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133 lines
2.9 KiB
133 lines
2.9 KiB
/* |
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* JFFS2 -- Journalling Flash File System, Version 2. |
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* |
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* Copyright © 2001-2007 Red Hat, Inc. |
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* Copyright © 2004-2010 David Woodhouse <[email protected]> |
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* |
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* Created by Arjan van de Ven <[email protected]> |
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* |
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* For licensing information, see the file 'LICENCE' in this directory. |
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* |
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* |
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* |
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* Very simple lz77-ish encoder. |
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* |
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* Theory of operation: Both encoder and decoder have a list of "last |
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* occurrences" for every possible source-value; after sending the |
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* first source-byte, the second byte indicated the "run" length of |
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* matches |
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* |
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* The algorithm is intended to only send "whole bytes", no bit-messing. |
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* |
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*/ |
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#include <linux/kernel.h> |
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#include <linux/types.h> |
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#include <linux/errno.h> |
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#include <linux/string.h> |
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#include <linux/jffs2.h> |
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#include "compr.h" |
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/* _compress returns the compressed size, -1 if bigger */ |
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static int jffs2_rtime_compress(unsigned char *data_in, |
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unsigned char *cpage_out, |
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uint32_t *sourcelen, uint32_t *dstlen) |
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{ |
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unsigned short positions[256]; |
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int outpos = 0; |
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int pos=0; |
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if (*dstlen <= 3) |
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return -1; |
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memset(positions,0,sizeof(positions)); |
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while (pos < (*sourcelen) && outpos <= (*dstlen)-2) { |
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int backpos, runlen=0; |
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unsigned char value; |
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value = data_in[pos]; |
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cpage_out[outpos++] = data_in[pos++]; |
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backpos = positions[value]; |
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positions[value]=pos; |
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while ((backpos < pos) && (pos < (*sourcelen)) && |
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(data_in[pos]==data_in[backpos++]) && (runlen<255)) { |
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pos++; |
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runlen++; |
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} |
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cpage_out[outpos++] = runlen; |
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} |
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if (outpos >= pos) { |
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/* We failed */ |
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return -1; |
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} |
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/* Tell the caller how much we managed to compress, and how much space it took */ |
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*sourcelen = pos; |
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*dstlen = outpos; |
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return 0; |
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} |
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static int jffs2_rtime_decompress(unsigned char *data_in, |
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unsigned char *cpage_out, |
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uint32_t srclen, uint32_t destlen) |
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{ |
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unsigned short positions[256]; |
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int outpos = 0; |
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int pos=0; |
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memset(positions,0,sizeof(positions)); |
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while (outpos<destlen) { |
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unsigned char value; |
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int backoffs; |
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int repeat; |
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value = data_in[pos++]; |
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cpage_out[outpos++] = value; /* first the verbatim copied byte */ |
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repeat = data_in[pos++]; |
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backoffs = positions[value]; |
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positions[value]=outpos; |
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if (repeat) { |
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if (backoffs + repeat >= outpos) { |
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while(repeat) { |
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cpage_out[outpos++] = cpage_out[backoffs++]; |
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repeat--; |
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} |
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} else { |
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memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat); |
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outpos+=repeat; |
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} |
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} |
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} |
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return 0; |
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} |
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static struct jffs2_compressor jffs2_rtime_comp = { |
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.priority = JFFS2_RTIME_PRIORITY, |
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.name = "rtime", |
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.compr = JFFS2_COMPR_RTIME, |
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.compress = &jffs2_rtime_compress, |
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.decompress = &jffs2_rtime_decompress, |
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#ifdef JFFS2_RTIME_DISABLED |
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.disabled = 1, |
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#else |
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.disabled = 0, |
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#endif |
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}; |
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int jffs2_rtime_init(void) |
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{ |
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return jffs2_register_compressor(&jffs2_rtime_comp); |
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} |
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void jffs2_rtime_exit(void) |
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{ |
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jffs2_unregister_compressor(&jffs2_rtime_comp); |
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}
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