Merge from trunk.
[emacs.git] / src / region-cache.c
blobd701f4d71b014df0c158f32e86847f9b9fa026e1
1 /* Caching facts about regions of the buffer, for optimization.
3 Copyright (C) 1985-1989, 1993, 1995, 2001-2011
4 Free Software Foundation, Inc.
6 This file is part of GNU Emacs.
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
11 (at your option) any later version.
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.
18 You should have received a copy of the GNU General Public License
19 along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */
22 #include <config.h>
23 #include <stdio.h>
24 #include <setjmp.h>
26 #include "lisp.h"
27 #include "buffer.h"
28 #include "region-cache.h"
31 /* Data structures. */
33 /* The region cache.
35 We want something that maps character positions in a buffer onto
36 values. The representation should deal well with long runs of
37 characters with the same value.
39 The tricky part: the representation should be very cheap to
40 maintain in the presence of many insertions and deletions. If the
41 overhead of maintaining the cache is too high, the speedups it
42 offers will be worthless.
45 We represent the region cache as a sorted array of struct
46 boundary's, each of which contains a buffer position and a value;
47 the value applies to all the characters after the buffer position,
48 until the position of the next boundary, or the end of the buffer.
50 The cache always has a boundary whose position is BUF_BEG, so
51 there's always a value associated with every character in the
52 buffer. Since the cache is sorted, this is always the first
53 element of the cache.
55 To facilitate the insertion and deletion of boundaries in the
56 cache, the cache has a gap, just like Emacs's text buffers do.
58 To help boundary positions float along with insertions and
59 deletions, all boundary positions before the cache gap are stored
60 relative to BUF_BEG (buf) (thus they're >= 0), and all boundary
61 positions after the gap are stored relative to BUF_Z (buf) (thus
62 they're <= 0). Look at BOUNDARY_POS to see this in action. See
63 revalidate_region_cache to see how this helps. */
65 struct boundary {
66 EMACS_INT pos;
67 int value;
70 struct region_cache {
71 /* A sorted array of locations where the known-ness of the buffer
72 changes. */
73 struct boundary *boundaries;
75 /* boundaries[gap_start ... gap_start + gap_len - 1] is the gap. */
76 EMACS_INT gap_start, gap_len;
78 /* The number of elements allocated to boundaries, not including the
79 gap. */
80 EMACS_INT cache_len;
82 /* The areas that haven't changed since the last time we cleaned out
83 invalid entries from the cache. These overlap when the buffer is
84 entirely unchanged. */
85 EMACS_INT beg_unchanged, end_unchanged;
87 /* The first and last positions in the buffer. Because boundaries
88 store their positions relative to the start (BEG) and end (Z) of
89 the buffer, knowing these positions allows us to accurately
90 interpret positions without having to pass the buffer structure
91 or its endpoints around all the time.
93 Yes, buffer_beg is always 1. It's there for symmetry with
94 buffer_end and the BEG and BUF_BEG macros. */
95 EMACS_INT buffer_beg, buffer_end;
98 /* Return the position of boundary i in cache c. */
99 #define BOUNDARY_POS(c, i) \
100 ((i) < (c)->gap_start \
101 ? (c)->buffer_beg + (c)->boundaries[(i)].pos \
102 : (c)->buffer_end + (c)->boundaries[(c)->gap_len + (i)].pos)
104 /* Return the value for text after boundary i in cache c. */
105 #define BOUNDARY_VALUE(c, i) \
106 ((i) < (c)->gap_start \
107 ? (c)->boundaries[(i)].value \
108 : (c)->boundaries[(c)->gap_len + (i)].value)
110 /* Set the value for text after boundary i in cache c to v. */
111 #define SET_BOUNDARY_VALUE(c, i, v) \
112 ((i) < (c)->gap_start \
113 ? ((c)->boundaries[(i)].value = (v))\
114 : ((c)->boundaries[(c)->gap_len + (i)].value = (v)))
117 /* How many elements to add to the gap when we resize the buffer. */
118 #define NEW_CACHE_GAP (40)
120 /* See invalidate_region_cache; if an invalidation would throw away
121 information about this many characters, call
122 revalidate_region_cache before doing the new invalidation, to
123 preserve that information, instead of throwing it away. */
124 #define PRESERVE_THRESHOLD (500)
126 static void revalidate_region_cache (struct buffer *buf, struct region_cache *c);
129 /* Interface: Allocating, initializing, and disposing of region caches. */
131 struct region_cache *
132 new_region_cache (void)
134 struct region_cache *c
135 = (struct region_cache *) xmalloc (sizeof (struct region_cache));
137 c->gap_start = 0;
138 c->gap_len = NEW_CACHE_GAP;
139 c->cache_len = 0;
140 c->boundaries =
141 (struct boundary *) xmalloc ((c->gap_len + c->cache_len)
142 * sizeof (*c->boundaries));
144 c->beg_unchanged = 0;
145 c->end_unchanged = 0;
146 c->buffer_beg = BEG;
147 c->buffer_end = BEG;
149 /* Insert the boundary for the buffer start. */
150 c->cache_len++;
151 c->gap_len--;
152 c->gap_start++;
153 c->boundaries[0].pos = 0; /* from buffer_beg */
154 c->boundaries[0].value = 0;
156 return c;
159 void
160 free_region_cache (struct region_cache *c)
162 xfree (c->boundaries);
163 xfree (c);
167 /* Finding positions in the cache. */
169 /* Return the index of the last boundary in cache C at or before POS.
170 In other words, return the boundary that specifies the value for
171 the region POS..(POS + 1).
173 This operation should be logarithmic in the number of cache
174 entries. It would be nice if it took advantage of locality of
175 reference, too, by searching entries near the last entry found. */
176 static EMACS_INT
177 find_cache_boundary (struct region_cache *c, EMACS_INT pos)
179 EMACS_INT low = 0, high = c->cache_len;
181 while (low + 1 < high)
183 /* mid is always a valid index, because low < high and ">> 1"
184 rounds down. */
185 EMACS_INT mid = (low + high) >> 1;
186 EMACS_INT boundary = BOUNDARY_POS (c, mid);
188 if (pos < boundary)
189 high = mid;
190 else
191 low = mid;
194 /* Some testing. */
195 if (BOUNDARY_POS (c, low) > pos
196 || (low + 1 < c->cache_len
197 && BOUNDARY_POS (c, low + 1) <= pos))
198 abort ();
200 return low;
205 /* Moving the cache gap around, inserting, and deleting. */
208 /* Move the gap of cache C to index POS, and make sure it has space
209 for at least MIN_SIZE boundaries. */
210 static void
211 move_cache_gap (struct region_cache *c, EMACS_INT pos, EMACS_INT min_size)
213 /* Copy these out of the cache and into registers. */
214 EMACS_INT gap_start = c->gap_start;
215 EMACS_INT gap_len = c->gap_len;
216 EMACS_INT buffer_beg = c->buffer_beg;
217 EMACS_INT buffer_end = c->buffer_end;
219 if (pos < 0
220 || pos > c->cache_len)
221 abort ();
223 /* We mustn't ever try to put the gap before the dummy start
224 boundary. That must always be start-relative. */
225 if (pos == 0)
226 abort ();
228 /* Need we move the gap right? */
229 while (gap_start < pos)
231 /* Copy one boundary from after to before the gap, and
232 convert its position to start-relative. */
233 c->boundaries[gap_start].pos
234 = (buffer_end
235 + c->boundaries[gap_start + gap_len].pos
236 - buffer_beg);
237 c->boundaries[gap_start].value
238 = c->boundaries[gap_start + gap_len].value;
239 gap_start++;
242 /* To enlarge the gap, we need to re-allocate the boundary array, and
243 then shift the area after the gap to the new end. Since the cost
244 is proportional to the amount of stuff after the gap, we do the
245 enlargement here, after a right shift but before a left shift,
246 when the portion after the gap is smallest. */
247 if (gap_len < min_size)
249 EMACS_INT i;
251 /* Always make at least NEW_CACHE_GAP elements, as long as we're
252 expanding anyway. */
253 if (min_size < NEW_CACHE_GAP)
254 min_size = NEW_CACHE_GAP;
256 c->boundaries =
257 (struct boundary *) xrealloc (c->boundaries,
258 ((min_size + c->cache_len)
259 * sizeof (*c->boundaries)));
261 /* Some systems don't provide a version of the copy routine that
262 can be trusted to shift memory upward into an overlapping
263 region. memmove isn't widely available. */
264 min_size -= gap_len;
265 for (i = c->cache_len - 1; i >= gap_start; i--)
267 c->boundaries[i + min_size].pos = c->boundaries[i + gap_len].pos;
268 c->boundaries[i + min_size].value = c->boundaries[i + gap_len].value;
271 gap_len = min_size;
274 /* Need we move the gap left? */
275 while (pos < gap_start)
277 gap_start--;
279 /* Copy one region from before to after the gap, and
280 convert its position to end-relative. */
281 c->boundaries[gap_start + gap_len].pos
282 = c->boundaries[gap_start].pos + buffer_beg - buffer_end;
283 c->boundaries[gap_start + gap_len].value
284 = c->boundaries[gap_start].value;
287 /* Assign these back into the cache. */
288 c->gap_start = gap_start;
289 c->gap_len = gap_len;
293 /* Insert a new boundary in cache C; it will have cache index I,
294 and have the specified POS and VALUE. */
295 static void
296 insert_cache_boundary (struct region_cache *c, EMACS_INT i, EMACS_INT pos,
297 int value)
299 /* i must be a valid cache index. */
300 if (i < 0 || i > c->cache_len)
301 abort ();
303 /* We must never want to insert something before the dummy first
304 boundary. */
305 if (i == 0)
306 abort ();
308 /* We must only be inserting things in order. */
309 if (! (BOUNDARY_POS (c, i - 1) < pos
310 && (i == c->cache_len
311 || pos < BOUNDARY_POS (c, i))))
312 abort ();
314 /* The value must be different from the ones around it. However, we
315 temporarily create boundaries that establish the same value as
316 the subsequent boundary, so we're not going to flag that case. */
317 if (BOUNDARY_VALUE (c, i - 1) == value)
318 abort ();
320 move_cache_gap (c, i, 1);
322 c->boundaries[i].pos = pos - c->buffer_beg;
323 c->boundaries[i].value = value;
324 c->gap_start++;
325 c->gap_len--;
326 c->cache_len++;
330 /* Delete the i'th entry from cache C if START <= i < END. */
332 static void
333 delete_cache_boundaries (struct region_cache *c,
334 EMACS_INT start, EMACS_INT end)
336 EMACS_INT len = end - start;
338 /* Gotta be in range. */
339 if (start < 0
340 || end > c->cache_len)
341 abort ();
343 /* Gotta be in order. */
344 if (start > end)
345 abort ();
347 /* Can't delete the dummy entry. */
348 if (start == 0
349 && end >= 1)
350 abort ();
352 /* Minimize gap motion. If we're deleting nothing, do nothing. */
353 if (len == 0)
355 /* If the gap is before the region to delete, delete from the start
356 forward. */
357 else if (c->gap_start <= start)
359 move_cache_gap (c, start, 0);
360 c->gap_len += len;
362 /* If the gap is after the region to delete, delete from the end
363 backward. */
364 else if (end <= c->gap_start)
366 move_cache_gap (c, end, 0);
367 c->gap_start -= len;
368 c->gap_len += len;
370 /* If the gap is in the region to delete, just expand it. */
371 else
373 c->gap_start = start;
374 c->gap_len += len;
377 c->cache_len -= len;
382 /* Set the value for a region. */
384 /* Set the value in cache C for the region START..END to VALUE. */
385 static void
386 set_cache_region (struct region_cache *c,
387 EMACS_INT start, EMACS_INT end, int value)
389 if (start > end)
390 abort ();
391 if (start < c->buffer_beg
392 || end > c->buffer_end)
393 abort ();
395 /* Eliminate this case; then we can assume that start and end-1 are
396 both the locations of real characters in the buffer. */
397 if (start == end)
398 return;
401 /* We need to make sure that there are no boundaries in the area
402 between start to end; the whole area will have the same value,
403 so those boundaries will not be necessary.
405 Let start_ix be the cache index of the boundary governing the
406 first character of start..end, and let end_ix be the cache
407 index of the earliest boundary after the last character in
408 start..end. (This tortured terminology is intended to answer
409 all the "< or <=?" sort of questions.) */
410 EMACS_INT start_ix = find_cache_boundary (c, start);
411 EMACS_INT end_ix = find_cache_boundary (c, end - 1) + 1;
413 /* We must remember the value established by the last boundary
414 before end; if that boundary's domain stretches beyond end,
415 we'll need to create a new boundary at end, and that boundary
416 must have that remembered value. */
417 int value_at_end = BOUNDARY_VALUE (c, end_ix - 1);
419 /* Delete all boundaries strictly within start..end; this means
420 those whose indices are between start_ix (exclusive) and end_ix
421 (exclusive). */
422 delete_cache_boundaries (c, start_ix + 1, end_ix);
424 /* Make sure we have the right value established going in to
425 start..end from the left, and no unnecessary boundaries. */
426 if (BOUNDARY_POS (c, start_ix) == start)
428 /* Is this boundary necessary? If no, remove it; if yes, set
429 its value. */
430 if (start_ix > 0
431 && BOUNDARY_VALUE (c, start_ix - 1) == value)
433 delete_cache_boundaries (c, start_ix, start_ix + 1);
434 start_ix--;
436 else
437 SET_BOUNDARY_VALUE (c, start_ix, value);
439 else
441 /* Do we need to add a new boundary here? */
442 if (BOUNDARY_VALUE (c, start_ix) != value)
444 insert_cache_boundary (c, start_ix + 1, start, value);
445 start_ix++;
449 /* This is equivalent to letting end_ix float (like a buffer
450 marker does) with the insertions and deletions we may have
451 done. */
452 end_ix = start_ix + 1;
454 /* Make sure we have the correct value established as we leave
455 start..end to the right. */
456 if (end == c->buffer_end)
457 /* There is no text after start..end; nothing to do. */
459 else if (end_ix >= c->cache_len
460 || end < BOUNDARY_POS (c, end_ix))
462 /* There is no boundary at end, but we may need one. */
463 if (value_at_end != value)
464 insert_cache_boundary (c, end_ix, end, value_at_end);
466 else
468 /* There is a boundary at end; should it be there? */
469 if (value == BOUNDARY_VALUE (c, end_ix))
470 delete_cache_boundaries (c, end_ix, end_ix + 1);
477 /* Interface: Invalidating the cache. Private: Re-validating the cache. */
479 /* Indicate that a section of BUF has changed, to invalidate CACHE.
480 HEAD is the number of chars unchanged at the beginning of the buffer.
481 TAIL is the number of chars unchanged at the end of the buffer.
482 NOTE: this is *not* the same as the ending position of modified
483 region.
484 (This way of specifying regions makes more sense than absolute
485 buffer positions in the presence of insertions and deletions; the
486 args to pass are the same before and after such an operation.) */
487 void
488 invalidate_region_cache (struct buffer *buf, struct region_cache *c,
489 EMACS_INT head, EMACS_INT tail)
491 /* Let chead = c->beg_unchanged, and
492 ctail = c->end_unchanged.
493 If z-tail < beg+chead by a large amount, or
494 z-ctail < beg+head by a large amount,
496 then cutting back chead and ctail to head and tail would lose a
497 lot of information that we could preserve by revalidating the
498 cache before processing this invalidation. Losing that
499 information may be more costly than revalidating the cache now.
500 So go ahead and call revalidate_region_cache if it seems that it
501 might be worthwhile. */
502 if (((BUF_BEG (buf) + c->beg_unchanged) - (BUF_Z (buf) - tail)
503 > PRESERVE_THRESHOLD)
504 || ((BUF_BEG (buf) + head) - (BUF_Z (buf) - c->end_unchanged)
505 > PRESERVE_THRESHOLD))
506 revalidate_region_cache (buf, c);
509 if (head < c->beg_unchanged)
510 c->beg_unchanged = head;
511 if (tail < c->end_unchanged)
512 c->end_unchanged = tail;
514 /* We now know nothing about the region between the unchanged head
515 and the unchanged tail (call it the "modified region"), not even
516 its length.
518 If the modified region has shrunk in size (deletions do this),
519 then the cache may now contain boundaries originally located in
520 text that doesn't exist any more.
522 If the modified region has increased in size (insertions do
523 this), then there may now be boundaries in the modified region
524 whose positions are wrong.
526 Even calling BOUNDARY_POS on boundaries still in the unchanged
527 head or tail may well give incorrect answers now, since
528 c->buffer_beg and c->buffer_end may well be wrong now. (Well,
529 okay, c->buffer_beg never changes, so boundaries in the unchanged
530 head will still be okay. But it's the principle of the thing.)
532 So things are generally a mess.
534 But we don't clean up this mess here; that would be expensive,
535 and this function gets called every time any buffer modification
536 occurs. Rather, we can clean up everything in one swell foop,
537 accounting for all the modifications at once, by calling
538 revalidate_region_cache before we try to consult the cache the
539 next time. */
543 /* Clean out any cache entries applying to the modified region, and
544 make the positions of the remaining entries accurate again.
546 After calling this function, the mess described in the comment in
547 invalidate_region_cache is cleaned up.
549 This function operates by simply throwing away everything it knows
550 about the modified region. It doesn't care exactly which
551 insertions and deletions took place; it just tosses it all.
553 For example, if you insert a single character at the beginning of
554 the buffer, and a single character at the end of the buffer (for
555 example), without calling this function in between the two
556 insertions, then the entire cache will be freed of useful
557 information. On the other hand, if you do manage to call this
558 function in between the two insertions, then the modified regions
559 will be small in both cases, no information will be tossed, and the
560 cache will know that it doesn't have knowledge of the first and
561 last characters any more.
563 Calling this function may be expensive; it does binary searches in
564 the cache, and causes cache gap motion. */
566 static void
567 revalidate_region_cache (struct buffer *buf, struct region_cache *c)
569 /* The boundaries now in the cache are expressed relative to the
570 buffer_beg and buffer_end values stored in the cache. Now,
571 buffer_beg and buffer_end may not be the same as BUF_BEG (buf)
572 and BUF_Z (buf), so we have two different "bases" to deal with
573 --- the cache's, and the buffer's. */
575 /* If the entire buffer is still valid, don't waste time. Yes, this
576 should be a >, not a >=; think about what beg_unchanged and
577 end_unchanged get set to when the only change has been an
578 insertion. */
579 if (c->buffer_beg + c->beg_unchanged
580 > c->buffer_end - c->end_unchanged)
581 return;
583 /* If all the text we knew about as of the last cache revalidation
584 is still there, then all of the information in the cache is still
585 valid. Because c->buffer_beg and c->buffer_end are out-of-date,
586 the modified region appears from the cache's point of view to be
587 a null region located someplace in the buffer.
589 Now, invalidating that empty string will have no actual affect on
590 the cache; instead, we need to update the cache's basis first
591 (which will give the modified region the same size in the cache
592 as it has in the buffer), and then invalidate the modified
593 region. */
594 if (c->buffer_beg + c->beg_unchanged
595 == c->buffer_end - c->end_unchanged)
597 /* Move the gap so that all the boundaries in the unchanged head
598 are expressed beg-relative, and all the boundaries in the
599 unchanged tail are expressed end-relative. That done, we can
600 plug in the new buffer beg and end, and all the positions
601 will be accurate.
603 The boundary which has jurisdiction over the modified region
604 should be left before the gap. */
605 move_cache_gap (c,
606 (find_cache_boundary (c, (c->buffer_beg
607 + c->beg_unchanged))
608 + 1),
611 c->buffer_beg = BUF_BEG (buf);
612 c->buffer_end = BUF_Z (buf);
614 /* Now that the cache's basis has been changed, the modified
615 region actually takes up some space in the cache, so we can
616 invalidate it. */
617 set_cache_region (c,
618 c->buffer_beg + c->beg_unchanged,
619 c->buffer_end - c->end_unchanged,
623 /* Otherwise, there is a non-empty region in the cache which
624 corresponds to the modified region of the buffer. */
625 else
627 EMACS_INT modified_ix;
629 /* These positions are correct, relative to both the cache basis
630 and the buffer basis. */
631 set_cache_region (c,
632 c->buffer_beg + c->beg_unchanged,
633 c->buffer_end - c->end_unchanged,
636 /* Now the cache contains only boundaries that are in the
637 unchanged head and tail; we've disposed of any boundaries
638 whose positions we can't be sure of given the information
639 we've saved.
641 If we put the cache gap between the unchanged head and the
642 unchanged tail, we can adjust all the boundary positions at
643 once, simply by setting buffer_beg and buffer_end.
645 The boundary which has jurisdiction over the modified region
646 should be left before the gap. */
647 modified_ix =
648 find_cache_boundary (c, (c->buffer_beg + c->beg_unchanged)) + 1;
649 move_cache_gap (c, modified_ix, 0);
651 c->buffer_beg = BUF_BEG (buf);
652 c->buffer_end = BUF_Z (buf);
654 /* Now, we may have shrunk the buffer when we changed the basis,
655 and brought the boundaries we created for the start and end
656 of the modified region together, giving them the same
657 position. If that's the case, we should collapse them into
658 one boundary. Or we may even delete them both, if the values
659 before and after them are the same. */
660 if (modified_ix < c->cache_len
661 && (BOUNDARY_POS (c, modified_ix - 1)
662 == BOUNDARY_POS (c, modified_ix)))
664 int value_after = BOUNDARY_VALUE (c, modified_ix);
666 /* Should we remove both of the boundaries? Yes, if the
667 latter boundary is now establishing the same value that
668 the former boundary's predecessor does. */
669 if (modified_ix - 1 > 0
670 && value_after == BOUNDARY_VALUE (c, modified_ix - 2))
671 delete_cache_boundaries (c, modified_ix - 1, modified_ix + 1);
672 else
674 /* We do need a boundary here; collapse the two
675 boundaries into one. */
676 SET_BOUNDARY_VALUE (c, modified_ix - 1, value_after);
677 delete_cache_boundaries (c, modified_ix, modified_ix + 1);
682 /* Now the entire cache is valid. */
683 c->beg_unchanged
684 = c->end_unchanged
685 = c->buffer_end - c->buffer_beg;
689 /* Interface: Adding information to the cache. */
691 /* Assert that the region of BUF between START and END (absolute
692 buffer positions) is "known," for the purposes of CACHE (e.g. "has
693 no newlines", in the case of the line cache). */
694 void
695 know_region_cache (struct buffer *buf, struct region_cache *c,
696 EMACS_INT start, EMACS_INT end)
698 revalidate_region_cache (buf, c);
700 set_cache_region (c, start, end, 1);
704 /* Interface: using the cache. */
706 /* Return true if the text immediately after POS in BUF is known, for
707 the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest
708 position after POS where the knownness changes. */
710 region_cache_forward (struct buffer *buf, struct region_cache *c,
711 EMACS_INT pos, EMACS_INT *next)
713 revalidate_region_cache (buf, c);
716 EMACS_INT i = find_cache_boundary (c, pos);
717 int i_value = BOUNDARY_VALUE (c, i);
718 EMACS_INT j;
720 /* Beyond the end of the buffer is unknown, by definition. */
721 if (pos >= BUF_Z (buf))
723 if (next) *next = BUF_Z (buf);
724 i_value = 0;
726 else if (next)
728 /* Scan forward from i to find the next differing position. */
729 for (j = i + 1; j < c->cache_len; j++)
730 if (BOUNDARY_VALUE (c, j) != i_value)
731 break;
733 if (j < c->cache_len)
734 *next = BOUNDARY_POS (c, j);
735 else
736 *next = BUF_Z (buf);
739 return i_value;
743 /* Return true if the text immediately before POS in BUF is known, for
744 the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest
745 position before POS where the knownness changes. */
746 int region_cache_backward (struct buffer *buf, struct region_cache *c,
747 EMACS_INT pos, EMACS_INT *next)
749 revalidate_region_cache (buf, c);
751 /* Before the beginning of the buffer is unknown, by
752 definition. */
753 if (pos <= BUF_BEG (buf))
755 if (next) *next = BUF_BEG (buf);
756 return 0;
760 EMACS_INT i = find_cache_boundary (c, pos - 1);
761 int i_value = BOUNDARY_VALUE (c, i);
762 EMACS_INT j;
764 if (next)
766 /* Scan backward from i to find the next differing position. */
767 for (j = i - 1; j >= 0; j--)
768 if (BOUNDARY_VALUE (c, j) != i_value)
769 break;
771 if (j >= 0)
772 *next = BOUNDARY_POS (c, j + 1);
773 else
774 *next = BUF_BEG (buf);
777 return i_value;
782 /* Debugging: pretty-print a cache to the standard error output. */
784 void pp_cache (struct region_cache *) EXTERNALLY_VISIBLE;
785 void
786 pp_cache (struct region_cache *c)
788 int i;
789 EMACS_INT beg_u = c->buffer_beg + c->beg_unchanged;
790 EMACS_INT end_u = c->buffer_end - c->end_unchanged;
792 fprintf (stderr,
793 "basis: %"pI"d..%"pI"d modified: %"pI"d..%"pI"d\n",
794 c->buffer_beg, c->buffer_end,
795 beg_u, end_u);
797 for (i = 0; i < c->cache_len; i++)
799 EMACS_INT pos = BOUNDARY_POS (c, i);
801 putc (((pos < beg_u) ? 'v'
802 : (pos == beg_u) ? '-'
803 : ' '),
804 stderr);
805 putc (((pos > end_u) ? '^'
806 : (pos == end_u) ? '-'
807 : ' '),
808 stderr);
809 fprintf (stderr, "%"pI"d : %d\n", pos, BOUNDARY_VALUE (c, i));