/*-------------------------------------------------------------------------
 *
 * pos.h--
 *    POSTGRES "position" definitions.
 *
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 * $Id: pos.h,v 1.2 1996/10/31 09:50:04 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef	POS_H
#define POS_H

/*
 * a 'position' used to be <pagenumber, offset> in postgres.  this has
 * been changed to just <offset> as the notion of having multiple pages
 * within a block has been removed.
 *
 * the 'offset' abstraction is somewhat confusing.  it is NOT a byte
 * offset within the page; instead, it is an offset into the line
 * pointer array contained on every page that store (heap or index)
 * tuples.
 */
typedef bits16		PositionIdData;
typedef PositionIdData	*PositionId;

/* ----------------
 *	support macros
 * ----------------
 */

/*
 * PositionIdIsValid --
 *	True iff the position identifier is valid.
 */
#define PositionIdIsValid(positionId) \
    PointerIsValid(positionId)

/*
 * PositionIdSetInvalid --
 *      Make an invalid position.
 */
#define PositionIdSetInvalid(positionId) \
    *(positionId) = (bits16) 0

/*
 * PositionIdSet --
 *	Sets a position identifier to the specified value.
 */
#define PositionIdSet(positionId, offsetNumber) \
    *(positionId) = (offsetNumber)

/*
 * PositionIdGetOffsetNumber --
 *	Retrieve the offset number from a position identifier.
 */
#define PositionIdGetOffsetNumber(positionId) \
    ((OffsetNumber) *(positionId))

#endif	/*  POS_H */
