Root/fs/jffs2/compr_rtime.c

1/*
2 * JFFS2 -- Journalling Flash File System, Version 2.
3 *
4 * Copyright © 2001-2007 Red Hat, Inc.
5 *
6 * Created by Arjan van de Ven <arjanv@redhat.com>
7 *
8 * For licensing information, see the file 'LICENCE' in this directory.
9 *
10 *
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>
26#include <linux/string.h>
27#include <linux/jffs2.h>
28#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
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
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;
81
82    memset(positions,0,sizeof(positions));
83
84    while (outpos<destlen) {
85        unsigned char value;
86        int backoffs;
87        int repeat;
88
89        value = data_in[pos++];
90        cpage_out[outpos++] = value; /* first the verbatim copied byte */
91        repeat = data_in[pos++];
92        backoffs = positions[value];
93
94        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);
103                outpos+=repeat;
104            }
105        }
106    }
107    return 0;
108}
109
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}
132

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