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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.
David Woodhouse6088c052010-08-08 14:15:22 +01005 * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -07006 *
7 * Created by Arjan van de Ven <arjanv@redhat.com>
8 *
9 * For licensing information, see the file 'LICENCE' in this directory.
10 *
Linus Torvalds1da177e2005-04-16 15:20:36 -070011 *
12 *
13 * Very simple lz77-ish encoder.
14 *
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
18 * matches
19 *
20 * The algorithm is intended to only send "whole bytes", no bit-messing.
21 *
22 */
23
24#include <linux/kernel.h>
25#include <linux/types.h>
26#include <linux/errno.h>
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000027#include <linux/string.h>
28#include <linux/jffs2.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070029#include "compr.h"
30
31/* _compress returns the compressed size, -1 if bigger */
32static int jffs2_rtime_compress(unsigned char *data_in,
33 unsigned char *cpage_out,
34 uint32_t *sourcelen, uint32_t *dstlen,
35 void *model)
36{
37 short positions[256];
38 int outpos = 0;
39 int pos=0;
40
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000041 memset(positions,0,sizeof(positions));
42
Linus Torvalds1da177e2005-04-16 15:20:36 -070043 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
44 int backpos, runlen=0;
45 unsigned char value;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000046
Linus Torvalds1da177e2005-04-16 15:20:36 -070047 value = data_in[pos];
48
49 cpage_out[outpos++] = data_in[pos++];
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000050
Linus Torvalds1da177e2005-04-16 15:20:36 -070051 backpos = positions[value];
52 positions[value]=pos;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000053
Linus Torvalds1da177e2005-04-16 15:20:36 -070054 while ((backpos < pos) && (pos < (*sourcelen)) &&
55 (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
56 pos++;
57 runlen++;
58 }
59 cpage_out[outpos++] = runlen;
60 }
61
62 if (outpos >= pos) {
63 /* We failed */
64 return -1;
65 }
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000066
Linus Torvalds1da177e2005-04-16 15:20:36 -070067 /* Tell the caller how much we managed to compress, and how much space it took */
68 *sourcelen = pos;
69 *dstlen = outpos;
70 return 0;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000071}
Linus Torvalds1da177e2005-04-16 15:20:36 -070072
73
74static int jffs2_rtime_decompress(unsigned char *data_in,
75 unsigned char *cpage_out,
76 uint32_t srclen, uint32_t destlen,
77 void *model)
78{
79 short positions[256];
80 int outpos = 0;
81 int pos=0;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000082
83 memset(positions,0,sizeof(positions));
84
Linus Torvalds1da177e2005-04-16 15:20:36 -070085 while (outpos<destlen) {
86 unsigned char value;
87 int backoffs;
88 int repeat;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000089
Linus Torvalds1da177e2005-04-16 15:20:36 -070090 value = data_in[pos++];
91 cpage_out[outpos++] = value; /* first the verbatim copied byte */
92 repeat = data_in[pos++];
93 backoffs = positions[value];
Thomas Gleixner182ec4e2005-11-07 11:16:07 +000094
Linus Torvalds1da177e2005-04-16 15:20:36 -070095 positions[value]=outpos;
96 if (repeat) {
97 if (backoffs + repeat >= outpos) {
98 while(repeat) {
99 cpage_out[outpos++] = cpage_out[backoffs++];
100 repeat--;
101 }
102 } else {
103 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
Thomas Gleixner182ec4e2005-11-07 11:16:07 +0000104 outpos+=repeat;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700105 }
106 }
107 }
David Woodhouseef53cb02007-07-10 10:01:22 +0100108 return 0;
Thomas Gleixner182ec4e2005-11-07 11:16:07 +0000109}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110
111static struct jffs2_compressor jffs2_rtime_comp = {
112 .priority = JFFS2_RTIME_PRIORITY,
113 .name = "rtime",
114 .compr = JFFS2_COMPR_RTIME,
115 .compress = &jffs2_rtime_compress,
116 .decompress = &jffs2_rtime_decompress,
117#ifdef JFFS2_RTIME_DISABLED
118 .disabled = 1,
119#else
120 .disabled = 0,
121#endif
122};
123
124int jffs2_rtime_init(void)
125{
126 return jffs2_register_compressor(&jffs2_rtime_comp);
127}
128
129void jffs2_rtime_exit(void)
130{
131 jffs2_unregister_compressor(&jffs2_rtime_comp);
132}