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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 */