2 * JFFS2 -- Journalling Flash File System, Version 2.
4 * Copyright (C) 2001-2003 Red Hat, Inc.
6 * Created by Arjan van de Ven <arjanv@redhat.com>
8 * For licensing information, see the file 'LICENCE' in this directory.
10 * $Id: compr_rtime.c,v 1.14 2004/06/23 16:34:40 havasi Exp $
13 * Very simple lz77-ish encoder.
15 * Theory of operation: Both encoder and decoder have a list of "last
16 * occurrences" for every possible source-value; after sending the
17 * first source-byte, the second byte indicated the "run" length of
20 * The algorithm is intended to only send "whole bytes", no bit-messing.
24 #include <linux/kernel.h>
25 #include <linux/types.h>
26 #include <linux/errno.h>
27 #include <linux/string.h>
28 #include <linux/jffs2.h>
31 /* _compress returns the compressed size, -1 if bigger */
32 int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out,
33 uint32_t *sourcelen, uint32_t *dstlen, void *model)
39 memset(positions,0,sizeof(positions));
41 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
42 int backpos, runlen=0;
47 cpage_out[outpos++] = data_in[pos++];
49 backpos = positions[value];
52 while ((backpos < pos) && (pos < (*sourcelen)) &&
53 (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
57 cpage_out[outpos++] = runlen;
65 /* Tell the caller how much we managed to compress, and how much space it took */
72 int jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
73 uint32_t srclen, uint32_t destlen, void *model)
79 memset(positions,0,sizeof(positions));
81 while (outpos<destlen) {
86 value = data_in[pos++];
87 cpage_out[outpos++] = value; /* first the verbatim copied byte */
88 repeat = data_in[pos++];
89 backoffs = positions[value];
91 positions[value]=outpos;
93 if (backoffs + repeat >= outpos) {
95 cpage_out[outpos++] = cpage_out[backoffs++];
99 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
107 static struct jffs2_compressor jffs2_rtime_comp = {
108 .priority = JFFS2_RTIME_PRIORITY,
110 .compr = JFFS2_COMPR_RTIME,
111 .compress = &jffs2_rtime_compress,
112 .decompress = &jffs2_rtime_decompress,
113 #ifdef JFFS2_RTIME_DISABLED
120 int jffs2_rtime_init(void)
122 return jffs2_register_compressor(&jffs2_rtime_comp);
125 void jffs2_rtime_exit(void)
127 jffs2_unregister_compressor(&jffs2_rtime_comp);