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{
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
73static 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
109static 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
122int jffs2_rtime_init(void)
123{
124    return jffs2_register_compressor(&jffs2_rtime_comp);
125}
126
127void jffs2_rtime_exit(void)
128{
129    jffs2_unregister_compressor(&jffs2_rtime_comp);
130}
131