sdir.h

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/*-------------------------------------------------------------------------
 *
 * sdir.h
 *    POSTGRES scan direction definitions.
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/sdir.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SDIR_H
#define SDIR_H
 
 
/*
 * Defines the direction for scanning a table or an index.  Scans are never
 * invoked using NoMovementScanDirectionScans.  For convenience, we use the
 * values -1 and 1 for backward and forward scans.  This allows us to perform
 * a few mathematical tricks such as what is done in ScanDirectionCombine.
 */
typedef enum ScanDirection
{
    BackwardScanDirection = -1,
    NoMovementScanDirection = 0,
    ForwardScanDirection = 1
} ScanDirection;
 
/*
 * Determine the net effect of two direction specifications.
 * This relies on having ForwardScanDirection = +1, BackwardScanDirection = -1,
 * and will probably not do what you want if applied to any other values.
 */
#define ScanDirectionCombine(a, b)  ((a) * (b))
 
/*
 * ScanDirectionIsValid
 *      True iff scan direction is valid.
 */
#define ScanDirectionIsValid(direction) \
    ((bool) (BackwardScanDirection <= (direction) && \
             (direction) <= ForwardScanDirection))
 
/*
 * ScanDirectionIsBackward
 *      True iff scan direction is backward.
 */
#define ScanDirectionIsBackward(direction) \
    ((bool) ((direction) == BackwardScanDirection))
 
/*
 * ScanDirectionIsNoMovement
 *      True iff scan direction indicates no movement.
 */
#define ScanDirectionIsNoMovement(direction) \
    ((bool) ((direction) == NoMovementScanDirection))
 
/*
 * ScanDirectionIsForward
 *      True iff scan direction is forward.
 */
#define ScanDirectionIsForward(direction) \
    ((bool) ((direction) == ForwardScanDirection))
 
#endif                          /* SDIR_H */