mppc.c

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/* -*- c-basic-offset: 8 -*-
   rdesktop: A Remote Desktop Protocol client.
   Protocol services - RDP decompression
   Copyright (C) Matthew Chapman 1999-2005

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License along
   with this program; if not, write to the Free Software Foundation, Inc.,
   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#include <precomp.h>

/* mppc decompression                       */
/* http://www.faqs.org/rfcs/rfc2118.html    */

/* Contacts:                                */

/* hifn contact mentioned in the faq is     */
/* Robert Friend rfriend at hifn dot com    */

/* if you have questions regarding MPPC     */
/* our contact is                           */
/* Guus Dhaeze  GDhaeze at hifn dot com     */

/* Licensing:                               */

/* decompression is alright as long as we   */
/* don't compress data                      */

/* Algorithm: */

/* as the rfc states the algorithm seems to */
/* be LZ77 with a sliding buffer            */
/* that is empty at init.                   */

/* the algorithm is called LZS and is       */
/* patented for another couple of years.    */

/* more information is available in         */
/* http://www.ietf.org/ietf/IPR/hifn-ipr-draft-friend-tls-lzs-compression.txt */


RDPCOMP g_mppc_dict;

int
mppc_expand(uint8 * data, uint32 clen, uint8 ctype, uint32 * roff, uint32 * rlen)
{
    int k, walker_len = 0, walker;
    uint32 i = 0;
    int next_offset, match_off;
    int match_len;
    int old_offset, match_bits;
    BOOL big = ctype & RDP_MPPC_BIG ? True : False;

    uint8 *dict = g_mppc_dict.hist;

    if ((ctype & RDP_MPPC_COMPRESSED) == 0)
    {
        *roff = 0;
        *rlen = clen;
        return 0;
    }

    if ((ctype & RDP_MPPC_RESET) != 0)
    {
        g_mppc_dict.roff = 0;
    }

    if ((ctype & RDP_MPPC_FLUSH) != 0)
    {
        memset(dict, 0, RDP_MPPC_DICT_SIZE);
        g_mppc_dict.roff = 0;
    }

    *roff = 0;
    *rlen = 0;

    walker = g_mppc_dict.roff;

    next_offset = walker;
    old_offset = next_offset;
    *roff = old_offset;
    if (clen == 0)
        return 0;
    clen += i;

    do
    {
        if (walker_len == 0)
        {
            if (i >= clen)
                break;
            walker = data[i++] << 24;
            walker_len = 8;
        }
        if (walker >= 0)
        {
            if (walker_len < 8)
            {
                if (i >= clen)
                {
                    if (walker != 0)
                        return -1;
                    break;
                }
                walker |= (data[i++] & 0xff) << (24 - walker_len);
                walker_len += 8;
            }
            if (next_offset >= RDP_MPPC_DICT_SIZE)
                return -1;
            dict[next_offset++] = (((uint32) walker) >> ((uint32) 24));
            walker <<= 8;
            walker_len -= 8;
            continue;
        }
        walker <<= 1;
        /* fetch next 8-bits */
        if (--walker_len == 0)
        {
            if (i >= clen)
                return -1;
            walker = data[i++] << 24;
            walker_len = 8;
        }
        /* literal decoding */
        if (walker >= 0)
        {
            if (walker_len < 8)
            {
                if (i >= clen)
                    return -1;
                walker |= (data[i++] & 0xff) << (24 - walker_len);
                walker_len += 8;
            }
            if (next_offset >= RDP_MPPC_DICT_SIZE)
                return -1;
            dict[next_offset++] = (uint8) (walker >> 24 | 0x80);
            walker <<= 8;
            walker_len -= 8;
            continue;
        }

        /* decode offset  */
        /* length pair    */
        walker <<= 1;
        if (--walker_len < (big ? 3 : 2))
        {
            if (i >= clen)
                return -1;
            walker |= (data[i++] & 0xff) << (24 - walker_len);
            walker_len += 8;
        }

        if (big)
        {
            /* offset decoding where offset len is:
               -63: 11111 followed by the lower 6 bits of the value
               64-319: 11110 followed by the lower 8 bits of the value ( value - 64 )
               320-2367: 1110 followed by lower 11 bits of the value ( value - 320 )
               2368-65535: 110 followed by lower 16 bits of the value ( value - 2368 )
             */
            switch (((uint32) walker) >> ((uint32) 29))
            {
                case 7: /* - 63 */
                    for (; walker_len < 9; walker_len += 8)
                    {
                        if (i >= clen)
                            return -1;
                        walker |= (data[i++] & 0xff) << (24 - walker_len);
                    }
                    walker <<= 3;
                    match_off = ((uint32) walker) >> ((uint32) 26);
                    walker <<= 6;
                    walker_len -= 9;
                    break;

                case 6: /* 64 - 319 */
                    for (; walker_len < 11; walker_len += 8)
                    {
                        if (i >= clen)
                            return -1;
                        walker |= (data[i++] & 0xff) << (24 - walker_len);
                    }

                    walker <<= 3;
                    match_off = (((uint32) walker) >> ((uint32) 24)) + 64;
                    walker <<= 8;
                    walker_len -= 11;
                    break;

                case 5:
                case 4: /* 320 - 2367 */
                    for (; walker_len < 13; walker_len += 8)
                    {
                        if (i >= clen)
                            return -1;
                        walker |= (data[i++] & 0xff) << (24 - walker_len);
                    }

                    walker <<= 2;
                    match_off = (((uint32) walker) >> ((uint32) 21)) + 320;
                    walker <<= 11;
                    walker_len -= 13;
                    break;

                default:    /* 2368 - 65535 */
                    for (; walker_len < 17; walker_len += 8)
                    {
                        if (i >= clen)
                            return -1;
                        walker |= (data[i++] & 0xff) << (24 - walker_len);
                    }

                    walker <<= 1;
                    match_off = (((uint32) walker) >> ((uint32) 16)) + 2368;
                    walker <<= 16;
                    walker_len -= 17;
                    break;
            }
        }
        else
        {
            /* offset decoding where offset len is:
               -63: 1111 followed by the lower 6 bits of the value
               64-319: 1110 followed by the lower 8 bits of the value ( value - 64 )
               320-8191: 110 followed by the lower 13 bits of the value ( value - 320 )
             */
            switch (((uint32) walker) >> ((uint32) 30))
            {
                case 3: /* - 63 */
                    if (walker_len < 8)
                    {
                        if (i >= clen)
                            return -1;
                        walker |= (data[i++] & 0xff) << (24 - walker_len);
                        walker_len += 8;
                    }
                    walker <<= 2;
                    match_off = ((uint32) walker) >> ((uint32) 26);
                    walker <<= 6;
                    walker_len -= 8;
                    break;

                case 2: /* 64 - 319 */
                    for (; walker_len < 10; walker_len += 8)
                    {
                        if (i >= clen)
                            return -1;
                        walker |= (data[i++] & 0xff) << (24 - walker_len);
                    }

                    walker <<= 2;
                    match_off = (((uint32) walker) >> ((uint32) 24)) + 64;
                    walker <<= 8;
                    walker_len -= 10;
                    break;

                default:    /* 320 - 8191 */
                    for (; walker_len < 14; walker_len += 8)
                    {
                        if (i >= clen)
                            return -1;
                        walker |= (data[i++] & 0xff) << (24 - walker_len);
                    }

                    match_off = (walker >> 18) + 320;
                    walker <<= 14;
                    walker_len -= 14;
                    break;
            }
        }
        if (walker_len == 0)
        {
            if (i >= clen)
                return -1;
            walker = data[i++] << 24;
            walker_len = 8;
        }

        /* decode length of match */
        match_len = 0;
        if (walker >= 0)
        {       /* special case - length of 3 is in bit 0 */
            match_len = 3;
            walker <<= 1;
            walker_len--;
        }
        else
        {
            /* this is how it works len of:
               4-7: 10 followed by 2 bits of the value
               8-15: 110 followed by 3 bits of the value
               16-31: 1110 followed by 4 bits of the value
               32-63: .... and so forth
               64-127:
               128-255:
               256-511:
               512-1023:
               1024-2047:
               2048-4095:
               4096-8191:

               i.e. 4097 is encoded as: 111111111110 000000000001
               meaning 4096 + 1...
             */
            match_bits = big ? 14 : 11; /* 11 or 14 bits of value at most */
            do
            {
                walker <<= 1;
                if (--walker_len == 0)
                {
                    if (i >= clen)
                        return -1;
                    walker = data[i++] << 24;
                    walker_len = 8;
                }
                if (walker >= 0)
                    break;
                if (--match_bits == 0)
                {
                    return -1;
                }
            }
            while (1);
            match_len = (big ? 16 : 13) - match_bits;
            walker <<= 1;
            if (--walker_len < match_len)
            {
                for (; walker_len < match_len; walker_len += 8)
                {
                    if (i >= clen)
                    {
                        return -1;
                    }
                    walker |= (data[i++] & 0xff) << (24 - walker_len);
                }
            }

            match_bits = match_len;
            match_len =
                ((walker >> (32 - match_bits)) & (~(-1 << match_bits))) | (1 <<
                                               match_bits);
            walker <<= match_bits;
            walker_len -= match_bits;
        }
        if (next_offset + match_len >= RDP_MPPC_DICT_SIZE)
        {
            return -1;
        }
        /* memory areas can overlap - meaning we can't use memXXX functions */
        k = (next_offset - match_off) & (big ? 65535 : 8191);
        do
        {
            dict[next_offset++] = dict[k++];
        }
        while (--match_len != 0);
    }
    while (1);

    /* store history offset */
    g_mppc_dict.roff = next_offset;

    *roff = old_offset;
    *rlen = next_offset - old_offset;

    return 0;
}