text: /* ----------
   * pg_lzcompress.c -
   *
   *		This is an implementation of LZ compression for PostgreSQL.
   *		It uses a simple history table and generates 2-3 byte tags
   *		capable of backward copy information for 3-273 bytes with
   *		a max offset of 4095.
   *
   *		Entry routines:
   *
   *			int32
   *			pglz_compress(const char *source, int32 slen, char *dest,
   *						  const PGLZ_Strategy *strategy);
   *
   *				source is the input data to be compressed.
   *
   *				slen is the length of the input data.
   *
   *				dest is the output area for the compressed result.
   *					It must be at least as big as PGLZ_MAX_OUTPUT(slen).
   *
   *				strategy is a pointer to some information controlling
   *					the compression algorithm. If NULL, the compiled
   *					in default strategy is used.
   *
   *				The return value is the number of bytes written in the
   *				buffer dest, or -1 if compression fails; in the latter
   *				case the contents of dest are undefined.
   *
   *			int32
   *			pglz_decompress(const char *source, int32 slen, char *dest,
   *							int32 rawsize)
   *
   *				source is the compressed input.
   *
   *				slen is the length of the compressed input.
   *
   *				dest is the area where the uncompressed data will be
   *					written to. It is the callers responsibility to
   *					provide enough space.
   *
   *					The data is written to buff exactly as it was handed
   *					to pglz_compress(). No terminating zero byte is added.
   *
   *				rawsize is the length of the uncompressed data.
   *
   *				The return value is the number of bytes written in the
   *				buffer dest, or -1 if decompression fails.
   *
   *		The decompression algorithm and internal data format:
   *
   *			It is made with the compressed data itself.
   *
   *			The data representation is easiest explained by describing
   *			the process of decompression.
   *
   *			If compressed_size == rawsize, then the data
   *			is stored uncompressed as plain bytes. Thus, the decompressor
   *			simply copies rawsize bytes to the destination.
   *
   *			Otherwise the first byte tells what to do the next 8 times.
   *			We call this the control byte.
   *
   *			An unset bit in the control byte means, that one uncompressed
   *			byte follows, which is copied from input to output.
   *
   *			A set bit in the control byte means, that a tag of 2-3 bytes
   *			follows. A tag contains information to copy some bytes, that
   *			are already in the output buffer, to the current location in
   *			the output. Let's call the three tag bytes T1, T2 and T3. The
   *			position of the data to copy is coded as an offset from the
   *			actual output position.
   *
   *			The offset is in the upper nibble of T1 and in T2.
   *			The length is in the lower nibble of T1.
   *
   *			So the 16 bits of a 2 byte tag are coded as
   *
   *				7---T1--0  7---T2--0
   *				OOOO LLLL  OOOO OOOO
   *
   *			This limits the offset to 1-4095 (12 bits) and the length
   *			to 3-18 (4 bits) because 3 is always added to it. To emit
   *			a tag of 2 bytes with a length of 2 only saves one control
   *			bit. But we lose one byte in the possible length of a tag.
   *
   *			In the actual implementation, the 2 byte tag's length is
   *			limited to 3-17, because the value 0xF in the length nibble
   *			has special meaning. It means, that the next following
   *			byte (T3) has to be added to the length value of 18. That
   *			makes total limits of 1-4095 for offset and 3-273 for length.
   *
   *			Now that we have successfully decoded a tag. We simply copy
   *			the output that occurred <offset> bytes back to the current
   *			output location in the specified <length>. Thus, a
   *			sequence of 200 spaces (think about bpchar fields) could be
   *			coded in 4 bytes. One literal space and a three byte tag to
   *			copy 199 bytes with a -1 offset. Whow - that's a compression
   *			rate of 98%! Well, the implementation needs to save the
   *			original data size too, so we need another 4 bytes for it
   *			and end up with a total compression rate of 96%, what's still
   *			worth a Whow.
   *
   *		The compression algorithm
   *
   *			The following uses numbers used in the default strategy.
   *
   *			The compressor works best for attributes of a size between
   *			1K and 1M. For smaller items there's not that much chance of
   *			redundancy in the character sequence (except for large areas
   *			of identical bytes like trailing spaces) and for bigger ones
   *			our 4K maximum look-back distance is too small.
   *
   *			The compressor creates a table for lists of positions.
   *			For each input position (except the last 3), a hash key is
   *			built from the 4 next input bytes and the position remembered
   *			in the appropriate list. Thus, the table points to linked
   *			lists of likely to be at least in the first 4 characters
   *			matching strings. This is done on the fly while the input
   *			is compressed into the output area.  Table entries are only
   *			kept for the last 4096 input positions, since we cannot use
   *			back-pointers larger than that anyway.  The size of the hash
   *			table is chosen based on the size of the input - a larger table
   *			has a larger startup cost, as it needs to be initialized to
   *			zero, but reduces the number of hash collisions on long inputs.
   *
   *			For each byte in the input, its hash key (built from this
   *			byte and the next 3) is used to find the appropriate list
   *			in the table. The lists remember the positions of all bytes
   *			that had the same hash key in the past in increasing backward
   *			offset order. Now for all entries in the used lists, the
   *			match length is computed by comparing the characters from the
   *			entries position with the characters from the actual input
   *			position.
   *
   *			The compressor starts with a so called "good_match" of 128.
   *			It is a "prefer speed against compression ratio" optimizer.
   *			So if the first entry looked at already has 128 or more
   *			matching characters, the lookup stops and that position is
   *			used for the next tag in the output.
   *
   *			For each subsequent entry in the history list, the "good_match"
   *			is lowered by 10%. So the compressor will be more happy with
   *			short matches the farer it has to go back in the history.
   *			Another "speed against ratio" preference characteristic of
   *			the algorithm.
   *
   *			Thus there are 3 stop conditions for the lookup of matches:
   *
   *				- a match >= good_match is found
   *				- there are no more history entries to look at
   *				- the next history entry is already too far back
   *				  to be coded into a tag.
   *
   *			Finally the match algorithm checks that at least a match
   *			of 3 or more bytes has been found, because thats the smallest
   *			amount of copy information to code into a tag. If so, a tag
   *			is omitted and all the input bytes covered by that are just
   *			scanned for the history add's, otherwise a literal character
   *			is omitted and only his history entry added.
   *
   *		Acknowledgements:
   *
   *			Many thanks to Adisak Pochanayon, who's article about SLZ
   *			inspired me to write the PostgreSQL compression this way.
   *
   *			Jan Wieck
   *
   * Copyright (c) 1999-2015, PostgreSQL Global Development Group
   *
   * src/common/pg_lzcompress.c
   * ----------
   */
  #ifndef FRONTEND
  #include "postgres.h"
  #else
  #include "postgres_fe.h"
  #endif
  
  #include <limits.h>
  
  #include "common/pg_lzcompress.h"
  
  
  /* ----------
   * Local definitions
   * ----------
   */
  #define PGLZ_MAX_HISTORY_LISTS	8192	/* must be power of 2 */
  #define PGLZ_HISTORY_SIZE		4096
  #define PGLZ_MAX_MATCH			273
  
  
  /* ----------
   * PGLZ_HistEntry -
   *
   *		Linked list for the backward history lookup
   *
   * All the entries sharing a hash key are linked in a doubly linked list.
   * This makes it easy to remove an entry when it's time to recycle it
   * (because it's more than 4K positions old).
   * ----------
   */
  typedef struct PGLZ_HistEntry
  {
  	struct PGLZ_HistEntry *next;	/* links for my hash key's list */
  	struct PGLZ_HistEntry *prev;
  	int			hindex;			/* my current hash key */
  	const char *pos;			/* my input position */
  } PGLZ_HistEntry;
  
  
  /* ----------
   * The provided standard strategies
   * ----------
   */
  static const PGLZ_Strategy strategy_default_data = {
  	32,							/* Data chunks less than 32 bytes are not
  								 * compressed */
  	INT_MAX,					/* No upper limit on what we'll try to
  								 * compress */
  	25,							/* Require 25% compression rate, or not worth
  								 * it */
  	1024,						/* Give up if no compression in the first 1KB */
  	128,						/* Stop history lookup if a match of 128 bytes
  								 * is found */
  	10							/* Lower good match size by 10% at every loop
  								 * iteration */
  };
  const PGLZ_Strategy *const PGLZ_strategy_default = &strategy_default_data;
  
  
  static const PGLZ_Strategy strategy_always_data = {
  	0,							/* Chunks of any size are compressed */
  	INT_MAX,
  	0,							/* It's enough to save one single byte */
  	INT_MAX,					/* Never give up early */
  	128,						/* Stop history lookup if a match of 128 bytes
  								 * is found */
  	6							/* Look harder for a good match */
  };
  const PGLZ_Strategy *const PGLZ_strategy_always = &strategy_always_data;
  
  
  /* ----------
   * Statically allocated work arrays for history
   * ----------
   */
  static int16 hist_start[PGLZ_MAX_HISTORY_LISTS];
  static PGLZ_HistEntry hist_entries[PGLZ_HISTORY_SIZE + 1];
  
  /*
   * Element 0 in hist_entries is unused, and means 'invalid'. Likewise,
   * INVALID_ENTRY_PTR in next/prev pointers mean 'invalid'.
   */
  #define INVALID_ENTRY			0
  #define INVALID_ENTRY_PTR		(&hist_entries[INVALID_ENTRY])
  
  /* ----------
   * pglz_hist_idx -
   *
   *		Computes the history table slot for the lookup by the next 4
   *		characters in the input.
   *
   * NB: because we use the next 4 characters, we are not guaranteed to
   * find 3-character matches; they very possibly will be in the wrong
   * hash list.  This seems an acceptable tradeoff for spreading out the
   * hash keys more.
   * ----------
   */
  #define pglz_hist_idx(_s,_e, _mask) (										\
  			((((_e) - (_s)) < 4) ? (int) (_s)[0] :							\
  			 (((_s)[0] << 6) ^ ((_s)[1] << 4) ^								\
  			  ((_s)[2] << 2) ^ (_s)[3])) & (_mask)				\
  		)
  
  
  /* ----------
   * pglz_hist_add -
   *
   *		Adds a new entry to the history table.
   *
   * If _recycle is true, then we are recycling a previously used entry,
   * and must first delink it from its old hashcode's linked list.
   *
   * NOTE: beware of multiple evaluations of macro's arguments, and note that
   * _hn and _recycle are modified in the macro.
   * ----------
   */
  #define pglz_hist_add(_hs,_he,_hn,_recycle,_s,_e, _mask)	\
  do {									\
  			int __hindex = pglz_hist_idx((_s),(_e), (_mask));				\
  			int16 *__myhsp = &(_hs)[__hindex];								\
  			PGLZ_HistEntry *__myhe = &(_he)[_hn];							\
  			if (_recycle) {													\
  				if (__myhe->prev == NULL)									\
  					(_hs)[__myhe->hindex] = __myhe->next - (_he);			\
  				else														\
  					__myhe->prev->next = __myhe->next;						\
  				if (__myhe->next != NULL)									\
  					__myhe->next->prev = __myhe->prev;						\
  			}																\
  			__myhe->next = &(_he)[*__myhsp];								\
  			__myhe->prev = NULL;											\
  			__myhe->hindex = __hindex;										\
  			__myhe->pos  = (_s);											\
  			/* If there was an existing entry in this hash slot, link */	\
  			/* this new entry to it. However, the 0th entry in the */		\
  			/* entries table is unused, so we can freely scribble on it. */ \
  			/* So don't bother checking if the slot was used - we'll */		\
  			/* scribble on the unused entry if it was not, but that's */	\
  			/* harmless. Avoiding the branch in this critical path */		\
  			/* speeds this up a little bit. */								\
  			/* if (*__myhsp != INVALID_ENTRY) */							\
  				(_he)[(*__myhsp)].prev = __myhe;							\
  			*__myhsp = _hn;													\
  			if (++(_hn) >= PGLZ_HISTORY_SIZE + 1) {							\
  				(_hn) = 1;													\
  				(_recycle) = true;											\
  			}																\
  } while (0)
  
  
  /* ----------
   * pglz_out_ctrl -
   *
   *		Outputs the last and allocates a new control byte if needed.
   * ----------
   */
  #define pglz_out_ctrl(__ctrlp,__ctrlb,__ctrl,__buf) \
  do { \
  	if ((__ctrl & 0xff) == 0)												\
  	{																		\
  		*(__ctrlp) = __ctrlb;												\
  		__ctrlp = (__buf)++;												\
  		__ctrlb = 0;														\
  		__ctrl = 1;															\
  	}																		\
  } while (0)
  
  
  /* ----------
   * pglz_out_literal -
   *
   *		Outputs a literal byte to the destination buffer including the
   *		appropriate control bit.
   * ----------
   */
  #define pglz_out_literal(_ctrlp,_ctrlb,_ctrl,_buf,_byte) \
  do { \
  	pglz_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf);								\
  	*(_buf)++ = (unsigned char)(_byte);										\
  	_ctrl <<= 1;															\
  } while (0)
  
  
  /* ----------
   * pglz_out_tag -
   *
   *		Outputs a backward reference tag of 2-4 bytes (depending on
   *		offset and length) to the destination buffer including the
   *		appropriate control bit.
   * ----------
   */
  #define pglz_out_tag(_ctrlp,_ctrlb,_ctrl,_buf,_len,_off) \
  do { \
  	pglz_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf);								\
  	_ctrlb |= _ctrl;														\
  	_ctrl <<= 1;															\
  	if (_len > 17)															\
  	{																		\
  		(_buf)[0] = (unsigned char)((((_off) & 0xf00) >> 4) | 0x0f);		\
  		(_buf)[1] = (unsigned char)(((_off) & 0xff));						\
  		(_buf)[2] = (unsigned char)((_len) - 18);							\
  		(_buf) += 3;														\
  	} else {																\
  		(_buf)[0] = (unsigned char)((((_off) & 0xf00) >> 4) | ((_len) - 3)); \
  		(_buf)[1] = (unsigned char)((_off) & 0xff);							\
  		(_buf) += 2;														\
  	}																		\
  } while (0)
  
  
  /* ----------
   * pglz_find_match -
   *
   *		Lookup the history table if the actual input stream matches
   *		another sequence of characters, starting somewhere earlier
   *		in the input buffer.
   * ----------
   */
  static inline int
  pglz_find_match(int16 *hstart, const char *input, const char *end,
  				int *lenp, int *offp, int good_match, int good_drop, int mask)
  {
  	PGLZ_HistEntry *hent;
  	int16		hentno;
  	int32		len = 0;
  	int32		off = 0;
  
  	/*
  	 * Traverse the linked history list until a good enough match is found.
  	 */
  	hentno = hstart[pglz_hist_idx(input, end, mask)];
  	hent = &hist_entries[hentno];
  	while (hent != INVALID_ENTRY_PTR)
  	{
  		const char *ip = input;
  		const char *hp = hent->pos;
  		int32		thisoff;
  		int32		thislen;
  
  		/*
  		 * Stop if the offset does not fit into our tag anymore.
  		 */
  		thisoff = ip - hp;
  		if (thisoff >= 0x0fff)
  			break;
  
  		/*
  		 * Determine length of match. A better match must be larger than the
  		 * best so far. And if we already have a match of 16 or more bytes,
  		 * it's worth the call overhead to use memcmp() to check if this match
  		 * is equal for the same size. After that we must fallback to
  		 * character by character comparison to know the exact position where
  		 * the diff occurred.
  		 */
  		thislen = 0;
  		if (len >= 16)
  		{
  			if (memcmp(ip, hp, len) == 0)
  			{
  				thislen = len;
  				ip += len;
  				hp += len;
  				while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH)
  				{
  					thislen++;
  					ip++;
  					hp++;
  				}
  			}
  		}
  		else
  		{
  			while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH)
  			{
  				thislen++;
  				ip++;
  				hp++;
  			}
  		}
  
  		/*
  		 * Remember this match as the best (if it is)
  		 */
  		if (thislen > len)
  		{
  			len = thislen;
  			off = thisoff;
  		}
  
  		/*
  		 * Advance to the next history entry
  		 */
  		hent = hent->next;
  
  		/*
  		 * Be happy with lesser good matches the more entries we visited. But
  		 * no point in doing calculation if we're at end of list.
  		 */
  		if (hent != INVALID_ENTRY_PTR)
  		{
  			if (len >= good_match)
  				break;
  			good_match -= (good_match * good_drop) / 100;
  		}
  	}
  
  	/*
  	 * Return match information only if it results at least in one byte
  	 * reduction.
  	 */
  	if (len > 2)
  	{
  		*lenp = len;
  		*offp = off;
  		return 1;
  	}
  
  	return 0;
  }
  
  
  /* ----------
   * pglz_compress -
   *
   *		Compresses source into dest using strategy. Returns the number of
   *		bytes written in buffer dest, or -1 if compression fails.
   * ----------
   */
  int32
  pglz_compress(const char *source, int32 slen, char *dest,
  			  const PGLZ_Strategy *strategy)
  {
  	unsigned char *bp = (unsigned char *) dest;
  	unsigned char *bstart = bp;
  	int			hist_next = 1;
  	bool		hist_recycle = false;
  	const char *dp = source;
  	const char *dend = source + slen;
  	unsigned char ctrl_dummy = 0;
  	unsigned char *ctrlp = &ctrl_dummy;
  	unsigned char ctrlb = 0;
  	unsigned char ctrl = 0;
  	bool		found_match = false;
  	int32		match_len;
  	int32		match_off;
  	int32		good_match;
  	int32		good_drop;
  	int32		result_size;
  	int32		result_max;
  	int32		need_rate;
  	int			hashsz;
  	int			mask;
  
  	/*
  	 * Our fallback strategy is the default.
  	 */
  	if (strategy == NULL)
  		strategy = PGLZ_strategy_default;
  
  	/*
  	 * If the strategy forbids compression (at all or if source chunk size out
  	 * of range), fail.
  	 */
  	if (strategy->match_size_good <= 0 ||
  		slen < strategy->min_input_size ||
  		slen > strategy->max_input_size)
  		return -1;
  
  	/*
  	 * Limit the match parameters to the supported range.
  	 */
  	good_match = strategy->match_size_good;
  	if (good_match > PGLZ_MAX_MATCH)
  		good_match = PGLZ_MAX_MATCH;
  	else if (good_match < 17)
  		good_match = 17;
  
  	good_drop = strategy->match_size_drop;
  	if (good_drop < 0)
  		good_drop = 0;
  	else if (good_drop > 100)
  		good_drop = 100;
  
  	need_rate = strategy->min_comp_rate;
  	if (need_rate < 0)
  		need_rate = 0;
  	else if (need_rate > 99)
  		need_rate = 99;
  
  	/*
  	 * Compute the maximum result size allowed by the strategy, namely the
  	 * input size minus the minimum wanted compression rate.  This had better
  	 * be <= slen, else we might overrun the provided output buffer.
  	 */
  	if (slen > (INT_MAX / 100))
  	{
  		/* Approximate to avoid overflow */
  		result_max = (slen / 100) * (100 - need_rate);
  	}
  	else
  		result_max = (slen * (100 - need_rate)) / 100;
  
  	/*
  	 * Experiments suggest that these hash sizes work pretty well. A large
  	 * hash table minimizes collision, but has a higher startup cost. For a
  	 * small input, the startup cost dominates. The table size must be a power
  	 * of two.
  	 */
  	if (slen < 128)
  		hashsz = 512;
  	else if (slen < 256)
  		hashsz = 1024;
  	else if (slen < 512)
  		hashsz = 2048;
  	else if (slen < 1024)
  		hashsz = 4096;
  	else
  		hashsz = 8192;
  	mask = hashsz - 1;
  
  	/*
  	 * Initialize the history lists to empty.  We do not need to zero the
  	 * hist_entries[] array; its entries are initialized as they are used.
  	 */
  	memset(hist_start, 0, hashsz * sizeof(int16));
  
  	/*
  	 * Compress the source directly into the output buffer.
  	 */
  	while (dp < dend)
  	{
  		/*
  		 * If we already exceeded the maximum result size, fail.
  		 *
  		 * We check once per loop; since the loop body could emit as many as 4
  		 * bytes (a control byte and 3-byte tag), PGLZ_MAX_OUTPUT() had better
  		 * allow 4 slop bytes.
  		 */
  		if (bp - bstart >= result_max)
  			return -1;
  
  		/*
  		 * If we've emitted more than first_success_by bytes without finding
  		 * anything compressible at all, fail.  This lets us fall out
  		 * reasonably quickly when looking at incompressible input (such as
  		 * pre-compressed data).
  		 */
  		if (!found_match && bp - bstart >= strategy->first_success_by)
  			return -1;
  
  		/*
  		 * Try to find a match in the history
  		 */
  		if (pglz_find_match(hist_start, dp, dend, &match_len,
  							&match_off, good_match, good_drop, mask))
  		{
  			/*
  			 * Create the tag and add history entries for all matched
  			 * characters.
  			 */
  			pglz_out_tag(ctrlp, ctrlb, ctrl, bp, match_len, match_off);
  			while (match_len--)
  			{
  				pglz_hist_add(hist_start, hist_entries,
  							  hist_next, hist_recycle,
  							  dp, dend, mask);
  				dp++;			/* Do not do this ++ in the line above! */
  				/* The macro would do it four times - Jan.  */
  			}
  			found_match = true;
  		}
  		else
  		{
  			/*
  			 * No match found. Copy one literal byte.
  			 */
  			pglz_out_literal(ctrlp, ctrlb, ctrl, bp, *dp);
  			pglz_hist_add(hist_start, hist_entries,
  						  hist_next, hist_recycle,
  						  dp, dend, mask);
  			dp++;				/* Do not do this ++ in the line above! */
  			/* The macro would do it four times - Jan.  */
  		}
  	}
  
  	/*
  	 * Write out the last control byte and check that we haven't overrun the
  	 * output size allowed by the strategy.
  	 */
  	*ctrlp = ctrlb;
  	result_size = bp - bstart;
  	if (result_size >= result_max)
  		return -1;
  
  	/* success */
  	return result_size;
  }
  
  
  /* ----------
   * pglz_decompress -
   *
   *		Decompresses source into dest. Returns the number of bytes
   *		decompressed in the destination buffer, or -1 if decompression
   *		fails.
   * ----------
   */
  int32
  pglz_decompress(const char *source, int32 slen, char *dest,
  				int32 rawsize)
  {
  	const unsigned char *sp;
  	const unsigned char *srcend;
  	unsigned char *dp;
  	unsigned char *destend;
  
  	sp = (const unsigned char *) source;
  	srcend = ((const unsigned char *) source) + slen;
  	dp = (unsigned char *) dest;
  	destend = dp + rawsize;
  
  	while (sp < srcend && dp < destend)
  	{
  		/*
  		 * Read one control byte and process the next 8 items (or as many as
  		 * remain in the compressed input).
  		 */
  		unsigned char ctrl = *sp++;
  		int			ctrlc;
  
  		for (ctrlc = 0; ctrlc < 8 && sp < srcend; ctrlc++)
  		{
  			if (ctrl & 1)
  			{
  				/*
  				 * Otherwise it contains the match length minus 3 and the
  				 * upper 4 bits of the offset. The next following byte
  				 * contains the lower 8 bits of the offset. If the length is
  				 * coded as 18, another extension tag byte tells how much
  				 * longer the match really was (0-255).
  				 */
  				int32		len;
  				int32		off;
  
  				len = (sp[0] & 0x0f) + 3;
  				off = ((sp[0] & 0xf0) << 4) | sp[1];
  				sp += 2;
  				if (len == 18)
  					len += *sp++;
  
  				/*
  				 * Check for output buffer overrun, to ensure we don't clobber
  				 * memory in case of corrupt input.  Note: we must advance dp
  				 * here to ensure the error is detected below the loop.  We
  				 * don't simply put the elog inside the loop since that will
  				 * probably interfere with optimization.
  				 */
  				if (dp + len > destend)
  				{
  					dp += len;
  					break;
  				}
  
  				/*
  				 * Now we copy the bytes specified by the tag from OUTPUT to
  				 * OUTPUT. It is dangerous and platform dependent to use
  				 * memcpy() here, because the copied areas could overlap
  				 * extremely!
  				 */
  				while (len--)
  				{
  					*dp = dp[-off];
  					dp++;
  				}
  			}
  			else
  			{
  				/*
  				 * An unset control bit means LITERAL BYTE. So we just copy
  				 * one from INPUT to OUTPUT.
  				 */
  				if (dp >= destend)		/* check for buffer overrun */
  					break;		/* do not clobber memory */
  
  				*dp++ = *sp++;
  			}
  
  			/*
  			 * Advance the control bit
  			 */
  			ctrl >>= 1;
  		}
  	}
  
  	/*
  	 * Check we decompressed the right amount.
  	 */
  	if (dp != destend || sp != srcend)
  		return -1;
  
  	/*
  	 * That's it.
  	 */
  	return rawsize;
  }
  