skipsupport.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * 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;
}