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 <[email protected]> 7 * 8 * For licensing information, see the file 'LICENCE' in this directory. 9 * 10 * $Id: compr_rtime.c,v 1.15 2005/03/17 20:23:06 gleixner 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 static int jffs2_rtime_compress(unsigned char *data_in, 33 unsigned char *cpage_out, 34 uint32_t *sourcelen, uint32_t *dstlen, 35 void *model) 36 { 37 short positions[256]; 38 int outpos = 0; 39 int pos=0; 40 41 memset(positions,0,sizeof(positions)); 42 43 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) { 44 int backpos, runlen=0; 45 unsigned char value; 46 47 value = data_in[pos]; 48 49 cpage_out[outpos++] = data_in[pos++]; 50 51 backpos = positions[value]; 52 positions[value]=pos; 53 54 while ((backpos < pos) && (pos < (*sourcelen)) && 55 (data_in[pos]==data_in[backpos++]) && (runlen<255)) { 56 pos++; 57 runlen++; 58 } 59 cpage_out[outpos++] = runlen; 60 } 61 62 if (outpos >= pos) { 63 /* We failed */ 64 return -1; 65 } 66 67 /* Tell the caller how much we managed to compress, and how much space it took */ 68 *sourcelen = pos; 69 *dstlen = outpos; 70 return 0; 71 } 72 73 74 static int jffs2_rtime_decompress(unsigned char *data_in, 75 unsigned char *cpage_out, 76 uint32_t srclen, uint32_t destlen, 77 void *model) 78 { 79 short positions[256]; 80 int outpos = 0; 81 int pos=0; 82 83 memset(positions,0,sizeof(positions)); 84 85 while (outpos<destlen) { 86 unsigned char value; 87 int backoffs; 88 int repeat; 89 90 value = data_in[pos++]; 91 cpage_out[outpos++] = value; /* first the verbatim copied byte */ 92 repeat = data_in[pos++]; 93 backoffs = positions[value]; 94 95 positions[value]=outpos; 96 if (repeat) { 97 if (backoffs + repeat >= outpos) { 98 while(repeat) { 99 cpage_out[outpos++] = cpage_out[backoffs++]; 100 repeat--; 101 } 102 } else { 103 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat); 104 outpos+=repeat; 105 } 106 } 107 } 108 return 0; 109 } 110 111 #if defined (__GNUC__) 112 static 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 #elif defined (MSVC) 125 static struct jffs2_compressor jffs2_rtime_comp = { 126 {NULL}, 127 JFFS2_RTIME_PRIORITY,//.priority = 128 "rtime",//.name = 129 JFFS2_COMPR_RTIME,//.compr = 130 &jffs2_rtime_compress,//.compress = 131 &jffs2_rtime_decompress,//.decompress = 132 0, 133 #ifdef JFFS2_RTIME_DISABLED 134 1,//.disabled = 135 #else 136 0,//.disabled = 137 #endif 138 NULL, 139 0, 140 0, 141 0, 142 0, 143 0 144 }; 145 #else 146 #endif 147 148 int jffs2_rtime_init(void) 149 { 150 return jffs2_register_compressor(&jffs2_rtime_comp); 151 } 152 153 void jffs2_rtime_exit(void) 154 { 155 jffs2_unregister_compressor(&jffs2_rtime_comp); 156 } 157