xrdp-proprietary/libxrdp/xrdp_mppc_enc.c

/**
 * FreeRDP: A Remote Desktop Protocol Implementation
 * Implements Microsoft Point to Point Compression (MPPC) protocol
 *
 * Copyright 2012-2013 Laxmikant Rashinkar <LK.Rashinkar@gmail.com>
 * Copyright 2012-2013 Jay Sorg <jay.sorg@gmail.com>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#if defined(HAVE_CONFIG_H)
#include <config_ac.h>
#endif

#include "libxrdp.h"

#define MPPC_ENC_DEBUG 0

#if MPPC_ENC_DEBUG
#define DLOG(_args) g_printf _args
#else
#define DLOG(_args) do { } while (0)
#endif

/* local defines */

#define RDP_40_HIST_BUF_LEN (1024 * 8) /* RDP 4.0 uses 8K history buf */
#define RDP_50_HIST_BUF_LEN (1024 * 64) /* RDP 5.0 uses 64K history buf */

/* Compression Types */
#define PACKET_COMPRESSED       0x20
#define PACKET_AT_FRONT         0x40
#define PACKET_FLUSHED          0x80
#define PACKET_COMPR_TYPE_8K    0x00
#define PACKET_COMPR_TYPE_64K   0x01
#define PACKET_COMPR_TYPE_RDP6  0x02
#define PACKET_COMPR_TYPE_RDP61 0x03
#define CompressionTypeMask     0x0F

#define CRC_INIT 0xFFFF
#define CRC(_crcval, _newchar) _crcval = \
    ((_crcval) >> 8) ^ g_crc_table[((_crcval) ^ (_newchar)) & 0x00ff]

/* CRC16 defs */
static const tui16 g_crc_table[256] =
{
    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
    0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
    0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
    0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
    0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
    0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
    0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
    0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
    0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
    0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
    0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
    0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
    0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
    0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
    0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
    0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
    0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
    0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
    0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
    0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
    0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
    0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
    0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
    0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
    0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
    0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
    0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

/*****************************************************************************
                     insert 2 bits into outputBuffer
******************************************************************************/
#define insert_2_bits(_data) \
do \
{ \
    if ((bits_left >= 3) && (bits_left <= 8)) \
    { \
        i = bits_left - 2; \
        outputBuffer[opb_index] |= _data << i; \
        bits_left = i; \
    } \
    else \
    { \
        i = 2 - bits_left; \
        j = 8 - i; \
        outputBuffer[opb_index++] |= _data >> i; \
        outputBuffer[opb_index] |= _data << j; \
        bits_left = j; \
    } \
} while (0)

/*****************************************************************************
                     insert 3 bits into outputBuffer
******************************************************************************/
#define insert_3_bits(_data) \
do \
{ \
    if ((bits_left >= 4) && (bits_left <= 8)) \
    { \
        i = bits_left - 3; \
        outputBuffer[opb_index] |= _data << i; \
        bits_left = i; \
    } \
    else \
    { \
        i = 3 - bits_left; \
        j = 8 - i; \
        outputBuffer[opb_index++] |= _data >> i; \
        outputBuffer[opb_index] |= _data << j; \
        bits_left = j; \
    } \
} while (0)

/*****************************************************************************
                     insert 4 bits into outputBuffer
******************************************************************************/
#define insert_4_bits(_data) \
do \
{ \
    if ((bits_left >= 5) && (bits_left <= 8)) \
    { \
        i = bits_left - 4; \
        outputBuffer[opb_index] |= _data << i; \
        bits_left = i; \
    } \
    else \
    { \
        i = 4 - bits_left; \
        j = 8 - i; \
        outputBuffer[opb_index++] |= _data >> i; \
        outputBuffer[opb_index] |= _data << j; \
        bits_left = j; \
    } \
} while (0)

/*****************************************************************************
                     insert 5 bits into outputBuffer
******************************************************************************/
#define insert_5_bits(_data) \
do \
{ \
    if ((bits_left >= 6) && (bits_left <= 8)) \
    { \
        i = bits_left - 5; \
        outputBuffer[opb_index] |= _data << i; \
        bits_left = i; \
    } \
    else \
    { \
        i = 5 - bits_left; \
        j = 8 - i; \
        outputBuffer[opb_index++] |= _data >> i; \
        outputBuffer[opb_index] |= _data << j; \
        bits_left = j; \
    } \
} while (0)

/*****************************************************************************
                     insert 6 bits into outputBuffer
******************************************************************************/
#define insert_6_bits(_data) \
do \
{ \
    if ((bits_left >= 7) && (bits_left <= 8)) \
    { \
        i = bits_left - 6; \
        outputBuffer[opb_index] |= (_data << i); \
        bits_left = i; \
    } \
    else \
    { \
        i = 6 - bits_left; \
        j = 8 - i; \
        outputBuffer[opb_index++] |= (_data >> i); \
        outputBuffer[opb_index] |= (_data << j); \
        bits_left = j; \
    } \
} while (0)

/*****************************************************************************
                     insert 7 bits into outputBuffer
******************************************************************************/
#define insert_7_bits(_data) \
do \
{ \
    if (bits_left == 8) \
    { \
        outputBuffer[opb_index] |= _data << 1; \
        bits_left = 1; \
    } \
    else \
    { \
        i = 7 - bits_left; \
        j = 8 - i; \
        outputBuffer[opb_index++] |= _data >> i; \
        outputBuffer[opb_index] |= _data << j; \
        bits_left = j; \
    } \
} while (0)

/*****************************************************************************
                     insert 8 bits into outputBuffer
******************************************************************************/
#define insert_8_bits(_data) \
do \
{ \
    if (bits_left == 8) \
    { \
        outputBuffer[opb_index++] |= _data; \
        bits_left = 8; \
    } \
    else \
    { \
        i = 8 - bits_left; \
        j = 8 - i; \
        outputBuffer[opb_index++] |= _data >> i; \
        outputBuffer[opb_index] |= _data << j; \
        bits_left = j; \
    } \
} while (0)

/*****************************************************************************
                     insert 9 bits into outputBuffer
******************************************************************************/
#define insert_9_bits(_data16) \
do \
{ \
    i = 9 - bits_left; \
    j = 8 - i; \
    outputBuffer[opb_index++] |= (char) (_data16 >> i); \
    outputBuffer[opb_index] |= (char) (_data16 << j); \
    bits_left = j; \
    if (bits_left == 0) \
    { \
        opb_index++; \
        bits_left = 8; \
    } \
} while (0)

/*****************************************************************************
                     insert 10 bits into outputBuffer
******************************************************************************/
#define insert_10_bits(_data16) \
do \
{ \
    i = 10 - bits_left; \
    if ((bits_left >= 3) && (bits_left <= 8)) \
    { \
        j = 8 - i; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index] |= (char) (_data16 << j); \
        bits_left = j; \
    } \
    else \
    { \
        j = i - 8; \
        k = 8 - j; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index++] |= (char) (_data16 >> j); \
        outputBuffer[opb_index] |= (char) (_data16 << k); \
        bits_left = k; \
    } \
} while (0)

/*****************************************************************************
                     insert 11 bits into outputBuffer
******************************************************************************/
#define insert_11_bits(_data16) \
do \
{ \
    i = 11 - bits_left; \
    if ((bits_left >= 4) && (bits_left <= 8)) \
    { \
        j = 8 - i; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index] |= (char) (_data16 << j); \
        bits_left = j; \
    } \
    else \
    { \
        j = i - 8;                                \
        k = 8 - j; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index++] |= (char) (_data16 >> j); \
        outputBuffer[opb_index] |= (char) (_data16 << k); \
        bits_left = k; \
    } \
} while (0)

/*****************************************************************************
                     insert 12 bits into outputBuffer
******************************************************************************/
#define insert_12_bits(_data16) \
do \
{ \
    i = 12 - bits_left; \
    if ((bits_left >= 5) && (bits_left <= 8)) \
    { \
        j = 8 - i; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index] |= (char) (_data16 << j); \
        bits_left = j; \
    } \
    else \
    { \
        j = i - 8; \
        k = 8 - j; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index++] |= (char) (_data16 >> j); \
        outputBuffer[opb_index] |= (char) (_data16 << k); \
        bits_left = k; \
    } \
} while (0)

/*****************************************************************************
                     insert 13 bits into outputBuffer
******************************************************************************/
#define insert_13_bits(_data16) \
do \
{ \
    i = 13 - bits_left; \
    if ((bits_left >= 6) && (bits_left <= 8)) \
    { \
        j = 8 - i; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index] |= (char) (_data16 << j); \
        bits_left = j; \
    } \
    else \
    { \
        j = i - 8; \
        k = 8 - j; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index++] |= (char) (_data16 >> j); \
        outputBuffer[opb_index] |= (char) (_data16 << k); \
        bits_left = k; \
    } \
} while (0)

/*****************************************************************************
                     insert 14 bits into outputBuffer
******************************************************************************/
#define insert_14_bits(_data16) \
do \
{ \
    i = 14 - bits_left; \
    if ((bits_left >= 7) && (bits_left <= 8)) \
    { \
        j = 8 - i; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index] |= (char) (_data16 << j); \
        bits_left = j; \
    } \
    else \
    { \
        j = i - 8; \
        k = 8 - j; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index++] |= (char) (_data16 >> j); \
        outputBuffer[opb_index] |= (char) (_data16 << k); \
        bits_left = k; \
    } \
} while (0)

/*****************************************************************************
                     insert 15 bits into outputBuffer
******************************************************************************/
#define insert_15_bits(_data16) \
do \
{ \
    i = 15 - bits_left; \
    if (bits_left == 8) \
    { \
        j = 8 - i; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index] |= (char) (_data16 << j); \
        bits_left = j; \
    } \
    else \
    { \
        j = i - 8; \
        k = 8 - j; \
        outputBuffer[opb_index++] |= (char) (_data16 >> i); \
        outputBuffer[opb_index++] |= (char) (_data16 >> j); \
        outputBuffer[opb_index] |= (char) (_data16 << k); \
        bits_left = k; \
    } \
} while (0)

/*****************************************************************************
                     insert 16 bits into outputBuffer
******************************************************************************/
#define insert_16_bits(_data16) \
do \
{ \
    i = 16 - bits_left; \
    j = i - 8; \
    k = 8 - j; \
    outputBuffer[opb_index++] |= (char) (_data16 >> i); \
    outputBuffer[opb_index++] |= (char) (_data16 >> j); \
    outputBuffer[opb_index] |= (char) (_data16 << k); \
    bits_left = k; \
} while (0)

/**
 * Initialize mppc_enc structure
 *
 * @param   protocol_type   PROTO_RDP_40 or PROTO_RDP_50
 *
 * @return  struct xrdp_mppc_enc* or nil on failure
 */

struct xrdp_mppc_enc * APP_CC
mppc_enc_new(int protocol_type)
{
    struct xrdp_mppc_enc *enc;

    enc = (struct xrdp_mppc_enc *) g_malloc(sizeof(struct xrdp_mppc_enc), 1);

    if (enc == 0)
    {
        return 0;
    }

    switch (protocol_type)
    {
        case PROTO_RDP_40:
            enc->protocol_type = PROTO_RDP_40;
            enc->buf_len = RDP_40_HIST_BUF_LEN;
            break;

        case PROTO_RDP_50:
            enc->protocol_type = PROTO_RDP_50;
            enc->buf_len = RDP_50_HIST_BUF_LEN;
            break;

        default:
            g_free(enc);
            return 0;
    }

    enc->flagsHold = PACKET_AT_FRONT;
    enc->historyBuffer = (char *) g_malloc(enc->buf_len, 1);

    if (enc->historyBuffer == 0)
    {
        g_free(enc);
        return 0;
    }

    enc->outputBufferPlus = (char *) g_malloc(enc->buf_len + 64, 1);

    if (enc->outputBufferPlus == 0)
    {
        g_free(enc->historyBuffer);
        g_free(enc);
        return 0;
    }

    enc->outputBuffer = enc->outputBufferPlus + 64;
    enc->hash_table = (tui16 *) g_malloc(enc->buf_len * 2, 1);

    if (enc->hash_table == 0)
    {
        g_free(enc->historyBuffer);
        g_free(enc->outputBufferPlus);
        g_free(enc);
        return 0;
    }

    return enc;
}

/**
 * deinit mppc_enc structure
 *
 * @param   enc  struct to be deinited
 */

void APP_CC
mppc_enc_free(struct xrdp_mppc_enc *enc)
{
    if (enc == 0)
    {
        return;
    }
    g_free(enc->historyBuffer);
    g_free(enc->outputBufferPlus);
    g_free(enc->hash_table);
    g_free(enc);
}

/**
 * encode (compress) data using RDP 4.0 protocol
 *
 * @param   enc           encoder state info
 * @param   srcData       uncompressed data
 * @param   len           length of srcData
 *
 * @return  TRUE on success, FALSE on failure
 */

static int APP_CC
compress_rdp_4(struct xrdp_mppc_enc *enc, tui8 *srcData, int len)
{
    /* RDP 4.0 encoding not yet implemented */
    return 0;
}

/**
 * encode (compress) data using RDP 5.0 protocol using hash table
 *
 * @param   enc           encoder state info
 * @param   srcData       uncompressed data
 * @param   len           length of srcData
 *
 * @return  TRUE on success, FALSE on failure
 */

static int APP_CC
compress_rdp_5(struct xrdp_mppc_enc *enc, tui8 *srcData, int len)
{
    char *outputBuffer;     /* points to enc->outputBuffer */
    char *hptr_end;         /* points to end of history data */
    char *historyPointer;   /* points to first byte of srcData in
                             * historyBuffer */
    char *hbuf_start;       /* points to start of history buffer */
    char *cptr1;
    char *cptr2;
    int opb_index;          /* index into outputBuffer */
    int bits_left;          /* unused bits in current byte in outputBuffer */
    tui32 copy_offset;      /* pattern match starts here... */
    tui32 lom;              /* ...and matches this many bytes */
    int last_crc_index;     /* don't compute CRC beyond this index */
    tui16 *hash_table;      /* hash table for pattern matching */

    tui32 i;
    tui32 j;
    tui32 k;
    tui32 x;
    tui8 data;
    tui16 data16;
    tui32 historyOffset;
    tui16 crc;
    tui32 ctr;
    tui32 saved_ctr;
    tui32 data_end;
    tui8 byte_val;

    crc = 0;
    opb_index = 0;
    bits_left = 8;
    copy_offset = 0;
    hash_table = enc->hash_table;
    hbuf_start = enc->historyBuffer;
    outputBuffer = enc->outputBuffer;
    g_memset(outputBuffer, 0, len);
    enc->flags = PACKET_COMPR_TYPE_64K;

    if ((enc->historyOffset + len) >= enc->buf_len - 3)
    {
        /* historyBuffer cannot hold srcData - rewind it */
        enc->historyOffset = 0;
        g_memset(hash_table, 0, enc->buf_len * 2);
        g_memset(enc->historyBuffer, 0, enc->buf_len); // added
        enc->flagsHold |= PACKET_AT_FRONT | PACKET_FLUSHED;
    }

    /* point to next free byte in historyBuffer */
    historyOffset = enc->historyOffset;

    /* add / append new data to historyBuffer */
    g_memcpy(&(enc->historyBuffer[historyOffset]), srcData, len);

    /* point to start of data to be compressed */
    historyPointer = &(enc->historyBuffer[historyOffset]);

    ctr = copy_offset = lom = 0;

    /* if we are at start of history buffer, do not attempt to compress */
    /* first 2 bytes, because minimum LoM is 3                          */
    if (historyOffset == 0)
    {
        /* encode first two bytes as literals */
        for (x = 0; x < 2; x++)
        {
            data = *(historyPointer + x);
            DLOG(("%.2x ", (tui8) data));
            if (data & 0x80)
            {
                /* insert encoded literal */
                insert_2_bits(0x02);
                data &= 0x7f;
                insert_7_bits(data);
            }
            else
            {
                /* insert literal */
                insert_8_bits(data);
            }
        }

        /* store hash for first two entries in historyBuffer */
        crc = CRC_INIT;
        byte_val = enc->historyBuffer[0];
        CRC(crc, byte_val);
        byte_val = enc->historyBuffer[1];
        CRC(crc, byte_val);
        byte_val = enc->historyBuffer[2];
        CRC(crc, byte_val);
        hash_table[crc] = 0;

        crc = CRC_INIT;
        byte_val = enc->historyBuffer[1];
        CRC(crc, byte_val);
        byte_val = enc->historyBuffer[2];
        CRC(crc, byte_val);
        byte_val = enc->historyBuffer[3];
        CRC(crc, byte_val);
        hash_table[crc] = 1;

        /* first two bytes have already been processed */
        ctr = 2;
    }

    enc->historyOffset += len;

    /* point to last byte in new data */
    hptr_end = &(enc->historyBuffer[enc->historyOffset - 1]);

    /* do not compute CRC beyond this */
    last_crc_index = enc->historyOffset - 3;

    /* do not search for pattern match beyond this */
    data_end = len - 2;

    /* start compressing data */

    while (ctr < data_end)
    {
        cptr1 = historyPointer + ctr;

        crc = CRC_INIT;
        byte_val = *cptr1;
        CRC(crc, byte_val);
        byte_val = *(cptr1 + 1);
        CRC(crc, byte_val);
        byte_val = *(cptr1 + 2);
        CRC(crc, byte_val);

        /* cptr2 points to start of pattern match */
        cptr2 = hbuf_start + hash_table[crc];
        copy_offset = cptr1 - cptr2;

        /* save current entry */
        hash_table[crc] = cptr1 - hbuf_start;

        /* double check that we have a pattern match */
        if ((*cptr1 != *cptr2) ||
            (*(cptr1 + 1) != *(cptr2 + 1)) ||
            (*(cptr1 + 2) != *(cptr2 + 2)))
        {
            /* no match found; encode literal byte */
            data = *cptr1;

            DLOG(("%.2x ", data));
            if (data < 0x80)
            {
                /* literal byte < 0x80 */
                insert_8_bits(data);
            }
            else
            {
                /* literal byte >= 0x80 */
                insert_2_bits(0x02);
                data &= 0x7f;
                insert_7_bits(data);
            }
            ctr++;
            continue;
        }

        /* we have a match - compute Length of Match */
        cptr1 += 3;
        cptr2 += 3;
        lom = 3;
        while ((cptr1 <= hptr_end) && (*(cptr1++) == *(cptr2++)))
        {
            lom++;
        }
        saved_ctr = ctr + lom;
        DLOG(("<%d: %ld,%d> ",  (historyPointer + ctr) - hbuf_start,
              copy_offset, lom));

        /* compute CRC for matching segment and store in hash table */

        cptr1 = historyPointer + ctr;
        if (cptr1 + lom > hbuf_start + last_crc_index)
        {
            /* we have gone beyond last_crc_index - go back */
            j = last_crc_index - (cptr1 - hbuf_start);
        }
        else
        {
            j = lom - 1;
        }
        ctr++;
        for (i = 0; i < j; i++)
        {
            cptr1 = historyPointer + ctr;

            /* compute CRC on triplet */
            crc = CRC_INIT;
            byte_val = *(cptr1++);
            CRC(crc, byte_val);
            byte_val = *(cptr1++);
            CRC(crc, byte_val);
            byte_val = *(cptr1++);
            CRC(crc, byte_val);

            /* save current entry */
            hash_table[crc] = (cptr1 - 3) - hbuf_start;

            /* point to next triplet */
            ctr++;
        }
        ctr = saved_ctr;

        /* encode copy_offset and insert into output buffer */

        if (copy_offset <= 63) /* (copy_offset >= 0) is always true */
        {
            /* insert binary header */
            data = 0x1f;
            insert_5_bits(data);

            /* insert 6 bits of copy_offset */
            data = (char) (copy_offset & 0x3f);
            insert_6_bits(data);
        }
        else if ((copy_offset >= 64) && (copy_offset <= 319))
        {
            /* insert binary header */
            data = 0x1e;
            insert_5_bits(data);

            /* insert 8 bits of copy offset */
            data = (char) (copy_offset - 64);
            insert_8_bits(data);
        }
        else if ((copy_offset >= 320) && (copy_offset <= 2367))
        {
            /* insert binary header */
            data = 0x0e;
            insert_4_bits(data);

            /* insert 11 bits of copy offset */
            data16 = copy_offset - 320;;
            insert_11_bits(data16);
        }
        else
        {
            /* copy_offset is 2368+ */

            /* insert binary header */
            data = 0x06;
            insert_3_bits(data);

            /* insert 16 bits of copy offset */
            data16 = copy_offset - 2368;;
            insert_16_bits(data16);
        }

        /* encode length of match and insert into output buffer */

        if (lom == 3)
        {
            /* binary header is 'zero'; since outputBuffer is zero */
            /* filled, all we have to do is update bits_left */
            bits_left--;
            if (bits_left == 0)
            {
                opb_index++;
                bits_left = 8;
            }
        }
        else if ((lom >= 4) && (lom <= 7))
        {
            /* insert binary header */
            data = 0x02;
            insert_2_bits(data);

            /* insert lower 2 bits of LoM */
            data = (char) (lom - 4);
            insert_2_bits(data);
        }
        else if ((lom >= 8) && (lom <= 15))
        {
            /* insert binary header */
            data = 0x06;
            insert_3_bits(data);

            /* insert lower 3 bits of LoM */
            data = (char) (lom - 8);
            insert_3_bits(data);
        }
        else if ((lom >= 16) && (lom <= 31))
        {
            /* insert binary header */
            data = 0x0e;
            insert_4_bits(data);

            /* insert lower 4 bits of LoM */
            data = (char) (lom - 16);
            insert_4_bits(data);
        }
        else if ((lom >= 32) && (lom <= 63))
        {
            /* insert binary header */
            data = 0x1e;
            insert_5_bits(data);

            /* insert lower 5 bits of LoM */
            data = (char) (lom - 32);
            insert_5_bits(data);
        }
        else if ((lom >= 64) && (lom <= 127))
        {
            /* insert binary header */
            data = 0x3e;
            insert_6_bits(data);

            /* insert lower 6 bits of LoM */
            data = (char) (lom - 64);
            insert_6_bits(data);
        }
        else if ((lom >= 128) && (lom <= 255))
        {
            /* insert binary header */
            data = 0x7e;
            insert_7_bits(data);

            /* insert lower 7 bits of LoM */
            data = (char) (lom - 128);
            insert_7_bits(data);
        }
        else if ((lom >= 256) && (lom <= 511))
        {
            /* insert binary header */
            data = 0xfe;
            insert_8_bits(data);

            /* insert lower 8 bits of LoM */
            data = (char) (lom - 256);
            insert_8_bits(data);
        }
        else if ((lom >= 512) && (lom <= 1023))
        {
            /* insert binary header */
            data16 = 0x1fe;
            insert_9_bits(data16);

            /* insert lower 9 bits of LoM */
            data16 = lom - 512;
            insert_9_bits(data16);
        }
        else if ((lom >= 1024) && (lom <= 2047))
        {
            /* insert binary header */
            data16 = 0x3fe;
            insert_10_bits(data16);

            /* insert 10 lower bits of LoM */
            data16 = lom - 1024;
            insert_10_bits(data16);
        }
        else if ((lom >= 2048) && (lom <= 4095))
        {
            /* insert binary header */
            data16 = 0x7fe;
            insert_11_bits(data16);

            /* insert 11 lower bits of LoM */
            data16 = lom - 2048;
            insert_11_bits(data16);
        }
        else if ((lom >= 4096) && (lom <= 8191))
        {
            /* insert binary header */
            data16 = 0xffe;
            insert_12_bits(data16);

            /* insert 12 lower bits of LoM */
            data16 = lom - 4096;
            insert_12_bits(data16);
        }
        else if ((lom >= 8192) && (lom <= 16383))
        {
            /* insert binary header */
            data16 = 0x1ffe;
            insert_13_bits(data16);

            /* insert 13 lower bits of LoM */
            data16 = lom - 8192;
            insert_13_bits(data16);
        }
        else if ((lom >= 16384) && (lom <= 32767))
        {
            /* insert binary header */
            data16 = 0x3ffe;
            insert_14_bits(data16);

            /* insert 14 lower bits of LoM */
            data16 = lom - 16384;
            insert_14_bits(data16);
        }
        else if ((lom >= 32768) && (lom <= 65535))
        {
            /* insert binary header */
            data16 = 0x7ffe;
            insert_15_bits(data16);

            /* insert 15 lower bits of LoM */
            data16 = lom - 32768;
            insert_15_bits(data16);
        }
    } /* end while (ctr < data_end) */

    /* add remaining data to the output */
    while (len - ctr > 0)
    {
        data = srcData[ctr];
        DLOG(("%.2x ", data));
        if (data < 0x80)
        {
            /* literal byte < 0x80 */
            insert_8_bits(data);
        }
        else
        {
            /* literal byte >= 0x80 */
            insert_2_bits(0x02);
            data &= 0x7f;
            insert_7_bits(data);
        }
        ctr++;
    }

    /* if bits_left != 8, increment opb_index, which is zero indexed */
    if (bits_left != 8)
    {
        opb_index++;
    }

    if (opb_index > len)
    {
        /* compressed data longer than uncompressed data */
        /* give up */
        enc->historyOffset = 0;
        g_memset(hash_table, 0, enc->buf_len * 2);
        g_memset(enc->historyBuffer, 0, enc->buf_len);
        enc->flagsHold |= PACKET_AT_FRONT | PACKET_FLUSHED;
        return 0;
    }

    enc->flags |= PACKET_COMPRESSED;
    enc->bytes_in_opb = opb_index;

    enc->flags |= enc->flagsHold;
    enc->flagsHold = 0;

    DLOG(("\n"));

    //g_writeln("compression ratio: %f", (float) len / (float) enc->bytes_in_opb);

    return 1;
}

/**
 * encode (compress) data
 *
 * @param   enc           encoder state info
 * @param   srcData       uncompressed data
 * @param   len           length of srcData
 *
 * @return  TRUE on success, FALSE on failure
 */

int APP_CC
compress_rdp(struct xrdp_mppc_enc *enc, tui8 *srcData, int len)
{
    if ((enc == 0) || (srcData == 0) || (len <= 0) || (len > enc->buf_len))
    {
        return 0;
    }

    switch (enc->protocol_type)
    {
        case PROTO_RDP_40:
            return compress_rdp_4(enc, srcData, len);
            break;

        case PROTO_RDP_50:
            return compress_rdp_5(enc, srcData, len);
            break;
    }

    return 0;
}