1 files changed, 67 insertions, 0 deletions
diff --git a/src/include/access/sdir.h b/src/include/access/sdir.h
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+++ b/src/include/access/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 */