fs/jffs2/compr_rtime.c

   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 1.2 2002/01/24 22:58:42 rfeany 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 <config.h>
  49 #if defined(CONFIG_CMD_JFFS2)
  50
  51 #include <jffs2/jffs2.h>
  52
  53 void rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
  54                       u32 srclen, u32 destlen)
  55 {
  56         int positions[256];
  57         int outpos;
  58         int pos;
  59         int i;
  60
  61         outpos = pos = 0;
  62
  63         for (i = 0; i < 256; positions[i++] = 0);
  64
  65         while (outpos<destlen) {
  66                 unsigned char value;
  67                 int backoffs;
  68                 int repeat;
  69
  70                 value = data_in[pos++];
  71                 cpage_out[outpos++] = value; /* first the verbatim copied byte */
  72                 repeat = data_in[pos++];
  73                 backoffs = positions[value];
  74
  75                 positions[value]=outpos;
  76                 if (repeat) {
  77                         if (backoffs + repeat >= outpos) {
  78                                 while(repeat) {
  79                                         cpage_out[outpos++] = cpage_out[backoffs++];
  80                                         repeat--;
  81                                 }
  82                         } else {
  83                                 for (i = 0; i < repeat; i++)
  84                                         *(cpage_out + outpos + i) = *(cpage_out + backoffs + i);
  85                                 outpos+=repeat;
  86                         }
  87                 }
  88         }
  89 }
  90
  91 #endif