1 /*
2 * JFFS2 -- Journalling Flash File System, Version 2.
3 *
4 * Copyright (C) 2001 Red Hat, Inc.
5 *
6 * Created by Arjan van de Ven <arjanv@redhat.com>
7 *
8 * The original JFFS, from which the design for JFFS2 was derived,
9 * was designed and implemented by Axis Communications AB.
10 *
11 * The contents of this file are subject to the Red Hat eCos Public
12 * License Version 1.1 (the "Licence"); you may not use this file
13 * except in compliance with the Licence. You may obtain a copy of
14 * the Licence at http://www.redhat.com/
15 *
16 * Software distributed under the Licence is distributed on an "AS IS"
17 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.
18 * See the Licence for the specific language governing rights and
19 * limitations under the Licence.
20 *
21 * The Original Code is JFFS2 - Journalling Flash File System, version 2
22 *
23 * Alternatively, the contents of this file may be used under the
24 * terms of the GNU General Public License version 2 (the "GPL"), in
25 * which case the provisions of the GPL are applicable instead of the
26 * above. If you wish to allow the use of your version of this file
27 * only under the terms of the GPL and not to allow others to use your
28 * version of this file under the RHEPL, indicate your decision by
29 * deleting the provisions above and replace them with the notice and
30 * other provisions required by the GPL. If you do not delete the
31 * provisions above, a recipient may use your version of this file
32 * under either the RHEPL or the GPL.
33 *
34 * $Id: compr_rtime.c,v 1.5 2001/03/15 15:38:23 dwmw2 Exp $
35 *
36 *
37 * Very simple lz77-ish encoder.
38 *
39 * Theory of operation: Both encoder and decoder have a list of "last
40 * occurances" for every possible source-value; after sending the
41 * first source-byte, the second byte indicated the "run" length of
42 * matches
43 *
44 * The algorithm is intended to only send "whole bytes", no bit-messing.
45 *
46 */
47
48 #include <linux/kernel.h>
49 #include <linux/types.h>
50 #include <linux/errno.h>
51 #include <linux/string.h>
52
53 /* _compress returns the compressed size, -1 if bigger */
rtime_compress(unsigned char * data_in,unsigned char * cpage_out,__u32 * sourcelen,__u32 * dstlen)54 int rtime_compress(unsigned char *data_in, unsigned char *cpage_out,
55 __u32 *sourcelen, __u32 *dstlen)
56 {
57 int positions[256];
58 int outpos = 0;
59 int pos=0;
60
61 memset(positions,0,sizeof(positions));
62
63 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
64 int backpos, runlen=0;
65 unsigned char value;
66
67 value = data_in[pos];
68
69 cpage_out[outpos++] = data_in[pos++];
70
71 backpos = positions[value];
72 positions[value]=pos;
73
74 while ((backpos < pos) && (pos < (*sourcelen)) &&
75 (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
76 pos++;
77 runlen++;
78 }
79 cpage_out[outpos++] = runlen;
80 }
81
82 if (outpos >= pos) {
83 /* We failed */
84 return -1;
85 }
86
87 /* Tell the caller how much we managed to compress, and how much space it took */
88 *sourcelen = pos;
89 *dstlen = outpos;
90 return 0;
91 }
92
93
rtime_decompress(unsigned char * data_in,unsigned char * cpage_out,__u32 srclen,__u32 destlen)94 void rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
95 __u32 srclen, __u32 destlen)
96 {
97 int positions[256];
98 int outpos = 0;
99 int pos=0;
100
101 memset(positions,0,sizeof(positions));
102
103 while (outpos<destlen) {
104 unsigned char value;
105 int backoffs;
106 int repeat;
107
108 value = data_in[pos++];
109 cpage_out[outpos++] = value; /* first the verbatim copied byte */
110 repeat = data_in[pos++];
111 backoffs = positions[value];
112
113 positions[value]=outpos;
114 if (repeat) {
115 if (backoffs + repeat >= outpos) {
116 while(repeat) {
117 cpage_out[outpos++] = cpage_out[backoffs++];
118 repeat--;
119 }
120 } else {
121 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
122 outpos+=repeat;
123 }
124 }
125 }
126 }
127
128
129