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	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
76static 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
112static 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
125int jffs2_rtime_init(void)
126{
127    return jffs2_register_compressor(&jffs2_rtime_comp);
128}
129
130void jffs2_rtime_exit(void)
131{
132    jffs2_unregister_compressor(&jffs2_rtime_comp);
133}
134