/* Caching facts about regions of the buffer, for optimization. Copyright (C) 1985, 1986, 1987, 1988, 1989, 1993, 1995, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. This file is part of GNU Emacs. GNU Emacs is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Emacs is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Emacs; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ #include <config.h> #include <stdio.h> #include "lisp.h" #include "buffer.h" #include "region-cache.h" /* Data structures. */ /* The region cache. We want something that maps character positions in a buffer onto values. The representation should deal well with long runs of characters with the same value. The tricky part: the representation should be very cheap to maintain in the presence of many insertions and deletions. If the overhead of maintaining the cache is too high, the speedups it offers will be worthless. We represent the region cache as a sorted array of struct boundary's, each of which contains a buffer position and a value; the value applies to all the characters after the buffer position, until the position of the next boundary, or the end of the buffer. The cache always has a boundary whose position is BUF_BEG, so there's always a value associated with every character in the buffer. Since the cache is sorted, this is always the first element of the cache. To facilitate the insertion and deletion of boundaries in the cache, the cache has a gap, just like Emacs's text buffers do. To help boundary positions float along with insertions and deletions, all boundary positions before the cache gap are stored relative to BUF_BEG (buf) (thus they're >= 0), and all boundary positions after the gap are stored relative to BUF_Z (buf) (thus they're <= 0). Look at BOUNDARY_POS to see this in action. See revalidate_region_cache to see how this helps. */ struct boundary { int pos; int value; }; struct region_cache { /* A sorted array of locations where the known-ness of the buffer changes. */ struct boundary *boundaries; /* boundaries[gap_start ... gap_start + gap_len - 1] is the gap. */ int gap_start, gap_len; /* The number of elements allocated to boundaries, not including the gap. */ int cache_len; /* The areas that haven't changed since the last time we cleaned out invalid entries from the cache. These overlap when the buffer is entirely unchanged. */ int beg_unchanged, end_unchanged; /* The first and last positions in the buffer. Because boundaries store their positions relative to the start (BEG) and end (Z) of the buffer, knowing these positions allows us to accurately interpret positions without having to pass the buffer structure or its endpoints around all the time. Yes, buffer_beg is always 1. It's there for symmetry with buffer_end and the BEG and BUF_BEG macros. */ int buffer_beg, buffer_end; }; /* Return the position of boundary i in cache c. */ #define BOUNDARY_POS(c, i) \ ((i) < (c)->gap_start \ ? (c)->buffer_beg + (c)->boundaries[(i)].pos \ : (c)->buffer_end + (c)->boundaries[(c)->gap_len + (i)].pos) /* Return the value for text after boundary i in cache c. */ #define BOUNDARY_VALUE(c, i) \ ((i) < (c)->gap_start \ ? (c)->boundaries[(i)].value \ : (c)->boundaries[(c)->gap_len + (i)].value) /* Set the value for text after boundary i in cache c to v. */ #define SET_BOUNDARY_VALUE(c, i, v) \ ((i) < (c)->gap_start \ ? ((c)->boundaries[(i)].value = (v))\ : ((c)->boundaries[(c)->gap_len + (i)].value = (v))) /* How many elements to add to the gap when we resize the buffer. */ #define NEW_CACHE_GAP (40) /* See invalidate_region_cache; if an invalidation would throw away information about this many characters, call revalidate_region_cache before doing the new invalidation, to preserve that information, instead of throwing it away. */ #define PRESERVE_THRESHOLD (500) static void revalidate_region_cache (); /* Interface: Allocating, initializing, and disposing of region caches. */ struct region_cache * new_region_cache () { struct region_cache *c = (struct region_cache *) xmalloc (sizeof (struct region_cache)); c->gap_start = 0; c->gap_len = NEW_CACHE_GAP; c->cache_len = 0; c->boundaries = (struct boundary *) xmalloc ((c->gap_len + c->cache_len) * sizeof (*c->boundaries)); c->beg_unchanged = 0; c->end_unchanged = 0; c->buffer_beg = BEG; c->buffer_end = BEG; /* Insert the boundary for the buffer start. */ c->cache_len++; c->gap_len--; c->gap_start++; c->boundaries[0].pos = 0; /* from buffer_beg */ c->boundaries[0].value = 0; return c; } void free_region_cache (c) struct region_cache *c; { xfree (c->boundaries); xfree (c); } /* Finding positions in the cache. */ /* Return the index of the last boundary in cache C at or before POS. In other words, return the boundary that specifies the value for the region POS..(POS + 1). This operation should be logarithmic in the number of cache entries. It would be nice if it took advantage of locality of reference, too, by searching entries near the last entry found. */ static int find_cache_boundary (c, pos) struct region_cache *c; int pos; { int low = 0, high = c->cache_len; while (low + 1 < high) { /* mid is always a valid index, because low < high and ">> 1" rounds down. */ int mid = (low + high) >> 1; int boundary = BOUNDARY_POS (c, mid); if (pos < boundary) high = mid; else low = mid; } /* Some testing. */ if (BOUNDARY_POS (c, low) > pos || (low + 1 < c->cache_len && BOUNDARY_POS (c, low + 1) <= pos)) abort (); return low; } /* Moving the cache gap around, inserting, and deleting. */ /* Move the gap of cache C to index POS, and make sure it has space for at least MIN_SIZE boundaries. */ static void move_cache_gap (c, pos, min_size) struct region_cache *c; int pos; int min_size; { /* Copy these out of the cache and into registers. */ int gap_start = c->gap_start; int gap_len = c->gap_len; int buffer_beg = c->buffer_beg; int buffer_end = c->buffer_end; if (pos < 0 || pos > c->cache_len) abort (); /* We mustn't ever try to put the gap before the dummy start boundary. That must always be start-relative. */ if (pos == 0) abort (); /* Need we move the gap right? */ while (gap_start < pos) { /* Copy one boundary from after to before the gap, and convert its position to start-relative. */ c->boundaries[gap_start].pos = (buffer_end + c->boundaries[gap_start + gap_len].pos - buffer_beg); c->boundaries[gap_start].value = c->boundaries[gap_start + gap_len].value; gap_start++; } /* To enlarge the gap, we need to re-allocate the boundary array, and then shift the area after the gap to the new end. Since the cost is proportional to the amount of stuff after the gap, we do the enlargement here, after a right shift but before a left shift, when the portion after the gap is smallest. */ if (gap_len < min_size) { int i; /* Always make at least NEW_CACHE_GAP elements, as long as we're expanding anyway. */ if (min_size < NEW_CACHE_GAP) min_size = NEW_CACHE_GAP; c->boundaries = (struct boundary *) xrealloc (c->boundaries, ((min_size + c->cache_len) * sizeof (*c->boundaries))); /* Some systems don't provide a version of the copy routine that can be trusted to shift memory upward into an overlapping region. memmove isn't widely available. */ min_size -= gap_len; for (i = c->cache_len - 1; i >= gap_start; i--) { c->boundaries[i + min_size].pos = c->boundaries[i + gap_len].pos; c->boundaries[i + min_size].value = c->boundaries[i + gap_len].value; } gap_len = min_size; } /* Need we move the gap left? */ while (pos < gap_start) { gap_start--; /* Copy one region from before to after the gap, and convert its position to end-relative. */ c->boundaries[gap_start + gap_len].pos = c->boundaries[gap_start].pos + buffer_beg - buffer_end; c->boundaries[gap_start + gap_len].value = c->boundaries[gap_start].value; } /* Assign these back into the cache. */ c->gap_start = gap_start; c->gap_len = gap_len; } /* Insert a new boundary in cache C; it will have cache index INDEX, and have the specified POS and VALUE. */ static void insert_cache_boundary (c, index, pos, value) struct region_cache *c; int index; int pos, value; { /* index must be a valid cache index. */ if (index < 0 || index > c->cache_len) abort (); /* We must never want to insert something before the dummy first boundary. */ if (index == 0) abort (); /* We must only be inserting things in order. */ if (! (BOUNDARY_POS (c, index-1) < pos && (index == c->cache_len || pos < BOUNDARY_POS (c, index)))) abort (); /* The value must be different from the ones around it. However, we temporarily create boundaries that establish the same value as the subsequent boundary, so we're not going to flag that case. */ if (BOUNDARY_VALUE (c, index-1) == value) abort (); move_cache_gap (c, index, 1); c->boundaries[index].pos = pos - c->buffer_beg; c->boundaries[index].value = value; c->gap_start++; c->gap_len--; c->cache_len++; } /* Delete the i'th entry from cache C if START <= i < END. */ static void delete_cache_boundaries (c, start, end) struct region_cache *c; int start, end; { int len = end - start; /* Gotta be in range. */ if (start < 0 || end > c->cache_len) abort (); /* Gotta be in order. */ if (start > end) abort (); /* Can't delete the dummy entry. */ if (start == 0 && end >= 1) abort (); /* Minimize gap motion. If we're deleting nothing, do nothing. */ if (len == 0) ; /* If the gap is before the region to delete, delete from the start forward. */ else if (c->gap_start <= start) { move_cache_gap (c, start, 0); c->gap_len += len; } /* If the gap is after the region to delete, delete from the end backward. */ else if (end <= c->gap_start) { move_cache_gap (c, end, 0); c->gap_start -= len; c->gap_len += len; } /* If the gap is in the region to delete, just expand it. */ else { c->gap_start = start; c->gap_len += len; } c->cache_len -= len; } /* Set the value for a region. */ /* Set the value in cache C for the region START..END to VALUE. */ static void set_cache_region (c, start, end, value) struct region_cache *c; int start, end; int value; { if (start > end) abort (); if (start < c->buffer_beg || end > c->buffer_end) abort (); /* Eliminate this case; then we can assume that start and end-1 are both the locations of real characters in the buffer. */ if (start == end) return; { /* We need to make sure that there are no boundaries in the area between start to end; the whole area will have the same value, so those boundaries will not be necessary. Let start_ix be the cache index of the boundary governing the first character of start..end, and let end_ix be the cache index of the earliest boundary after the last character in start..end. (This tortured terminology is intended to answer all the "< or <=?" sort of questions.) */ int start_ix = find_cache_boundary (c, start); int end_ix = find_cache_boundary (c, end - 1) + 1; /* We must remember the value established by the last boundary before end; if that boundary's domain stretches beyond end, we'll need to create a new boundary at end, and that boundary must have that remembered value. */ int value_at_end = BOUNDARY_VALUE (c, end_ix - 1); /* Delete all boundaries strictly within start..end; this means those whose indices are between start_ix (exclusive) and end_ix (exclusive). */ delete_cache_boundaries (c, start_ix + 1, end_ix); /* Make sure we have the right value established going in to start..end from the left, and no unnecessary boundaries. */ if (BOUNDARY_POS (c, start_ix) == start) { /* Is this boundary necessary? If no, remove it; if yes, set its value. */ if (start_ix > 0 && BOUNDARY_VALUE (c, start_ix - 1) == value) { delete_cache_boundaries (c, start_ix, start_ix + 1); start_ix--; } else SET_BOUNDARY_VALUE (c, start_ix, value); } else { /* Do we need to add a new boundary here? */ if (BOUNDARY_VALUE (c, start_ix) != value) { insert_cache_boundary (c, start_ix + 1, start, value); start_ix++; } } /* This is equivalent to letting end_ix float (like a buffer marker does) with the insertions and deletions we may have done. */ end_ix = start_ix + 1; /* Make sure we have the correct value established as we leave start..end to the right. */ if (end == c->buffer_end) /* There is no text after start..end; nothing to do. */ ; else if (end_ix >= c->cache_len || end < BOUNDARY_POS (c, end_ix)) { /* There is no boundary at end, but we may need one. */ if (value_at_end != value) insert_cache_boundary (c, end_ix, end, value_at_end); } else { /* There is a boundary at end; should it be there? */ if (value == BOUNDARY_VALUE (c, end_ix)) delete_cache_boundaries (c, end_ix, end_ix + 1); } } } /* Interface: Invalidating the cache. Private: Re-validating the cache. */ /* Indicate that a section of BUF has changed, to invalidate CACHE. HEAD is the number of chars unchanged at the beginning of the buffer. TAIL is the number of chars unchanged at the end of the buffer. NOTE: this is *not* the same as the ending position of modified region. (This way of specifying regions makes more sense than absolute buffer positions in the presence of insertions and deletions; the args to pass are the same before and after such an operation.) */ void invalidate_region_cache (buf, c, head, tail) struct buffer *buf; struct region_cache *c; int head, tail; { /* Let chead = c->beg_unchanged, and ctail = c->end_unchanged. If z-tail < beg+chead by a large amount, or z-ctail < beg+head by a large amount, then cutting back chead and ctail to head and tail would lose a lot of information that we could preserve by revalidating the cache before processing this invalidation. Losing that information may be more costly than revalidating the cache now. So go ahead and call revalidate_region_cache if it seems that it might be worthwhile. */ if (((BUF_BEG (buf) + c->beg_unchanged) - (BUF_Z (buf) - tail) > PRESERVE_THRESHOLD) || ((BUF_BEG (buf) + head) - (BUF_Z (buf) - c->end_unchanged) > PRESERVE_THRESHOLD)) revalidate_region_cache (buf, c); if (head < c->beg_unchanged) c->beg_unchanged = head; if (tail < c->end_unchanged) c->end_unchanged = tail; /* We now know nothing about the region between the unchanged head and the unchanged tail (call it the "modified region"), not even its length. If the modified region has shrunk in size (deletions do this), then the cache may now contain boundaries originally located in text that doesn't exist any more. If the modified region has increased in size (insertions do this), then there may now be boundaries in the modified region whose positions are wrong. Even calling BOUNDARY_POS on boundaries still in the unchanged head or tail may well give incorrect answers now, since c->buffer_beg and c->buffer_end may well be wrong now. (Well, okay, c->buffer_beg never changes, so boundaries in the unchanged head will still be okay. But it's the principle of the thing.) So things are generally a mess. But we don't clean up this mess here; that would be expensive, and this function gets called every time any buffer modification occurs. Rather, we can clean up everything in one swell foop, accounting for all the modifications at once, by calling revalidate_region_cache before we try to consult the cache the next time. */ } /* Clean out any cache entries applying to the modified region, and make the positions of the remaining entries accurate again. After calling this function, the mess described in the comment in invalidate_region_cache is cleaned up. This function operates by simply throwing away everything it knows about the modified region. It doesn't care exactly which insertions and deletions took place; it just tosses it all. For example, if you insert a single character at the beginning of the buffer, and a single character at the end of the buffer (for example), without calling this function in between the two insertions, then the entire cache will be freed of useful information. On the other hand, if you do manage to call this function in between the two insertions, then the modified regions will be small in both cases, no information will be tossed, and the cache will know that it doesn't have knowledge of the first and last characters any more. Calling this function may be expensive; it does binary searches in the cache, and causes cache gap motion. */ static void revalidate_region_cache (buf, c) struct buffer *buf; struct region_cache *c; { /* The boundaries now in the cache are expressed relative to the buffer_beg and buffer_end values stored in the cache. Now, buffer_beg and buffer_end may not be the same as BUF_BEG (buf) and BUF_Z (buf), so we have two different "bases" to deal with --- the cache's, and the buffer's. */ /* If the entire buffer is still valid, don't waste time. Yes, this should be a >, not a >=; think about what beg_unchanged and end_unchanged get set to when the only change has been an insertion. */ if (c->buffer_beg + c->beg_unchanged > c->buffer_end - c->end_unchanged) return; /* If all the text we knew about as of the last cache revalidation is still there, then all of the information in the cache is still valid. Because c->buffer_beg and c->buffer_end are out-of-date, the modified region appears from the cache's point of view to be a null region located someplace in the buffer. Now, invalidating that empty string will have no actual affect on the cache; instead, we need to update the cache's basis first (which will give the modified region the same size in the cache as it has in the buffer), and then invalidate the modified region. */ if (c->buffer_beg + c->beg_unchanged == c->buffer_end - c->end_unchanged) { /* Move the gap so that all the boundaries in the unchanged head are expressed beg-relative, and all the boundaries in the unchanged tail are expressed end-relative. That done, we can plug in the new buffer beg and end, and all the positions will be accurate. The boundary which has jurisdiction over the modified region should be left before the gap. */ move_cache_gap (c, (find_cache_boundary (c, (c->buffer_beg + c->beg_unchanged)) + 1), 0); c->buffer_beg = BUF_BEG (buf); c->buffer_end = BUF_Z (buf); /* Now that the cache's basis has been changed, the modified region actually takes up some space in the cache, so we can invalidate it. */ set_cache_region (c, c->buffer_beg + c->beg_unchanged, c->buffer_end - c->end_unchanged, 0); } /* Otherwise, there is a non-empty region in the cache which corresponds to the modified region of the buffer. */ else { int modified_ix; /* These positions are correct, relative to both the cache basis and the buffer basis. */ set_cache_region (c, c->buffer_beg + c->beg_unchanged, c->buffer_end - c->end_unchanged, 0); /* Now the cache contains only boundaries that are in the unchanged head and tail; we've disposed of any boundaries whose positions we can't be sure of given the information we've saved. If we put the cache gap between the unchanged head and the unchanged tail, we can adjust all the boundary positions at once, simply by setting buffer_beg and buffer_end. The boundary which has jurisdiction over the modified region should be left before the gap. */ modified_ix = find_cache_boundary (c, (c->buffer_beg + c->beg_unchanged)) + 1; move_cache_gap (c, modified_ix, 0); c->buffer_beg = BUF_BEG (buf); c->buffer_end = BUF_Z (buf); /* Now, we may have shrunk the buffer when we changed the basis, and brought the boundaries we created for the start and end of the modified region together, giving them the same position. If that's the case, we should collapse them into one boundary. Or we may even delete them both, if the values before and after them are the same. */ if (modified_ix < c->cache_len && (BOUNDARY_POS (c, modified_ix - 1) == BOUNDARY_POS (c, modified_ix))) { int value_after = BOUNDARY_VALUE (c, modified_ix); /* Should we remove both of the boundaries? Yes, if the latter boundary is now establishing the same value that the former boundary's predecessor does. */ if (modified_ix - 1 > 0 && value_after == BOUNDARY_VALUE (c, modified_ix - 2)) delete_cache_boundaries (c, modified_ix - 1, modified_ix + 1); else { /* We do need a boundary here; collapse the two boundaries into one. */ SET_BOUNDARY_VALUE (c, modified_ix - 1, value_after); delete_cache_boundaries (c, modified_ix, modified_ix + 1); } } } /* Now the entire cache is valid. */ c->beg_unchanged = c->end_unchanged = c->buffer_end - c->buffer_beg; } /* Interface: Adding information to the cache. */ /* Assert that the region of BUF between START and END (absolute buffer positions) is "known," for the purposes of CACHE (e.g. "has no newlines", in the case of the line cache). */ void know_region_cache (buf, c, start, end) struct buffer *buf; struct region_cache *c; int start, end; { revalidate_region_cache (buf, c); set_cache_region (c, start, end, 1); } /* Interface: using the cache. */ /* Return true if the text immediately after POS in BUF is known, for the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest position after POS where the knownness changes. */ int region_cache_forward (buf, c, pos, next) struct buffer *buf; struct region_cache *c; int pos; int *next; { revalidate_region_cache (buf, c); { int i = find_cache_boundary (c, pos); int i_value = BOUNDARY_VALUE (c, i); int j; /* Beyond the end of the buffer is unknown, by definition. */ if (pos >= BUF_Z (buf)) { if (next) *next = BUF_Z (buf); i_value = 0; } else if (next) { /* Scan forward from i to find the next differing position. */ for (j = i + 1; j < c->cache_len; j++) if (BOUNDARY_VALUE (c, j) != i_value) break; if (j < c->cache_len) *next = BOUNDARY_POS (c, j); else *next = BUF_Z (buf); } return i_value; } } /* Return true if the text immediately before POS in BUF is known, for the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest position before POS where the knownness changes. */ int region_cache_backward (buf, c, pos, next) struct buffer *buf; struct region_cache *c; int pos; int *next; { revalidate_region_cache (buf, c); /* Before the beginning of the buffer is unknown, by definition. */ if (pos <= BUF_BEG (buf)) { if (next) *next = BUF_BEG (buf); return 0; } { int i = find_cache_boundary (c, pos - 1); int i_value = BOUNDARY_VALUE (c, i); int j; if (next) { /* Scan backward from i to find the next differing position. */ for (j = i - 1; j >= 0; j--) if (BOUNDARY_VALUE (c, j) != i_value) break; if (j >= 0) *next = BOUNDARY_POS (c, j + 1); else *next = BUF_BEG (buf); } return i_value; } } /* Debugging: pretty-print a cache to the standard error output. */ void pp_cache (c) struct region_cache *c; { int i; int beg_u = c->buffer_beg + c->beg_unchanged; int end_u = c->buffer_end - c->end_unchanged; fprintf (stderr, "basis: %d..%d modified: %d..%d\n", c->buffer_beg, c->buffer_end, beg_u, end_u); for (i = 0; i < c->cache_len; i++) { int pos = BOUNDARY_POS (c, i); putc (((pos < beg_u) ? 'v' : (pos == beg_u) ? '-' : ' '), stderr); putc (((pos > end_u) ? '^' : (pos == end_u) ? '-' : ' '), stderr); fprintf (stderr, "%d : %d\n", pos, BOUNDARY_VALUE (c, i)); } } /* arch-tag: 98c29f3f-2ca2-4e3a-92f0-f2249200a17d (do not change this comment) */