/* Header file: Caching facts about regions of the buffer, for optimization. Copyright (C) 1985, 1986, 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. */ /* This code was written by Jim Blandy <jimb@cs.oberlin.edu> to help GNU Emacs better support the gene editor written for the University of Illinois at Urbana-Champagne's Ribosome Database Project (RDP). Emacs implements line operations (finding the beginning/end of the line, vertical motion, all the redisplay stuff) by searching for newlines in the buffer. Usually, this is a good design; it's very clean to just represent the buffer as an unstructured string of characters, and the lines in most files are very short (less than eighty characters), meaning that scanning usually costs about the same as the overhead of maintaining some more complicated data structure. However, some applications, like gene editing, make use of very long lines --- on the order of tens of kilobytes. In such cases, it may well be worthwhile to try to avoid scanning, because the scans have become two orders of magnitude more expensive. It would be nice if this speedup could preserve the simplicity of the existing data structure, and disturb as little of the existing code as possible. So here's the tack. We add some caching to the scan_buffer function, so that when it searches for a newline, it notes that the region between the start and end of the search contained no newlines; then, the next time around, it consults this cache to see if there are regions of text it can skip over completely. The buffer modification primitives invalidate this cache. (Note: Since the redisplay code needs similar information on modified regions of the buffer, we can use the code that helps out redisplay as a guide to where we need to add our own code to invalidate our cache. prepare_to_modify_buffer seems to be the central spot.) Note that the cache code itself never mentions newlines specifically, so if you wanted to cache other properties of regions of the buffer, you could use this code pretty much unchanged. So this cache really holds "known/unknown" information --- "I know this region has property P" vs. "I don't know if this region has property P or not." */ /* Allocate, initialize and return a new, empty region cache. */ struct region_cache *new_region_cache P_ ((void)); /* Free a region cache. */ void free_region_cache P_ ((struct region_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). */ extern void know_region_cache P_ ((struct buffer *BUF, struct region_cache *CACHE, int START, int END)); /* 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.) */ extern void invalidate_region_cache P_ ((struct buffer *BUF, struct region_cache *CACHE, int HEAD, int TAIL)); /* The scanning functions. Basically, if you're scanning forward/backward from position POS, and region_cache_forward/backward returns true, you can skip all the text between POS and *NEXT. And if the function returns false, you should examine all the text from POS to *NEXT, and call know_region_cache depending on what you find there; this way, you might be able to avoid scanning it again. */ /* 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. */ extern int region_cache_forward P_ ((struct buffer *BUF, struct region_cache *CACHE, int POS, int *NEXT)); /* 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. */ extern int region_cache_backward P_ ((struct buffer *BUF, struct region_cache *CACHE, int POS, int *NEXT)); /* arch-tag: 70f79125-ef22-4f58-9aec-a48ca2791435 (do not change this comment) */