/*-------------------------------------------------------------------------
 *
 * itemptr.h--
 *    POSTGRES disk item pointer definitions.
 *
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 * $Id: itemptr.h,v 1.2 1996/10/19 04:01:41 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef	ITEMPTR_H
#define ITEMPTR_H

#include "storage/block.h" 
#include "storage/off.h"

/*
 * ItemPointer:
 *
 * this is a pointer to an item on another disk page in the same file.
 * blkid tells us which block, posid tells us which entry in the linp
 * (ItemIdData) array we want.
 */
typedef struct ItemPointerData {
    BlockIdData		ip_blkid;
    OffsetNumber	ip_posid;
} ItemPointerData;

typedef ItemPointerData	*ItemPointer;

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

/*
 * ItemPointerIsValid --
 *	True iff the disk item pointer is not NULL.
 */
#define ItemPointerIsValid(pointer) \
    ((bool) (PointerIsValid(pointer) && ((pointer)->ip_posid != 0)))

/*
 * ItemPointerGetBlockNumber --
 *	Returns the block number of a disk item pointer.
 */
#define ItemPointerGetBlockNumber(pointer) \
    (AssertMacro(ItemPointerIsValid(pointer)) ? \
     BlockIdGetBlockNumber(&(pointer)->ip_blkid) : (BlockNumber) 0)

/*
 * ItemPointerGetOffsetNumber --
 *	Returns the offset number of a disk item pointer.
 */
#define ItemPointerGetOffsetNumber(pointer) \
    (AssertMacro(ItemPointerIsValid(pointer)) ? \
     (pointer)->ip_posid : \
     InvalidOffsetNumber)

/*
 * ItemPointerSet --
 *	Sets a disk item pointer to the specified block and offset.
 */
#define ItemPointerSet(pointer, blockNumber, offNum) \
    Assert(PointerIsValid(pointer)); \
    BlockIdSet(&((pointer)->ip_blkid), blockNumber); \
    (pointer)->ip_posid = offNum

/*
 * ItemPointerSetBlockNumber --
 *	Sets a disk item pointer to the specified block.
 */
#define ItemPointerSetBlockNumber(pointer, blockNumber) \
    Assert(PointerIsValid(pointer)); \
    BlockIdSet(&((pointer)->ip_blkid), blockNumber)

/*
 * ItemPointerSetOffsetNumber --
 *	Sets a disk item pointer to the specified offset.
 */
#define ItemPointerSetOffsetNumber(pointer, offsetNumber) \
    AssertMacro(PointerIsValid(pointer)); \
    (pointer)->ip_posid = (offsetNumber)

/*
 * ItemPointerCopy --
 *	Copies the contents of one disk item pointer to another.
 */
#define ItemPointerCopy(fromPointer, toPointer) \
    Assert(PointerIsValid(toPointer)); \
    Assert(PointerIsValid(fromPointer)); \
    *(toPointer) = *(fromPointer)

/*
 * ItemPointerSetInvalid --
 *	Sets a disk item pointer to be invalid.
 */
#define ItemPointerSetInvalid(pointer) \
    Assert(PointerIsValid(pointer)); \
    BlockIdSet(&((pointer)->ip_blkid), InvalidBlockNumber); \
    (pointer)->ip_posid = InvalidOffsetNumber

/* ----------------
 *	externs
 * ----------------
 */

extern bool ItemPointerEquals(ItemPointer pointer1, ItemPointer pointer2);

#endif	/* ITEMPTR_H */

