395     vim_memset(uep, 0, sizeof(u_entry_T));
1396 #ifdef U_DEBUG
1397     uep->ue_magic = UE_MAGIC;
1398 #endif
1399     uep->ue_top = undo_read_4c(bi);
1400     uep->ue_bot = undo_read_4c(bi);
1401     uep->ue_lcount = undo_read_4c(bi);
1402     uep->ue_size = undo_read_4c(bi);
1403     if (uep->ue_size > 0)
1404     {
1405 	array = (char_u **)U_ALLOC_LINE(sizeof(char_u *) * uep->ue_size);
1406 	if (array == NULL)
1407 	{
1408 	    *error = TRUE;
1409 	    return uep;
1410 	}
1411 	vim_memset(array, 0, sizeof(char_u *) * uep->ue_size);
1412     }
1413     else
1414 	array = NULL;
1415     uep->ue_array = array;
1416 
1417     for (i = 0; i < uep->ue_size; ++i)
1418     {
1419 	line_len = undo_read_4c(bi);
1420 	if (line_len >= 0)
1421 	    line = read_string_decrypt(bi, line_len);
1422 	else
1423 	{
1424 	    line = NULL;
1425 	    corruption_error("line length", file_name);
1426 	}
1427 	if (line == NULL)
1428 	{
1429 	    *error = TRUE;
1430 	    return uep;
1431 	}
1432 	array[i] = line;
1433     }
1434     return uep;
1435 }
1436 
1437 /*
1438  * Serialize "pos".
1439  */
1440     static void
1441 serialize_pos(bufinfo_T *bi, pos_T pos)
1442 {
1443     undo_write_bytes(bi, (long_u)pos.lnum, 4);
1444     undo_write_bytes(bi, (long_u)pos.col, 4);
1445 #ifdef FEAT_VIRTUALEDIT
1446     undo_write_bytes(bi, (long_u)pos.coladd, 4);
1447 #else
1448     undo_write_bytes(bi, (long_u)0, 4);
1449 #endif
1450 }
1451 
1452 /*
1453  * Unserialize the pos_T at the current position.
1454  */
1455     static void
1456 unserialize_pos(bufinfo_T *bi, pos_T *pos)
1457 {
1458     pos->lnum = undo_read_4c(bi);
1459     if (pos->lnum < 0)
1460 	pos->lnum = 0;
1461     pos->col = undo_read_4c(bi);
1462     if (pos->col < 0)
1463 	pos->col = 0;
1464 #ifdef FEAT_VIRTUALEDIT
1465     pos->coladd = undo_read_4c(bi);
1466     if (pos->coladd < 0)
1467 	pos->coladd = 0;
1468 #else
1469     (void)undo_read_4c(bi);
1470 #endif
1471 }
1472 
1473 /*
1474  * Serialize "info".
1475  */
1476     static void
1477 serialize_visualinfo(bufinfo_T *bi, visualinfo_T *info)
1478 {
1479     serialize_pos(bi, info->vi_start);
1480     serialize_pos(bi, info->vi_end);
1481     undo_write_bytes(bi, (long_u)info->vi_mode, 4);
1482     undo_write_bytes(bi, (long_u)info->vi_curswant, 4);
1483 }
1484 
1485 /*
1486  * Unserialize the visualinfo_T at the current position.
1487  */
1488     static void
1489 unserialize_visualinfo(bufinfo_T *bi, visualinfo_T *info)
1490 {
1491     unserialize_pos(bi, &info->vi_start);
1492     unserialize_pos(bi, &info->vi_end);
1493     info->vi_mode = undo_read_4c(bi);
1494     info->vi_curswant = undo_read_4c(bi);
1495 }
1496 
1497 /*
1498  * Write the undo tree in an undo file.
1499  * When "name" is not NULL, use it as the name of the undo file.
1500  * Otherwise use buf->b_ffname to generate the undo file name.
1501  * "buf" must never be null, buf->b_ffname is used to obtain the original file
1502  * permissions.
1503  * "forceit" is TRUE for ":wundo!", FALSE otherwise.
1504  * "hash[UNDO_HASH_SIZE]" must be the hash value of the buffer text.
1505  */
1506     void
1507 u_write_undo(
1508     char_u	*name,
1509     int		forceit,
1510     buf_T	*buf,
1511     char_u	*hash)
1512 {
1513     u_header_T	*uhp;
1514     char_u	*file_name;
1515     int		mark;
1516 #ifdef U_DEBUG
1517     int		headers_written = 0;
1518 #endif
1519     int		fd;
1520     FILE	*fp = NULL;
1521     int		perm;
1522     int		write_ok = FALSE;
1523 #ifdef UNIX
1524     int		st_old_valid = FALSE;
1525     stat_T	st_old;
1526     stat_T	st_new;
1527 #endif
1528     bufinfo_T	bi;
1529 
1530     vim_memset(&bi, 0, sizeof(bi));
1531 
1532     if (name == NULL)
1533     {
1534 	file_name = u_get_undo_file_name(buf->b_ffname, FALSE);
1535 	if (file_name == NULL)
1536 	{
1537 	    if (p_verbose > 0)
1538 	    {
1539 		verbose_enter();
1540 		smsg((char_u *)
1541 		   _("Cannot write undo file in any directory in 'undodir'"));
1542 		verbose_leave();
1543 	    }
1544 	    return;
1545 	}
1546     }
1547     else
1548 	file_name = name;
1549 
1550     /*
1551      * Decide about the permission to use for the undo file.  If the buffer
1552      * has a name use the permission of the original file.  Otherwise only
1553      * allow the user to access the undo file.
1554      */
1555     perm = 0600;
1556     if (buf->b_ffname != NULL)
1557     {
1558 #ifdef UNIX
1559 	if (mch_stat((char *)buf->b_ffname, &st_old) >= 0)
1560 	{
1561 	    perm = st_old.st_mode;
1562 	    st_old_valid = TRUE;
1563 	}
1564 #else
1565 	perm = mch_getperm(buf->b_ffname);
1566 	if (perm < 0)
1567 	    perm = 0600;
1568 #endif
1569     }
1570 
1571     /* strip any s-bit and executable bit */
1572     perm = perm & 0666;
1573 
1574     /* If the undo file already exists, verify that it actually is an undo
1575      * file, and delete it. */
1576     if (mch_getperm(file_name) >= 0)
1577     {
1578 	if (name == NULL || !forceit)
1579 	{
1580 	    /* Check we can read it and it's an undo file. */
1581 	    fd = mch_open((char *)file_name, O_RDONLY|O_EXTRA, 0);
1582 	    if (fd < 0)
1583 	    {
1584 		if (name != NULL || p_verbose > 0)
1585 		{
1586 		    if (name == NULL)
1587 			verbose_enter();
1588 		    smsg((char_u *)
1589 		      _("Will not overwrite with undo file, cannot read: %s"),
1590 								   file_name);
1591 		    if (name == NULL)
1592 			verbose_leave();
1593 		}
1594 		goto theend;
1595 	    }
1596 	    else
1597 	    {
1598 		char_u	mbuf[UF_START_MAGIC_LEN];
1599 		int	len;
1600 
1601 		len = read_eintr(fd, mbuf, UF_START_MAGIC_LEN);
1602 		close(fd);
1603 		if (len < UF_START_MAGIC_LEN
1604 		      || memcmp(mbuf, UF_START_MAGIC, UF_START_MAGIC_LEN) != 0)
1605 		{
1606 		    if (name != NULL || p_verbose > 0)
1607 		    {
1608 			if (name == NULL)
1609 			    verbose_enter();
1610 			smsg((char_u *)
1611 			_("Will not overwrite, this is not an undo file: %s"),
1612 								   file_name);
1613 			if (name == NULL)
1614 			    verbose_leave();
1615 		    }
1616 		    goto theend;
1617 		}
1618 	    }
1619 	}
1620 	mch_remove(file_name);
1621     }
1622 
1623     /* If there is no undo information at all, quit here after deleting any
1624      * existing undo file. */
1625     if (buf->b_u_numhead == 0 && buf->b_u_line_ptr == NULL)
1626     {
1627 	if (p_verbose > 0)
1628 	    verb_msg((char_u *)_("Skipping undo file write, nothing to undo"));
1629 	goto theend;
1630     }
1631 
1632     fd = mch_open((char *)file_name,
1633 			    O_CREAT|O_EXTRA|O_WRONLY|O_EXCL|O_NOFOLLOW, perm);
1634     if (fd < 0)
1635     {
1636 	EMSG2(_(e_not_open), file_name);
1637 	goto theend;
1638     }
1639     (void)mch_setperm(file_name, perm);
1640     if (p_verbose > 0)
1641     {
1642 	verbose_enter();
1643 	smsg((char_u *)_("Writing undo file: %s"), file_name);
1644 	verbose_leave();
1645     }
1646 
1647 #ifdef U_DEBUG
1648     /* Check there is no problem in undo info before writing. */
1649     u_check(FALSE);
1650 #endif
1651 
1652 #ifdef UNIX
1653     /*
1654      * Try to set the group of the undo file same as the original file. If
1655      * this fails, set the protection bits for the group same as the
1656      * protection bits for others.
1657      */
1658     if (st_old_valid
1659 	    && mch_stat((char *)file_name, &st_new) >= 0
1660 	    && st_new.st_gid != st_old.st_gid
1661 # ifdef HAVE_FCHOWN  /* sequent-ptx lacks fchown() */
1662 	    && fchown(fd, (uid_t)-1, st_old.st_gid) != 0
1663 # endif
1664        )
1665 	mch_setperm(file_name, (perm & 0707) | ((perm & 07) << 3));
1666 # if defined(HAVE_SELINUX) || defined(HAVE_SMACK)
1667     if (buf->b_ffname != NULL)
1668 	mch_copy_sec(buf->b_ffname, file_name);
1669 # endif
1670 #endif
1671 
1672     fp = fdopen(fd, "w");
1673     if (fp == NULL)
1674     {
1675 	EMSG2(_(e_not_open), file_name);
1676 	close(fd);
1677 	mch_remove(file_name);
1678 	goto theend;
1679     }
1680 
1681     /* Undo must be synced. */
1682     u_sync(TRUE);
1683 
1684     /*
1685      * Write the header.  Initializes encryption, if enabled.
1686      */
1687     bi.bi_buf = buf;
1688     bi.bi_fp = fp;
1689     if (serialize_header(&bi, hash) == FAIL)
1690 	goto write_error;
1691 
1692     /*
1693      * Iteratively serialize UHPs and their UEPs from the top down.
1694      */
1695     mark = ++lastmark;
1696     uhp = buf->b_u_oldhead;
1697     while (uhp != NULL)
1698     {
1699 	/* Serialize current UHP if we haven't seen it */
1700 	if (uhp->uh_walk != mark)
1701 	{
1702 	    uhp->uh_walk = mark;
1703 #ifdef U_DEBUG
1704 	    ++headers_written;
1705 #endif
1706 	    if (serialize_uhp(&bi, uhp) == FAIL)
1707 		goto write_error;
1708 	}
1709 
1710 	/* Now walk through the tree - algorithm from undo_time(). */
1711 	if (uhp->uh_prev.ptr != NULL && uhp->uh_prev.ptr->uh_walk != mark)
1712 	    uhp = uhp->uh_prev.ptr;
1713 	else if (uhp->uh_alt_next.ptr != NULL
1714 				     && uhp->uh_alt_next.ptr->uh_walk != mark)
1715 	    uhp = uhp->uh_alt_next.ptr;
1716 	else if (uhp->uh_next.ptr != NULL && uhp->uh_alt_prev.ptr == NULL
1717 					 && uhp->uh_next.ptr->uh_walk != mark)
1718 	    uhp = uhp->uh_next.ptr;
1719 	else if (uhp->uh_alt_prev.ptr != NULL)
1720 	    uhp = uhp->uh_alt_prev.ptr;
1721 	else
1722 	    uhp = uhp->uh_next.ptr;
1723     }
1724 
1725     if (undo_write_bytes(&bi, (long_u)UF_HEADER_END_MAGIC, 2) == OK)
1726 	write_ok = TRUE;
1727 #ifdef U_DEBUG
1728     if (headers_written != buf->b_u_numhead)
1729     {
1730 	EMSGN("Written %ld headers, ...", headers_written);
1731 	EMSGN("... but numhead is %ld", buf->b_u_numhead);
1732     }
1733 #endif
1734 
1735 #ifdef FEAT_CRYPT
1736     if (bi.bi_state != NULL && undo_flush(&bi) == FAIL)
1737 	write_ok = FALSE;
1738 #endif
1739 
1740 write_error:
1741     fclose(fp);
1742     if (!write_ok)
1743 	EMSG2(_("E829: write error in undo file: %s"), file_name);
1744 
1745 #if defined(MACOS_CLASSIC) || defined(WIN3264)
1746     /* Copy file attributes; for systems where this can only be done after
1747      * closing the file. */
1748     if (buf->b_ffname != NULL)
1749 	(void)mch_copy_file_attribute(buf->b_ffname, file_name);
1750 #endif
1751 #ifdef HAVE_ACL
1752     if (buf->b_ffname != NULL)
1753     {
1754 	vim_acl_T	    acl;
1755 
1756 	/* For systems that support ACL: get the ACL from the original file. */
1757 	acl = mch_get_acl(buf->b_ffname);
1758 	mch_set_acl(file_name, acl);
1759 	mch_free_acl(acl);
1760     }
1761 #endif
1762 
1763 theend:
1764 #ifdef FEAT_CRYPT
1765     if (bi.bi_state != NULL)
1766 	crypt_free_state(bi.bi_state);
1767     vim_free(bi.bi_buffer);
1768 #endif
1769     if (file_name != name)
1770 	vim_free(file_name);
1771 }
1772 
1773 /*
1774  * Load the undo tree from an undo file.
1775  * If "name" is not NULL use it as the undo file name.  This also means being
1776  * a bit more verbose.
1777  * Otherwise use curbuf->b_ffname to generate the undo file name.
1778  * "hash[UNDO_HASH_SIZE]" must be the hash value of the buffer text.
1779  */
1780     void
1781 u_read_undo(char_u *name, char_u *hash, char_u *orig_name)
1782 {
1783     char_u	*file_name;
1784     FILE	*fp;
1785     long	version, str_len;
1786     char_u	*line_ptr = NULL;
1787     linenr_T	line_lnum;
1788     colnr_T	line_colnr;
1789     linenr_T	line_count;
1790     int		num_head = 0;
1791     long	old_header_seq, new_header_seq, cur_header_seq;
1792     long	seq_last, seq_cur;
1793     long	last_save_nr = 0;
1794     short	old_idx = -1, new_idx = -1, cur_idx = -1;
1795     long	num_read_uhps = 0;
1796     time_t	seq_time;
1797     int		i, j;
1798     int		c;
1799     u_header_T	*uhp;
1800     u_header_T	**uhp_table = NULL;
1801     char_u	read_hash[UNDO_HASH_SIZE];
1802     char_u	magic_buf[UF_START_MAGIC_LEN];
1803 #ifdef U_DEBUG
1804     int		*uhp_table_used;
1805 #endif
1806 #ifdef UNIX
1807     stat_T	st_orig;
1808     stat_T	st_undo;
1809 #endif
1810     bufinfo_T	bi;
1811 
1812     vim_memset(&bi, 0, sizeof(bi));
1813     if (name == NULL)
1814     {
1815 	file_name = u_get_undo_file_name(curbuf->b_ffname, TRUE);
1816 	if (file_name == NULL)
1817 	    return;
1818 
1819 #ifdef UNIX
1820 	/* For safety we only read an undo file if the owner is equal to the
1821 	 * owner of the text file or equal to the current user. */
1822 	if (mch_stat((char *)orig_name, &st_orig) >= 0
1823 		&& mch_stat((char *)file_name, &st_undo) >= 0
1824 		&& st_orig.st_uid != st_undo.st_uid
1825 		&& st_undo.st_uid != getuid())
1826 	{
1827 	    if (p_verbose > 0)
1828 	    {
1829 		verbose_enter();
1830 		smsg((char_u *)_("Not reading undo file, owner differs: %s"),
1831 								   file_name);
1832 		verbose_leave();
1833 	    }
1834 	    return;
1835 	}
1836 #endif
1837     }
1838     else
1839 	file_name = name;
1840 
1841     if (p_verbose > 0)
1842     {
1843 	verbose_enter();
1844 	smsg((char_u *)_("Reading undo file: %s"), file_name);
1845 	verbose_leave();
1846     }
1847 
1848     fp = mch_fopen((char *)file_name, "r");
1849     if (fp == NULL)
1850     {
1851 	if (name != NULL || p_verbose > 0)
1852 	    EMSG2(_("E822: Cannot open undo file for reading: %s"), file_name);
1853 	goto error;
1854     }
1855     bi.bi_buf = curbuf;
1856     bi.bi_fp = fp;
1857 
1858     /*
1859      * Read the undo file header.
1860      */
1861     if (fread(magic_buf, UF_START_MAGIC_LEN, 1, fp) != 1
1862 		|| memcmp(magic_buf, UF_START_MAGIC, UF_START_MAGIC_LEN) != 0)
1863     {
1864 	EMSG2(_("E823: Not an undo file: %s"), file_name);
1865 	goto error;
1866     }
1867     version = get2c(fp);
1868     if (version == UF_VERSION_CRYPT)
1869     {
1870 #ifdef FEAT_CRYPT
1871 	if (*curbuf->b_p_key == NUL)
1872 	{
1873 	    EMSG2(_("E832: Non-encrypted file has encrypted undo file: %s"),
1874 								   file_name);
1875 	    goto error;
1876 	}
1877 	bi.bi_state = crypt_create_from_file(fp, curbuf->b_p_key);
1878 	if (bi.bi_state == NULL)
1879 	{
1880 	    EMSG2(_("E826: Undo file decryption failed: %s"), file_name);
1881 	    goto error;
1882 	}
1883 	if (crypt_whole_undofile(bi.bi_state->method_nr))
1884 	{
1885 	    bi.bi_buffer = alloc(CRYPT_BUF_SIZE);
1886 	    if (bi.bi_buffer == NULL)
1887 	    {
1888 		crypt_free_state(bi.bi_state);
1889 		bi.bi_state = NULL;
1890 		goto error;
1891 	    }
1892 	    bi.bi_avail = 0;
1893 	    bi.bi_used = 0;
1894 	}
1895 #else
1896 	EMSG2(_("E827: Undo file is encrypted: %s"), file_name);
1897 	goto error;
1898 #endif
1899     }
1900     else if (version != UF_VERSION)
1901     {
1902 	EMSG2(_("E824: Incompatible undo file: %s"), file_name);
1903 	goto error;
1904     }
1905 
1906     if (undo_read(&bi, read_hash, (size_t)UNDO_HASH_SIZE) == FAIL)
1907     {
1908 	corruption_error("hash", file_name);
1909 	goto error;
1910     }
1911     line_count = (linenr_T)undo_read_4c(&bi);
1912     if (memcmp(hash, read_hash, UNDO_HASH_SIZE) != 0
1913 				  || line_count != curbuf->b_ml.ml_line_count)
1914     {
1915 	if (p_verbose > 0 || name != NULL)
1916 	{
1917 	    if (name == NULL)
1918 		verbose_enter();
1919 	    give_warning((char_u *)
1920 		      _("File contents changed, cannot use undo info"), TRUE);
1921 	    if (name == NULL)
1922 		verbose_leave();
1923 	}
1924 	goto error;
1925     }
1926 
1927     /* Read undo data for "U" command. */
1928     str_len = undo_read_4c(&bi);
1929     if (str_len < 0)
1930 	goto error;
1931     if (str_len > 0)
1932 	line_ptr = read_string_decrypt(&bi, str_len);
1933     line_lnum = (linenr_T)undo_read_4c(&bi);
1934     line_colnr = (colnr_T)undo_read_4c(&bi);
1935     if (line_lnum < 0 || line_colnr < 0)
1936     {
1937 	corruption_error("line lnum/col", file_name);
1938 	goto error;
1939     }
1940 
1941     /* Begin general undo data */
1942     old_header_seq = undo_read_4c(&bi);
1943     new_header_seq = undo_read_4c(&bi);
1944     cur_header_seq = undo_read_4c(&bi);
1945     num_head = undo_read_4c(&bi);
1946     seq_last = undo_read_4c(&bi);
1947     seq_cur = undo_read_4c(&bi);
1948     seq_time = undo_read_time(&bi);
1949 
1950     /* Optional header fields. */
1951     for (;;)
1952     {
1953 	int len = undo_read_byte(&bi);
1954 	int what;
1955 
1956 	if (len == 0 || len == EOF)
1957 	    break;
1958 	what = undo_read_byte(&bi);
1959 	switch (what)
1960 	{
1961 	    case UF_LAST_SAVE_NR:
1962 		last_save_nr = undo_read_4c(&bi);
1963 		break;
1964 	    default:
1965 		/* field not supported, skip */
1966 		while (--len >= 0)
1967 		    (void)undo_read_byte(&bi);
1968 	}
1969     }
1970 
1971     /* uhp_table will store the freshly created undo headers we allocate
1972      * until we insert them into curbuf. The table remains sorted by the
1973      * sequence numbers of the headers.
1974      * When there are no headers uhp_table is NULL. */
1975     if (num_head > 0)
1976     {
1977 	uhp_table = (u_header_T **)U_ALLOC_LINE(
1978 					     num_head * sizeof(u_header_T *));
1979 	if (uhp_table == NULL)
1980 	    goto error;
1981     }
1982 
1983     while ((c = undo_read_2c(&bi)) == UF_HEADER_MAGIC)
1984     {
1985 	if (num_read_uhps >= num_head)
1986 	{
1987 	    corruption_error("num_head too small", file_name);
1988 	    goto error;
1989 	}
1990 
1991 	uhp = unserialize_uhp(&bi, file_name);
1992 	if (uhp == NULL)
1993 	    goto error;
1994 	uhp_table[num_read_uhps++] = uhp;
1995     }
1996 
1997     if (num_read_uhps != num_head)
1998     {
1999 	corruption_error("num_head", file_name);
2000 	goto error;
2001     }
2002     if (c != UF_HEADER_END_MAGIC)
2003     {
2004 	corruption_error("end marker", file_name);
2005 	goto error;
2006     }
2007 
2008 #ifdef U_DEBUG
2009     uhp_table_used = (int *)alloc_clear(
2010 				     (unsigned)(sizeof(int) * num_head + 1));
2011 # define SET_FLAG(j) ++uhp_table_used[j]
2012 #else
2013 # define SET_FLAG(j)
2014 #endif
2015 
2016     /* We have put all of the headers into a table. Now we iterate through the
2017      * table and swizzle each sequence number we have stored in uh_*_seq into
2018      * a pointer corresponding to the header with that sequence number. */
2019     for (i = 0; i < num_head; i++)
2020     {
2021 	uhp = uhp_table[i];
2022 	if (uhp == NULL)
2023 	    continue;
2024 	for (j = 0; j < num_head; j++)
2025 	    if (uhp_table[j] != NULL && i != j
2026 			      && uhp_table[i]->uh_seq == uhp_table[j]->uh_seq)
2027 	    {
2028 		corruption_error("duplicate uh_seq", file_name);
2029 		goto error;
2030 	    }
2031 	for (j = 0; j < num_head; j++)
2032 	    if (uhp_table[j] != NULL
2033 				  && uhp_table[j]->uh_seq == uhp->uh_next.seq)
2034 	    {
2035 		uhp->uh_next.ptr = uhp_table[j];
2036 		SET_FLAG(j);
2037 		break;
2038 	    }
2039 	for (j = 0; j < num_head; j++)
2040 	    if (uhp_table[j] != NULL
2041 				  && uhp_table[j]->uh_seq == uhp->uh_prev.seq)
2042 	    {
2043 		uhp->uh_prev.ptr = uhp_table[j];
2044 		SET_FLAG(j);
2045 		break;
2046 	    }
2047 	for (j = 0; j < num_head; j++)
2048 	    if (uhp_table[j] != NULL
2049 			      && uhp_table[j]->uh_seq == uhp->uh_alt_next.seq)
2050 	    {
2051 		uhp->uh_alt_next.ptr = uhp_table[j];
2052 		SET_FLAG(j);
2053 		break;
2054 	    }
2055 	for (j = 0; j < num_head; j++)
2056 	    if (uhp_table[j] != NULL
2057 			      && uhp_table[j]->uh_seq == uhp->uh_alt_prev.seq)
2058 	    {
2059 		uhp->uh_alt_prev.ptr = uhp_table[j];
2060 		SET_FLAG(j);
2061 		break;
2062 	    }
2063 	if (old_header_seq > 0 && old_idx < 0 && uhp->uh_seq == old_header_seq)
2064 	{
2065 	    old_idx = i;
2066 	    SET_FLAG(i);
2067 	}
2068 	if (new_header_seq > 0 && new_idx < 0 && uhp->uh_seq == new_header_seq)
2069 	{
2070 	    new_idx = i;
2071 	    SET_FLAG(i);
2072 	}
2073 	if (cur_header_seq > 0 && cur_idx < 0 && uhp->uh_seq == cur_header_seq)
2074 	{
2075 	    cur_idx = i;
2076 	    SET_FLAG(i);
2077 	}
2078     }
2079 
2080     /* Now that we have read the undo info successfully, free the current undo
2081      * info and use the info from the file. */
2082     u_blockfree(curbuf);
2083     curbuf->b_u_oldhead = old_idx < 0 ? NULL : uhp_table[old_idx];
2084     curbuf->b_u_newhead = new_idx < 0 ? NULL : uhp_table[new_idx];
2085     curbuf->b_u_curhead = cur_idx < 0 ? NULL : uhp_table[cur_idx];
2086     curbuf->b_u_line_ptr = line_ptr;
2087     curbuf->b_u_line_lnum = line_lnum;
2088     curbuf->b_u_line_colnr = line_colnr;
2089     curbuf->b_u_numhead = num_head;
2090     curbuf->b_u_seq_last = seq_last;
2091     curbuf->b_u_seq_cur = seq_cur;
2092     curbuf->b_u_time_cur = seq_time;
2093     curbuf->b_u_save_nr_last = last_save_nr;
2094     curbuf->b_u_save_nr_cur = last_save_nr;
2095 
2096     curbuf->b_u_synced = TRUE;
2097     vim_free(uhp_table);
2098 
2099 #ifdef U_DEBUG
2100     for (i = 0; i < num_head; ++i)
2101 	if (uhp_table_used[i] == 0)
2102 	    EMSGN("uhp_table entry %ld not used, leaking memory", i);
2103     vim_free(uhp_table_used);
2104     u_check(TRUE);
2105 #endif
2106 
2107     if (name != NULL)
2108 	smsg((char_u *)_("Finished reading undo file %s"), file_name);
2109     goto theend;
2110 
2111 error:
2112     vim_free(line_ptr);
2113     if (uhp_table != NULL)
2114     {
2115 	for (i = 0; i < num_read_uhps; i++)
2116 	    if (uhp_table[i] != NULL)
2117 		u_free_uhp(uhp_table[i]);
2118 	vim_free(uhp_table);
2119     }
2120 
2121 theend:
2122 #ifdef FEAT_CRYPT
2123     if (bi.bi_state != NULL)
2124 	crypt_free_state(bi.bi_state);
2125     vim_free(bi.bi_buffer);
2126 #endif
2127     if (fp != NULL)
2128 	fclose(fp);
2129     if (file_name != name)
2130 	vim_free(file_name);
2131     return;
2132 }
2133 
2134 #endif /* FEAT_PERSISTENT_UNDO */
2135 
2136 
2137 /*
2138  * If 'cpoptions' contains 'u': Undo the previous undo or redo (vi compatible).
2139  * If 'cpoptions' does not contain 'u': Always undo.
2140  */
2141     void
2142 u_undo(int count)
2143 {
2144     /*
2145      * If we get an undo command while executing a macro, we behave like the
2146      * original vi. If this happens twice in one macro the result will not
2147      * be compatible.
2148      */
2149     if (curbuf->b_u_synced == FALSE)
2150     {
2151 	u_sync(TRUE);
2152 	count = 1;
2153     }
2154 
2155     if (vim_strchr(p_cpo, CPO_UNDO) == NULL)
2156 	undo_undoes = TRUE;
2157     else
2158 	undo_undoes = !undo_undoes;
2159     u_doit(count);
2160 }
2161 
2162 /*
2163  * If 'cpoptions' contains 'u': Repeat the previous undo or redo.
2164  * If 'cpoptions' does not contain 'u': Always redo.
2165  */
2166     void
2167 u_redo(int count)
2168 {
2169     if (vim_strchr(p_cpo, CPO_UNDO) == NULL)
2170 	undo_undoes = FALSE;
2171     u_doit(count);
2172 }
2173 
2174 /*
2175  * Undo or redo, depending on 'undo_undoes', 'count' times.
2176  */
2177     static void
2178 u_doit(int startcount)
2179 {
2180     int count = startcount;
2181 
2182     if (!undo_allowed())
2183 	return;
2184 
2185     u_newcount = 0;
2186     u_oldcount = 0;
2187     if (curbuf->b_ml.ml_flags & ML_EMPTY)
2188 	u_oldcount = -1;
2189     while (count--)
2190     {
2191 	/* Do the change warning now, so that it triggers FileChangedRO when
2192 	 * needed.  This may cause the file to be reloaded, that must happen
2193 	 * before we do anything, because it may change curbuf->b_u_curhead
2194 	 * and more. */
2195 	change_warning(0);
2196 
2197 	if (undo_undoes)
2198 	{
2199 	    if (curbuf->b_u_curhead == NULL)		/* first undo */
2200 		curbuf->b_u_curhead = curbuf->b_u_newhead;
2201 	    else if (get_undolevel() > 0)		/* multi level undo */
2202 		/* get next undo */
2203 		curbuf->b_u_curhead = curbuf->b_u_curhead->uh_next.ptr;
2204 	    /* nothing to undo */
2205 	    if (curbuf->b_u_numhead == 0 || curbuf->b_u_curhead == NULL)
2206 	    {
2207 		/* stick curbuf->b_u_curhead at end */
2208 		curbuf->b_u_curhead = curbuf->b_u_oldhead;
2209 		beep_flush();
2210 		if (count == startcount - 1)
2211 		{
2212 		    MSG(_("Already at oldest change"));
2213 		    return;
2214 		}
2215 		break;
2216 	    }
2217 
2218 	    u_undoredo(TRUE);
2219 	}
2220 	else
2221 	{
2222 	    if (curbuf->b_u_curhead == NULL || get_undolevel() <= 0)
2223 	    {
2224 		beep_flush();	/* nothing to redo */
2225 		if (count == startcount - 1)
2226 		{
2227 		    MSG(_("Already at newest change"));
2228 		    return;
2229 		}
2230 		break;
2231 	    }
2232 
2233 	    u_undoredo(FALSE);
2234 
2235 	    /* Advance for next redo.  Set "newhead" when at the end of the
2236 	     * redoable changes. */
2237 	    if (curbuf->b_u_curhead->uh_prev.ptr == NULL)
2238 		curbuf->b_u_newhead = curbuf->b_u_curhead;
2239 	    curbuf->b_u_curhead = curbuf->b_u_curhead->uh_prev.ptr;
2240 	}
2241     }
2242     u_undo_end(undo_undoes, FALSE);
2243 }
2244 
2245 /*
2246  * Undo or redo over the timeline.
2247  * When "step" is negative go back in time, otherwise goes forward in time.
2248  * When "sec" is FALSE make "step" steps, when "sec" is TRUE use "step" as
2249  * seconds.
2250  * When "file" is TRUE use "step" as a number of file writes.
2251  * When "absolute" is TRUE use "step" as the sequence number to jump to.
2252  * "sec" must be FALSE then.
2253  */
2254     void
2255 undo_time(
2256     long	step,
2257     int		sec,
2258     int		file,
2259     int		absolute)
2260 {
2261     long	    target;
2262     long	    closest;
2263     long	    closest_start;
2264     long	    closest_seq = 0;
2265     long	    val;
2266     u_header_T	    *uhp;
2267     u_header_T	    *last;
2268     int		    mark;
2269     int		    nomark;
2270     int		    round;
2271     int		    dosec = sec;
2272     int		    dofile = file;
2273     int		    above = FALSE;
2274     int		    did_undo = TRUE;
2275 
2276     /* First make sure the current undoable change is synced. */
2277     if (curbuf->b_u_synced == FALSE)
2278 	u_sync(TRUE);
2279 
2280     u_newcount = 0;
2281     u_oldcount = 0;
2282     if (curbuf->b_ml.ml_flags & ML_EMPTY)
2283 	u_oldcount = -1;
2284 
2285     /* "target" is the node below which we want to be.
2286      * Init "closest" to a value we can't reach. */
2287     if (absolute)
2288     {
2289 	if (step == 0)
2290 	{
2291 	    /* target 0 does not exist, got to 1 and above it. */
2292 	    target = 1;
2293 	    above = TRUE;
2294 	}
2295 	else
2296 	    target = step;
2297 	closest = -1;
2298     }
2299     else
2300     {
2301 	/* When doing computations with time_t subtract starttime, because
2302 	 * time_t converted to a long may result in a wrong number. */
2303 	if (dosec)
2304 	    target = (long)(curbuf->b_u_time_cur - starttime) + step;
2305 	else if (dofile)
2306 	{
2307 	    if (step < 0)
2308 	    {
2309 		/* Going back to a previous write. If there were changes after
2310 		 * the last write, count that as moving one file-write, so
2311 		 * that ":earlier 1f" undoes all changes since the last save. */
2312 		uhp = curbuf->b_u_curhead;
2313 		if (uhp != NULL)
2314 		    uhp = uhp->uh_next.ptr;
2315 		else
2316 		    uhp = curbuf->b_u_newhead;
2317 		if (uhp != NULL && uhp->uh_save_nr != 0)
2318 		    /* "uh_save_nr" was set in the last block, that means
2319 		     * there were no changes since the last write */
2320 		    target = curbuf->b_u_save_nr_cur + step;
2321 		else
2322 		    /* count the changes since the last write as one step */
2323 		    target = curbuf->b_u_save_nr_cur + step + 1;
2324 		if (target <= 0)
2325 		    /* Go to before first write: before the oldest change. Use
2326 		     * the sequence number for that. */
2327 		    dofile = FALSE;
2328 	    }
2329 	    else
2330 	    {
2331 		/* Moving forward to a newer write. */
2332 		target = curbuf->b_u_save_nr_cur + step;
2333 		if (target > curbuf->b_u_save_nr_last)
2334 		{
2335 		    /* Go to after last write: after the latest change. Use
2336 		     * the sequence number for that. */
2337 		    target = curbuf->b_u_seq_last + 1;
2338 		    dofile = FALSE;
2339 		}
2340 	    }
2341 	}
2342 	else
2343 	    target = curbuf->b_u_seq_cur + step;
2344 	if (step < 0)
2345 	{
2346 	    if (target < 0)
2347 		target = 0;
2348 	    closest = -1;
2349 	}
2350 	else
2351 	{
2352 	    if (dosec)
2353 		closest = (long)(vim_time() - starttime + 1);
2354 	    else if (dofile)
2355 		closest = curbuf->b_u_save_nr_last + 2;
2356 	    else
2357 		closest = curbuf->b_u_seq_last + 2;
2358 	    if (target >= closest)
2359 		target = closest - 1;
2360 	}
2361     }
2362     closest_start = closest;
2363     closest_seq = curbuf->b_u_seq_cur;
2364 
2365     /*
2366      * May do this twice:
2367      * 1. Search for "target", update "closest" to the best match found.
2368      * 2. If "target" not found search for "closest".
2369      *
2370      * When using the closest time we use the sequence number in the second
2371      * round, because there may be several entries with the same time.
2372      */
2373     for (round = 1; round <= 2; ++round)
2374     {
2375 	/* Find the path from the current state to where we want to go.  The
2376 	 * desired state can be anywhere in the undo tree, need to go all over
2377 	 * it.  We put "nomark" in uh_walk where we have been without success,
2378 	 * "mark" where it could possibly be. */
2379 	mark = ++lastmark;
2380 	nomark = ++lastmark;
2381 
2382 	if (curbuf->b_u_curhead == NULL)	/* at leaf of the tree */
2383 	    uhp = curbuf->b_u_newhead;
2384 	else
2385 	    uhp = curbuf->b_u_curhead;
2386 
2387 	while (uhp != NULL)
2388 	{
2389 	    uhp->uh_walk = mark;
2390 	    if (dosec)
2391 		val = (long)(uhp->uh_time - starttime);
2392 	    else if (dofile)
2393 		val = uhp->uh_save_nr;
2394 	    else
2395 		val = uhp->uh_seq;
2396 
2397 	    if (round == 1 && !(dofile && val == 0))
2398 	    {
2399 		/* Remember the header that is closest to the target.
2400 		 * It must be at least in the right direction (checked with
2401 		 * "b_u_seq_cur").  When the timestamp is equal find the
2402 		 * highest/lowest sequence number. */
2403 		if ((step < 0 ? uhp->uh_seq <= curbuf->b_u_seq_cur
2404 			      : uhp->uh_seq > curbuf->b_u_seq_cur)
2405 			&& ((dosec && val == closest)
2406 			    ? (step < 0
2407 				? uhp->uh_seq < closest_seq
2408 				: uhp->uh_seq > closest_seq)
2409 			    : closest == closest_start
2410 				|| (val > target
2411 				    ? (closest > target
2412 					? val - target <= closest - target
2413 					: val - target <= target - closest)
2414 				    : (closest > target
2415 					? target - val <= closest - target
2416 					: target - val <= target - closest))))
2417 		{
2418 		    closest = val;
2419 		    closest_seq = uhp->uh_seq;
2420 		}
2421 	    }
2422 
2423 	    /* Quit searching when we found a match.  But when searching for a
2424 	     * time we need to continue looking for the best uh_seq. */
2425 	    if (target == val && !dosec)
2426 	    {
2427 		target = uhp->uh_seq;
2428 		break;
2429 	    }
2430 
2431 	    /* go down in the tree if we haven't been there */
2432 	    if (uhp->uh_prev.ptr != NULL && uhp->uh_prev.ptr->uh_walk != nomark
2433 					 && uhp->uh_prev.ptr->uh_walk != mark)
2434 		uhp = uhp->uh_prev.ptr;
2435 
2436 	    /* go to alternate branch if we haven't been there */
2437 	    else if (uhp->uh_alt_next.ptr != NULL
2438 		    && uhp->uh_alt_next.ptr->uh_walk != nomark
2439 		    && uhp->uh_alt_next.ptr->uh_walk != mark)
2440 		uhp = uhp->uh_alt_next.ptr;
2441 
2442 	    /* go up in the tree if we haven't been there and we are at the
2443 	     * start of alternate branches */
2444 	    else if (uhp->uh_next.ptr != NULL && uhp->uh_alt_prev.ptr == NULL
2445 		    && uhp->uh_next.ptr->uh_walk != nomark
2446 		    && uhp->uh_next.ptr->uh_walk != mark)
2447 	    {
2448 		/* If still at the start we don't go through this change. */
2449 		if (uhp == curbuf->b_u_curhead)
2450 		    uhp->uh_walk = nomark;
2451 		uhp = uhp->uh_next.ptr;
2452 	    }
2453 
2454 	    else
2455 	    {
2456 		/* need to backtrack; mark this node as useless */
2457 		uhp->uh_walk = nomark;
2458 		if (uhp->uh_alt_prev.ptr != NULL)
2459 		    uhp = uhp->uh_alt_prev.ptr;
2460 		else
2461 		    uhp = uhp->uh_next.ptr;
2462 	    }
2463 	}
2464 
2465 	if (uhp != NULL)    /* found it */
2466 	    break;
2467 
2468 	if (absolute)
2469 	{
2470 	    EMSGN(_("E830: Undo number %ld not found"), step);
2471 	    return;
2472 	}
2473 
2474 	if (closest == closest_start)
2475 	{
2476 	    if (step < 0)
2477 		MSG(_("Already at oldest change"));
2478 	    else
2479 		MSG(_("Already at newest change"));
2480 	    return;
2481 	}
2482 
2483 	target = closest_seq;
2484 	dosec = FALSE;
2485 	dofile = FALSE;
2486 	if (step < 0)
2487 	    above = TRUE;	/* stop above the header */
2488     }
2489 
2490     /* If we found it: Follow the path to go to where we want to be. */
2491     if (uhp != NULL)
2492     {
2493 	/*
2494 	 * First go up the tree as much as needed.
2495 	 */
2496 	while (!got_int)
2497 	{
2498 	    /* Do the change warning now, for the same reason as above. */
2499 	    change_warning(0);
2500 
2501 	    uhp = curbuf->b_u_curhead;
2502 	    if (uhp == NULL)
2503 		uhp = curbuf->b_u_newhead;
2504 	    else
2505 		uhp = uhp->uh_next.ptr;
2506 	    if (uhp == NULL || uhp->uh_walk != mark
2507 					 || (uhp->uh_seq == target && !above))
2508 		break;
2509 	    curbuf->b_u_curhead = uhp;
2510 	    u_undoredo(TRUE);
2511 	    uhp->uh_walk = nomark;	/* don't go back down here */
2512 	}
2513 
2514 	/*
2515 	 * And now go down the tree (redo), branching off where needed.
2516 	 */
2517 	while (!got_int)
2518 	{
2519 	    /* Do the change warning now, for the same reason as above. */
2520 	    change_warning(0);
2521 
2522 	    uhp = curbuf->b_u_curhead;
2523 	    if (uhp == NULL)
2524 		break;
2525 
2526 	    /* Go back to the first branch with a mark. */
2527 	    while (uhp->uh_alt_prev.ptr != NULL
2528 				     && uhp->uh_alt_prev.ptr->uh_walk == mark)
2529 		uhp = uhp->uh_alt_prev.ptr;
2530 
2531 	    /* Find the last branch with a mark, that's the one. */
2532 	    last = uhp;
2533 	    while (last->uh_alt_next.ptr != NULL
2534 				    && last->uh_alt_next.ptr->uh_walk == mark)
2535 		last = last->uh_alt_next.ptr;
2536 	    if (last != uhp)
2537 	    {
2538 		/* Make the used branch the first entry in the list of
2539 		 * alternatives to make "u" and CTRL-R take this branch. */
2540 		while (uhp->uh_alt_prev.ptr != NULL)
2541 		    uhp = uhp->uh_alt_prev.ptr;
2542 		if (last->uh_alt_next.ptr != NULL)
2543 		    last->uh_alt_next.ptr->uh_alt_prev.ptr =
2544 							last->uh_alt_prev.ptr;
2545 		last->uh_alt_prev.ptr->uh_alt_next.ptr = last->uh_alt_next.ptr;
2546 		last->uh_alt_prev.ptr = NULL;
2547 		last->uh_alt_next.ptr = uhp;
2548 		uhp->uh_alt_prev.ptr = last;
2549 
2550 		if (curbuf->b_u_oldhead == uhp)
2551 		    curbuf->b_u_oldhead = last;
2552 		uhp = last;
2553 		if (uhp->uh_next.ptr != NULL)
2554 		    uhp->uh_next.ptr->uh_prev.ptr = uhp;
2555 	    }
2556 	    curbuf->b_u_curhead = uhp;
2557 
2558 	    if (uhp->uh_walk != mark)
2559 		break;	    /* must have reached the target */
2560 
2561 	    /* Stop when going backwards in time and didn't find the exact
2562 	     * header we were looking for. */
2563 	    if (uhp->uh_seq == target && above)
2564 	    {
2565 		curbuf->b_u_seq_cur = target - 1;
2566 		break;
2567 	    }
2568 
2569 	    u_undoredo(FALSE);
2570 
2571 	    /* Advance "curhead" to below the header we last used.  If it
2572 	     * becomes NULL then we need to set "newhead" to this leaf. */
2573 	    if (uhp->uh_prev.ptr == NULL)
2574 		curbuf->b_u_newhead = uhp;
2575 	    curbuf->b_u_curhead = uhp->uh_prev.ptr;
2576 	    did_undo = FALSE;
2577 
2578 	    if (uhp->uh_seq == target)	/* found it! */
2579 		break;
2580 
2581 	    uhp = uhp->uh_prev.ptr;
2582 	    if (uhp == NULL || uhp->uh_walk != mark)
2583 	    {
2584 		/* Need to redo more but can't find it... */
2585 		EMSG2(_(e_intern2), "undo_time()");
2586 		break;
2587 	    }
2588 	}
2589     }
2590     u_undo_end(did_undo, absolute);
2591 }
2592 
2593 /*
2594  * u_undoredo: common code for undo and redo
2595  *
2596  * The lines in the file are replaced by the lines in the entry list at
2597  * curbuf->b_u_curhead. The replaced lines in the file are saved in the entry
2598  * list for the next undo/redo.
2599  *
2600  * When "undo" is TRUE we go up in the tree, when FALSE we go down.
2601  */
2602     static void
2603 u_undoredo(int undo)
2604 {
2605     char_u	**newarray = NULL;
2606     linenr_T	oldsize;
2607     linenr_T	newsize;
2608     linenr_T	top, bot;
2609     linenr_T	lnum;
2610     linenr_T	newlnum = MAXLNUM;
2611     long	i;
2612     u_entry_T	*uep, *nuep;
2613     u_entry_T	*newlist = NULL;
2614     int		old_flags;
2615     int		new_flags;
2616     pos_T	namedm[NMARKS];
2617     visualinfo_T visualinfo;
2618     int		empty_buffer;		    /* buffer became empty */
2619     u_header_T	*curhead = curbuf->b_u_curhead;
2620 
2621 #ifdef FEAT_AUTOCMD
2622     /* Don't want autocommands using the undo structures here, they are
2623      * invalid till the end. */
2624     block_autocmds();
2625 #endif
2626 
2627 #ifdef U_DEBUG
2628     u_check(FALSE);
2629 #endif
2630     old_flags = curhead->uh_flags;
2631     new_flags = (curbuf->b_changed ? UH_CHANGED : 0) +
2632 	       ((curbuf->b_ml.ml_flags & ML_EMPTY) ? UH_EMPTYBUF : 0);
2633     setpcmark();
2634 
2635     /*
2636      * save marks before undo/redo
2637      */
2638     mch_memmove(namedm, curbuf->b_namedm, sizeof(pos_T) * NMARKS);
2639     visualinfo = curbuf->b_visual;
2640     curbuf->b_op_start.lnum = curbuf->b_ml.ml_line_count;
2641     curbuf->b_op_start.col = 0;
2642     curbuf->b_op_end.lnum = 0;
2643     curbuf->b_op_end.col = 0;
2644 
2645     for (uep = curhead->uh_entry; uep != NULL; uep = nuep)
2646     {
2647 	top = uep->ue_top;
2648 	bot = uep->ue_bot;
2649 	if (bot == 0)
2650 	    bot = curbuf->b_ml.ml_line_count + 1;
2651 	if (top > curbuf->b_ml.ml_line_count || top >= bot
2652 				      || bot > curbuf->b_ml.ml_line_count + 1)
2653 	{
2654 #ifdef FEAT_AUTOCMD
2655 	    unblock_autocmds();
2656 #endif
2657 	    EMSG(_("E438: u_undo: line numbers wrong"));
2658 	    changed();		/* don't want UNCHANGED now */
2659 	    return;
2660 	}
2661 
2662 	oldsize = bot - top - 1;    /* number of lines before undo */
2663 	newsize = uep->ue_size;	    /* number of lines after undo */
2664 
2665 	if (top < newlnum)
2666 	{
2667 	    /* If the saved cursor is somewhere in this undo block, move it to
2668 	     * the remembered position.  Makes "gwap" put the cursor back
2669 	     * where it was. */
2670 	    lnum = curhead->uh_cursor.lnum;
2671 	    if (lnum >= top && lnum <= top + newsize + 1)
2672 	    {
2673 		curwin->w_cursor = curhead->uh_cursor;
2674 		newlnum = curwin->w_cursor.lnum - 1;
2675 	    }
2676 	    else
2677 	    {
2678 		/* Use the first line that actually changed.  Avoids that
2679 		 * undoing auto-formatting puts the cursor in the previous
2680 		 * line. */
2681 		for (i = 0; i < newsize && i < oldsize; ++i)
2682 		    if (STRCMP(uep->ue_array[i], ml_get(top + 1 + i)) != 0)
2683 			break;
2684 		if (i == newsize && newlnum == MAXLNUM && uep->ue_next == NULL)
2685 		{
2686 		    newlnum = top;
2687 		    curwin->w_cursor.lnum = newlnum + 1;
2688 		}
2689 		else if (i < newsize)
2690 		{
2691 		    newlnum = top + i;
2692 		    curwin->w_cursor.lnum = newlnum + 1;
2693 		}
2694 	    }
2695 	}
2696 
2697 	empty_buffer = FALSE;
2698 
2699 	/* delete the lines between top and bot and save them in newarray */
2700 	if (oldsize > 0)
2701 	{
2702 	    if ((newarray = (char_u **)U_ALLOC_LINE(
2703 					 sizeof(char_u *) * oldsize)) == NULL)
2704 	    {
2705 		do_outofmem_msg((long_u)(sizeof(char_u *) * oldsize));
2706 		/*
2707 		 * We have messed up the entry list, repair is impossible.
2708 		 * we have to free the rest of the list.
2709 		 */
2710 		while (uep != NULL)
2711 		{
2712 		    nuep = uep->ue_next;
2713 		    u_freeentry(uep, uep->ue_size);
2714 		    uep = nuep;
2715 		}
2716 		break;
2717 	    }
2718 	    /* delete backwards, it goes faster in most cases */
2719 	    for (lnum = bot - 1, i = oldsize; --i >= 0; --lnum)
2720 	    {
2721 		/* what can we do when we run out of memory? */
2722 		if ((newarray[i] = u_save_line(lnum)) == NULL)
2723 		    do_outofmem_msg((long_u)0);
2724 		/* remember we deleted the last line in the buffer, and a
2725 		 * dummy empty line will be inserted */
2726 		if (curbuf->b_ml.ml_line_count == 1)
2727 		    empty_buffer = TRUE;
2728 		ml_delete(lnum, FALSE);
2729 	    }
2730 	}
2731 	else
2732 	    newarray = NULL;
2733 
2734 	/* insert the lines in u_array between top and bot */
2735 	if (newsize)
2736 	{
2737 	    for (lnum = top, i = 0; i < newsize; ++i, ++lnum)
2738 	    {
2739 		/*
2740 		 * If the file is empty, there is an empty line 1 that we
2741 		 * should get rid of, by replacing it with the new line
2742 		 */
2743 		if (empty_buffer && lnum == 0)
2744 		    ml_replace((linenr_T)1, uep->ue_array[i], TRUE);
2745 		else
2746 		    ml_append(lnum, uep->ue_array[i], (colnr_T)0, FALSE);
2747 		vim_free(uep->ue_array[i]);
2748 	    }
2749 	    vim_free((char_u *)uep->ue_array);
2750 	}
2751 
2752 	/* adjust marks */
2753 	if (oldsize != newsize)
2754 	{
2755 	    mark_adjust(top + 1, top + oldsize, (long)MAXLNUM,
2756 					       (long)newsize - (long)oldsize);
2757 	    if (curbuf->b_op_start.lnum > top + oldsize)
2758 		curbuf->b_op_start.lnum += newsize - oldsize;
2759 	    if (curbuf->b_op_end.lnum > top + oldsize)
2760 		curbuf->b_op_end.lnum += newsize - oldsize;
2761 	}
2762 
2763 	changed_lines(top + 1, 0, bot, newsize - oldsize);
2764 
2765 	/* set '[ and '] mark */
2766 	if (top + 1 < curbuf->b_op_start.lnum)
2767 	    curbuf->b_op_start.lnum = top + 1;
2768 	if (newsize == 0 && top + 1 > curbuf->b_op_end.lnum)
2769 	    curbuf->b_op_end.lnum = top + 1;
2770 	else if (top + newsize > curbuf->b_op_end.lnum)
2771 	    curbuf->b_op_end.lnum = top + newsize;
2772 
2773 	u_newcount += newsize;
2774 	u_oldcount += oldsize;
2775 	uep->ue_size = oldsize;
2776 	uep->ue_array = newarray;
2777 	uep->ue_bot = top + newsize + 1;
2778 
2779 	/*
2780 	 * insert this entry in front of the new entry list
2781 	 */
2782 	nuep = uep->ue_next;
2783 	uep->ue_next = newlist;
2784 	newlist = uep;
2785     }
2786 
2787     curhead->uh_entry = newlist;
2788     curhead->uh_flags = new_flags;
2789     if ((old_flags & UH_EMPTYBUF) && bufempty())
2790 	curbuf->b_ml.ml_flags |= ML_EMPTY;
2791     if (old_flags & UH_CHANGED)
2792 	changed();
2793     else
2794 #ifdef FEAT_NETBEANS_INTG
2795 	/* per netbeans undo rules, keep it as modified */
2796 	if (!isNetbeansModified(curbuf))
2797 #endif
2798 	unchanged(curbuf, FALSE);
2799 
2800     /*
2801      * restore marks from before undo/redo
2802      */
2803     for (i = 0; i < NMARKS; ++i)
2804     {
2805 	if (curhead->uh_namedm[i].lnum != 0)
2806 	    curbuf->b_namedm[i] = curhead->uh_namedm[i];
2807 	if (namedm[i].lnum != 0)
2808 	    curhead->uh_namedm[i] = namedm[i];
2809 	else
2810 	    curhead->uh_namedm[i].lnum = 0;
2811     }
2812     if (curhead->uh_visual.vi_start.lnum != 0)
2813     {
2814 	curbuf->b_visual = curhead->uh_visual;
2815 	curhead->uh_visual = visualinfo;
2816     }
2817 
2818     /*
2819      * If the cursor is only off by one line, put it at the same position as
2820      * before starting the change (for the "o" command).
2821      * Otherwise the cursor should go to the first undone line.
2822      */
2823     if (curhead->uh_cursor.lnum + 1 == curwin->w_cursor.lnum
2824 						 && curwin->w_cursor.lnum > 1)
2825 	--curwin->w_cursor.lnum;
2826     if (curwin->w_cursor.lnum <= curbuf->b_ml.ml_line_count)
2827     {
2828 	if (curhead->uh_cursor.lnum == curwin->w_cursor.lnum)
2829 	{
2830 	    curwin->w_cursor.col = curhead->uh_cursor.col;
2831 #ifdef FEAT_VIRTUALEDIT
2832 	    if (virtual_active() && curhead->uh_cursor_vcol >= 0)
2833 		coladvance((colnr_T)curhead->uh_cursor_vcol);
2834 	    else
2835 		curwin->w_cursor.coladd = 0;
2836 #endif
2837 	}
2838 	else
2839 	    beginline(BL_SOL | BL_FIX);
2840     }
2841     else
2842     {
2843 	/* We get here with the current cursor line being past the end (eg
2844 	 * after adding lines at the end of the file, and then undoing it).
2845 	 * check_cursor() will move the cursor to the last line.  Move it to
2846 	 * the first column here. */
2847 	curwin->w_cursor.col = 0;
2848 #ifdef FEAT_VIRTUALEDIT
2849 	curwin->w_cursor.coladd = 0;
2850 #endif
2851     }
2852 
2853     /* Make sure the cursor is on an existing line and column. */
2854     check_cursor();
2855 
2856     /* Remember where we are for "g-" and ":earlier 10s". */
2857     curbuf->b_u_seq_cur = curhead->uh_seq;
2858     if (undo)
2859 	/* We are below the previous undo.  However, to make ":earlier 1s"
2860 	 * work we compute this as being just above the just undone change. */
2861 	--curbuf->b_u_seq_cur;
2862 
2863     /* Remember where we are for ":earlier 1f" and ":later 1f". */
2864     if (curhead->uh_save_nr != 0)
2865     {
2866 	if (undo)
2867 	    curbuf->b_u_save_nr_cur = curhead->uh_save_nr - 1;
2868 	else
2869 	    curbuf->b_u_save_nr_cur = curhead->uh_save_nr;
2870     }
2871 
2872     /* The timestamp can be the same for multiple changes, just use the one of
2873      * the undone/redone change. */
2874     curbuf->b_u_time_cur = curhead->uh_time;
2875 
2876 #ifdef FEAT_AUTOCMD
2877     unblock_autocmds();
2878 #endif
2879 #ifdef U_DEBUG
2880     u_check(FALSE);
2881 #endif
2882 }
2883 
2884 /*
2885  * If we deleted or added lines, report the number of less/more lines.
2886  * Otherwise, report the number of changes (this may be incorrect
2887  * in some cases, but it's better than nothing).
2888  */
2889     static void
2890 u_undo_end(
2891     int		did_undo,	/* just did an undo */
2892     int		absolute)	/* used ":undo N" */
2893 {
2894     char	*msgstr;
2895     u_header_T	*uhp;
2896     char_u	msgbuf[80];
2897 
2898 #ifdef FEAT_FOLDING
2899     if ((fdo_flags & FDO_UNDO) && KeyTyped)
2900 	foldOpenCursor();
2901 #endif
2902 
2903     if (global_busy	    /* no messages now, wait until global is finished */
2904 	    || !messaging())  /* 'lazyredraw' set, don't do messages now */
2905 	return;
2906 
2907     if (curbuf->b_ml.ml_flags & ML_EMPTY)
2908 	--u_newcount;
2909 
2910     u_oldcount -= u_newcount;
2911     if (u_oldcount == -1)
2912 	msgstr = N_("more line");
2913     else if (u_oldcount < 0)
2914 	msgstr = N_("more lines");
2915     else if (u_oldcount == 1)
2916 	msgstr = N_("line less");
2917     else if (u_oldcount > 1)
2918 	msgstr = N_("fewer lines");
2919     else
2920     {
2921 	u_oldcount = u_newcount;
2922 	if (u_newcount == 1)
2923 	    msgstr = N_("change");
2924 	else
2925 	    msgstr = N_("changes");
2926     }
2927 
2928     if (curbuf->b_u_curhead != NULL)
2929     {
2930 	/* For ":undo N" we prefer a "after #N" message. */
2931 	if (absolute && curbuf->b_u_curhead->uh_next.ptr != NULL)
2932 	{
2933 	    uhp = curbuf->b_u_curhead->uh_next.ptr;
2934 	    did_undo = FALSE;
2935 	}
2936 	else if (did_undo)
2937 	    uhp = curbuf->b_u_curhead;
2938 	else
2939 	    uhp = curbuf->b_u_curhead->uh_next.ptr;
2940     }
2941     else
2942 	uhp = curbuf->b_u_newhead;
2943 
2944     if (uhp == NULL)
2945 	*msgbuf = NUL;
2946     else
2947 	u_add_time(msgbuf, sizeof(msgbuf), uhp->uh_time);
2948 
2949 #ifdef FEAT_CONCEAL
2950     {
2951 	win_T	*wp;
2952 
2953 	FOR_ALL_WINDOWS(wp)
2954 	{
2955 	    if (wp->w_buffer == curbuf && wp->w_p_cole > 0)
2956 		redraw_win_later(wp, NOT_VALID);
2957 	}
2958     }
2959 #endif
2960 
2961     smsg((char_u *)_("%ld %s; %s #%ld  %s"),
2962 	    u_oldcount < 0 ? -u_oldcount : u_oldcount,
2963 	    _(msgstr),
2964 	    did_undo ? _("before") : _("after"),
2965 	    uhp == NULL ? 0L : uhp->uh_seq,
2966 	    msgbuf);
2967 }
2968 
2969 /*
2970  * u_sync: stop adding to the current entry list
2971  */
2972     void
2973 u_sync(
2974     int	    force)	/* Also sync when no_u_sync is set. */
2975 {
2976     /* Skip it when already synced or syncing is disabled. */
2977     if (curbuf->b_u_synced || (!force && no_u_sync > 0))
2978 	return;
2979 #if defined(FEAT_XIM) && defined(FEAT_GUI_GTK)
2980     if (im_is_preediting())
2981 	return;		    /* XIM is busy, don't break an undo sequence */
2982 #endif
2983     if (get_undolevel() < 0)
2984 	curbuf->b_u_synced = TRUE;  /* no entries, nothing to do */
2985     else
2986     {
2987 	u_getbot();		    /* compute ue_bot of previous u_save */
2988 	curbuf->b_u_curhead = NULL;
2989     }
2990 }
2991 
2992 /*
2993  * ":undolist": List the leafs of the undo tree
2994  */
2995     void
2996 ex_undolist(exarg_T *eap UNUSED)
2997 {
2998     garray_T	ga;
2999     u_header_T	*uhp;
3000     int		mark;
3001     int		nomark;
3002     int		changes = 1;
3003     int		i;
3004 
3005     /*
3006      * 1: walk the tree to find all leafs, put the info in "ga".
3007      * 2: sort the lines
3008      * 3: display the list
3009      */
3010     mark = ++lastmark;
3011     nomark = ++lastmark;
3012     ga_init2(&ga, (int)sizeof(char *), 20);
3013 
3014     uhp = curbuf->b_u_oldhead;
3015     while (uhp != NULL)
3016     {
3017 	if (uhp->uh_prev.ptr == NULL && uhp->uh_walk != nomark
3018 						      && uhp->uh_walk != mark)
3019 	{
3020 	    if (ga_grow(&ga, 1) == FAIL)
3021 		break;
3022 	    vim_snprintf((char *)IObuff, IOSIZE, "%6ld %7ld  ",
3023 							uhp->uh_seq, changes);
3024 	    u_add_time(IObuff + STRLEN(IObuff), IOSIZE - STRLEN(IObuff),
3025 								uhp->uh_time);
3026 	    if (uhp->uh_save_nr > 0)
3027 	    {
3028 		while (STRLEN(IObuff) < 33)
3029 		    STRCAT(IObuff, " ");
3030 		vim_snprintf_add((char *)IObuff, IOSIZE,
3031 						   "  %3ld", uhp->uh_save_nr);
3032 	    }
3033 	    ((char_u **)(ga.ga_data))[ga.ga_len++] = vim_strsave(IObuff);
3034 	}
3035 
3036 	uhp->uh_walk = mark;
3037 
3038 	/* go down in the tree if we haven't been there */
3039 	if (uhp->uh_prev.ptr != NULL && uhp->uh_prev.ptr->uh_walk != nomark
3040 					 && uhp->uh_prev.ptr->uh_walk != mark)
3041 	{
3042 	    uhp = uhp->uh_prev.ptr;
3043 	    ++changes;
3044 	}
3045 
3046 	/* go to alternate branch if we haven't been there */
3047 	else if (uhp->uh_alt_next.ptr != NULL
3048 		&& uhp->uh_alt_next.ptr->uh_walk != nomark
3049 		&& uhp->uh_alt_next.ptr->uh_walk != mark)
3050 	    uhp = uhp->uh_alt_next.ptr;
3051 
3052 	/* go up in the tree if we haven't been there and we are at the
3053 	 * start of alternate branches */
3054 	else if (uhp->uh_next.ptr != NULL && uhp->uh_alt_prev.ptr == NULL
3055 		&& uhp->uh_next.ptr->uh_walk != nomark
3056 		&& uhp->uh_next.ptr->uh_walk != mark)
3057 	{
3058 	    uhp = uhp->uh_next.ptr;
3059 	    --changes;
3060 	}
3061 
3062 	else
3063 	{
3064 	    /* need to backtrack; mark this node as done */
3065 	    uhp->uh_walk = nomark;
3066 	    if (uhp->uh_alt_prev.ptr != NULL)
3067 		uhp = uhp->uh_alt_prev.ptr;
3068 	    else
3069 	    {
3070 		uhp = uhp->uh_next.ptr;
3071 		--changes;
3072 	    }
3073 	}
3074     }
3075 
3076     if (ga.ga_len == 0)
3077 	MSG(_("Nothing to undo"));
3078     else
3079     {
3080 	sort_strings((char_u **)ga.ga_data, ga.ga_len);
3081 
3082 	msg_start();
3083 	msg_puts_attr((char_u *)_("number changes  when               saved"),
3084 							      hl_attr(HLF_T));
3085 	for (i = 0; i < ga.ga_len && !got_int; ++i)
3086 	{
3087 	    msg_putchar('\n');
3088 	    if (got_int)
3089 		break;
3090 	    msg_puts(((char_u **)ga.ga_data)[i]);
3091 	}
3092 	msg_end();
3093 
3094 	ga_clear_strings(&ga);
3095     }
3096 }
3097 
3098 /*
3099  * Put the timestamp of an undo header in "buf[buflen]" in a nice format.
3100  */
3101     static void
3102 u_add_time(char_u *buf, size_t buflen, time_t tt)
3103 {
3104 #ifdef HAVE_STRFTIME
3105     struct tm	*curtime;
3106 
3107     if (vim_time() - tt >= 100)
3108     {
3109 	curtime = localtime(&tt);
3110 	if (vim_time() - tt < (60L * 60L * 12L))
3111 	    /* within 12 hours */
3112 	    (void)strftime((char *)buf, buflen, "%H:%M:%S", curtime);
3113 	else
3114 	    /* longer ago */
3115 	    (void)strftime((char *)buf, buflen, "%Y/%m/%d %H:%M:%S", curtime);
3116     }
3117     else
3118 #endif
3119 	vim_snprintf((char *)buf, buflen, _("%ld seconds ago"),
3120 						      (long)(vim_time() - tt));
3121 }
3122 
3123 /*
3124  * ":undojoin": continue adding to the last entry list
3125  */
3126     void
3127 ex_undojoin(exarg_T *eap UNUSED)
3128 {
3129     if (curbuf->b_u_newhead == NULL)
3130 	return;		    /* nothing changed before */
3131     if (curbuf->b_u_curhead != NULL)
3132     {
3133 	EMSG(_("E790: undojoin is not allowed after undo"));
3134 	return;
3135     }
3136     if (!curbuf->b_u_synced)
3137 	return;		    /* already unsynced */
3138     if (get_undolevel() < 0)
3139 	return;		    /* no entries, nothing to do */
3140     else
3141     {
3142 	/* Go back to the last entry */
3143 	curbuf->b_u_curhead = curbuf->b_u_newhead;
3144 	curbuf->b_u_synced = FALSE;  /* no entries, nothing to do */
3145     }
3146 }
3147 
3148 /*
3149  * Called after writing or reloading the file and setting b_changed to FALSE.
3150  * Now an undo means that the buffer is modified.
3151  */
3152     void
3153 u_unchanged(buf_T *buf)
3154 {
3155     u_unch_branch(buf->b_u_oldhead);
3156     buf->b_did_warn = FALSE;
3157 }
3158 
3159 /*
3160  * After reloading a buffer which was saved for 'undoreload': Find the first
3161  * line that was changed and set the cursor there.
3162  */
3163     void
3164 u_find_first_changed(void)
3165 {
3166     u_header_T	*uhp = curbuf->b_u_newhead;
3167     u_entry_T   *uep;
3168     linenr_T	lnum;
3169 
3170     if (curbuf->b_u_curhead != NULL || uhp == NULL)
3171 	return;  /* undid something in an autocmd? */
3172 
3173     /* Check that the last undo block was for the whole file. */
3174     uep = uhp->uh_entry;
3175     if (uep->ue_top != 0 || uep->ue_bot != 0)
3176 	return;
3177 
3178     for (lnum = 1; lnum < curbuf->b_ml.ml_line_count
3179 					      && lnum <= uep->ue_size; ++lnum)
3180 	if (STRCMP(ml_get_buf(curbuf, lnum, FALSE),
3181 						uep->ue_array[lnum - 1]) != 0)
3182 	{
3183 	    clearpos(&(uhp->uh_cursor));
3184 	    uhp->uh_cursor.lnum = lnum;
3185 	    return;
3186 	}
3187     if (curbuf->b_ml.ml_line_count != uep->ue_size)
3188     {
3189 	/* lines added or deleted at the end, put the cursor there */
3190 	clearpos(&(uhp->uh_cursor));
3191 	uhp->uh_cursor.lnum = lnum;
3192     }
3193 }
3194 
3195 /*
3196  * Increase the write count, store it in the last undo header, what would be
3197  * used for "u".
3198  */
3199     void
3200 u_update_save_nr(buf_T *buf)
3201 {
3202     u_header_T	*uhp;
3203 
3204     ++buf->b_u_save_nr_last;
3205     buf->b_u_save_nr_cur = buf->b_u_save_nr_last;
3206     uhp = buf->b_u_curhead;
3207     if (uhp != NULL)
3208 	uhp = uhp->uh_next.ptr;
3209     else
3210 	uhp = buf->b_u_newhead;
3211     if (uhp != NULL)
3212 	uhp->uh_save_nr = buf->b_u_save_nr_last;
3213 }
3214 
3215     static void
3216 u_unch_branch(u_header_T *uhp)
3217 {
3218     u_header_T	*uh;
3219 
3220     for (uh = uhp; uh != NULL; uh = uh->uh_prev.ptr)
3221     {
3222 	uh->uh_flags |= UH_CHANGED;
3223 	if (uh->uh_alt_next.ptr != NULL)
3224 	    u_unch_branch(uh->uh_alt_next.ptr);	    /* recursive */
3225     }
3226 }
3227 
3228 /*
3229  * Get pointer to last added entry.
3230  * If it's not valid, give an error message and return NULL.
3231  */
3232     static u_entry_T *
3233 u_get_headentry(void)
3234 {
3235     if (curbuf->b_u_newhead == NULL || curbuf->b_u_newhead->uh_entry == NULL)
3236     {
3237 	EMSG(_("E439: undo list corrupt"));
3238 	return NULL;
3239     }
3240     return curbuf->b_u_newhead->uh_entry;
3241 }
3242 
3243 /*
3244  * u_getbot(): compute the line number of the previous u_save
3245  *		It is called only when b_u_synced is FALSE.
3246  */
3247     static void
3248 u_getbot(void)
3249 {
3250     u_entry_T	*uep;
3251     linenr_T	extra;
3252 
3253     uep = u_get_headentry();	/* check for corrupt undo list */
3254     if (uep == NULL)
3255 	return;
3256 
3257     uep = curbuf->b_u_newhead->uh_getbot_entry;
3258     if (uep != NULL)
3259     {
3260 	/*
3261 	 * the new ue_bot is computed from the number of lines that has been
3262 	 * inserted (0 - deleted) since calling u_save. This is equal to the
3263 	 * old line count subtracted from the current line count.
3264 	 */
3265 	extra = curbuf->b_ml.ml_line_count - uep->ue_lcount;
3266 	uep->ue_bot = uep->ue_top + uep->ue_size + 1 + extra;
3267 	if (uep->ue_bot < 1 || uep->ue_bot > curbuf->b_ml.ml_line_count)
3268 	{
3269 	    EMSG(_("E440: undo line missing"));
3270 	    uep->ue_bot = uep->ue_top + 1;  /* assume all lines deleted, will
3271 					     * get all the old lines back
3272 					     * without deleting the current
3273 					     * ones */
3274 	}
3275 
3276 	curbuf->b_u_newhead->uh_getbot_entry = NULL;
3277     }
3278 
3279     curbuf->b_u_synced = TRUE;
3280 }
3281 
3282 /*
3283  * Free one header "uhp" and its entry list and adjust the pointers.
3284  */
3285     static void
3286 u_freeheader(
3287     buf_T	    *buf,
3288     u_header_T	    *uhp,
3289     u_header_T	    **uhpp)	/* if not NULL reset when freeing this header */
3290 {
3291     u_header_T	    *uhap;
3292 
3293     /* When there is an alternate redo list free that branch completely,
3294      * because we can never go there. */
3295     if (uhp->uh_alt_next.ptr != NULL)
3296 	u_freebranch(buf, uhp->uh_alt_next.ptr, uhpp);
3297 
3298     if (uhp->uh_alt_prev.ptr != NULL)
3299 	uhp->uh_alt_prev.ptr->uh_alt_next.ptr = NULL;
3300 
3301     /* Update the links in the list to remove the header. */
3302     if (uhp->uh_next.ptr == NULL)
3303 	buf->b_u_oldhead = uhp->uh_prev.ptr;
3304     else
3305 	uhp->uh_next.ptr->uh_prev.ptr = uhp->uh_prev.ptr;
3306 
3307     if (uhp->uh_prev.ptr == NULL)
3308 	buf->b_u_newhead = uhp->uh_next.ptr;
3309     else
3310 	for (uhap = uhp->uh_prev.ptr; uhap != NULL;
3311 						 uhap = uhap->uh_alt_next.ptr)
3312 	    uhap->uh_next.ptr = uhp->uh_next.ptr;
3313 
3314     u_freeentries(buf, uhp, uhpp);
3315 }
3316 
3317 /*
3318  * Free an alternate branch and any following alternate branches.
3319  */
3320     static void
3321 u_freebranch(
3322     buf_T	    *buf,
3323     u_header_T	    *uhp,
3324     u_header_T	    **uhpp)	/* if not NULL reset when freeing this header */
3325 {
3326     u_header_T	    *tofree, *next;
3327 
3328     /* If this is the top branch we may need to use u_freeheader() to update
3329      * all the pointers. */
3330     if (uhp == buf->b_u_oldhead)
3331     {
3332 	while (buf->b_u_oldhead != NULL)
3333 	    u_freeheader(buf, buf->b_u_oldhead, uhpp);
3334 	return;
3335     }
3336 
3337     if (uhp->uh_alt_prev.ptr != NULL)
3338 	uhp->uh_alt_prev.ptr->uh_alt_next.ptr = NULL;
3339 
3340     next = uhp;
3341     while (next != NULL)
3342     {
3343 	tofree = next;
3344 	if (tofree->uh_alt_next.ptr != NULL)
3345 	    u_freebranch(buf, tofree->uh_alt_next.ptr, uhpp);   /* recursive */
3346 	next = tofree->uh_prev.ptr;
3347 	u_freeentries(buf, tofree, uhpp);
3348     }
3349 }
3350 
3351 /*
3352  * Free all the undo entries for one header and the header itself.
3353  * This means that "uhp" is invalid when returning.
3354  */
3355     static void
3356 u_freeentries(
3357     buf_T	    *buf,
3358     u_header_T	    *uhp,
3359     u_header_T	    **uhpp)	/* if not NULL reset when freeing this header */
3360 {
3361     u_entry_T	    *uep, *nuep;
3362 
3363     /* Check for pointers to the header that become invalid now. */
3364     if (buf->b_u_curhead == uhp)
3365 	buf->b_u_curhead = NULL;
3366     if (buf->b_u_newhead == uhp)
3367 	buf->b_u_newhead = NULL;  /* freeing the newest entry */
3368     if (uhpp != NULL && uhp == *uhpp)
3369 	*uhpp = NULL;
3370 
3371     for (uep = uhp->uh_entry; uep != NULL; uep = nuep)
3372     {
3373 	nuep = uep->ue_next;
3374 	u_freeentry(uep, uep->ue_size);
3375     }
3376 
3377 #ifdef U_DEBUG
3378     uhp->uh_magic = 0;
3379 #endif
3380     vim_free((char_u *)uhp);
3381     --buf->b_u_numhead;
3382 }
3383 
3384 /*
3385  * free entry 'uep' and 'n' lines in uep->ue_array[]
3386  */
3387     static void
3388 u_freeentry(u_entry_T *uep, long n)
3389 {
3390     while (n > 0)
3391 	vim_free(uep->ue_array[--n]);
3392     vim_free((char_u *)uep->ue_array);
3393 #ifdef U_DEBUG
3394     uep->ue_magic = 0;
3395 #endif
3396     vim_free((char_u *)uep);
3397 }
3398 
3399 /*
3400  * invalidate the undo buffer; called when storage has already been released
3401  */
3402     void
3403 u_clearall(buf_T *buf)
3404 {
3405     buf->b_u_newhead = buf->b_u_oldhead = buf->b_u_curhead = NULL;
3406     buf->b_u_synced = TRUE;
3407     buf->b_u_numhead = 0;
3408     buf->b_u_line_ptr = NULL;
3409     buf->b_u_line_lnum = 0;
3410 }
3411 
3412 /*
3413  * save the line "lnum" for the "U" command
3414  */
3415     void
3416 u_saveline(linenr_T lnum)
3417 {
3418     if (lnum == curbuf->b_u_line_lnum)	    /* line is already saved */
3419 	return;
3420     if (lnum < 1 || lnum > curbuf->b_ml.ml_line_count) /* should never happen */
3421 	return;
3422     u_clearline();
3423     curbuf->b_u_line_lnum = lnum;
3424     if (curwin->w_cursor.lnum == lnum)
3425 	curbuf->b_u_line_colnr = curwin->w_cursor.col;
3426     else
3427 	curbuf->b_u_line_colnr = 0;
3428     if ((curbuf->b_u_line_ptr = u_save_line(lnum)) == NULL)
3429 	do_outofmem_msg((long_u)0);
3430 }
3431 
3432 /*
3433  * clear the line saved for the "U" command
3434  * (this is used externally for crossing a line while in insert mode)
3435  */
3436     void
3437 u_clearline(void)
3438 {
3439     if (curbuf->b_u_line_ptr != NULL)
3440     {
3441 	vim_free(curbuf->b_u_line_ptr);
3442 	curbuf->b_u_line_ptr = NULL;
3443 	curbuf->b_u_line_lnum = 0;
3444     }
3445 }
3446 
3447 /*
3448  * Implementation of the "U" command.
3449  * Differentiation from vi: "U" can be undone with the next "U".
3450  * We also allow the cursor to be in another line.
3451  * Careful: may trigger autocommands that reload the buffer.
3452  */
3453     void
3454 u_undoline(void)
3455 {
3456     colnr_T t;
3457     char_u  *oldp;
3458 
3459     if (undo_off)
3460 	return;
3461 
3462     if (curbuf->b_u_line_ptr == NULL
3463 			|| curbuf->b_u_line_lnum > curbuf->b_ml.ml_line_count)
3464     {
3465 	beep_flush();
3466 	return;
3467     }
3468 
3469     /* first save the line for the 'u' command */
3470     if (u_savecommon(curbuf->b_u_line_lnum - 1,
3471 		       curbuf->b_u_line_lnum + 1, (linenr_T)0, FALSE) == FAIL)
3472 	return;
3473     oldp = u_save_line(curbuf->b_u_line_lnum);
3474     if (oldp == NULL)
3475     {
3476 	do_outofmem_msg((long_u)0);
3477 	return;
3478     }
3479     ml_replace(curbuf->b_u_line_lnum, curbuf->b_u_line_ptr, TRUE);
3480     changed_bytes(curbuf->b_u_line_lnum, 0);
3481     vim_free(curbuf->b_u_line_ptr);
3482     curbuf->b_u_line_ptr = oldp;
3483 
3484     t = curbuf->b_u_line_colnr;
3485     if (curwin->w_cursor.lnum == curbuf->b_u_line_lnum)
3486 	curbuf->b_u_line_colnr = curwin->w_cursor.col;
3487     curwin->w_cursor.col = t;
3488     curwin->w_cursor.lnum = curbuf->b_u_line_lnum;
3489     check_cursor_col();
3490 }
3491 
3492 /*
3493  * Free all allocated memory blocks for the buffer 'buf'.
3494  */
3495     void
3496 u_blockfree(buf_T *buf)
3497 {
3498     while (buf->b_u_oldhead != NULL)
3499 	u_freeheader(buf, buf->b_u_oldhead, NULL);
3500     vim_free(buf->b_u_line_ptr);
3501 }
3502 
3503 /*
3504  * u_save_line(): allocate memory and copy line 'lnum' into it.
3505  * Returns NULL when out of memory.
3506  */
3507     static char_u *
3508 u_save_line(linenr_T lnum)
3509 {
3510     return vim_strsave(ml_get(lnum));
3511 }
3512 
3513 /*
3514  * Check if the 'modified' flag is set, or 'ff' has changed (only need to
3515  * check the first character, because it can only be "dos", "unix" or "mac").
3516  * "nofile" and "scratch" type buffers are considered to always be unchanged.
3517  */
3518     int
3519 bufIsChanged(buf_T *buf)
3520 {
3521     return
3522 #ifdef FEAT_QUICKFIX
3523 	    !bt_dontwrite(buf) &&
3524 #endif
3525 	    (buf->b_changed || file_ff_differs(buf, TRUE));
3526 }
3527 
3528     int
3529 curbufIsChanged(void)
3530 {
3531     return
3532 #ifdef FEAT_QUICKFIX
3533 	!bt_dontwrite(curbuf) &&
3534 #endif
3535 	(curbuf->b_changed || file_ff_differs(curbuf, TRUE));
3536 }
3537 
3538 #if defined(FEAT_EVAL) || defined(PROTO)
3539 /*
3540  * For undotree(): Append the list of undo blocks at "first_uhp" to "list".
3541  * Recursive.
3542  */
3543     void
3544 u_eval_tree(u_header_T *first_uhp, list_T *list)
3545 {
3546     u_header_T  *uhp = first_uhp;
3547     dict_T	*dict;
3548 
3549     while (uhp != NULL)
3550     {
3551 	dict = dict_alloc();
3552 	if (dict == NULL)
3553 	    return;
3554 	dict_add_nr_str(dict, "seq", uhp->uh_seq, NULL);
3555 	dict_add_nr_str(dict, "time", (long)uhp->uh_time, NULL);
3556 	if (uhp == curbuf->b_u_newhead)
3557 	    dict_add_nr_str(dict, "newhead", 1, NULL);
3558 	if (uhp == curbuf->b_u_curhead)
3559 	    dict_add_nr_str(dict, "curhead", 1, NULL);
3560 	if (uhp->uh_save_nr > 0)
3561 	    dict_add_nr_str(dict, "save", uhp->uh_save_nr, NULL);
3562 
3563 	if (uhp->uh_alt_next.ptr != NULL)
3564 	{
3565 	    list_T	*alt_list = list_alloc();
3566 
3567 	    if (alt_list != NULL)
3568 	    {
3569 		/* Recursive call to add alternate undo tree. */
3570 		u_eval_tree(uhp->uh_alt_next.ptr, alt_list);
3571 		dict_add_list(dict, "alt", alt_list);
3572 	    }
3573 	}
3574 
3575 	list_append_dict(list, dict);
3576 	uhp = uhp->uh_prev.ptr;
3577     }
3578 }
3579 #endif
3580