1 /* 2 * JFFS2 -- Journalling Flash File System, Version 2. 3 * 4 * Copyright © 2001-2007 Red Hat, Inc. 5 * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org> 6 * 7 * Created by Arjan van de Ven <arjanv@redhat.com> 8 * 9 * For licensing information, see the file 'LICENCE' in this directory. 10 * 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 { 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 { 77 short positions[256]; 78 int outpos = 0; 79 int pos=0; 80 81 memset(positions,0,sizeof(positions)); 82 83 while (outpos<destlen) { 84 unsigned char value; 85 int backoffs; 86 int repeat; 87 88 value = data_in[pos++]; 89 cpage_out[outpos++] = value; /* first the verbatim copied byte */ 90 repeat = data_in[pos++]; 91 backoffs = positions[value]; 92 93 positions[value]=outpos; 94 if (repeat) { 95 if (backoffs + repeat >= outpos) { 96 while(repeat) { 97 cpage_out[outpos++] = cpage_out[backoffs++]; 98 repeat--; 99 } 100 } else { 101 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat); 102 outpos+=repeat; 103 } 104 } 105 } 106 return 0; 107 } 108 109 static struct jffs2_compressor jffs2_rtime_comp = { 110 .priority = JFFS2_RTIME_PRIORITY, 111 .name = "rtime", 112 .compr = JFFS2_COMPR_RTIME, 113 .compress = &jffs2_rtime_compress, 114 .decompress = &jffs2_rtime_decompress, 115 #ifdef JFFS2_RTIME_DISABLED 116 .disabled = 1, 117 #else 118 .disabled = 0, 119 #endif 120 }; 121 122 int jffs2_rtime_init(void) 123 { 124 return jffs2_register_compressor(&jffs2_rtime_comp); 125 } 126 127 void jffs2_rtime_exit(void) 128 { 129 jffs2_unregister_compressor(&jffs2_rtime_comp); 130 } 131