1 /*
2 * JFFS2 -- Journalling Flash File System, Version 2.
3 *
4 * Copyright © 2001-2007 Red Hat, Inc.
5 * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
6 *
7 * Created by Arjan van de Ven <arjanv@redhat.com>
8 *
9 * For licensing information, see the file 'LICENCE' in this directory.
10 *
11 *
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>
27 #include <linux/string.h>
28 #include <linux/jffs2.h>
29 #include "compr.h"
30
31 /* _compress returns the compressed size, -1 if bigger */
32 static int jffs2_rtime_compress(unsigned char *data_in,
33 unsigned char *cpage_out,
34 uint32_t *sourcelen, uint32_t *dstlen)
35 {
36 unsigned short positions[256];
37 int outpos = 0;
38 int pos=0;
39
40 if (*dstlen <= 3)
41 return -1;
42
43 memset(positions,0,sizeof(positions));
44
45 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
46 int backpos, runlen=0;
47 unsigned char value;
48
49 value = data_in[pos];
50
51 cpage_out[outpos++] = data_in[pos++];
52
53 backpos = positions[value];
54 positions[value]=pos;
55
56 while ((backpos < pos) && (pos < (*sourcelen)) &&
57 (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
58 pos++;
59 runlen++;
60 }
61 cpage_out[outpos++] = runlen;
62 }
63
64 if (outpos >= pos) {
65 /* We failed */
66 return -1;
67 }
68
69 /* Tell the caller how much we managed to compress, and how much space it took */
70 *sourcelen = pos;
71 *dstlen = outpos;
72 return 0;
73 }
74
75
76 static int jffs2_rtime_decompress(unsigned char *data_in,
77 unsigned char *cpage_out,
78 uint32_t srclen, uint32_t destlen)
79 {
80 unsigned short positions[256];
81 int outpos = 0;
82 int pos=0;
83
84 memset(positions,0,sizeof(positions));
85
86 while (outpos<destlen) {
87 unsigned char value;
88 int backoffs;
89 int repeat;
90
91 value = data_in[pos++];
92 cpage_out[outpos++] = value; /* first the verbatim copied byte */
93 repeat = data_in[pos++];
94 backoffs = positions[value];
95
96 positions[value]=outpos;
97 if (repeat) {
98 if (backoffs + repeat >= outpos) {
99 while(repeat) {
100 cpage_out[outpos++] = cpage_out[backoffs++];
101 repeat--;
102 }
103 } else {
104 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
105 outpos+=repeat;
106 }
107 }
108 }
109 return 0;
110 }
111
112 static struct jffs2_compressor jffs2_rtime_comp = {
113 .priority = JFFS2_RTIME_PRIORITY,
114 .name = "rtime",
115 .compr = JFFS2_COMPR_RTIME,
116 .compress = &jffs2_rtime_compress,
117 .decompress = &jffs2_rtime_decompress,
118 #ifdef JFFS2_RTIME_DISABLED
119 .disabled = 1,
120 #else
121 .disabled = 0,
122 #endif
123 };
124
125 int jffs2_rtime_init(void)
126 {
127 return jffs2_register_compressor(&jffs2_rtime_comp);
128 }
129
130 void jffs2_rtime_exit(void)
131 {
132 jffs2_unregister_compressor(&jffs2_rtime_comp);
133 }
134
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