fs/jffs2/compr_rtime.c

   1 /*
   2  * JFFS2 -- Journalling Flash File System, Version 2.
   3  *
   4  * Copyright (C) 2001-2003 Red Hat, Inc.
   5  *
   6  * Created by Arjan van de Ven <arjanv@redhat.com>
   7  *
   8  * For licensing information, see the file 'LICENCE' in this directory.
   9  *
  10  * $Id: compr_rtime.c,v 1.14 2004/06/23 16:34:40 havasi Exp $
  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 */
  32 int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out,
  33                    uint32_t *sourcelen, uint32_t *dstlen, void *model)
  34 {
  35         short positions[256];
  36         int outpos = 0;
  37         int pos=0;
  38
  39         memset(positions,0,sizeof(positions));
  40
  41         while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
  42                 int backpos, runlen=0;
  43                 unsigned char value;
  44
  45                 value = data_in[pos];
  46
  47                 cpage_out[outpos++] = data_in[pos++];
  48
  49                 backpos = positions[value];
  50                 positions[value]=pos;
  51
  52                 while ((backpos < pos) && (pos < (*sourcelen)) &&
  53                        (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
  54                         pos++;
  55                         runlen++;
  56                 }
  57                 cpage_out[outpos++] = runlen;
  58         }
  59
  60         if (outpos >= pos) {
  61                 /* We failed */
  62                 return -1;
  63         }
  64
  65         /* Tell the caller how much we managed to compress, and how much space it took */
  66         *sourcelen = pos;
  67         *dstlen = outpos;
  68         return 0;
  69 }
  70
  71
  72 int jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
  73                       uint32_t srclen, uint32_t destlen, void *model)
  74 {
  75         short positions[256];
  76         int outpos = 0;
  77         int pos=0;
  78
  79         memset(positions,0,sizeof(positions));
  80
  81         while (outpos<destlen) {
  82                 unsigned char value;
  83                 int backoffs;
  84                 int repeat;
  85
  86                 value = data_in[pos++];
  87                 cpage_out[outpos++] = value; /* first the verbatim copied byte */
  88                 repeat = data_in[pos++];
  89                 backoffs = positions[value];
  90
  91                 positions[value]=outpos;
  92                 if (repeat) {
  93                         if (backoffs + repeat >= outpos) {
  94                                 while(repeat) {
  95                                         cpage_out[outpos++] = cpage_out[backoffs++];
  96                                         repeat--;
  97                                 }
  98                         } else {
  99                                 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
 100                                 outpos+=repeat;
 101                         }
 102                 }
 103         }
 104         return 0;
 105 }
 106
 107 static struct jffs2_compressor jffs2_rtime_comp = {
 108     .priority = JFFS2_RTIME_PRIORITY,
 109     .name = "rtime",
 110     .compr = JFFS2_COMPR_RTIME,
 111     .compress = &jffs2_rtime_compress,
 112     .decompress = &jffs2_rtime_decompress,
 113 #ifdef JFFS2_RTIME_DISABLED
 114     .disabled = 1,
 115 #else
 116     .disabled = 0,
 117 #endif
 118 };
 119
 120 int jffs2_rtime_init(void)
 121 {
 122     return jffs2_register_compressor(&jffs2_rtime_comp);
 123 }
 124
 125 void jffs2_rtime_exit(void)
 126 {
 127     jffs2_unregister_compressor(&jffs2_rtime_comp);
 128 }