src/include/storage/off.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * off.h
   4  *        POSTGRES disk "offset" definitions.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/storage/off.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef OFF_H
  15 #define OFF_H
  16
  17 #include "storage/itemid.h"
  18 /*
  19  * OffsetNumber:
  20  *
  21  * this is a 1-based index into the linp (ItemIdData) array in the
  22  * header of each disk page.
  23  */
  24 typedef uint16 OffsetNumber;
  25
  26 #define InvalidOffsetNumber             ((OffsetNumber) 0)
  27 #define FirstOffsetNumber               ((OffsetNumber) 1)
  28 #define MaxOffsetNumber                 ((OffsetNumber) (BLCKSZ / sizeof(ItemIdData)))
  29
  30 /* ----------------
  31  *              support macros
  32  * ----------------
  33  */
  34
  35 /*
  36  * OffsetNumberIsValid
  37  *              True iff the offset number is valid.
  38  */
  39 #define OffsetNumberIsValid(offsetNumber) \
  40         ((bool) ((offsetNumber != InvalidOffsetNumber) && \
  41                          (offsetNumber <= MaxOffsetNumber)))
  42
  43 /*
  44  * OffsetNumberNext
  45  * OffsetNumberPrev
  46  *              Increments/decrements the argument.  These macros look pointless
  47  *              but they help us disambiguate the different manipulations on
  48  *              OffsetNumbers (e.g., sometimes we subtract one from an
  49  *              OffsetNumber to move back, and sometimes we do so to form a
  50  *              real C array index).
  51  */
  52 #define OffsetNumberNext(offsetNumber) \
  53         ((OffsetNumber) (1 + (offsetNumber)))
  54 #define OffsetNumberPrev(offsetNumber) \
  55         ((OffsetNumber) (-1 + (offsetNumber)))
  56
  57 #endif                                                  /* OFF_H */