* lisp/textmodes/table.el (table-insert): Don't use `symbol-name' on
[emacs.git] / src / region-cache.c
blob832f4bfd2146f4656efd29daa189194ca742725b
1 /* Caching facts about regions of the buffer, for optimization.
3 Copyright (C) 1985-1989, 1993, 1995, 2001-2012
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>
25 #include "lisp.h"
26 #include "character.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 ptrdiff_t 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 ptrdiff_t gap_start, gap_len;
78 /* The number of elements allocated to boundaries, not including the
79 gap. */
80 ptrdiff_t 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 ptrdiff_t 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 ptrdiff_t 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 = xmalloc (sizeof *c);
136 c->gap_start = 0;
137 c->gap_len = NEW_CACHE_GAP;
138 c->cache_len = 0;
139 c->boundaries = xmalloc ((c->gap_len + c->cache_len)
140 * sizeof (*c->boundaries));
142 c->beg_unchanged = 0;
143 c->end_unchanged = 0;
144 c->buffer_beg = BEG;
145 c->buffer_end = BEG;
147 /* Insert the boundary for the buffer start. */
148 c->cache_len++;
149 c->gap_len--;
150 c->gap_start++;
151 c->boundaries[0].pos = 0; /* from buffer_beg */
152 c->boundaries[0].value = 0;
154 return c;
157 void
158 free_region_cache (struct region_cache *c)
160 xfree (c->boundaries);
161 xfree (c);
165 /* Finding positions in the cache. */
167 /* Return the index of the last boundary in cache C at or before POS.
168 In other words, return the boundary that specifies the value for
169 the region POS..(POS + 1).
171 This operation should be logarithmic in the number of cache
172 entries. It would be nice if it took advantage of locality of
173 reference, too, by searching entries near the last entry found. */
174 static ptrdiff_t
175 find_cache_boundary (struct region_cache *c, ptrdiff_t pos)
177 ptrdiff_t low = 0, high = c->cache_len;
179 while (low + 1 < high)
181 /* mid is always a valid index, because low < high and ">> 1"
182 rounds down. */
183 ptrdiff_t mid = (low >> 1) + (high >> 1) + (low & high & 1);
184 ptrdiff_t boundary = BOUNDARY_POS (c, mid);
186 if (pos < boundary)
187 high = mid;
188 else
189 low = mid;
192 /* Some testing. */
193 if (BOUNDARY_POS (c, low) > pos
194 || (low + 1 < c->cache_len
195 && BOUNDARY_POS (c, low + 1) <= pos))
196 emacs_abort ();
198 return low;
203 /* Moving the cache gap around, inserting, and deleting. */
206 /* Move the gap of cache C to index POS, and make sure it has space
207 for at least MIN_SIZE boundaries. */
208 static void
209 move_cache_gap (struct region_cache *c, ptrdiff_t pos, ptrdiff_t min_size)
211 /* Copy these out of the cache and into registers. */
212 ptrdiff_t gap_start = c->gap_start;
213 ptrdiff_t gap_len = c->gap_len;
214 ptrdiff_t buffer_beg = c->buffer_beg;
215 ptrdiff_t buffer_end = c->buffer_end;
217 if (pos < 0
218 || pos > c->cache_len)
219 emacs_abort ();
221 /* We mustn't ever try to put the gap before the dummy start
222 boundary. That must always be start-relative. */
223 if (pos == 0)
224 emacs_abort ();
226 /* Need we move the gap right? */
227 while (gap_start < pos)
229 /* Copy one boundary from after to before the gap, and
230 convert its position to start-relative. */
231 c->boundaries[gap_start].pos
232 = (buffer_end
233 + c->boundaries[gap_start + gap_len].pos
234 - buffer_beg);
235 c->boundaries[gap_start].value
236 = c->boundaries[gap_start + gap_len].value;
237 gap_start++;
240 /* To enlarge the gap, we need to re-allocate the boundary array, and
241 then shift the area after the gap to the new end. Since the cost
242 is proportional to the amount of stuff after the gap, we do the
243 enlargement here, after a right shift but before a left shift,
244 when the portion after the gap is smallest. */
245 if (gap_len < min_size)
247 ptrdiff_t i, nboundaries = c->cache_len;
249 c->boundaries =
250 xpalloc (c->boundaries, &nboundaries, min_size - gap_len, -1,
251 sizeof *c->boundaries);
253 /* Some systems don't provide a version of the copy routine that
254 can be trusted to shift memory upward into an overlapping
255 region. memmove isn't widely available. */
256 min_size = nboundaries - c->cache_len - gap_len;
257 for (i = c->cache_len - 1; i >= gap_start; i--)
259 c->boundaries[i + min_size].pos = c->boundaries[i + gap_len].pos;
260 c->boundaries[i + min_size].value = c->boundaries[i + gap_len].value;
263 gap_len = min_size;
266 /* Need we move the gap left? */
267 while (pos < gap_start)
269 gap_start--;
271 /* Copy one region from before to after the gap, and
272 convert its position to end-relative. */
273 c->boundaries[gap_start + gap_len].pos
274 = c->boundaries[gap_start].pos + buffer_beg - buffer_end;
275 c->boundaries[gap_start + gap_len].value
276 = c->boundaries[gap_start].value;
279 /* Assign these back into the cache. */
280 c->gap_start = gap_start;
281 c->gap_len = gap_len;
285 /* Insert a new boundary in cache C; it will have cache index I,
286 and have the specified POS and VALUE. */
287 static void
288 insert_cache_boundary (struct region_cache *c, ptrdiff_t i, ptrdiff_t pos,
289 int value)
291 /* i must be a valid cache index. */
292 if (i < 0 || i > c->cache_len)
293 emacs_abort ();
295 /* We must never want to insert something before the dummy first
296 boundary. */
297 if (i == 0)
298 emacs_abort ();
300 /* We must only be inserting things in order. */
301 if (! (BOUNDARY_POS (c, i - 1) < pos
302 && (i == c->cache_len
303 || pos < BOUNDARY_POS (c, i))))
304 emacs_abort ();
306 /* The value must be different from the ones around it. However, we
307 temporarily create boundaries that establish the same value as
308 the subsequent boundary, so we're not going to flag that case. */
309 if (BOUNDARY_VALUE (c, i - 1) == value)
310 emacs_abort ();
312 move_cache_gap (c, i, 1);
314 c->boundaries[i].pos = pos - c->buffer_beg;
315 c->boundaries[i].value = value;
316 c->gap_start++;
317 c->gap_len--;
318 c->cache_len++;
322 /* Delete the i'th entry from cache C if START <= i < END. */
324 static void
325 delete_cache_boundaries (struct region_cache *c,
326 ptrdiff_t start, ptrdiff_t end)
328 ptrdiff_t len = end - start;
330 /* Gotta be in range. */
331 if (start < 0
332 || end > c->cache_len)
333 emacs_abort ();
335 /* Gotta be in order. */
336 if (start > end)
337 emacs_abort ();
339 /* Can't delete the dummy entry. */
340 if (start == 0
341 && end >= 1)
342 emacs_abort ();
344 /* Minimize gap motion. If we're deleting nothing, do nothing. */
345 if (len == 0)
347 /* If the gap is before the region to delete, delete from the start
348 forward. */
349 else if (c->gap_start <= start)
351 move_cache_gap (c, start, 0);
352 c->gap_len += len;
354 /* If the gap is after the region to delete, delete from the end
355 backward. */
356 else if (end <= c->gap_start)
358 move_cache_gap (c, end, 0);
359 c->gap_start -= len;
360 c->gap_len += len;
362 /* If the gap is in the region to delete, just expand it. */
363 else
365 c->gap_start = start;
366 c->gap_len += len;
369 c->cache_len -= len;
374 /* Set the value for a region. */
376 /* Set the value in cache C for the region START..END to VALUE. */
377 static void
378 set_cache_region (struct region_cache *c,
379 ptrdiff_t start, ptrdiff_t end, int value)
381 if (start > end)
382 emacs_abort ();
383 if (start < c->buffer_beg
384 || end > c->buffer_end)
385 emacs_abort ();
387 /* Eliminate this case; then we can assume that start and end-1 are
388 both the locations of real characters in the buffer. */
389 if (start == end)
390 return;
393 /* We need to make sure that there are no boundaries in the area
394 between start to end; the whole area will have the same value,
395 so those boundaries will not be necessary.
397 Let start_ix be the cache index of the boundary governing the
398 first character of start..end, and let end_ix be the cache
399 index of the earliest boundary after the last character in
400 start..end. (This tortured terminology is intended to answer
401 all the "< or <=?" sort of questions.) */
402 ptrdiff_t start_ix = find_cache_boundary (c, start);
403 ptrdiff_t end_ix = find_cache_boundary (c, end - 1) + 1;
405 /* We must remember the value established by the last boundary
406 before end; if that boundary's domain stretches beyond end,
407 we'll need to create a new boundary at end, and that boundary
408 must have that remembered value. */
409 int value_at_end = BOUNDARY_VALUE (c, end_ix - 1);
411 /* Delete all boundaries strictly within start..end; this means
412 those whose indices are between start_ix (exclusive) and end_ix
413 (exclusive). */
414 delete_cache_boundaries (c, start_ix + 1, end_ix);
416 /* Make sure we have the right value established going in to
417 start..end from the left, and no unnecessary boundaries. */
418 if (BOUNDARY_POS (c, start_ix) == start)
420 /* Is this boundary necessary? If no, remove it; if yes, set
421 its value. */
422 if (start_ix > 0
423 && BOUNDARY_VALUE (c, start_ix - 1) == value)
425 delete_cache_boundaries (c, start_ix, start_ix + 1);
426 start_ix--;
428 else
429 SET_BOUNDARY_VALUE (c, start_ix, value);
431 else
433 /* Do we need to add a new boundary here? */
434 if (BOUNDARY_VALUE (c, start_ix) != value)
436 insert_cache_boundary (c, start_ix + 1, start, value);
437 start_ix++;
441 /* This is equivalent to letting end_ix float (like a buffer
442 marker does) with the insertions and deletions we may have
443 done. */
444 end_ix = start_ix + 1;
446 /* Make sure we have the correct value established as we leave
447 start..end to the right. */
448 if (end == c->buffer_end)
449 /* There is no text after start..end; nothing to do. */
451 else if (end_ix >= c->cache_len
452 || end < BOUNDARY_POS (c, end_ix))
454 /* There is no boundary at end, but we may need one. */
455 if (value_at_end != value)
456 insert_cache_boundary (c, end_ix, end, value_at_end);
458 else
460 /* There is a boundary at end; should it be there? */
461 if (value == BOUNDARY_VALUE (c, end_ix))
462 delete_cache_boundaries (c, end_ix, end_ix + 1);
469 /* Interface: Invalidating the cache. Private: Re-validating the cache. */
471 /* Indicate that a section of BUF has changed, to invalidate CACHE.
472 HEAD is the number of chars unchanged at the beginning of the buffer.
473 TAIL is the number of chars unchanged at the end of the buffer.
474 NOTE: this is *not* the same as the ending position of modified
475 region.
476 (This way of specifying regions makes more sense than absolute
477 buffer positions in the presence of insertions and deletions; the
478 args to pass are the same before and after such an operation.) */
479 void
480 invalidate_region_cache (struct buffer *buf, struct region_cache *c,
481 ptrdiff_t head, ptrdiff_t tail)
483 /* Let chead = c->beg_unchanged, and
484 ctail = c->end_unchanged.
485 If z-tail < beg+chead by a large amount, or
486 z-ctail < beg+head by a large amount,
488 then cutting back chead and ctail to head and tail would lose a
489 lot of information that we could preserve by revalidating the
490 cache before processing this invalidation. Losing that
491 information may be more costly than revalidating the cache now.
492 So go ahead and call revalidate_region_cache if it seems that it
493 might be worthwhile. */
494 if (((BUF_BEG (buf) + c->beg_unchanged) - (BUF_Z (buf) - tail)
495 > PRESERVE_THRESHOLD)
496 || ((BUF_BEG (buf) + head) - (BUF_Z (buf) - c->end_unchanged)
497 > PRESERVE_THRESHOLD))
498 revalidate_region_cache (buf, c);
501 if (head < c->beg_unchanged)
502 c->beg_unchanged = head;
503 if (tail < c->end_unchanged)
504 c->end_unchanged = tail;
506 /* We now know nothing about the region between the unchanged head
507 and the unchanged tail (call it the "modified region"), not even
508 its length.
510 If the modified region has shrunk in size (deletions do this),
511 then the cache may now contain boundaries originally located in
512 text that doesn't exist any more.
514 If the modified region has increased in size (insertions do
515 this), then there may now be boundaries in the modified region
516 whose positions are wrong.
518 Even calling BOUNDARY_POS on boundaries still in the unchanged
519 head or tail may well give incorrect answers now, since
520 c->buffer_beg and c->buffer_end may well be wrong now. (Well,
521 okay, c->buffer_beg never changes, so boundaries in the unchanged
522 head will still be okay. But it's the principle of the thing.)
524 So things are generally a mess.
526 But we don't clean up this mess here; that would be expensive,
527 and this function gets called every time any buffer modification
528 occurs. Rather, we can clean up everything in one swell foop,
529 accounting for all the modifications at once, by calling
530 revalidate_region_cache before we try to consult the cache the
531 next time. */
535 /* Clean out any cache entries applying to the modified region, and
536 make the positions of the remaining entries accurate again.
538 After calling this function, the mess described in the comment in
539 invalidate_region_cache is cleaned up.
541 This function operates by simply throwing away everything it knows
542 about the modified region. It doesn't care exactly which
543 insertions and deletions took place; it just tosses it all.
545 For example, if you insert a single character at the beginning of
546 the buffer, and a single character at the end of the buffer (for
547 example), without calling this function in between the two
548 insertions, then the entire cache will be freed of useful
549 information. On the other hand, if you do manage to call this
550 function in between the two insertions, then the modified regions
551 will be small in both cases, no information will be tossed, and the
552 cache will know that it doesn't have knowledge of the first and
553 last characters any more.
555 Calling this function may be expensive; it does binary searches in
556 the cache, and causes cache gap motion. */
558 static void
559 revalidate_region_cache (struct buffer *buf, struct region_cache *c)
561 /* The boundaries now in the cache are expressed relative to the
562 buffer_beg and buffer_end values stored in the cache. Now,
563 buffer_beg and buffer_end may not be the same as BUF_BEG (buf)
564 and BUF_Z (buf), so we have two different "bases" to deal with
565 --- the cache's, and the buffer's. */
567 /* If the entire buffer is still valid, don't waste time. Yes, this
568 should be a >, not a >=; think about what beg_unchanged and
569 end_unchanged get set to when the only change has been an
570 insertion. */
571 if (c->buffer_beg + c->beg_unchanged
572 > c->buffer_end - c->end_unchanged)
573 return;
575 /* If all the text we knew about as of the last cache revalidation
576 is still there, then all of the information in the cache is still
577 valid. Because c->buffer_beg and c->buffer_end are out-of-date,
578 the modified region appears from the cache's point of view to be
579 a null region located someplace in the buffer.
581 Now, invalidating that empty string will have no actual affect on
582 the cache; instead, we need to update the cache's basis first
583 (which will give the modified region the same size in the cache
584 as it has in the buffer), and then invalidate the modified
585 region. */
586 if (c->buffer_beg + c->beg_unchanged
587 == c->buffer_end - c->end_unchanged)
589 /* Move the gap so that all the boundaries in the unchanged head
590 are expressed beg-relative, and all the boundaries in the
591 unchanged tail are expressed end-relative. That done, we can
592 plug in the new buffer beg and end, and all the positions
593 will be accurate.
595 The boundary which has jurisdiction over the modified region
596 should be left before the gap. */
597 move_cache_gap (c,
598 (find_cache_boundary (c, (c->buffer_beg
599 + c->beg_unchanged))
600 + 1),
603 c->buffer_beg = BUF_BEG (buf);
604 c->buffer_end = BUF_Z (buf);
606 /* Now that the cache's basis has been changed, the modified
607 region actually takes up some space in the cache, so we can
608 invalidate it. */
609 set_cache_region (c,
610 c->buffer_beg + c->beg_unchanged,
611 c->buffer_end - c->end_unchanged,
615 /* Otherwise, there is a non-empty region in the cache which
616 corresponds to the modified region of the buffer. */
617 else
619 ptrdiff_t modified_ix;
621 /* These positions are correct, relative to both the cache basis
622 and the buffer basis. */
623 set_cache_region (c,
624 c->buffer_beg + c->beg_unchanged,
625 c->buffer_end - c->end_unchanged,
628 /* Now the cache contains only boundaries that are in the
629 unchanged head and tail; we've disposed of any boundaries
630 whose positions we can't be sure of given the information
631 we've saved.
633 If we put the cache gap between the unchanged head and the
634 unchanged tail, we can adjust all the boundary positions at
635 once, simply by setting buffer_beg and buffer_end.
637 The boundary which has jurisdiction over the modified region
638 should be left before the gap. */
639 modified_ix =
640 find_cache_boundary (c, (c->buffer_beg + c->beg_unchanged)) + 1;
641 move_cache_gap (c, modified_ix, 0);
643 c->buffer_beg = BUF_BEG (buf);
644 c->buffer_end = BUF_Z (buf);
646 /* Now, we may have shrunk the buffer when we changed the basis,
647 and brought the boundaries we created for the start and end
648 of the modified region together, giving them the same
649 position. If that's the case, we should collapse them into
650 one boundary. Or we may even delete them both, if the values
651 before and after them are the same. */
652 if (modified_ix < c->cache_len
653 && (BOUNDARY_POS (c, modified_ix - 1)
654 == BOUNDARY_POS (c, modified_ix)))
656 int value_after = BOUNDARY_VALUE (c, modified_ix);
658 /* Should we remove both of the boundaries? Yes, if the
659 latter boundary is now establishing the same value that
660 the former boundary's predecessor does. */
661 if (modified_ix - 1 > 0
662 && value_after == BOUNDARY_VALUE (c, modified_ix - 2))
663 delete_cache_boundaries (c, modified_ix - 1, modified_ix + 1);
664 else
666 /* We do need a boundary here; collapse the two
667 boundaries into one. */
668 SET_BOUNDARY_VALUE (c, modified_ix - 1, value_after);
669 delete_cache_boundaries (c, modified_ix, modified_ix + 1);
674 /* Now the entire cache is valid. */
675 c->beg_unchanged
676 = c->end_unchanged
677 = c->buffer_end - c->buffer_beg;
681 /* Interface: Adding information to the cache. */
683 /* Assert that the region of BUF between START and END (absolute
684 buffer positions) is "known," for the purposes of CACHE (e.g. "has
685 no newlines", in the case of the line cache). */
686 void
687 know_region_cache (struct buffer *buf, struct region_cache *c,
688 ptrdiff_t start, ptrdiff_t end)
690 revalidate_region_cache (buf, c);
692 set_cache_region (c, start, end, 1);
696 /* Interface: using the cache. */
698 /* Return true if the text immediately after POS in BUF is known, for
699 the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest
700 position after POS where the knowledge changes. */
702 region_cache_forward (struct buffer *buf, struct region_cache *c,
703 ptrdiff_t pos, ptrdiff_t *next)
705 revalidate_region_cache (buf, c);
708 ptrdiff_t i = find_cache_boundary (c, pos);
709 int i_value = BOUNDARY_VALUE (c, i);
710 ptrdiff_t j;
712 /* Beyond the end of the buffer is unknown, by definition. */
713 if (pos >= BUF_Z (buf))
715 if (next) *next = BUF_Z (buf);
716 i_value = 0;
718 else if (next)
720 /* Scan forward from i to find the next differing position. */
721 for (j = i + 1; j < c->cache_len; j++)
722 if (BOUNDARY_VALUE (c, j) != i_value)
723 break;
725 if (j < c->cache_len)
726 *next = BOUNDARY_POS (c, j);
727 else
728 *next = BUF_Z (buf);
731 return i_value;
735 /* Return true if the text immediately before POS in BUF is known, for
736 the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest
737 position before POS where the knowledge changes. */
738 int region_cache_backward (struct buffer *buf, struct region_cache *c,
739 ptrdiff_t pos, ptrdiff_t *next)
741 revalidate_region_cache (buf, c);
743 /* Before the beginning of the buffer is unknown, by
744 definition. */
745 if (pos <= BUF_BEG (buf))
747 if (next) *next = BUF_BEG (buf);
748 return 0;
752 ptrdiff_t i = find_cache_boundary (c, pos - 1);
753 int i_value = BOUNDARY_VALUE (c, i);
754 ptrdiff_t j;
756 if (next)
758 /* Scan backward from i to find the next differing position. */
759 for (j = i - 1; j >= 0; j--)
760 if (BOUNDARY_VALUE (c, j) != i_value)
761 break;
763 if (j >= 0)
764 *next = BOUNDARY_POS (c, j + 1);
765 else
766 *next = BUF_BEG (buf);
769 return i_value;
774 /* Debugging: pretty-print a cache to the standard error output. */
776 void pp_cache (struct region_cache *) EXTERNALLY_VISIBLE;
777 void
778 pp_cache (struct region_cache *c)
780 ptrdiff_t i;
781 ptrdiff_t beg_u = c->buffer_beg + c->beg_unchanged;
782 ptrdiff_t end_u = c->buffer_end - c->end_unchanged;
784 fprintf (stderr,
785 "basis: %"pD"d..%"pD"d modified: %"pD"d..%"pD"d\n",
786 c->buffer_beg, c->buffer_end,
787 beg_u, end_u);
789 for (i = 0; i < c->cache_len; i++)
791 ptrdiff_t pos = BOUNDARY_POS (c, i);
793 putc (((pos < beg_u) ? 'v'
794 : (pos == beg_u) ? '-'
795 : ' '),
796 stderr);
797 putc (((pos > end_u) ? '^'
798 : (pos == end_u) ? '-'
799 : ' '),
800 stderr);
801 fprintf (stderr, "%"pD"d : %d\n", pos, BOUNDARY_VALUE (c, i));