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pg_include/storage/itemptr.h

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+/*-------------------------------------------------------------------------
+ *
+ * itemptr.h
+ *	  POSTGRES disk item pointer definitions.
+ *
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/itemptr.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef ITEMPTR_H
+#define ITEMPTR_H
+
+#include "storage/block.h"
+#include "storage/off.h"
+
+/*
+ * ItemPointer:
+ *
+ * This is a pointer to an item within a disk page of a known file
+ * (for example, a cross-link from an index to its parent table).
+ * blkid tells us which block, posid tells us which entry in the linp
+ * (ItemIdData) array we want.
+ *
+ * Note: because there is an item pointer in each tuple header and index
+ * tuple header on disk, it's very important not to waste space with
+ * structure padding bytes.  The struct is designed to be six bytes long
+ * (it contains three int16 fields) but a few compilers will pad it to
+ * eight bytes unless coerced.	We apply appropriate persuasion where
+ * possible, and to cope with unpersuadable compilers, we try to use
+ * "SizeOfIptrData" rather than "sizeof(ItemPointerData)" when computing
+ * on-disk sizes.
+ */
+typedef struct ItemPointerData
+{
+	BlockIdData ip_blkid;
+	OffsetNumber ip_posid;
+}
+
+#ifdef __arm__
+__attribute__((packed))			/* Appropriate whack upside the head for ARM */
+#endif
+ItemPointerData;
+
+#define SizeOfIptrData	\
+	(offsetof(ItemPointerData, ip_posid) + sizeof(OffsetNumber))
+
+typedef ItemPointerData *ItemPointer;
+
+/* ----------------
+ *		support macros
+ * ----------------
+ */
+
+/*
+ * ItemPointerIsValid
+ *		True iff the disk item pointer is not NULL.
+ */
+#define ItemPointerIsValid(pointer) \
+	((bool) (PointerIsValid(pointer) && ((pointer)->ip_posid != 0)))
+
+/*
+ * ItemPointerGetBlockNumber
+ *		Returns the block number of a disk item pointer.
+ */
+#define ItemPointerGetBlockNumber(pointer) \
+( \
+	AssertMacro(ItemPointerIsValid(pointer)), \
+	BlockIdGetBlockNumber(&(pointer)->ip_blkid) \
+)
+
+/*
+ * ItemPointerGetOffsetNumber
+ *		Returns the offset number of a disk item pointer.
+ */
+#define ItemPointerGetOffsetNumber(pointer) \
+( \
+	AssertMacro(ItemPointerIsValid(pointer)), \
+	(pointer)->ip_posid \
+)
+
+/*
+ * ItemPointerSet
+ *		Sets a disk item pointer to the specified block and offset.
+ */
+#define ItemPointerSet(pointer, blockNumber, offNum) \
+( \
+	AssertMacro(PointerIsValid(pointer)), \
+	BlockIdSet(&((pointer)->ip_blkid), blockNumber), \
+	(pointer)->ip_posid = offNum \
+)
+
+/*
+ * ItemPointerSetBlockNumber
+ *		Sets a disk item pointer to the specified block.
+ */
+#define ItemPointerSetBlockNumber(pointer, blockNumber) \
+( \
+	AssertMacro(PointerIsValid(pointer)), \
+	BlockIdSet(&((pointer)->ip_blkid), blockNumber) \
+)
+
+/*
+ * ItemPointerSetOffsetNumber
+ *		Sets a disk item pointer to the specified offset.
+ */
+#define ItemPointerSetOffsetNumber(pointer, offsetNumber) \
+( \
+	AssertMacro(PointerIsValid(pointer)), \
+	(pointer)->ip_posid = (offsetNumber) \
+)
+
+/*
+ * ItemPointerCopy
+ *		Copies the contents of one disk item pointer to another.
+ */
+#define ItemPointerCopy(fromPointer, toPointer) \
+( \
+	AssertMacro(PointerIsValid(toPointer)), \
+	AssertMacro(PointerIsValid(fromPointer)), \
+	*(toPointer) = *(fromPointer) \
+)
+
+/*
+ * ItemPointerSetInvalid
+ *		Sets a disk item pointer to be invalid.
+ */
+#define ItemPointerSetInvalid(pointer) \
+( \
+	AssertMacro(PointerIsValid(pointer)), \
+	BlockIdSet(&((pointer)->ip_blkid), InvalidBlockNumber), \
+	(pointer)->ip_posid = InvalidOffsetNumber \
+)
+
+/* ----------------
+ *		externs
+ * ----------------
+ */
+
+extern bool ItemPointerEquals(ItemPointer pointer1, ItemPointer pointer2);
+extern int32 ItemPointerCompare(ItemPointer arg1, ItemPointer arg2);
+
+#endif   /* ITEMPTR_H */