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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * JFFS2 -- Journalling Flash File System, Version 2.
3 *
David Woodhousec00c3102007-04-25 14:16:47 +01004 * Copyright © 2001-2007 Red Hat, Inc.
Linus Torvalds1da177e2005-04-16 15:20:36 -07005 *
6 * Created by Arjan van de Ven <arjanv@redhat.com>
7 *
8 * For licensing information, see the file 'LICENCE' in this directory.
9 *
Linus Torvalds1da177e2005-04-16 15:20:36 -070010 *
11 *
12 * Very simple lz77-ish encoder.
13 *
14 * Theory of operation: Both encoder and decoder have a list of "last
15 * occurrences" for every possible source-value; after sending the
16 * first source-byte, the second byte indicated the "run" length of
17 * matches
18 *
19 * The algorithm is intended to only send "whole bytes", no bit-messing.
20 *
21 */
22
23#include <linux/kernel.h>
24#include <linux/types.h>
25#include <linux/errno.h>
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000026#include <linux/string.h>
27#include <linux/jffs2.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070028#include "compr.h"
29
30/* _compress returns the compressed size, -1 if bigger */
31static int jffs2_rtime_compress(unsigned char *data_in,
32 unsigned char *cpage_out,
33 uint32_t *sourcelen, uint32_t *dstlen,
34 void *model)
35{
36 short positions[256];
37 int outpos = 0;
38 int pos=0;
39
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000040 memset(positions,0,sizeof(positions));
41
Linus Torvalds1da177e2005-04-16 15:20:36 -070042 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
43 int backpos, runlen=0;
44 unsigned char value;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000045
Linus Torvalds1da177e2005-04-16 15:20:36 -070046 value = data_in[pos];
47
48 cpage_out[outpos++] = data_in[pos++];
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000049
Linus Torvalds1da177e2005-04-16 15:20:36 -070050 backpos = positions[value];
51 positions[value]=pos;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000052
Linus Torvalds1da177e2005-04-16 15:20:36 -070053 while ((backpos < pos) && (pos < (*sourcelen)) &&
54 (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
55 pos++;
56 runlen++;
57 }
58 cpage_out[outpos++] = runlen;
59 }
60
61 if (outpos >= pos) {
62 /* We failed */
63 return -1;
64 }
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000065
Linus Torvalds1da177e2005-04-16 15:20:36 -070066 /* Tell the caller how much we managed to compress, and how much space it took */
67 *sourcelen = pos;
68 *dstlen = outpos;
69 return 0;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000070}
Linus Torvalds1da177e2005-04-16 15:20:36 -070071
72
73static int jffs2_rtime_decompress(unsigned char *data_in,
74 unsigned char *cpage_out,
75 uint32_t srclen, uint32_t destlen,
76 void *model)
77{
78 short positions[256];
79 int outpos = 0;
80 int pos=0;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000081
82 memset(positions,0,sizeof(positions));
83
Linus Torvalds1da177e2005-04-16 15:20:36 -070084 while (outpos<destlen) {
85 unsigned char value;
86 int backoffs;
87 int repeat;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000088
Linus Torvalds1da177e2005-04-16 15:20:36 -070089 value = data_in[pos++];
90 cpage_out[outpos++] = value; /* first the verbatim copied byte */
91 repeat = data_in[pos++];
92 backoffs = positions[value];
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000093
Linus Torvalds1da177e2005-04-16 15:20:36 -070094 positions[value]=outpos;
95 if (repeat) {
96 if (backoffs + repeat >= outpos) {
97 while(repeat) {
98 cpage_out[outpos++] = cpage_out[backoffs++];
99 repeat--;
100 }
101 } else {
102 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
Thomas Gleixner182ec4e2005-11-07 11:16:07 +0000103 outpos+=repeat;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104 }
105 }
106 }
107 return 0;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +0000108}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700109
110static struct jffs2_compressor jffs2_rtime_comp = {
111 .priority = JFFS2_RTIME_PRIORITY,
112 .name = "rtime",
113 .compr = JFFS2_COMPR_RTIME,
114 .compress = &jffs2_rtime_compress,
115 .decompress = &jffs2_rtime_decompress,
116#ifdef JFFS2_RTIME_DISABLED
117 .disabled = 1,
118#else
119 .disabled = 0,
120#endif
121};
122
123int jffs2_rtime_init(void)
124{
125 return jffs2_register_compressor(&jffs2_rtime_comp);
126}
127
128void jffs2_rtime_exit(void)
129{
130 jffs2_unregister_compressor(&jffs2_rtime_comp);
131}