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/*-------------------------------------------------------------------------
*
* off.h
* POSTGRES disk "offset" definitions.
*
*
* Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/off.h
*
*-------------------------------------------------------------------------
*/
#ifndef OFF_H
#define OFF_H
#include "storage/itemid.h"
/*
* OffsetNumber:
*
* this is a 1-based index into the linp (ItemIdData) array in the
* header of each disk page.
*/
typedef uint16 OffsetNumber;
#define InvalidOffsetNumber ((OffsetNumber) 0)
#define FirstOffsetNumber ((OffsetNumber) 1)
#define MaxOffsetNumber ((OffsetNumber) (BLCKSZ / sizeof(ItemIdData)))
#define OffsetNumberMask (0xffff) /* valid uint16 bits */
/* ----------------
* support macros
* ----------------
*/
/*
* OffsetNumberIsValid
* True iff the offset number is valid.
*/
#define OffsetNumberIsValid(offsetNumber) \
((bool) ((offsetNumber != InvalidOffsetNumber) && \
(offsetNumber <= MaxOffsetNumber)))
/*
* OffsetNumberNext
* OffsetNumberPrev
* Increments/decrements the argument. These macros look pointless
* but they help us disambiguate the different manipulations on
* OffsetNumbers (e.g., sometimes we subtract one from an
* OffsetNumber to move back, and sometimes we do so to form a
* real C array index).
*/
#define OffsetNumberNext(offsetNumber) \
((OffsetNumber) (1 + (offsetNumber)))
#define OffsetNumberPrev(offsetNumber) \
((OffsetNumber) (-1 + (offsetNumber)))
#endif /* OFF_H */
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