58 lines
1.5 KiB
C
58 lines
1.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* off.h
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* POSTGRES disk "offset" definitions.
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*
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/off.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef OFF_H
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#define OFF_H
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#include "storage/itemid.h"
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/*
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* OffsetNumber:
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*
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* this is a 1-based index into the linp (ItemIdData) array in the
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* header of each disk page.
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*/
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typedef uint16 OffsetNumber;
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#define InvalidOffsetNumber ((OffsetNumber) 0)
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#define FirstOffsetNumber ((OffsetNumber) 1)
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#define MaxOffsetNumber ((OffsetNumber) (BLCKSZ / sizeof(ItemIdData)))
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/* ----------------
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* support macros
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* ----------------
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*/
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/*
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* OffsetNumberIsValid
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* True iff the offset number is valid.
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*/
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#define OffsetNumberIsValid(offsetNumber) \
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((bool) ((offsetNumber != InvalidOffsetNumber) && \
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(offsetNumber <= MaxOffsetNumber)))
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/*
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* OffsetNumberNext
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* OffsetNumberPrev
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* Increments/decrements the argument. These macros look pointless
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* but they help us disambiguate the different manipulations on
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* OffsetNumbers (e.g., sometimes we subtract one from an
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* OffsetNumber to move back, and sometimes we do so to form a
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* real C array index).
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*/
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#define OffsetNumberNext(offsetNumber) \
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((OffsetNumber) (1 + (offsetNumber)))
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#define OffsetNumberPrev(offsetNumber) \
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((OffsetNumber) (-1 + (offsetNumber)))
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#endif /* OFF_H */
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