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Most of this change is to boilerplate commentary such as license URLs. This change was prompted by ftp://ftp.gnu.org's going-away party, planned for November. Change these FTP URLs to https://ftp.gnu.org instead. Make similar changes for URLs to other organizations moving away from FTP. Also, change HTTP to HTTPS for URLs to gnu.org and fsf.org when this works, as this will further help defend against man-in-the-middle attacks (for this part I omitted the MS-DOS and MS-Windows sources and the test tarballs to keep the workload down). HTTPS is not fully working to lists.gnu.org so I left those URLs alone for now.
112 lines
5.2 KiB
C
112 lines
5.2 KiB
C
/* Header file: Caching facts about regions of the buffer, for optimization.
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Copyright (C) 1985-1986, 1993, 1995, 2001-2017 Free Software Foundation,
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Inc.
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This file is part of GNU Emacs.
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GNU Emacs is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or (at
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your option) any later version.
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GNU Emacs is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
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#ifndef EMACS_REGION_CACHE_H
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#define EMACS_REGION_CACHE_H
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/* This code was written by Jim Blandy <jimb@cs.oberlin.edu> to help
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GNU Emacs better support the gene editor written for the University
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of Illinois at Urbana-Champagne's Ribosome Database Project (RDP).
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Emacs implements line operations (finding the beginning/end of the
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line, vertical motion, all the redisplay stuff) by searching for
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newlines in the buffer. Usually, this is a good design; it's very
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clean to just represent the buffer as an unstructured string of
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characters, and the lines in most files are very short (less than
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eighty characters), meaning that scanning usually costs about the
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same as the overhead of maintaining some more complicated data
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structure.
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However, some applications, like gene editing, make use of very
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long lines --- on the order of tens of kilobytes. In such cases,
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it may well be worthwhile to try to avoid scanning, because the
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scans have become two orders of magnitude more expensive. It would
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be nice if this speedup could preserve the simplicity of the
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existing data structure, and disturb as little of the existing code
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as possible.
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So here's the tack. We add some caching to the find_newline
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function, so that when it searches for a newline, it notes that the
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region between the start and end of the search contained no
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newlines; then, the next time around, it consults this cache to see
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if there are regions of text it can skip over completely. The
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buffer modification primitives invalidate this cache.
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(Note: Since the redisplay code needs similar information on
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modified regions of the buffer, we can use the code that helps out
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redisplay as a guide to where we need to add our own code to
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invalidate our cache. prepare_to_modify_buffer seems to be the
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central spot.)
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Note that the cache code itself never mentions newlines
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specifically, so if you wanted to cache other properties of regions
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of the buffer, you could use this code pretty much unchanged. So
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this cache really holds "known/unknown" information --- "I know
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this region has property P" vs. "I don't know if this region has
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property P or not." */
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struct buffer;
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/* Allocate, initialize and return a new, empty region cache. */
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struct region_cache *new_region_cache (void);
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/* Free a region cache. */
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void free_region_cache (struct region_cache *);
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/* Assert that the region of BUF between START and END (absolute
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buffer positions) is "known," for the purposes of CACHE (e.g. "has
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no newlines", in the case of the line cache). */
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extern void know_region_cache (struct buffer *BUF,
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struct region_cache *CACHE,
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ptrdiff_t START, ptrdiff_t END);
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/* Indicate that a section of BUF has changed, to invalidate CACHE.
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HEAD is the number of chars unchanged at the beginning of the buffer.
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TAIL is the number of chars unchanged at the end of the buffer.
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NOTE: this is *not* the same as the ending position of modified
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region.
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(This way of specifying regions makes more sense than absolute
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buffer positions in the presence of insertions and deletions; the
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args to pass are the same before and after such an operation.) */
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extern void invalidate_region_cache (struct buffer *BUF,
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struct region_cache *CACHE,
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ptrdiff_t HEAD, ptrdiff_t TAIL);
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/* The scanning functions.
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Basically, if you're scanning forward/backward from position POS,
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and region_cache_forward/backward returns nonzero, you can skip all
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the text between POS and *NEXT. And if the function returns zero,
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you should examine all the text from POS to *NEXT, and call
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know_region_cache depending on what you find there; this way, you
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might be able to avoid scanning it again. */
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/* Return the value for the text immediately after POS in BUF if the value
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is known, for the purposes of CACHE, and return zero otherwise.
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If NEXT is non-zero, set *NEXT to the nearest
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position after POS where the knowledge changes. */
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extern int region_cache_forward (struct buffer *buf, struct region_cache *c,
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ptrdiff_t pos, ptrdiff_t *next);
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/* Likewise, except before POS rather than after POS. */
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extern int region_cache_backward (struct buffer *buf, struct region_cache *c,
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ptrdiff_t pos, ptrdiff_t *next);
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#endif /* EMACS_REGION_CACHE_H */
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