Commit | Line | Data |
---|---|---|
b9c5136f | 1 | /* Header file: Caching facts about regions of the buffer, for optimization. |
95df8112 | 2 | |
ab422c4d PE |
3 | Copyright (C) 1985-1986, 1993, 1995, 2001-2013 Free Software Foundation, |
4 | Inc. | |
b9c5136f KH |
5 | |
6 | This file is part of GNU Emacs. | |
7 | ||
b9b1cc14 | 8 | GNU Emacs is free software: you can redistribute it and/or modify |
b9c5136f | 9 | it under the terms of the GNU General Public License as published by |
b9b1cc14 GM |
10 | the Free Software Foundation, either version 3 of the License, or |
11 | (at your option) any later version. | |
b9c5136f KH |
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 | |
b9b1cc14 | 19 | along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */ |
b9c5136f KH |
20 | |
21 | ||
22 | /* This code was written by Jim Blandy <jimb@cs.oberlin.edu> to help | |
23 | GNU Emacs better support the gene editor written for the University | |
24 | of Illinois at Urbana-Champagne's Ribosome Database Project (RDP). | |
25 | ||
26 | Emacs implements line operations (finding the beginning/end of the | |
27 | line, vertical motion, all the redisplay stuff) by searching for | |
28 | newlines in the buffer. Usually, this is a good design; it's very | |
29 | clean to just represent the buffer as an unstructured string of | |
30 | characters, and the lines in most files are very short (less than | |
31 | eighty characters), meaning that scanning usually costs about the | |
32 | same as the overhead of maintaining some more complicated data | |
33 | structure. | |
34 | ||
35 | However, some applications, like gene editing, make use of very | |
36 | long lines --- on the order of tens of kilobytes. In such cases, | |
37 | it may well be worthwhile to try to avoid scanning, because the | |
38 | scans have become two orders of magnitude more expensive. It would | |
39 | be nice if this speedup could preserve the simplicity of the | |
40 | existing data structure, and disturb as little of the existing code | |
41 | as possible. | |
42 | ||
43 | So here's the tack. We add some caching to the scan_buffer | |
44 | function, so that when it searches for a newline, it notes that the | |
45 | region between the start and end of the search contained no | |
46 | newlines; then, the next time around, it consults this cache to see | |
47 | if there are regions of text it can skip over completely. The | |
48 | buffer modification primitives invalidate this cache. | |
49 | ||
50 | (Note: Since the redisplay code needs similar information on | |
51 | modified regions of the buffer, we can use the code that helps out | |
52 | redisplay as a guide to where we need to add our own code to | |
53 | invalidate our cache. prepare_to_modify_buffer seems to be the | |
54 | central spot.) | |
55 | ||
56 | Note that the cache code itself never mentions newlines | |
57 | specifically, so if you wanted to cache other properties of regions | |
58 | of the buffer, you could use this code pretty much unchanged. So | |
59 | this cache really holds "known/unknown" information --- "I know | |
60 | this region has property P" vs. "I don't know if this region has | |
61 | property P or not." */ | |
62 | ||
63 | ||
64 | /* Allocate, initialize and return a new, empty region cache. */ | |
383e0970 | 65 | struct region_cache *new_region_cache (void); |
b9c5136f KH |
66 | |
67 | /* Free a region cache. */ | |
383e0970 | 68 | void free_region_cache (struct region_cache *); |
b9c5136f KH |
69 | |
70 | /* Assert that the region of BUF between START and END (absolute | |
71 | buffer positions) is "known," for the purposes of CACHE (e.g. "has | |
72 | no newlines", in the case of the line cache). */ | |
383e0970 J |
73 | extern void know_region_cache (struct buffer *BUF, |
74 | struct region_cache *CACHE, | |
0065d054 | 75 | ptrdiff_t START, ptrdiff_t END); |
b9c5136f KH |
76 | |
77 | /* Indicate that a section of BUF has changed, to invalidate CACHE. | |
78 | HEAD is the number of chars unchanged at the beginning of the buffer. | |
79 | TAIL is the number of chars unchanged at the end of the buffer. | |
80 | NOTE: this is *not* the same as the ending position of modified | |
81 | region. | |
82 | (This way of specifying regions makes more sense than absolute | |
83 | buffer positions in the presence of insertions and deletions; the | |
84 | args to pass are the same before and after such an operation.) */ | |
383e0970 J |
85 | extern void invalidate_region_cache (struct buffer *BUF, |
86 | struct region_cache *CACHE, | |
0065d054 | 87 | ptrdiff_t HEAD, ptrdiff_t TAIL); |
b9c5136f | 88 | |
177c0ea7 | 89 | /* The scanning functions. |
b9c5136f KH |
90 | |
91 | Basically, if you're scanning forward/backward from position POS, | |
92 | and region_cache_forward/backward returns true, you can skip all | |
93 | the text between POS and *NEXT. And if the function returns false, | |
94 | you should examine all the text from POS to *NEXT, and call | |
95 | know_region_cache depending on what you find there; this way, you | |
96 | might be able to avoid scanning it again. */ | |
97 | ||
98 | /* Return true if the text immediately after POS in BUF is known, for | |
177c0ea7 | 99 | the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest |
333f9019 | 100 | position after POS where the knowledge changes. */ |
383e0970 J |
101 | extern int region_cache_forward (struct buffer *BUF, |
102 | struct region_cache *CACHE, | |
0065d054 PE |
103 | ptrdiff_t POS, |
104 | ptrdiff_t *NEXT); | |
b9c5136f KH |
105 | |
106 | /* Return true if the text immediately before POS in BUF is known, for | |
107 | the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest | |
333f9019 | 108 | position before POS where the knowledge changes. */ |
383e0970 J |
109 | extern int region_cache_backward (struct buffer *BUF, |
110 | struct region_cache *CACHE, | |
0065d054 PE |
111 | ptrdiff_t POS, |
112 | ptrdiff_t *NEXT); |