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 */
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
41	memset(positions,0,sizeof(positions));
42
43	while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
44		int backpos, runlen=0;
45		unsigned char value;
46
47		value = data_in[pos];
48
49		cpage_out[outpos++] = data_in[pos++];
50
51		backpos = positions[value];
52		positions[value]=pos;
53
54		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	}
66
67	/* Tell the caller how much we managed to compress, and how much space it took */
68	*sourcelen = pos;
69	*dstlen = outpos;
70	return 0;
71}
72
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;
82
83	memset(positions,0,sizeof(positions));
84
85	while (outpos<destlen) {
86		unsigned char value;
87		int backoffs;
88		int repeat;
89
90		value = data_in[pos++];
91		cpage_out[outpos++] = value; /* first the verbatim copied byte */
92		repeat = data_in[pos++];
93		backoffs = positions[value];
94
95		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);
104				outpos+=repeat;
105			}
106		}
107	}
108	return 0;
109}
110
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}
133