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b9c5136f | 1 | /* Header file: Caching facts about regions of the buffer, for optimization. |
f8c25f1b | 2 | Copyright (C) 1985, 1986, 1993, 1995 Free Software Foundation, Inc. |
b9c5136f KH |
3 | |
4 | This file is part of GNU Emacs. | |
5 | ||
6 | GNU Emacs is free software; you can redistribute it and/or modify | |
7 | it under the terms of the GNU General Public License as published by | |
8 | the Free Software Foundation; either version 2, or (at your option) | |
9 | any later version. | |
10 | ||
11 | GNU Emacs is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | GNU General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU General Public License | |
17 | along with GNU Emacs; see the file COPYING. If not, write to | |
3b7ad313 EN |
18 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
19 | Boston, MA 02111-1307, USA. */ | |
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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. */ | |
4c571d09 | 65 | struct region_cache *new_region_cache P_ ((void)); |
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66 | |
67 | /* Free a region cache. */ | |
4c571d09 | 68 | void free_region_cache P_ ((struct region_cache *)); |
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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). */ | |
4c571d09 | 73 | extern void know_region_cache P_ ((struct buffer *BUF, |
b9c5136f | 74 | struct region_cache *CACHE, |
4c571d09 | 75 | int START, int 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.) */ | |
4c571d09 AS |
85 | extern void invalidate_region_cache P_ ((struct buffer *BUF, |
86 | struct region_cache *CACHE, | |
87 | int HEAD, int TAIL)); | |
b9c5136f | 88 | |
177c0ea7 | 89 | /* The scanning functions. |
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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 |
b9c5136f | 100 | position after POS where the knownness changes. */ |
4c571d09 | 101 | extern int region_cache_forward P_ ((struct buffer *BUF, |
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102 | struct region_cache *CACHE, |
103 | int POS, | |
4c571d09 | 104 | int *NEXT)); |
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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 | |
108 | position before POS where the knownness changes. */ | |
4c571d09 | 109 | extern int region_cache_backward P_ ((struct buffer *BUF, |
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110 | struct region_cache *CACHE, |
111 | int POS, | |
4c571d09 | 112 | int *NEXT)); |
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113 | |
114 | /* arch-tag: 70f79125-ef22-4f58-9aec-a48ca2791435 | |
115 | (do not change this comment) */ |