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/*

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

 *

 * Copyright (C) 2001 Red Hat, Inc.

 *

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

 *

 * The original JFFS, from which the design for JFFS2 was derived,

 * was designed and implemented by Axis Communications AB.

 *

 * The contents of this file are subject to the Red Hat eCos Public

 * License Version 1.1 (the "Licence"); you may not use this file

 * except in compliance with the Licence.  You may obtain a copy of

 * the Licence at http://www.redhat.com/

 *

 * Software distributed under the Licence is distributed on an "AS IS"

 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.

 * See the Licence for the specific language governing rights and

 * limitations under the Licence.

 *

 * The Original Code is JFFS2 - Journalling Flash File System, version 2

 *

 * Alternatively, the contents of this file may be used under the

 * terms of the GNU General Public License version 2 (the "GPL"), in

 * which case the provisions of the GPL are applicable instead of the

 * above.  If you wish to allow the use of your version of this file

 * only under the terms of the GPL and not to allow others to use your

 * version of this file under the RHEPL, indicate your decision by

 * deleting the provisions above and replace them with the notice and

 * other provisions required by the GPL.  If you do not delete the

 * provisions above, a recipient may use your version of this file

 * under either the RHEPL or the GPL.

 *

 * $Id: compr_rtime.c,v 1.1.1.1 2004-04-15 01:11:03 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 rtime_compress(unsigned char *data_in, unsigned char *cpage_out,

                   __u32 *sourcelen, __u32 *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 rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,

                      __u32 srclen, __u32 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;

                        }

                }

        }

}