bitmapset.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

	/* Check extra words in a */
	for (; i < a->nwords; i++)
	{
		if (a->words[i] != 0)
			return true;
	}
	return false;
}

/*
 * bms_singleton_member - return the sole integer member of set
 *
 * Raises error if |a| is not 1.
 */
int
bms_singleton_member(const Bitmapset *a)
{
	int			result = -1;
	int			nwords;
	int			wordnum;

	if (a == NULL)
		elog(ERROR, "bitmapset is empty");
	nwords = a->nwords;
	for (wordnum = 0; wordnum < nwords; wordnum++)
	{
		bitmapword	w = a->words[wordnum];

		if (w != 0)
		{
			if (result >= 0 || HAS_MULTIPLE_ONES(w))
				elog(ERROR, "bitmapset has multiple members");
			result = wordnum * BITS_PER_BITMAPWORD;
			while ((w & 255) == 0)
			{
				w >>= 8;
				result += 8;
			}
			result += rightmost_one_pos[w & 255];
		}
	}
	if (result < 0)
		elog(ERROR, "bitmapset is empty");
	return result;
}

/*
 * bms_num_members - count members of set
 */
int
bms_num_members(const Bitmapset *a)
{
	int			result = 0;
	int			nwords;
	int			wordnum;

	if (a == NULL)
		return 0;
	nwords = a->nwords;
	for (wordnum = 0; wordnum < nwords; wordnum++)
	{
		bitmapword	w = a->words[wordnum];

		/* we assume here that bitmapword is an unsigned type */
		while (w != 0)
		{
			result += number_of_ones[w & 255];
			w >>= 8;
		}
	}
	return result;
}

/*
 * bms_membership - does a set have zero, one, or multiple members?
 *
 * This is faster than making an exact count with bms_num_members().
 */
BMS_Membership
bms_membership(const Bitmapset *a)
{
	BMS_Membership result = BMS_EMPTY_SET;
	int			nwords;
	int			wordnum;

	if (a == NULL)
		return BMS_EMPTY_SET;
	nwords = a->nwords;
	for (wordnum = 0; wordnum < nwords; wordnum++)
	{
		bitmapword	w = a->words[wordnum];

		if (w != 0)
		{
			if (result != BMS_EMPTY_SET || HAS_MULTIPLE_ONES(w))
				return BMS_MULTIPLE;
			result = BMS_SINGLETON;
		}
	}
	return result;
}

/*
 * bms_is_empty - is a set empty?
 *
 * This is even faster than bms_membership().
 */
bool
bms_is_empty(const Bitmapset *a)
{
	int			nwords;
	int			wordnum;

	if (a == NULL)
		return true;
	nwords = a->nwords;
	for (wordnum = 0; wordnum < nwords; wordnum++)
	{
		bitmapword	w = a->words[wordnum];

		if (w != 0)
			return false;
	}
	return true;
}


/*
 * These operations all "recycle" their non-const inputs, ie, either
 * return the modified input or pfree it if it can't hold the result.
 *
 * These should generally be used in the style
 *
 *		foo = bms_add_member(foo, x);
 */


/*
 * bms_add_member - add a specified member to set
 *
 * Input set is modified or recycled!
 */
Bitmapset *
bms_add_member(Bitmapset *a, int x)
{
	int			wordnum,
				bitnum;

	if (x < 0)
		elog(ERROR, "negative bitmapset member not allowed");
	if (a == NULL)
		return bms_make_singleton(x);
	wordnum = WORDNUM(x);
	bitnum = BITNUM(x);
	if (wordnum >= a->nwords)
	{
		/* Slow path: make a larger set and union the input set into it */
		Bitmapset  *result;
		int			nwords;
		int			i;

		result = bms_make_singleton(x);
		nwords = a->nwords;
		for (i = 0; i < nwords; i++)
			result->words[i] |= a->words[i];
		pfree(a);
		return result;
	}
	/* Fast path: x fits in existing set */
	a->words[wordnum] |= ((bitmapword) 1 << bitnum);
	return a;
}

/*
 * bms_del_member - remove a specified member from set
 *
 * No error if x is not currently a member of set
 *
 * Input set is modified in-place!
 */
Bitmapset *
bms_del_member(Bitmapset *a, int x)
{
	int			wordnum,
				bitnum;

	if (x < 0)
		elog(ERROR, "negative bitmapset member not allowed");
	if (a == NULL)
		return NULL;
	wordnum = WORDNUM(x);
	bitnum = BITNUM(x);
	if (wordnum < a->nwords)
		a->words[wordnum] &= ~((bitmapword) 1 << bitnum);
	return a;
}

/*
 * bms_add_members - like bms_union, but left input is recycled
 */
Bitmapset *
bms_add_members(Bitmapset *a, const Bitmapset *b)
{
	Bitmapset  *result;
	const Bitmapset *other;
	int			otherlen;
	int			i;

	/* Handle cases where either input is NULL */
	if (a == NULL)
		return bms_copy(b);
	if (b == NULL)
		return a;
	/* Identify shorter and longer input; copy the longer one if needed */
	if (a->nwords < b->nwords)
	{
		result = bms_copy(b);
		other = a;
	}
	else
	{
		result = a;
		other = b;
	}
	/* And union the shorter input into the result */
	otherlen = other->nwords;
	for (i = 0; i < otherlen; i++)
		result->words[i] |= other->words[i];
	if (result != a)
		pfree(a);
	return result;
}

/*
 * bms_int_members - like bms_intersect, but left input is recycled
 */
Bitmapset *
bms_int_members(Bitmapset *a, const Bitmapset *b)
{
	int			shortlen;
	int			i;

	/* Handle cases where either input is NULL */
	if (a == NULL)
		return NULL;
	if (b == NULL)
	{
		pfree(a);
		return NULL;
	}
	/* Intersect b into a; we need never copy */
	shortlen = Min(a->nwords, b->nwords);
	for (i = 0; i < shortlen; i++)
		a->words[i] &= b->words[i];
	for (; i < a->nwords; i++)
		a->words[i] = 0;
	return a;
}

/*
 * bms_del_members - like bms_difference, but left input is recycled
 */
Bitmapset *
bms_del_members(Bitmapset *a, const Bitmapset *b)
{
	int			shortlen;
	int			i;

	/* Handle cases where either input is NULL */
	if (a == NULL)
		return NULL;
	if (b == NULL)
		return a;
	/* Remove b's bits from a; we need never copy */
	shortlen = Min(a->nwords, b->nwords);
	for (i = 0; i < shortlen; i++)
		a->words[i] &= ~b->words[i];
	return a;
}

/*
 * bms_join - like bms_union, but *both* inputs are recycled
 */
Bitmapset *
bms_join(Bitmapset *a, Bitmapset *b)
{
	Bitmapset  *result;
	Bitmapset  *other;
	int			otherlen;
	int			i;

	/* Handle cases where either input is NULL */
	if (a == NULL)
		return b;
	if (b == NULL)
		return a;
	/* Identify shorter and longer input; use longer one as result */
	if (a->nwords < b->nwords)
	{
		result = b;
		other = a;
	}
	else
	{
		result = a;
		other = b;
	}
	/* And union the shorter input into the result */
	otherlen = other->nwords;
	for (i = 0; i < otherlen; i++)
		result->words[i] |= other->words[i];
	if (other != result)		/* pure paranoia */
		pfree(other);
	return result;
}

/*----------
 * bms_first_member - find and remove first member of a set
 *
 * Returns -1 if set is empty.	NB: set is destructively modified!
 *
 * This is intended as support for iterating through the members of a set.
 * The typical pattern is
 *
 *			tmpset = bms_copy(inputset);
 *			while ((x = bms_first_member(tmpset)) >= 0)
 *				process member x;
 *			bms_free(tmpset);
 *----------
 */
int
bms_first_member(Bitmapset *a)
{
	int			nwords;
	int			wordnum;

	if (a == NULL)
		return -1;
	nwords = a->nwords;
	for (wordnum = 0; wordnum < nwords; wordnum++)
	{
		bitmapword	w = a->words[wordnum];

		if (w != 0)
		{
			int			result;

			w = RIGHTMOST_ONE(w);
			a->words[wordnum] &= ~w;

			result = wordnum * BITS_PER_BITMAPWORD;
			while ((w & 255) == 0)
			{
				w >>= 8;
				result += 8;
			}
			result += rightmost_one_pos[w & 255];
			return result;
		}
	}
	return -1;
}

/*
 * bms_hash_value - compute a hash key for a Bitmapset
 *
 * Note: we must ensure that any two bitmapsets that are bms_equal() will
 * hash to the same value; in practice this means that trailing all-zero
 * words cannot affect the result.	The circular-shift-and-XOR hash method
 * used here has this property, so long as we work from back to front.
 *
 * Note: you might wonder why we bother with the circular shift; at first
 * glance a straight longitudinal XOR seems as good and much simpler.  The
 * reason is empirical: this gives a better distribution of hash values on
 * the bitmapsets actually generated by the planner.  A common way to have
 * multiword bitmapsets is "a JOIN b JOIN c JOIN d ...", which gives rise
 * to rangetables in which base tables and JOIN nodes alternate; so
 * bitmapsets of base table RT indexes tend to use only odd-numbered or only
 * even-numbered bits.	A straight longitudinal XOR would preserve this
 * property, leading to a much smaller set of possible outputs than if
 * we include a shift.
 */
uint32
bms_hash_value(const Bitmapset *a)
{
	bitmapword	result = 0;
	int			wordnum;

	if (a == NULL || a->nwords <= 0)
		return 0;				/* All empty sets hash to 0 */
	for (wordnum = a->nwords; --wordnum > 0;)
	{
		result ^= a->words[wordnum];
		if (result & ((bitmapword) 1 << (BITS_PER_BITMAPWORD - 1)))
			result = (result << 1) | 1;
		else
			result = (result << 1);
	}
	result ^= a->words[0];
	return (uint32) result;
}