rdesktop/mppc.c

#include <stdio.h>
#include <string.h>

#include "rdesktop.h"

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

/* TODO: research the below statements      */

/* there exists one or more patents         */
/* related to compression algorithms        */

/* since we are only decompressing I        */
/* think the end-user is safe.              */

/* even if that isn't true, aren't you      */
/* already paying royalties                 */
/* through the CAL licenses?                */

/* the dictionary is empty when init. like  */
/* LZ78,  which is not patented             */


RDPCOMP mppc_dict;

int
mppc_expand(uint8 * data, uint32 clen, uint8 ctype, uint32 * roff, uint32 * rlen)
{
	int k, walker_len = 0, walker;
	int i = 0;
	int next_offset, match_off;
	int match_len;
	int old_offset, match_bits;

	signed char *dict = &(mppc_dict.hist);

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

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

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

	*roff = 0;
	*rlen = 0;

	walker = 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 < 2)
		{
			if (i >= clen)
				return -1;
			walker |= (data[i++] & 0xff) << (24 - walker_len);
			walker_len += 8;
		}
		/* 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 = 11;	/* 11 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 = 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 & (RDP_MPPC_DICT_SIZE - 1);
		do
		{
			dict[next_offset++] = dict[k++];
		}
		while (--match_len != 0);
	}
	while (1);

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

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

	return 0;
}