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 */
jffs2_rtime_compress(unsigned char * data_in,unsigned char * cpage_out,uint32_t * sourcelen,uint32_t * dstlen)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 memset(positions,0,sizeof(positions));
41
42 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
43 int backpos, runlen=0;
44 unsigned char value;
45
46 value = data_in[pos];
47
48 cpage_out[outpos++] = data_in[pos++];
49
50 backpos = positions[value];
51 positions[value]=pos;
52
53 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 }
65
66 /* Tell the caller how much we managed to compress, and how much space it took */
67 *sourcelen = pos;
68 *dstlen = outpos;
69 return 0;
70 }
71
72
jffs2_rtime_decompress(unsigned char * data_in,unsigned char * cpage_out,uint32_t srclen,uint32_t destlen)73 static int jffs2_rtime_decompress(unsigned char *data_in,
74 unsigned char *cpage_out,
75 uint32_t srclen, uint32_t destlen)
76 {
77 unsigned short positions[256];
78 int outpos = 0;
79 int pos=0;
80
81 memset(positions,0,sizeof(positions));
82
83 while (outpos<destlen) {
84 unsigned char value;
85 int backoffs;
86 int repeat;
87
88 value = data_in[pos++];
89 cpage_out[outpos++] = value; /* first the verbatim copied byte */
90 repeat = data_in[pos++];
91 backoffs = positions[value];
92
93 positions[value]=outpos;
94 if (repeat) {
95 if (backoffs + repeat >= outpos) {
96 while(repeat) {
97 cpage_out[outpos++] = cpage_out[backoffs++];
98 repeat--;
99 }
100 } else {
101 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
102 outpos+=repeat;
103 }
104 }
105 }
106 return 0;
107 }
108
109 static struct jffs2_compressor jffs2_rtime_comp = {
110 .priority = JFFS2_RTIME_PRIORITY,
111 .name = "rtime",
112 .compr = JFFS2_COMPR_RTIME,
113 .compress = &jffs2_rtime_compress,
114 .decompress = &jffs2_rtime_decompress,
115 #ifdef JFFS2_RTIME_DISABLED
116 .disabled = 1,
117 #else
118 .disabled = 0,
119 #endif
120 };
121
jffs2_rtime_init(void)122 int jffs2_rtime_init(void)
123 {
124 return jffs2_register_compressor(&jffs2_rtime_comp);
125 }
126
jffs2_rtime_exit(void)127 void jffs2_rtime_exit(void)
128 {
129 jffs2_unregister_compressor(&jffs2_rtime_comp);
130 }
131