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 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 static struct jffs2_compressor jffs2_rtime_comp = { 112 .priority = JFFS2_RTIME_PRIORITY, 113 .name = "rtime", 114 .compr = JFFS2_COMPR_RTIME, 115 .compress = &jffs2_rtime_compress, 116 .decompress = &jffs2_rtime_decompress, 117 #ifdef JFFS2_RTIME_DISABLED 118 .disabled = 1, 119 #else 120 .disabled = 0, 121 #endif 122 }; 123 124 int jffs2_rtime_init(void) 125 { 126 return jffs2_register_compressor(&jffs2_rtime_comp); 127 } 128 129 void jffs2_rtime_exit(void) 130 { 131 jffs2_unregister_compressor(&jffs2_rtime_comp); 132 } 133