/*-------------------------------------------------------------------------

 *

 * skipsupport.c

 *    Support routines for B-Tree skip scan.

 *

 *

 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group

 * Portions Copyright (c) 1994, Regents of the University of California

 *

 * IDENTIFICATION

 *    src/backend/utils/adt/skipsupport.c

 *

 *-------------------------------------------------------------------------

 */

#include "postgres.h"

#include "access/nbtree.h"

#include "utils/lsyscache.h"

#include "utils/skipsupport.h"

/*

 * Fill in SkipSupport given an operator class (opfamily + opcintype).

 *

 * On success, returns skip support struct, allocating in caller's memory

 * context.  Otherwise returns NULL, indicating that operator class has no

 * skip support function.

 */

SkipSupport

PrepareSkipSupportFromOpclass(Oid opfamily, Oid opcintype, bool reverse)

{

  Oid     skipSupportFunction;

  SkipSupport sksup;

  /* Look for a skip support function */

  skipSupportFunction = get_opfamily_proc(opfamily, opcintype, opcintype,

                      BTSKIPSUPPORT_PROC);

  if (!OidIsValid(skipSupportFunction))

    return NULL;

  sksup = palloc_object(SkipSupportData);

  OidFunctionCall1(skipSupportFunction, PointerGetDatum(sksup));

  if (reverse)

  {

    /*

     * DESC/reverse case: swap low_elem with high_elem, and swap decrement

     * with increment

     */

    Datum   low_elem = sksup->low_elem;

    SkipSupportIncDec decrement = sksup->decrement;

    sksup->low_elem = sksup->high_elem;

    sksup->decrement = sksup->increment;

    sksup->high_elem = low_elem;

    sksup->increment = decrement;

  }

  return sksup;

}