| /* |
| * JFFS2 -- Journalling Flash File System, Version 2. |
| * |
| * Copyright (C) 2001-2003 Red Hat, Inc. |
| * |
| * Created by Arjan van de Ven <arjanv@redhat.com> |
| * |
| * For licensing information, see the file 'LICENCE' in this directory. |
| * |
| * Very simple lz77-ish encoder. |
| * |
| * Theory of operation: Both encoder and decoder have a list of "last |
| * occurrences" for every possible source-value; after sending the |
| * first source-byte, the second byte indicated the "run" length of |
| * matches |
| * |
| * The algorithm is intended to only send "whole bytes", no bit-messing. |
| * |
| */ |
| |
| #include <stdint.h> |
| #include <string.h> |
| #include "compr.h" |
| |
| /* _compress returns the compressed size, -1 if bigger */ |
| static int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out, |
| uint32_t *sourcelen, uint32_t *dstlen, void *model) |
| { |
| short positions[256]; |
| int outpos = 0; |
| int pos=0; |
| |
| memset(positions,0,sizeof(positions)); |
| |
| while (pos < (*sourcelen) && outpos <= (*dstlen)-2) { |
| int backpos, runlen=0; |
| unsigned char value; |
| |
| value = data_in[pos]; |
| |
| cpage_out[outpos++] = data_in[pos++]; |
| |
| backpos = positions[value]; |
| positions[value]=pos; |
| |
| while ((backpos < pos) && (pos < (*sourcelen)) && |
| (data_in[pos]==data_in[backpos++]) && (runlen<255)) { |
| pos++; |
| runlen++; |
| } |
| cpage_out[outpos++] = runlen; |
| } |
| |
| if (outpos >= pos) { |
| /* We failed */ |
| return -1; |
| } |
| |
| /* Tell the caller how much we managed to compress, and how much space it took */ |
| *sourcelen = pos; |
| *dstlen = outpos; |
| return 0; |
| } |
| |
| |
| static int jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out, |
| uint32_t srclen, uint32_t destlen, void *model) |
| { |
| short positions[256]; |
| int outpos = 0; |
| int pos=0; |
| |
| memset(positions,0,sizeof(positions)); |
| |
| while (outpos<destlen) { |
| unsigned char value; |
| int backoffs; |
| int repeat; |
| |
| value = data_in[pos++]; |
| cpage_out[outpos++] = value; /* first the verbatim copied byte */ |
| repeat = data_in[pos++]; |
| backoffs = positions[value]; |
| |
| positions[value]=outpos; |
| if (repeat) { |
| if (backoffs + repeat >= outpos) { |
| while(repeat) { |
| cpage_out[outpos++] = cpage_out[backoffs++]; |
| repeat--; |
| } |
| } else { |
| memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat); |
| outpos+=repeat; |
| } |
| } |
| } |
| return 0; |
| } |
| |
| |
| static struct jffs2_compressor jffs2_rtime_comp = { |
| .priority = JFFS2_RTIME_PRIORITY, |
| .name = "rtime", |
| .disabled = 0, |
| .compr = JFFS2_COMPR_RTIME, |
| .compress = &jffs2_rtime_compress, |
| .decompress = &jffs2_rtime_decompress, |
| }; |
| |
| int jffs2_rtime_init(void) |
| { |
| return jffs2_register_compressor(&jffs2_rtime_comp); |
| } |
| |
| void jffs2_rtime_exit(void) |
| { |
| jffs2_unregister_compressor(&jffs2_rtime_comp); |
| } |