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b9c5136f | 1 | /* Header file: Caching facts about regions of the buffer, for optimization. |
429ab54e | 2 | Copyright (C) 1985, 1986, 1993, 1995, 2001, 2002, 2003, 2004, |
76b6f707 | 3 | 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. |
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4 | |
5 | This file is part of GNU Emacs. | |
6 | ||
b9b1cc14 | 7 | GNU Emacs is free software: you can redistribute it and/or modify |
b9c5136f | 8 | it under the terms of the GNU General Public License as published by |
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9 | the Free Software Foundation, either version 3 of the License, or |
10 | (at your option) any later version. | |
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11 | |
12 | GNU Emacs is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 | GNU General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU General Public License | |
b9b1cc14 | 18 | along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */ |
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19 | |
20 | ||
21 | /* This code was written by Jim Blandy <jimb@cs.oberlin.edu> to help | |
22 | GNU Emacs better support the gene editor written for the University | |
23 | of Illinois at Urbana-Champagne's Ribosome Database Project (RDP). | |
24 | ||
25 | Emacs implements line operations (finding the beginning/end of the | |
26 | line, vertical motion, all the redisplay stuff) by searching for | |
27 | newlines in the buffer. Usually, this is a good design; it's very | |
28 | clean to just represent the buffer as an unstructured string of | |
29 | characters, and the lines in most files are very short (less than | |
30 | eighty characters), meaning that scanning usually costs about the | |
31 | same as the overhead of maintaining some more complicated data | |
32 | structure. | |
33 | ||
34 | However, some applications, like gene editing, make use of very | |
35 | long lines --- on the order of tens of kilobytes. In such cases, | |
36 | it may well be worthwhile to try to avoid scanning, because the | |
37 | scans have become two orders of magnitude more expensive. It would | |
38 | be nice if this speedup could preserve the simplicity of the | |
39 | existing data structure, and disturb as little of the existing code | |
40 | as possible. | |
41 | ||
42 | So here's the tack. We add some caching to the scan_buffer | |
43 | function, so that when it searches for a newline, it notes that the | |
44 | region between the start and end of the search contained no | |
45 | newlines; then, the next time around, it consults this cache to see | |
46 | if there are regions of text it can skip over completely. The | |
47 | buffer modification primitives invalidate this cache. | |
48 | ||
49 | (Note: Since the redisplay code needs similar information on | |
50 | modified regions of the buffer, we can use the code that helps out | |
51 | redisplay as a guide to where we need to add our own code to | |
52 | invalidate our cache. prepare_to_modify_buffer seems to be the | |
53 | central spot.) | |
54 | ||
55 | Note that the cache code itself never mentions newlines | |
56 | specifically, so if you wanted to cache other properties of regions | |
57 | of the buffer, you could use this code pretty much unchanged. So | |
58 | this cache really holds "known/unknown" information --- "I know | |
59 | this region has property P" vs. "I don't know if this region has | |
60 | property P or not." */ | |
61 | ||
62 | ||
63 | /* Allocate, initialize and return a new, empty region cache. */ | |
4c571d09 | 64 | struct region_cache *new_region_cache P_ ((void)); |
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65 | |
66 | /* Free a region cache. */ | |
4c571d09 | 67 | void free_region_cache P_ ((struct region_cache *)); |
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68 | |
69 | /* Assert that the region of BUF between START and END (absolute | |
70 | buffer positions) is "known," for the purposes of CACHE (e.g. "has | |
71 | no newlines", in the case of the line cache). */ | |
4c571d09 | 72 | extern void know_region_cache P_ ((struct buffer *BUF, |
b9c5136f | 73 | struct region_cache *CACHE, |
4c571d09 | 74 | int START, int END)); |
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75 | |
76 | /* Indicate that a section of BUF has changed, to invalidate CACHE. | |
77 | HEAD is the number of chars unchanged at the beginning of the buffer. | |
78 | TAIL is the number of chars unchanged at the end of the buffer. | |
79 | NOTE: this is *not* the same as the ending position of modified | |
80 | region. | |
81 | (This way of specifying regions makes more sense than absolute | |
82 | buffer positions in the presence of insertions and deletions; the | |
83 | args to pass are the same before and after such an operation.) */ | |
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84 | extern void invalidate_region_cache P_ ((struct buffer *BUF, |
85 | struct region_cache *CACHE, | |
86 | int HEAD, int TAIL)); | |
b9c5136f | 87 | |
177c0ea7 | 88 | /* The scanning functions. |
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89 | |
90 | Basically, if you're scanning forward/backward from position POS, | |
91 | and region_cache_forward/backward returns true, you can skip all | |
92 | the text between POS and *NEXT. And if the function returns false, | |
93 | you should examine all the text from POS to *NEXT, and call | |
94 | know_region_cache depending on what you find there; this way, you | |
95 | might be able to avoid scanning it again. */ | |
96 | ||
97 | /* Return true if the text immediately after POS in BUF is known, for | |
177c0ea7 | 98 | the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest |
b9c5136f | 99 | position after POS where the knownness changes. */ |
4c571d09 | 100 | extern int region_cache_forward P_ ((struct buffer *BUF, |
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101 | struct region_cache *CACHE, |
102 | int POS, | |
4c571d09 | 103 | int *NEXT)); |
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104 | |
105 | /* Return true if the text immediately before POS in BUF is known, for | |
106 | the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest | |
107 | position before POS where the knownness changes. */ | |
4c571d09 | 108 | extern int region_cache_backward P_ ((struct buffer *BUF, |
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109 | struct region_cache *CACHE, |
110 | int POS, | |
4c571d09 | 111 | int *NEXT)); |
ab5796a9 MB |
112 | |
113 | /* arch-tag: 70f79125-ef22-4f58-9aec-a48ca2791435 | |
114 | (do not change this comment) */ |