1 files changed, 57 insertions, 0 deletions
diff --git a/src/include/storage/off.h b/src/include/storage/off.h
new file mode 100644
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--- /dev/null
+++ b/src/include/storage/off.h
@@ -0,0 +1,57 @@
+/*-------------------------------------------------------------------------
+ *
+ * off.h
+ *	  POSTGRES disk "offset" definitions.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/off.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef OFF_H
+#define OFF_H
+
+#include "storage/itemid.h"
+/*
+ * OffsetNumber:
+ *
+ * this is a 1-based index into the linp (ItemIdData) array in the
+ * header of each disk page.
+ */
+typedef uint16 OffsetNumber;
+
+#define InvalidOffsetNumber		((OffsetNumber) 0)
+#define FirstOffsetNumber		((OffsetNumber) 1)
+#define MaxOffsetNumber			((OffsetNumber) (BLCKSZ / sizeof(ItemIdData)))
+
+/* ----------------
+ *		support macros
+ * ----------------
+ */
+
+/*
+ * OffsetNumberIsValid
+ *		True iff the offset number is valid.
+ */
+#define OffsetNumberIsValid(offsetNumber) \
+	((bool) ((offsetNumber != InvalidOffsetNumber) && \
+			 (offsetNumber <= MaxOffsetNumber)))
+
+/*
+ * OffsetNumberNext
+ * OffsetNumberPrev
+ *		Increments/decrements the argument.  These macros look pointless
+ *		but they help us disambiguate the different manipulations on
+ *		OffsetNumbers (e.g., sometimes we subtract one from an
+ *		OffsetNumber to move back, and sometimes we do so to form a
+ *		real C array index).
+ */
+#define OffsetNumberNext(offsetNumber) \
+	((OffsetNumber) (1 + (offsetNumber)))
+#define OffsetNumberPrev(offsetNumber) \
+	((OffsetNumber) (-1 + (offsetNumber)))
+
+#endif							/* OFF_H */