text: /*
   * contrib/hstore/hstore_gist.c
   */
  #include "postgres.h"
  
  #include "access/gist.h"
  #include "access/stratnum.h"
  #include "catalog/pg_type.h"
  #include "hstore.h"
  #include "utils/pg_crc.h"
  
  /* bigint defines */
  #define BITBYTE 8
  #define SIGLENINT  4			/* >122 => key will toast, so very slow!!! */
  #define SIGLEN	( sizeof(int)*SIGLENINT )
  #define SIGLENBIT (SIGLEN*BITBYTE)
  
  typedef char BITVEC[SIGLEN];
  typedef char *BITVECP;
  
  #define LOOPBYTE \
  			for(i=0;i<SIGLEN;i++)
  
  #define LOOPBIT \
  			for(i=0;i<SIGLENBIT;i++)
  
  /* beware of multiple evaluation of arguments to these macros! */
  #define GETBYTE(x,i) ( *( (BITVECP)(x) + (int)( (i) / BITBYTE ) ) )
  #define GETBITBYTE(x,i) ( (*((char*)(x)) >> (i)) & 0x01 )
  #define CLRBIT(x,i)   GETBYTE(x,i) &= ~( 0x01 << ( (i) % BITBYTE ) )
  #define SETBIT(x,i)   GETBYTE(x,i) |=  ( 0x01 << ( (i) % BITBYTE ) )
  #define GETBIT(x,i) ( (GETBYTE(x,i) >> ( (i) % BITBYTE )) & 0x01 )
  #define HASHVAL(val) (((unsigned int)(val)) % SIGLENBIT)
  #define HASH(sign, val) SETBIT((sign), HASHVAL(val))
  
  typedef struct
  {
  	int32		vl_len_;		/* varlena header (do not touch directly!) */
  	int32		flag;
  	char		data[FLEXIBLE_ARRAY_MEMBER];
  } GISTTYPE;
  
  #define ALLISTRUE		0x04
  
  #define ISALLTRUE(x)	( ((GISTTYPE*)x)->flag & ALLISTRUE )
  
  #define GTHDRSIZE		(VARHDRSZ + sizeof(int32))
  #define CALCGTSIZE(flag) ( GTHDRSIZE+(((flag) & ALLISTRUE) ? 0 : SIGLEN) )
  
  #define GETSIGN(x)		( (BITVECP)( (char*)x+GTHDRSIZE ) )
  
  #define SUMBIT(val) (		\
  	GETBITBYTE((val),0) + \
  	GETBITBYTE((val),1) + \
  	GETBITBYTE((val),2) + \
  	GETBITBYTE((val),3) + \
  	GETBITBYTE((val),4) + \
  	GETBITBYTE((val),5) + \
  	GETBITBYTE((val),6) + \
  	GETBITBYTE((val),7)   \
  )
  
  #define GETENTRY(vec,pos) ((GISTTYPE *) DatumGetPointer((vec)->vector[(pos)].key))
  
  #define WISH_F(a,b,c) (double)( -(double)(((a)-(b))*((a)-(b))*((a)-(b)))*(c) )
  
  /* shorthand for calculating CRC-32 of a single chunk of data. */
  static pg_crc32
  crc32_sz(char *buf, int size)
  {
  	pg_crc32	crc;
  
  	INIT_TRADITIONAL_CRC32(crc);
  	COMP_TRADITIONAL_CRC32(crc, buf, size);
  	FIN_TRADITIONAL_CRC32(crc);
  
  	return crc;
  }
  
  
  PG_FUNCTION_INFO_V1(ghstore_in);
  PG_FUNCTION_INFO_V1(ghstore_out);
  
  
  Datum
  ghstore_in(PG_FUNCTION_ARGS)
  {
  	elog(ERROR, "Not implemented");
  	PG_RETURN_DATUM(0);
  }
  
  Datum
  ghstore_out(PG_FUNCTION_ARGS)
  {
  	elog(ERROR, "Not implemented");
  	PG_RETURN_DATUM(0);
  }
  
  PG_FUNCTION_INFO_V1(ghstore_consistent);
  PG_FUNCTION_INFO_V1(ghstore_compress);
  PG_FUNCTION_INFO_V1(ghstore_decompress);
  PG_FUNCTION_INFO_V1(ghstore_penalty);
  PG_FUNCTION_INFO_V1(ghstore_picksplit);
  PG_FUNCTION_INFO_V1(ghstore_union);
  PG_FUNCTION_INFO_V1(ghstore_same);
  
  Datum
  ghstore_compress(PG_FUNCTION_ARGS)
  {
  	GISTENTRY  *entry = (GISTENTRY *) PG_GETARG_POINTER(0);
  	GISTENTRY  *retval = entry;
  
  	if (entry->leafkey)
  	{
  		GISTTYPE   *res = (GISTTYPE *) palloc0(CALCGTSIZE(0));
  		HStore	   *val = DatumGetHStoreP(entry->key);
  		HEntry	   *hsent = ARRPTR(val);
  		char	   *ptr = STRPTR(val);
  		int			count = HS_COUNT(val);
  		int			i;
  
  		SET_VARSIZE(res, CALCGTSIZE(0));
  
  		for (i = 0; i < count; ++i)
  		{
  			int			h;
  
  			h = crc32_sz((char *) HSTORE_KEY(hsent, ptr, i),
  						 HSTORE_KEYLEN(hsent, i));
  			HASH(GETSIGN(res), h);
  			if (!HSTORE_VALISNULL(hsent, i))
  			{
  				h = crc32_sz((char *) HSTORE_VAL(hsent, ptr, i),
  							 HSTORE_VALLEN(hsent, i));
  				HASH(GETSIGN(res), h);
  			}
  		}
  
  		retval = (GISTENTRY *) palloc(sizeof(GISTENTRY));
  		gistentryinit(*retval, PointerGetDatum(res),
  					  entry->rel, entry->page,
  					  entry->offset,
  					  false);
  	}
  	else if (!ISALLTRUE(DatumGetPointer(entry->key)))
  	{
  		int32		i;
  		GISTTYPE   *res;
  		BITVECP		sign = GETSIGN(DatumGetPointer(entry->key));
  
  		LOOPBYTE
  		{
  			if ((sign[i] & 0xff) != 0xff)
  				PG_RETURN_POINTER(retval);
  		}
  
  		res = (GISTTYPE *) palloc(CALCGTSIZE(ALLISTRUE));
  		SET_VARSIZE(res, CALCGTSIZE(ALLISTRUE));
  		res->flag = ALLISTRUE;
  
  		retval = (GISTENTRY *) palloc(sizeof(GISTENTRY));
  		gistentryinit(*retval, PointerGetDatum(res),
  					  entry->rel, entry->page,
  					  entry->offset,
  					  false);
  	}
  
  	PG_RETURN_POINTER(retval);
  }
  
  /*
   * Since type ghstore isn't toastable (and doesn't need to be),
   * this function can be a no-op.
   */
  Datum
  ghstore_decompress(PG_FUNCTION_ARGS)
  {
  	PG_RETURN_POINTER(PG_GETARG_POINTER(0));
  }
  
  Datum
  ghstore_same(PG_FUNCTION_ARGS)
  {
  	GISTTYPE   *a = (GISTTYPE *) PG_GETARG_POINTER(0);
  	GISTTYPE   *b = (GISTTYPE *) PG_GETARG_POINTER(1);
  	bool	   *result = (bool *) PG_GETARG_POINTER(2);
  
  	if (ISALLTRUE(a) && ISALLTRUE(b))
  		*result = true;
  	else if (ISALLTRUE(a))
  		*result = false;
  	else if (ISALLTRUE(b))
  		*result = false;
  	else
  	{
  		int32		i;
  		BITVECP		sa = GETSIGN(a),
  					sb = GETSIGN(b);
  
  		*result = true;
  		LOOPBYTE
  		{
  			if (sa[i] != sb[i])
  			{
  				*result = false;
  				break;
  			}
  		}
  	}
  	PG_RETURN_POINTER(result);
  }
  
  static int32
  sizebitvec(BITVECP sign)
  {
  	int32		size = 0,
  				i;
  
  	LOOPBYTE
  	{
  		size += SUMBIT(sign);
  		sign = (BITVECP) (((char *) sign) + 1);
  	}
  	return size;
  }
  
  static int
  hemdistsign(BITVECP a, BITVECP b)
  {
  	int			i,
  				dist = 0;
  
  	LOOPBIT
  	{
  		if (GETBIT(a, i) != GETBIT(b, i))
  			dist++;
  	}
  	return dist;
  }
  
  static int
  hemdist(GISTTYPE *a, GISTTYPE *b)
  {
  	if (ISALLTRUE(a))
  	{
  		if (ISALLTRUE(b))
  			return 0;
  		else
  			return SIGLENBIT - sizebitvec(GETSIGN(b));
  	}
  	else if (ISALLTRUE(b))
  		return SIGLENBIT - sizebitvec(GETSIGN(a));
  
  	return hemdistsign(GETSIGN(a), GETSIGN(b));
  }
  
  static int32
  unionkey(BITVECP sbase, GISTTYPE *add)
  {
  	int32		i;
  	BITVECP		sadd = GETSIGN(add);
  
  	if (ISALLTRUE(add))
  		return 1;
  	LOOPBYTE
  		sbase[i] |= sadd[i];
  	return 0;
  }
  
  Datum
  ghstore_union(PG_FUNCTION_ARGS)
  {
  	GistEntryVector *entryvec = (GistEntryVector *) PG_GETARG_POINTER(0);
  	int32		len = entryvec->n;
  
  	int		   *size = (int *) PG_GETARG_POINTER(1);
  	BITVEC		base;
  	int32		i;
  	int32		flag = 0;
  	GISTTYPE   *result;
  
  	MemSet((void *) base, 0, sizeof(BITVEC));
  	for (i = 0; i < len; i++)
  	{
  		if (unionkey(base, GETENTRY(entryvec, i)))
  		{
  			flag = ALLISTRUE;
  			break;
  		}
  	}
  
  	len = CALCGTSIZE(flag);
  	result = (GISTTYPE *) palloc(len);
  	SET_VARSIZE(result, len);
  	result->flag = flag;
  	if (!ISALLTRUE(result))
  		memcpy((void *) GETSIGN(result), (void *) base, sizeof(BITVEC));
  	*size = len;
  
  	PG_RETURN_POINTER(result);
  }
  
  Datum
  ghstore_penalty(PG_FUNCTION_ARGS)
  {
  	GISTENTRY  *origentry = (GISTENTRY *) PG_GETARG_POINTER(0); /* always ISSIGNKEY */
  	GISTENTRY  *newentry = (GISTENTRY *) PG_GETARG_POINTER(1);
  	float	   *penalty = (float *) PG_GETARG_POINTER(2);
  	GISTTYPE   *origval = (GISTTYPE *) DatumGetPointer(origentry->key);
  	GISTTYPE   *newval = (GISTTYPE *) DatumGetPointer(newentry->key);
  
  	*penalty = hemdist(origval, newval);
  	PG_RETURN_POINTER(penalty);
  }
  
  
  typedef struct
  {
  	OffsetNumber pos;
  	int32		cost;
  } SPLITCOST;
  
  static int
  comparecost(const void *a, const void *b)
  {
  	return ((const SPLITCOST *) a)->cost - ((const SPLITCOST *) b)->cost;
  }
  
  
  Datum
  ghstore_picksplit(PG_FUNCTION_ARGS)
  {
  	GistEntryVector *entryvec = (GistEntryVector *) PG_GETARG_POINTER(0);
  	OffsetNumber maxoff = entryvec->n - 2;
  
  	GIST_SPLITVEC *v = (GIST_SPLITVEC *) PG_GETARG_POINTER(1);
  	OffsetNumber k,
  				j;
  	GISTTYPE   *datum_l,
  			   *datum_r;
  	BITVECP		union_l,
  				union_r;
  	int32		size_alpha,
  				size_beta;
  	int32		size_waste,
  				waste = -1;
  	int32		nbytes;
  	OffsetNumber seed_1 = 0,
  				seed_2 = 0;
  	OffsetNumber *left,
  			   *right;
  	BITVECP		ptr;
  	int			i;
  	SPLITCOST  *costvector;
  	GISTTYPE   *_k,
  			   *_j;
  
  	nbytes = (maxoff + 2) * sizeof(OffsetNumber);
  	v->spl_left = (OffsetNumber *) palloc(nbytes);
  	v->spl_right = (OffsetNumber *) palloc(nbytes);
  
  	for (k = FirstOffsetNumber; k < maxoff; k = OffsetNumberNext(k))
  	{
  		_k = GETENTRY(entryvec, k);
  		for (j = OffsetNumberNext(k); j <= maxoff; j = OffsetNumberNext(j))
  		{
  			size_waste = hemdist(_k, GETENTRY(entryvec, j));
  			if (size_waste > waste)
  			{
  				waste = size_waste;
  				seed_1 = k;
  				seed_2 = j;
  			}
  		}
  	}
  
  	left = v->spl_left;
  	v->spl_nleft = 0;
  	right = v->spl_right;
  	v->spl_nright = 0;
  
  	if (seed_1 == 0 || seed_2 == 0)
  	{
  		seed_1 = 1;
  		seed_2 = 2;
  	}
  
  	/* form initial .. */
  	if (ISALLTRUE(GETENTRY(entryvec, seed_1)))
  	{
  		datum_l = (GISTTYPE *) palloc(GTHDRSIZE);
  		SET_VARSIZE(datum_l, GTHDRSIZE);
  		datum_l->flag = ALLISTRUE;
  	}
  	else
  	{
  		datum_l = (GISTTYPE *) palloc(GTHDRSIZE + SIGLEN);
  		SET_VARSIZE(datum_l, GTHDRSIZE + SIGLEN);
  		datum_l->flag = 0;
  		memcpy((void *) GETSIGN(datum_l), (void *) GETSIGN(GETENTRY(entryvec, seed_1)), sizeof(BITVEC))
  			;
  	}
  	if (ISALLTRUE(GETENTRY(entryvec, seed_2)))
  	{
  		datum_r = (GISTTYPE *) palloc(GTHDRSIZE);
  		SET_VARSIZE(datum_r, GTHDRSIZE);
  		datum_r->flag = ALLISTRUE;
  	}
  	else
  	{
  		datum_r = (GISTTYPE *) palloc(GTHDRSIZE + SIGLEN);
  		SET_VARSIZE(datum_r, GTHDRSIZE + SIGLEN);
  		datum_r->flag = 0;
  		memcpy((void *) GETSIGN(datum_r), (void *) GETSIGN(GETENTRY(entryvec, seed_2)), sizeof(BITVEC));
  	}
  
  	maxoff = OffsetNumberNext(maxoff);
  	/* sort before ... */
  	costvector = (SPLITCOST *) palloc(sizeof(SPLITCOST) * maxoff);
  	for (j = FirstOffsetNumber; j <= maxoff; j = OffsetNumberNext(j))
  	{
  		costvector[j - 1].pos = j;
  		_j = GETENTRY(entryvec, j);
  		size_alpha = hemdist(datum_l, _j);
  		size_beta = hemdist(datum_r, _j);
  		costvector[j - 1].cost = abs(size_alpha - size_beta);
  	}
  	qsort((void *) costvector, maxoff, sizeof(SPLITCOST), comparecost);
  
  	union_l = GETSIGN(datum_l);
  	union_r = GETSIGN(datum_r);
  
  	for (k = 0; k < maxoff; k++)
  	{
  		j = costvector[k].pos;
  		if (j == seed_1)
  		{
  			*left++ = j;
  			v->spl_nleft++;
  			continue;
  		}
  		else if (j == seed_2)
  		{
  			*right++ = j;
  			v->spl_nright++;
  			continue;
  		}
  		_j = GETENTRY(entryvec, j);
  		size_alpha = hemdist(datum_l, _j);
  		size_beta = hemdist(datum_r, _j);
  
  		if (size_alpha < size_beta + WISH_F(v->spl_nleft, v->spl_nright, 0.0001))
  		{
  			if (ISALLTRUE(datum_l) || ISALLTRUE(_j))
  			{
  				if (!ISALLTRUE(datum_l))
  					MemSet((void *) union_l, 0xff, sizeof(BITVEC));
  			}
  			else
  			{
  				ptr = GETSIGN(_j);
  				LOOPBYTE
  					union_l[i] |= ptr[i];
  			}
  			*left++ = j;
  			v->spl_nleft++;
  		}
  		else
  		{
  			if (ISALLTRUE(datum_r) || ISALLTRUE(_j))
  			{
  				if (!ISALLTRUE(datum_r))
  					MemSet((void *) union_r, 0xff, sizeof(BITVEC));
  			}
  			else
  			{
  				ptr = GETSIGN(_j);
  				LOOPBYTE
  					union_r[i] |= ptr[i];
  			}
  			*right++ = j;
  			v->spl_nright++;
  		}
  	}
  
  	*right = *left = FirstOffsetNumber;
  
  	v->spl_ldatum = PointerGetDatum(datum_l);
  	v->spl_rdatum = PointerGetDatum(datum_r);
  
  	PG_RETURN_POINTER(v);
  }
  
  
  Datum
  ghstore_consistent(PG_FUNCTION_ARGS)
  {
  	GISTTYPE   *entry = (GISTTYPE *) DatumGetPointer(((GISTENTRY *) PG_GETARG_POINTER(0))->key);
  	StrategyNumber strategy = (StrategyNumber) PG_GETARG_UINT16(2);
  
  	/* Oid		subtype = PG_GETARG_OID(3); */
  	bool	   *recheck = (bool *) PG_GETARG_POINTER(4);
  	bool		res = true;
  	BITVECP		sign;
  
  	/* All cases served by this function are inexact */
  	*recheck = true;
  
  	if (ISALLTRUE(entry))
  		PG_RETURN_BOOL(true);
  
  	sign = GETSIGN(entry);
  
  	if (strategy == HStoreContainsStrategyNumber ||
  		strategy == HStoreOldContainsStrategyNumber)
  	{
  		HStore	   *query = PG_GETARG_HSTORE_P(1);
  		HEntry	   *qe = ARRPTR(query);
  		char	   *qv = STRPTR(query);
  		int			count = HS_COUNT(query);
  		int			i;
  
  		for (i = 0; res && i < count; ++i)
  		{
  			int			crc = crc32_sz((char *) HSTORE_KEY(qe, qv, i),
  									   HSTORE_KEYLEN(qe, i));
  
  			if (GETBIT(sign, HASHVAL(crc)))
  			{
  				if (!HSTORE_VALISNULL(qe, i))
  				{
  					crc = crc32_sz((char *) HSTORE_VAL(qe, qv, i),
  								   HSTORE_VALLEN(qe, i));
  					if (!GETBIT(sign, HASHVAL(crc)))
  						res = false;
  				}
  			}
  			else
  				res = false;
  		}
  	}
  	else if (strategy == HStoreExistsStrategyNumber)
  	{
  		text	   *query = PG_GETARG_TEXT_PP(1);
  		int			crc = crc32_sz(VARDATA_ANY(query), VARSIZE_ANY_EXHDR(query));
  
  		res = (GETBIT(sign, HASHVAL(crc))) ? true : false;
  	}
  	else if (strategy == HStoreExistsAllStrategyNumber)
  	{
  		ArrayType  *query = PG_GETARG_ARRAYTYPE_P(1);
  		Datum	   *key_datums;
  		bool	   *key_nulls;
  		int			key_count;
  		int			i;
  
  		deconstruct_array(query,
  						  TEXTOID, -1, false, TYPALIGN_INT,
  						  &key_datums, &key_nulls, &key_count);
  
  		for (i = 0; res && i < key_count; ++i)
  		{
  			int			crc;
  
  			if (key_nulls[i])
  				continue;
  			crc = crc32_sz(VARDATA(key_datums[i]), VARSIZE(key_datums[i]) - VARHDRSZ);
  			if (!(GETBIT(sign, HASHVAL(crc))))
  				res = false;
  		}
  	}
  	else if (strategy == HStoreExistsAnyStrategyNumber)
  	{
  		ArrayType  *query = PG_GETARG_ARRAYTYPE_P(1);
  		Datum	   *key_datums;
  		bool	   *key_nulls;
  		int			key_count;
  		int			i;
  
  		deconstruct_array(query,
  						  TEXTOID, -1, false, TYPALIGN_INT,
  						  &key_datums, &key_nulls, &key_count);
  
  		res = false;
  
  		for (i = 0; !res && i < key_count; ++i)
  		{
  			int			crc;
  
  			if (key_nulls[i])
  				continue;
  			crc = crc32_sz(VARDATA(key_datums[i]), VARSIZE(key_datums[i]) - VARHDRSZ);
  			if (GETBIT(sign, HASHVAL(crc)))
  				res = true;
  		}
  	}
  	else
  		elog(ERROR, "Unsupported strategy number: %d", strategy);
  
  	PG_RETURN_BOOL(res);
  }
  