1 /* 2 * JFFS2 -- Journalling Flash File System, Version 2. 3 * 4 * Copyright © 2001-2007 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 * 11 * 12 * Very simple lz77-ish encoder. 13 * 14 * Theory of operation: Both encoder and decoder have a list of "last 15 * occurrences" for every possible source-value; after sending the 16 * first source-byte, the second byte indicated the "run" length of 17 * matches 18 * 19 * The algorithm is intended to only send "whole bytes", no bit-messing. 20 * 21 */ 22 23 #include <linux/kernel.h> 24 #include <linux/types.h> 25 #include <linux/errno.h> 26 #include <linux/string.h> 27 #include <linux/jffs2.h> 28 #include "compr.h" 29 30 /* _compress returns the compressed size, -1 if bigger */ 31 static int jffs2_rtime_compress(unsigned char *data_in, 32 unsigned char *cpage_out, 33 uint32_t *sourcelen, uint32_t *dstlen, 34 void *model) 35 { 36 short positions[256]; 37 int outpos = 0; 38 int pos=0; 39 40 memset(positions,0,sizeof(positions)); 41 42 while (pos < (*sourcelen) && outpos <= (*dstlen)-2) { 43 int backpos, runlen=0; 44 unsigned char value; 45 46 value = data_in[pos]; 47 48 cpage_out[outpos++] = data_in[pos++]; 49 50 backpos = positions[value]; 51 positions[value]=pos; 52 53 while ((backpos < pos) && (pos < (*sourcelen)) && 54 (data_in[pos]==data_in[backpos++]) && (runlen<255)) { 55 pos++; 56 runlen++; 57 } 58 cpage_out[outpos++] = runlen; 59 } 60 61 if (outpos >= pos) { 62 /* We failed */ 63 return -1; 64 } 65 66 /* Tell the caller how much we managed to compress, and how much space it took */ 67 *sourcelen = pos; 68 *dstlen = outpos; 69 return 0; 70 } 71 72 73 static int jffs2_rtime_decompress(unsigned char *data_in, 74 unsigned char *cpage_out, 75 uint32_t srclen, uint32_t destlen, 76 void *model) 77 { 78 short positions[256]; 79 int outpos = 0; 80 int pos=0; 81 82 memset(positions,0,sizeof(positions)); 83 84 while (outpos<destlen) { 85 unsigned char value; 86 int backoffs; 87 int repeat; 88 89 value = data_in[pos++]; 90 cpage_out[outpos++] = value; /* first the verbatim copied byte */ 91 repeat = data_in[pos++]; 92 backoffs = positions[value]; 93 94 positions[value]=outpos; 95 if (repeat) { 96 if (backoffs + repeat >= outpos) { 97 while(repeat) { 98 cpage_out[outpos++] = cpage_out[backoffs++]; 99 repeat--; 100 } 101 } else { 102 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat); 103 outpos+=repeat; 104 } 105 } 106 } 107 return 0; 108 } 109 110 static struct jffs2_compressor jffs2_rtime_comp = { 111 .priority = JFFS2_RTIME_PRIORITY, 112 .name = "rtime", 113 .compr = JFFS2_COMPR_RTIME, 114 .compress = &jffs2_rtime_compress, 115 .decompress = &jffs2_rtime_decompress, 116 #ifdef JFFS2_RTIME_DISABLED 117 .disabled = 1, 118 #else 119 .disabled = 0, 120 #endif 121 }; 122 123 int jffs2_rtime_init(void) 124 { 125 return jffs2_register_compressor(&jffs2_rtime_comp); 126 } 127 128 void jffs2_rtime_exit(void) 129 { 130 jffs2_unregister_compressor(&jffs2_rtime_comp); 131 } 132