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diff --git a/src/include/access/itup.h b/src/include/access/itup.h
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+/*-------------------------------------------------------------------------
+ *
+ * itup.h
+ *	  POSTGRES index tuple definitions.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/access/itup.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef ITUP_H
+#define ITUP_H
+
+#include "access/tupdesc.h"
+#include "access/tupmacs.h"
+#include "storage/bufpage.h"
+#include "storage/itemptr.h"
+
+/*
+ * Index tuple header structure
+ *
+ * All index tuples start with IndexTupleData.  If the HasNulls bit is set,
+ * this is followed by an IndexAttributeBitMapData.  The index attribute
+ * values follow, beginning at a MAXALIGN boundary.
+ *
+ * Note that the space allocated for the bitmap does not vary with the number
+ * of attributes; that is because we don't have room to store the number of
+ * attributes in the header.  Given the MAXALIGN constraint there's no space
+ * savings to be had anyway, for usual values of INDEX_MAX_KEYS.
+ */
+
+typedef struct IndexTupleData
+{
+	ItemPointerData t_tid;		/* reference TID to heap tuple */
+
+	/* ---------------
+	 * t_info is laid out in the following fashion:
+	 *
+	 * 15th (high) bit: has nulls
+	 * 14th bit: has var-width attributes
+	 * 13th bit: AM-defined meaning
+	 * 12-0 bit: size of tuple
+	 * ---------------
+	 */
+
+	unsigned short t_info;		/* various info about tuple */
+
+} IndexTupleData;				/* MORE DATA FOLLOWS AT END OF STRUCT */
+
+typedef IndexTupleData *IndexTuple;
+
+typedef struct IndexAttributeBitMapData
+{
+	bits8		bits[(INDEX_MAX_KEYS + 8 - 1) / 8];
+}			IndexAttributeBitMapData;
+
+typedef IndexAttributeBitMapData * IndexAttributeBitMap;
+
+/*
+ * t_info manipulation macros
+ */
+#define INDEX_SIZE_MASK 0x1FFF
+#define INDEX_AM_RESERVED_BIT 0x2000	/* reserved for index-AM specific
+										 * usage */
+#define INDEX_VAR_MASK	0x4000
+#define INDEX_NULL_MASK 0x8000
+
+#define IndexTupleSize(itup)		((Size) ((itup)->t_info & INDEX_SIZE_MASK))
+#define IndexTupleHasNulls(itup)	((((IndexTuple) (itup))->t_info & INDEX_NULL_MASK))
+#define IndexTupleHasVarwidths(itup) ((((IndexTuple) (itup))->t_info & INDEX_VAR_MASK))
+
+
+/*
+ * Takes an infomask as argument (primarily because this needs to be usable
+ * at index_form_tuple time so enough space is allocated).
+ */
+#define IndexInfoFindDataOffset(t_info) \
+( \
+	(!((t_info) & INDEX_NULL_MASK)) ? \
+	( \
+		(Size)MAXALIGN(sizeof(IndexTupleData)) \
+	) \
+	: \
+	( \
+		(Size)MAXALIGN(sizeof(IndexTupleData) + sizeof(IndexAttributeBitMapData)) \
+	) \
+)
+
+/* ----------------
+ *		index_getattr
+ *
+ *		This gets called many times, so we macro the cacheable and NULL
+ *		lookups, and call nocache_index_getattr() for the rest.
+ *
+ * ----------------
+ */
+#define index_getattr(tup, attnum, tupleDesc, isnull) \
+( \
+	AssertMacro(PointerIsValid(isnull) && (attnum) > 0), \
+	*(isnull) = false, \
+	!IndexTupleHasNulls(tup) ? \
+	( \
+		TupleDescAttr((tupleDesc), (attnum)-1)->attcacheoff >= 0 ? \
+		( \
+			fetchatt(TupleDescAttr((tupleDesc), (attnum)-1), \
+			(char *) (tup) + IndexInfoFindDataOffset((tup)->t_info) \
+			+ TupleDescAttr((tupleDesc), (attnum)-1)->attcacheoff) \
+		) \
+		: \
+			nocache_index_getattr((tup), (attnum), (tupleDesc)) \
+	) \
+	: \
+	( \
+		(att_isnull((attnum)-1, (char *)(tup) + sizeof(IndexTupleData))) ? \
+		( \
+			*(isnull) = true, \
+			(Datum)NULL \
+		) \
+		: \
+		( \
+			nocache_index_getattr((tup), (attnum), (tupleDesc)) \
+		) \
+	) \
+)
+
+/*
+ * MaxIndexTuplesPerPage is an upper bound on the number of tuples that can
+ * fit on one index page.  An index tuple must have either data or a null
+ * bitmap, so we can safely assume it's at least 1 byte bigger than a bare
+ * IndexTupleData struct.  We arrive at the divisor because each tuple
+ * must be maxaligned, and it must have an associated line pointer.
+ *
+ * To be index-type-independent, this does not account for any special space
+ * on the page, and is thus conservative.
+ *
+ * Note: in btree non-leaf pages, the first tuple has no key (it's implicitly
+ * minus infinity), thus breaking the "at least 1 byte bigger" assumption.
+ * On such a page, N tuples could take one MAXALIGN quantum less space than
+ * estimated here, seemingly allowing one more tuple than estimated here.
+ * But such a page always has at least MAXALIGN special space, so we're safe.
+ */
+#define MaxIndexTuplesPerPage	\
+	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
+			(MAXALIGN(sizeof(IndexTupleData) + 1) + sizeof(ItemIdData))))
+
+
+/* routines in indextuple.c */
+extern IndexTuple index_form_tuple(TupleDesc tupleDescriptor,
+								   Datum *values, bool *isnull);
+extern Datum nocache_index_getattr(IndexTuple tup, int attnum,
+								   TupleDesc tupleDesc);
+extern void index_deform_tuple(IndexTuple tup, TupleDesc tupleDescriptor,
+							   Datum *values, bool *isnull);
+extern IndexTuple CopyIndexTuple(IndexTuple source);
+extern IndexTuple index_truncate_tuple(TupleDesc sourceDescriptor,
+									   IndexTuple source, int leavenatts);
+
+#endif							/* ITUP_H */