2 * JFFS2 -- Journalling Flash File System, Version 2.
4 * Copyright (C) 2001-2003 Red Hat, Inc.
6 * Created by Arjan van de Ven <arjanv@redhat.com>
8 * For licensing information, see the file 'LICENCE' in this directory.
10 * $Id: compr_rtime.c,v 1.11 2003/10/04 08:33:06 dwmw2 Exp $
13 * Very simple lz77-ish encoder.
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
20 * The algorithm is intended to only send "whole bytes", no bit-messing.
24 #include <linux/kernel.h>
25 #include <linux/types.h>
26 #include <linux/errno.h>
27 #include <linux/string.h>
29 /* _compress returns the compressed size, -1 if bigger */
30 int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out,
31 uint32_t *sourcelen, uint32_t *dstlen)
37 memset(positions,0,sizeof(positions));
39 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
40 int backpos, runlen=0;
45 cpage_out[outpos++] = data_in[pos++];
47 backpos = positions[value];
50 while ((backpos < pos) && (pos < (*sourcelen)) &&
51 (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
55 cpage_out[outpos++] = runlen;
63 /* Tell the caller how much we managed to compress, and how much space it took */
70 void jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
71 uint32_t srclen, uint32_t destlen)
77 memset(positions,0,sizeof(positions));
79 while (outpos<destlen) {
84 value = data_in[pos++];
85 cpage_out[outpos++] = value; /* first the verbatim copied byte */
86 repeat = data_in[pos++];
87 backoffs = positions[value];
89 positions[value]=outpos;
91 if (backoffs + repeat >= outpos) {
93 cpage_out[outpos++] = cpage_out[backoffs++];
97 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);