1 /* Caching facts about regions of the buffer, for optimization.
2
3 Copyright (C) 1985-1989, 1993, 1995, 2001-2023 Free Software Foundation,
4 Inc.
5
6 This file is part of GNU Emacs.
7
8 GNU Emacs is free software: you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation, either version 3 of the License, or (at
11 your option) any later version.
12
13 GNU Emacs is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
17
18 You should have received a copy of the GNU General Public License
19 along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
20
21
22 #include <config.h>
23 #include <stdio.h>
24
25 #include "lisp.h"
26 #include "buffer.h"
27 #include "region-cache.h"
28
29
30 /* Data structures. */
31
32 /* The region cache.
33
34 We want something that maps character positions in a buffer onto
35 values. The representation should deal well with long runs of
36 characters with the same value.
37
38 The tricky part: the representation should be very cheap to
39 maintain in the presence of many insertions and deletions. If the
40 overhead of maintaining the cache is too high, the speedups it
41 offers will be worthless.
42
43
44 We represent the region cache as a sorted array of struct
45 boundary's, each of which contains a buffer position and a value;
46 the value applies to all the characters after the buffer position,
47 until the position of the next boundary, or the end of the buffer.
48
49 The cache always has a boundary whose position is BUF_BEG, so
50 there's always a value associated with every character in the
51 buffer. Since the cache is sorted, this is always the first
52 element of the cache.
53
54 To facilitate the insertion and deletion of boundaries in the
55 cache, the cache has a gap, just like Emacs's text buffers do.
56
57 To help boundary positions float along with insertions and
58 deletions, all boundary positions before the cache gap are stored
59 relative to BUF_BEG (buf) (thus they're >= 0), and all boundary
60 positions after the gap are stored relative to BUF_Z (buf) (thus
61 they're <= 0). Look at BOUNDARY_POS to see this in action. See
62 revalidate_region_cache to see how this helps. */
63
64 struct boundary {
65 ptrdiff_t pos;
66 int value;
67 };
68
69 struct region_cache {
70 /* A sorted array of locations where the known-ness of the buffer
71 changes. */
72 struct boundary *boundaries;
73
74 /* boundaries[gap_start ... gap_start + gap_len - 1] is the gap. */
75 ptrdiff_t gap_start, gap_len;
76
77 /* The number of elements allocated to boundaries, not including the
78 gap. */
79 ptrdiff_t cache_len;
80
81 /* The areas that haven't changed since the last time we cleaned out
82 invalid entries from the cache. These overlap when the buffer is
83 entirely unchanged. */
84 ptrdiff_t beg_unchanged, end_unchanged;
85
86 /* The first and last positions in the buffer. Because boundaries
87 store their positions relative to the start (BEG) and end (Z) of
88 the buffer, knowing these positions allows us to accurately
89 interpret positions without having to pass the buffer structure
90 or its endpoints around all the time.
91
92 Yes, buffer_beg is always 1. It's there for symmetry with
93 buffer_end and the BEG and BUF_BEG macros. */
94 ptrdiff_t buffer_beg, buffer_end;
95 };
96
97 /* Return the position of boundary i in cache c. */
98 #define BOUNDARY_POS(c, i) \
99 ((i) < (c)->gap_start \
100 ? (c)->buffer_beg + (c)->boundaries[(i)].pos \
101 : (c)->buffer_end + (c)->boundaries[(c)->gap_len + (i)].pos)
102
103 /* Return the value for text after boundary i in cache c. */
104 #define BOUNDARY_VALUE(c, i) \
105 ((i) < (c)->gap_start \
106 ? (c)->boundaries[(i)].value \
107 : (c)->boundaries[(c)->gap_len + (i)].value)
108
109 /* Set the value for text after boundary i in cache c to v. */
110 #define SET_BOUNDARY_VALUE(c, i, v) \
111 ((i) < (c)->gap_start \
112 ? ((c)->boundaries[(i)].value = (v))\
113 : ((c)->boundaries[(c)->gap_len + (i)].value = (v)))
114
115
116 /* How many elements to add to the gap when we resize the buffer. */
117 #define NEW_CACHE_GAP (40)
118
119 /* See invalidate_region_cache; if an invalidation would throw away
120 information about this many characters, call
121 revalidate_region_cache before doing the new invalidation, to
122 preserve that information, instead of throwing it away. */
123 #define PRESERVE_THRESHOLD (500)
124
125 static void revalidate_region_cache (struct buffer *buf, struct region_cache *c);
126
127
128 /* Interface: Allocating, initializing, and disposing of region caches. */
129
130 struct region_cache *
131 new_region_cache (void)
132 {
133 struct region_cache *c = xmalloc (sizeof *c);
134
135 c->gap_start = 0;
136 c->gap_len = NEW_CACHE_GAP;
137 c->cache_len = 0;
138 c->boundaries = xmalloc ((c->gap_len + c->cache_len)
139 * sizeof (*c->boundaries));
140
141 c->beg_unchanged = 0;
142 c->end_unchanged = 0;
143 c->buffer_beg = BEG;
144 c->buffer_end = BEG;
145
146 /* Insert the boundary for the buffer start. */
147 c->cache_len++;
148 c->gap_len--;
149 c->gap_start++;
150 c->boundaries[0].pos = 0; /* from buffer_beg */
151 c->boundaries[0].value = 0;
152
153 return c;
154 }
155
156 void
157 free_region_cache (struct region_cache *c)
158 {
159 xfree (c->boundaries);
160 xfree (c);
161 }
162
163
164 /* Finding positions in the cache. */
165
166 /* Return the index of the last boundary in cache C at or before POS.
167 In other words, return the boundary that specifies the value for
168 the region POS..(POS + 1).
169
170 This operation should be logarithmic in the number of cache
171 entries. It would be nice if it took advantage of locality of
172 reference, too, by searching entries near the last entry found. */
173 static ptrdiff_t
174 find_cache_boundary (struct region_cache *c, ptrdiff_t pos)
175 {
176 ptrdiff_t low = 0, high = c->cache_len;
177
178 while (low + 1 < high)
179 {
180 /* mid is always a valid index, because low < high and ">> 1"
181 rounds down. */
182 ptrdiff_t mid = (low >> 1) + (high >> 1) + (low & high & 1);
183 ptrdiff_t boundary = BOUNDARY_POS (c, mid);
184
185 if (pos < boundary)
186 high = mid;
187 else
188 low = mid;
189 }
190
191 /* Some testing. */
192 eassert (!(BOUNDARY_POS (c, low) > pos
193 || (low + 1 < c->cache_len
194 && BOUNDARY_POS (c, low + 1) <= pos)));
195
196 return low;
197 }
198
199
200
201 /* Moving the cache gap around, inserting, and deleting. */
202
203
204 /* Move the gap of cache C to index POS, and make sure it has space
205 for at least MIN_SIZE boundaries. */
206 static void
207 move_cache_gap (struct region_cache *c, ptrdiff_t pos, ptrdiff_t min_size)
208 {
209 /* Copy these out of the cache and into registers. */
210 ptrdiff_t gap_start = c->gap_start;
211 ptrdiff_t gap_len = c->gap_len;
212 ptrdiff_t buffer_beg = c->buffer_beg;
213 ptrdiff_t buffer_end = c->buffer_end;
214
215 /* We mustn't ever try to put the gap before the dummy start
216 boundary. That must always be start-relative. */
217 eassert (0 < pos && pos <= c->cache_len);
218
219 /* Need we move the gap right? */
220 while (gap_start < pos)
221 {
222 /* Copy one boundary from after to before the gap, and
223 convert its position to start-relative. */
224 c->boundaries[gap_start].pos
225 = (buffer_end
226 + c->boundaries[gap_start + gap_len].pos
227 - buffer_beg);
228 c->boundaries[gap_start].value
229 = c->boundaries[gap_start + gap_len].value;
230 gap_start++;
231 }
232
233 /* To enlarge the gap, we need to re-allocate the boundary array, and
234 then shift the area after the gap to the new end. Since the cost
235 is proportional to the amount of stuff after the gap, we do the
236 enlargement here, after a right shift but before a left shift,
237 when the portion after the gap is smallest. */
238 if (gap_len < min_size)
239 {
240 ptrdiff_t i, nboundaries = c->cache_len;
241
242 c->boundaries =
243 xpalloc (c->boundaries, &nboundaries, min_size - gap_len, -1,
244 sizeof *c->boundaries);
245
246 /* Some systems don't provide a version of the copy routine that
247 can be trusted to shift memory upward into an overlapping
248 region. memmove isn't widely available. */
249 min_size = nboundaries - c->cache_len - gap_len;
250 for (i = c->cache_len - 1; i >= gap_start; i--)
251 {
252 c->boundaries[i + min_size].pos = c->boundaries[i + gap_len].pos;
253 c->boundaries[i + min_size].value = c->boundaries[i + gap_len].value;
254 }
255
256 gap_len = min_size;
257 }
258
259 /* Need we move the gap left? */
260 while (pos < gap_start)
261 {
262 gap_start--;
263
264 /* Copy one region from before to after the gap, and
265 convert its position to end-relative. */
266 c->boundaries[gap_start + gap_len].pos
267 = c->boundaries[gap_start].pos + buffer_beg - buffer_end;
268 c->boundaries[gap_start + gap_len].value
269 = c->boundaries[gap_start].value;
270 }
271
272 /* Assign these back into the cache. */
273 c->gap_start = gap_start;
274 c->gap_len = gap_len;
275 }
276
277
278 /* Insert a new boundary in cache C; it will have cache index I,
279 and have the specified POS and VALUE. */
280 static void
281 insert_cache_boundary (struct region_cache *c, ptrdiff_t i, ptrdiff_t pos,
282 int value)
283 {
284 /* I must be a valid cache index, and we must never want
285 to insert something before the dummy first boundary. */
286 eassert (0 < i && i <= c->cache_len);
287
288 /* We must only be inserting things in order. */
289 eassert ((BOUNDARY_POS (c, i - 1) < pos
290 && (i == c->cache_len
291 || pos < BOUNDARY_POS (c, i))));
292
293 /* The value must be different from the ones around it. However, we
294 temporarily create boundaries that establish the same value as
295 the subsequent boundary, so we're not going to flag that case. */
296 eassert (BOUNDARY_VALUE (c, i - 1) != value);
297
298 move_cache_gap (c, i, 1);
299
300 c->boundaries[i].pos = pos - c->buffer_beg;
301 c->boundaries[i].value = value;
302 c->gap_start++;
303 c->gap_len--;
304 c->cache_len++;
305 }
306
307
308 /* Delete the i'th entry from cache C if START <= i < END. */
309
310 static void
311 delete_cache_boundaries (struct region_cache *c,
312 ptrdiff_t start, ptrdiff_t end)
313 {
314 ptrdiff_t len = end - start;
315
316 /* Gotta be in range. */
317 eassert (0 <= start && end <= c->cache_len);
318
319 /* Gotta be in order. */
320 eassert (start <= end);
321
322 /* Can't delete the dummy entry. */
323 eassert (!(start == 0 && end >= 1));
324
325 /* Minimize gap motion. If we're deleting nothing, do nothing. */
326 if (len == 0)
327 ;
328 /* If the gap is before the region to delete, delete from the start
329 forward. */
330 else if (c->gap_start <= start)
331 {
332 move_cache_gap (c, start, 0);
333 c->gap_len += len;
334 }
335 /* If the gap is after the region to delete, delete from the end
336 backward. */
337 else if (end <= c->gap_start)
338 {
339 move_cache_gap (c, end, 0);
340 c->gap_start -= len;
341 c->gap_len += len;
342 }
343 /* If the gap is in the region to delete, just expand it. */
344 else
345 {
346 c->gap_start = start;
347 c->gap_len += len;
348 }
349
350 c->cache_len -= len;
351 }
352
353
354
355 /* Set the value for a region. */
356
357 /* Set the value in cache C for the region START..END to VALUE. */
358 static void
359 set_cache_region (struct region_cache *c,
360 ptrdiff_t start, ptrdiff_t end, int value)
361 {
362 eassert (start <= end);
363 eassert (c->buffer_beg <= start && end <= c->buffer_end);
364
365 /* Eliminate this case; then we can assume that start and end-1 are
366 both the locations of real characters in the buffer. */
367 if (start == end)
368 return;
369
370 {
371 /* We need to make sure that there are no boundaries in the area
372 between start to end; the whole area will have the same value,
373 so those boundaries will not be necessary.
374
375 Let start_ix be the cache index of the boundary governing the
376 first character of start..end, and let end_ix be the cache
377 index of the earliest boundary after the last character in
378 start..end. (This tortured terminology is intended to answer
379 all the "< or <=?" sort of questions.) */
380 ptrdiff_t start_ix = find_cache_boundary (c, start);
381 ptrdiff_t end_ix = find_cache_boundary (c, end - 1) + 1;
382
383 /* We must remember the value established by the last boundary
384 before end; if that boundary's domain stretches beyond end,
385 we'll need to create a new boundary at end, and that boundary
386 must have that remembered value. */
387 int value_at_end = BOUNDARY_VALUE (c, end_ix - 1);
388
389 /* Delete all boundaries strictly within start..end; this means
390 those whose indices are between start_ix (exclusive) and end_ix
391 (exclusive). */
392 delete_cache_boundaries (c, start_ix + 1, end_ix);
393
394 /* Make sure we have the right value established going in to
395 start..end from the left, and no unnecessary boundaries. */
396 if (BOUNDARY_POS (c, start_ix) == start)
397 {
398 /* Is this boundary necessary? If no, remove it; if yes, set
399 its value. */
400 if (start_ix > 0
401 && BOUNDARY_VALUE (c, start_ix - 1) == value)
402 {
403 delete_cache_boundaries (c, start_ix, start_ix + 1);
404 start_ix--;
405 }
406 else
407 SET_BOUNDARY_VALUE (c, start_ix, value);
408 }
409 else
410 {
411 /* Do we need to add a new boundary here? */
412 if (BOUNDARY_VALUE (c, start_ix) != value)
413 {
414 insert_cache_boundary (c, start_ix + 1, start, value);
415 start_ix++;
416 }
417 }
418
419 /* This is equivalent to letting end_ix float (like a buffer
420 marker does) with the insertions and deletions we may have
421 done. */
422 end_ix = start_ix + 1;
423
424 /* Make sure we have the correct value established as we leave
425 start..end to the right. */
426 if (end == c->buffer_end)
427 /* There is no text after start..end; nothing to do. */
428 ;
429 else if (end_ix >= c->cache_len
430 || end < BOUNDARY_POS (c, end_ix))
431 {
432 /* There is no boundary at end, but we may need one. */
433 if (value_at_end != value)
434 insert_cache_boundary (c, end_ix, end, value_at_end);
435 }
436 else
437 {
438 /* There is a boundary at end; should it be there? */
439 if (value == BOUNDARY_VALUE (c, end_ix))
440 delete_cache_boundaries (c, end_ix, end_ix + 1);
441 }
442 }
443 }
444
445
446
447 /* Interface: Invalidating the cache. Private: Re-validating the cache. */
448
449 /* Indicate that a section of BUF has changed, to invalidate CACHE.
450 HEAD is the number of chars unchanged at the beginning of the buffer.
451 TAIL is the number of chars unchanged at the end of the buffer.
452 NOTE: this is *not* the same as the ending position of modified
453 region.
454 (This way of specifying regions makes more sense than absolute
455 buffer positions in the presence of insertions and deletions; the
456 args to pass are the same before and after such an operation.) */
457 void
458 invalidate_region_cache (struct buffer *buf, struct region_cache *c,
459 ptrdiff_t head, ptrdiff_t tail)
460 {
461 /* Let chead = c->beg_unchanged, and
462 ctail = c->end_unchanged.
463 If z-tail < beg+chead by a large amount, or
464 z-ctail < beg+head by a large amount,
465
466 then cutting back chead and ctail to head and tail would lose a
467 lot of information that we could preserve by revalidating the
468 cache before processing this invalidation. Losing that
469 information may be more costly than revalidating the cache now.
470 So go ahead and call revalidate_region_cache if it seems that it
471 might be worthwhile. */
472 if (((BUF_BEG (buf) + c->beg_unchanged) - (BUF_Z (buf) - tail)
473 > PRESERVE_THRESHOLD)
474 || ((BUF_BEG (buf) + head) - (BUF_Z (buf) - c->end_unchanged)
475 > PRESERVE_THRESHOLD))
476 revalidate_region_cache (buf, c);
477
478
479 if (head < c->beg_unchanged)
480 c->beg_unchanged = head;
481 if (tail < c->end_unchanged)
482 c->end_unchanged = tail;
483
484 /* We now know nothing about the region between the unchanged head
485 and the unchanged tail (call it the "modified region"), not even
486 its length.
487
488 If the modified region has shrunk in size (deletions do this),
489 then the cache may now contain boundaries originally located in
490 text that doesn't exist any more.
491
492 If the modified region has increased in size (insertions do
493 this), then there may now be boundaries in the modified region
494 whose positions are wrong.
495
496 Even calling BOUNDARY_POS on boundaries still in the unchanged
497 head or tail may well give incorrect answers now, since
498 c->buffer_beg and c->buffer_end may well be wrong now. (Well,
499 okay, c->buffer_beg never changes, so boundaries in the unchanged
500 head will still be okay. But it's the principle of the thing.)
501
502 So things are generally a mess.
503
504 But we don't clean up this mess here; that would be expensive,
505 and this function gets called every time any buffer modification
506 occurs. Rather, we can clean up everything in one swell foop,
507 accounting for all the modifications at once, by calling
508 revalidate_region_cache before we try to consult the cache the
509 next time. */
510 }
511
512
513 /* Clean out any cache entries applying to the modified region, and
514 make the positions of the remaining entries accurate again.
515
516 After calling this function, the mess described in the comment in
517 invalidate_region_cache is cleaned up.
518
519 This function operates by simply throwing away everything it knows
520 about the modified region. It doesn't care exactly which
521 insertions and deletions took place; it just tosses it all.
522
523 For example, if you insert a single character at the beginning of
524 the buffer, and a single character at the end of the buffer (for
525 example), without calling this function in between the two
526 insertions, then the entire cache will be freed of useful
527 information. On the other hand, if you do manage to call this
528 function in between the two insertions, then the modified regions
529 will be small in both cases, no information will be tossed, and the
530 cache will know that it doesn't have knowledge of the first and
531 last characters any more.
532
533 Calling this function may be expensive; it does binary searches in
534 the cache, and causes cache gap motion. */
535
536 static void
537 revalidate_region_cache (struct buffer *buf, struct region_cache *c)
538 {
539 /* The boundaries now in the cache are expressed relative to the
540 buffer_beg and buffer_end values stored in the cache. Now,
541 buffer_beg and buffer_end may not be the same as BUF_BEG (buf)
542 and BUF_Z (buf), so we have two different "bases" to deal with
543 --- the cache's, and the buffer's. */
544
545 /* If the entire buffer is still valid, don't waste time. Yes, this
546 should be a >, not a >=; think about what beg_unchanged and
547 end_unchanged get set to when the only change has been an
548 insertion. */
549 if (c->buffer_beg + c->beg_unchanged
550 > c->buffer_end - c->end_unchanged)
551 return;
552
553 /* If all the text we knew about as of the last cache revalidation
554 is still there, then all of the information in the cache is still
555 valid. Because c->buffer_beg and c->buffer_end are out-of-date,
556 the modified region appears from the cache's point of view to be
557 a null region located someplace in the buffer.
558
559 Now, invalidating that empty string will have no actual affect on
560 the cache; instead, we need to update the cache's basis first
561 (which will give the modified region the same size in the cache
562 as it has in the buffer), and then invalidate the modified
563 region. */
564 if (c->buffer_beg + c->beg_unchanged
565 == c->buffer_end - c->end_unchanged)
566 {
567 /* Move the gap so that all the boundaries in the unchanged head
568 are expressed beg-relative, and all the boundaries in the
569 unchanged tail are expressed end-relative. That done, we can
570 plug in the new buffer beg and end, and all the positions
571 will be accurate.
572
573 The boundary which has jurisdiction over the modified region
574 should be left before the gap. */
575 move_cache_gap (c,
576 (find_cache_boundary (c, (c->buffer_beg
577 + c->beg_unchanged))
578 + 1),
579 0);
580
581 c->buffer_beg = BUF_BEG (buf);
582 c->buffer_end = BUF_Z (buf);
583
584 /* Now that the cache's basis has been changed, the modified
585 region actually takes up some space in the cache, so we can
586 invalidate it. */
587 set_cache_region (c,
588 c->buffer_beg + c->beg_unchanged,
589 c->buffer_end - c->end_unchanged,
590 0);
591 }
592
593 /* Otherwise, there is a non-empty region in the cache which
594 corresponds to the modified region of the buffer. */
595 else
596 {
597 ptrdiff_t modified_ix;
598
599 /* These positions are correct, relative to both the cache basis
600 and the buffer basis. */
601 set_cache_region (c,
602 c->buffer_beg + c->beg_unchanged,
603 c->buffer_end - c->end_unchanged,
604 0);
605
606 /* Now the cache contains only boundaries that are in the
607 unchanged head and tail; we've disposed of any boundaries
608 whose positions we can't be sure of given the information
609 we've saved.
610
611 If we put the cache gap between the unchanged head and the
612 unchanged tail, we can adjust all the boundary positions at
613 once, simply by setting buffer_beg and buffer_end.
614
615 The boundary which has jurisdiction over the modified region
616 should be left before the gap. */
617 modified_ix =
618 find_cache_boundary (c, (c->buffer_beg + c->beg_unchanged)) + 1;
619 move_cache_gap (c, modified_ix, 0);
620
621 c->buffer_beg = BUF_BEG (buf);
622 c->buffer_end = BUF_Z (buf);
623
624 /* Now, we may have shrunk the buffer when we changed the basis,
625 and brought the boundaries we created for the start and end
626 of the modified region together, giving them the same
627 position. If that's the case, we should collapse them into
628 one boundary. Or we may even delete them both, if the values
629 before and after them are the same. */
630 if (modified_ix < c->cache_len
631 && (BOUNDARY_POS (c, modified_ix - 1)
632 == BOUNDARY_POS (c, modified_ix)))
633 {
634 int value_after = BOUNDARY_VALUE (c, modified_ix);
635
636 /* Should we remove both of the boundaries? Yes, if the
637 latter boundary is now establishing the same value that
638 the former boundary's predecessor does. */
639 if (modified_ix - 1 > 0
640 && value_after == BOUNDARY_VALUE (c, modified_ix - 2))
641 delete_cache_boundaries (c, modified_ix - 1, modified_ix + 1);
642 else
643 {
644 /* We do need a boundary here; collapse the two
645 boundaries into one. */
646 SET_BOUNDARY_VALUE (c, modified_ix - 1, value_after);
647 delete_cache_boundaries (c, modified_ix, modified_ix + 1);
648 }
649 }
650 }
651
652 /* Now the entire cache is valid. */
653 c->beg_unchanged
654 = c->end_unchanged
655 = c->buffer_end - c->buffer_beg;
656 }
657
658
659 /* Interface: Adding information to the cache. */
660
661 /* Assert that the region of BUF between START and END (absolute
662 buffer positions) is "known," for the purposes of CACHE (e.g. "has
663 no newlines", in the case of the line cache). */
664 void
665 know_region_cache (struct buffer *buf, struct region_cache *c,
666 ptrdiff_t start, ptrdiff_t end)
667 {
668 revalidate_region_cache (buf, c);
669
670 set_cache_region (c, start, end, 1);
671 }
672
673
674 /* Interface: using the cache. */
675
676 /* Return the value for the text immediately after POS in BUF if the value
677 is known, for the purposes of CACHE, and return zero otherwise.
678 If NEXT is non-zero, set *NEXT to the nearest
679 position after POS where the knowledge changes. */
680 int
681 region_cache_forward (struct buffer *buf, struct region_cache *c,
682 ptrdiff_t pos, ptrdiff_t *next)
683 {
684 revalidate_region_cache (buf, c);
685
686 {
687 ptrdiff_t i = find_cache_boundary (c, pos);
688 int i_value = BOUNDARY_VALUE (c, i);
689 ptrdiff_t j;
690
691 /* Beyond the end of the buffer is unknown, by definition. */
692 if (pos >= BUF_Z (buf))
693 {
694 if (next) *next = BUF_Z (buf);
695 i_value = 0;
696 }
697 else if (next)
698 {
699 /* Scan forward from i to find the next differing position. */
700 for (j = i + 1; j < c->cache_len; j++)
701 if (BOUNDARY_VALUE (c, j) != i_value)
702 break;
703
704 if (j < c->cache_len)
705 *next = BOUNDARY_POS (c, j);
706 else
707 *next = BUF_Z (buf);
708 }
709
710 return i_value;
711 }
712 }
713
714 /* Return the value for the text immediately before POS in BUF if the
715 value is known, for the purposes of CACHE, and return zero
716 otherwise. If NEXT is non-zero, set *NEXT to the nearest
717 position before POS where the knowledge changes. */
718 int
719 region_cache_backward (struct buffer *buf, struct region_cache *c,
720 ptrdiff_t pos, ptrdiff_t *next)
721 {
722 revalidate_region_cache (buf, c);
723
724 /* Before the beginning of the buffer is unknown, by
725 definition. */
726 if (pos <= BUF_BEG (buf))
727 {
728 if (next) *next = BUF_BEG (buf);
729 return 0;
730 }
731
732 {
733 ptrdiff_t i = find_cache_boundary (c, pos - 1);
734 int i_value = BOUNDARY_VALUE (c, i);
735 ptrdiff_t j;
736
737 if (next)
738 {
739 /* Scan backward from i to find the next differing position. */
740 for (j = i - 1; j >= 0; j--)
741 if (BOUNDARY_VALUE (c, j) != i_value)
742 break;
743
744 if (j >= 0)
745 *next = BOUNDARY_POS (c, j + 1);
746 else
747 *next = BUF_BEG (buf);
748 }
749
750 return i_value;
751 }
752 }
753
754 #ifdef ENABLE_CHECKING
755
756 /* Debugging: pretty-print a cache to the standard error output. */
757
758 void pp_cache (struct region_cache *) EXTERNALLY_VISIBLE;
759 void
760 pp_cache (struct region_cache *c)
761 {
762 ptrdiff_t beg_u = c->buffer_beg + c->beg_unchanged;
763 ptrdiff_t end_u = c->buffer_end - c->end_unchanged;
764
765 fprintf (stderr,
766 "basis: %"pD"d..%"pD"d modified: %"pD"d..%"pD"d\n",
767 c->buffer_beg, c->buffer_end,
768 beg_u, end_u);
769
770 for (ptrdiff_t i = 0; i < c->cache_len; i++)
771 {
772 ptrdiff_t pos = BOUNDARY_POS (c, i);
773
774 fprintf (stderr, "%c%c%"pD"d : %d\n",
775 pos < beg_u ? 'v' : pos == beg_u ? '-' : ' ',
776 pos > end_u ? '^' : pos == end_u ? '-' : ' ',
777 pos, BOUNDARY_VALUE (c, i));
778 }
779 }
780
781 #endif /* ENABLE_CHECKING */