134 lines
2.9 KiB
C
134 lines
2.9 KiB
C
/*
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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 <dwmw2@infradead.org>
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*
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* Created by Arjan van de Ven <arjanv@redhat.com>
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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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