1 files changed, 121 insertions, 0 deletions
diff --git a/src/include/storage/block.h b/src/include/storage/block.h
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+++ b/src/include/storage/block.h
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+/*-------------------------------------------------------------------------
+ *
+ * block.h
+ *	  POSTGRES disk block definitions.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/block.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef BLOCK_H
+#define BLOCK_H
+
+/*
+ * BlockNumber:
+ *
+ * each data file (heap or index) is divided into postgres disk blocks
+ * (which may be thought of as the unit of i/o -- a postgres buffer
+ * contains exactly one disk block).  the blocks are numbered
+ * sequentially, 0 to 0xFFFFFFFE.
+ *
+ * InvalidBlockNumber is the same thing as P_NEW in bufmgr.h.
+ *
+ * the access methods, the buffer manager and the storage manager are
+ * more or less the only pieces of code that should be accessing disk
+ * blocks directly.
+ */
+typedef uint32 BlockNumber;
+
+#define InvalidBlockNumber		((BlockNumber) 0xFFFFFFFF)
+
+#define MaxBlockNumber			((BlockNumber) 0xFFFFFFFE)
+
+/*
+ * BlockId:
+ *
+ * this is a storage type for BlockNumber.  in other words, this type
+ * is used for on-disk structures (e.g., in HeapTupleData) whereas
+ * BlockNumber is the type on which calculations are performed (e.g.,
+ * in access method code).
+ *
+ * there doesn't appear to be any reason to have separate types except
+ * for the fact that BlockIds can be SHORTALIGN'd (and therefore any
+ * structures that contains them, such as ItemPointerData, can also be
+ * SHORTALIGN'd).  this is an important consideration for reducing the
+ * space requirements of the line pointer (ItemIdData) array on each
+ * page and the header of each heap or index tuple, so it doesn't seem
+ * wise to change this without good reason.
+ */
+typedef struct BlockIdData
+{
+	uint16		bi_hi;
+	uint16		bi_lo;
+} BlockIdData;
+
+typedef BlockIdData *BlockId;	/* block identifier */
+
+/* ----------------
+ *		support macros
+ * ----------------
+ */
+
+/*
+ * BlockNumberIsValid
+ *		True iff blockNumber is valid.
+ */
+#define BlockNumberIsValid(blockNumber) \
+	((bool) ((BlockNumber) (blockNumber) != InvalidBlockNumber))
+
+/*
+ * BlockIdIsValid
+ *		True iff the block identifier is valid.
+ */
+#define BlockIdIsValid(blockId) \
+	((bool) PointerIsValid(blockId))
+
+/*
+ * BlockIdSet
+ *		Sets a block identifier to the specified value.
+ */
+#define BlockIdSet(blockId, blockNumber) \
+( \
+	AssertMacro(PointerIsValid(blockId)), \
+	(blockId)->bi_hi = (blockNumber) >> 16, \
+	(blockId)->bi_lo = (blockNumber) & 0xffff \
+)
+
+/*
+ * BlockIdCopy
+ *		Copy a block identifier.
+ */
+#define BlockIdCopy(toBlockId, fromBlockId) \
+( \
+	AssertMacro(PointerIsValid(toBlockId)), \
+	AssertMacro(PointerIsValid(fromBlockId)), \
+	(toBlockId)->bi_hi = (fromBlockId)->bi_hi, \
+	(toBlockId)->bi_lo = (fromBlockId)->bi_lo \
+)
+
+/*
+ * BlockIdEquals
+ *		Check for block number equality.
+ */
+#define BlockIdEquals(blockId1, blockId2) \
+	((blockId1)->bi_hi == (blockId2)->bi_hi && \
+	 (blockId1)->bi_lo == (blockId2)->bi_lo)
+
+/*
+ * BlockIdGetBlockNumber
+ *		Retrieve the block number from a block identifier.
+ */
+#define BlockIdGetBlockNumber(blockId) \
+( \
+	AssertMacro(BlockIdIsValid(blockId)), \
+	(BlockNumber) (((blockId)->bi_hi << 16) | ((uint16) (blockId)->bi_lo)) \
+)
+
+#endif							/* BLOCK_H */