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/*

 * JFFS2 -- Journalling Flash File System, Version 2.

 *

 * Copyright (C) 2001, 2002 Red Hat, Inc.

 *

 * Created by Arjan van de Ven <arjanv@redhat.com>

 *

 * For licensing information, see the file 'LICENCE' in this directory.

 *

 * $Id: compr_rtime.c,v 1.1.1.1 2004-02-14 13:29:19 phoenix Exp $

 *

 *

 * Very simple lz77-ish encoder.

 *

 * Theory of operation: Both encoder and decoder have a list of "last

 * occurances" 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 <linux/kernel.h>

#include <linux/types.h>

#include <linux/errno.h>

#include <linux/string.h> 

/* _compress returns the compressed size, -1 if bigger */

int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out,

                   uint32_t *sourcelen, uint32_t *dstlen)

{

        int 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;

}

void jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,

                      uint32_t srclen, uint32_t destlen)

{

        int 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;

                        }

                }

        }

}