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[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [packages/] [fs/] [jffs2/] [v2_0/] [src/] [compr_rtime.c] - Blame information for rev 27

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/*
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 * JFFS2 -- Journalling Flash File System, Version 2.
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 *
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 * Copyright (C) 2001, 2002 Red Hat, Inc.
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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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 * $Id: compr_rtime.c,v 1.1.1.1 2004-02-14 13:29:19 phoenix Exp $
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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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 * occurances" 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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/* _compress returns the compressed size, -1 if bigger */
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int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out,
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                   uint32_t *sourcelen, uint32_t *dstlen)
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{
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        int 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 (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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void jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
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                      uint32_t srclen, uint32_t destlen)
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{
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        int 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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}
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