Line data    Source code

       1              : /*-------------------------------------------------------------------------
       2              :  *
       3              :  * itemptr.c
       4              :  *    POSTGRES disk item pointer code.
       5              :  *
       6              :  * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
       7              :  * Portions Copyright (c) 1994, Regents of the University of California
       8              :  *
       9              :  *
      10              :  * IDENTIFICATION
      11              :  *    src/backend/storage/page/itemptr.c
      12              :  *
      13              :  *-------------------------------------------------------------------------
      14              :  */
      15              : #include "postgres.h"
      16              : 
      17              : #include "storage/itemptr.h"
      18              : 
      19              : 
      20              : /*
      21              :  * We really want ItemPointerData to be exactly 6 bytes.
      22              :  */
      23              : StaticAssertDecl(sizeof(ItemPointerData) == 3 * sizeof(uint16),
      24              :                  "ItemPointerData struct is improperly padded");
      25              : 
      26              : /*
      27              :  * ItemPointerEquals
      28              :  *  Returns true if both item pointers point to the same item,
      29              :  *   otherwise returns false.
      30              :  *
      31              :  * Note:
      32              :  *  Asserts that the disk item pointers are both valid!
      33              :  */
      34              : bool
      35      9510227 : ItemPointerEquals(const ItemPointerData *pointer1, const ItemPointerData *pointer2)
      36              : {
      37     19020454 :     if (ItemPointerGetBlockNumber(pointer1) ==
      38     12577965 :         ItemPointerGetBlockNumber(pointer2) &&
      39      3067738 :         ItemPointerGetOffsetNumber(pointer1) ==
      40      3067738 :         ItemPointerGetOffsetNumber(pointer2))
      41       945216 :         return true;
      42              :     else
      43      8565011 :         return false;
      44              : }
      45              : 
      46              : /*
      47              :  * ItemPointerCompare
      48              :  *      Generic btree-style comparison for item pointers.
      49              :  */
      50              : int32
      51     13805167 : ItemPointerCompare(const ItemPointerData *arg1, const ItemPointerData *arg2)
      52              : {
      53              :     /*
      54              :      * Use ItemPointerGet{Offset,Block}NumberNoCheck to avoid asserting
      55              :      * ip_posid != 0, which may not be true for a user-supplied TID.
      56              :      */
      57     13805167 :     BlockNumber b1 = ItemPointerGetBlockNumberNoCheck(arg1);
      58     13805167 :     BlockNumber b2 = ItemPointerGetBlockNumberNoCheck(arg2);
      59              : 
      60     13805167 :     if (b1 < b2)
      61       281850 :         return -1;
      62     13523317 :     else if (b1 > b2)
      63      9900982 :         return 1;
      64      7244670 :     else if (ItemPointerGetOffsetNumberNoCheck(arg1) <
      65      3622335 :              ItemPointerGetOffsetNumberNoCheck(arg2))
      66       565188 :         return -1;
      67      6114294 :     else if (ItemPointerGetOffsetNumberNoCheck(arg1) >
      68      3057147 :              ItemPointerGetOffsetNumberNoCheck(arg2))
      69      2129213 :         return 1;
      70              :     else
      71       927934 :         return 0;
      72              : }
      73              : 
      74              : /*
      75              :  * ItemPointerInc
      76              :  *      Increment 'pointer' by 1 only paying attention to the ItemPointer's
      77              :  *      type's range limits and not MaxOffsetNumber and FirstOffsetNumber.
      78              :  *      This may result in 'pointer' becoming !OffsetNumberIsValid.
      79              :  *
      80              :  * If the pointer is already the maximum possible values permitted by the
      81              :  * range of the ItemPointer's types, then do nothing.
      82              :  */
      83              : void
      84           53 : ItemPointerInc(ItemPointer pointer)
      85              : {
      86           53 :     BlockNumber blk = ItemPointerGetBlockNumberNoCheck(pointer);
      87           53 :     OffsetNumber off = ItemPointerGetOffsetNumberNoCheck(pointer);
      88              : 
      89           53 :     if (off == PG_UINT16_MAX)
      90              :     {
      91            6 :         if (blk != InvalidBlockNumber)
      92              :         {
      93            3 :             off = 0;
      94            3 :             blk++;
      95              :         }
      96              :     }
      97              :     else
      98           47 :         off++;
      99              : 
     100           53 :     ItemPointerSet(pointer, blk, off);
     101           53 : }
     102              : 
     103              : /*
     104              :  * ItemPointerDec
     105              :  *      Decrement 'pointer' by 1 only paying attention to the ItemPointer's
     106              :  *      type's range limits and not MaxOffsetNumber and FirstOffsetNumber.
     107              :  *      This may result in 'pointer' becoming !OffsetNumberIsValid.
     108              :  *
     109              :  * If the pointer is already the minimum possible values permitted by the
     110              :  * range of the ItemPointer's types, then do nothing.  This does rely on
     111              :  * FirstOffsetNumber being 1 rather than 0.
     112              :  */
     113              : void
     114           77 : ItemPointerDec(ItemPointer pointer)
     115              : {
     116           77 :     BlockNumber blk = ItemPointerGetBlockNumberNoCheck(pointer);
     117           77 :     OffsetNumber off = ItemPointerGetOffsetNumberNoCheck(pointer);
     118              : 
     119           77 :     if (off == 0)
     120              :     {
     121           45 :         if (blk != 0)
     122              :         {
     123           36 :             off = PG_UINT16_MAX;
     124           36 :             blk--;
     125              :         }
     126              :     }
     127              :     else
     128           32 :         off--;
     129              : 
     130           77 :     ItemPointerSet(pointer, blk, off);
     131           77 : }