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/*-------------------------------------------------------------------------
*
* skipsupport.c
* Support routines for B-Tree skip scan.
*
*
* Portions Copyright (c) 1996-2025, 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(sizeof(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;
}
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