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diff --git a/src/include/utils/arrayaccess.h b/src/include/utils/arrayaccess.h
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+/*-------------------------------------------------------------------------
+ *
+ * arrayaccess.h
+ *	  Declarations for element-by-element access to Postgres arrays.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/utils/arrayaccess.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef ARRAYACCESS_H
+#define ARRAYACCESS_H
+
+#include "access/tupmacs.h"
+#include "utils/array.h"
+
+
+/*
+ * Functions for iterating through elements of a flat or expanded array.
+ * These require a state struct "array_iter iter".
+ *
+ * Use "array_iter_setup(&iter, arrayptr);" to prepare to iterate, and
+ * "datumvar = array_iter_next(&iter, &isnullvar, index, ...);" to fetch
+ * the next element into datumvar/isnullvar.
+ * "index" must be the zero-origin element number; we make caller provide
+ * this since caller is generally counting the elements anyway.  Despite
+ * that, these functions can only fetch elements sequentially.
+ */
+
+typedef struct array_iter
+{
+	/* datumptr being NULL or not tells if we have flat or expanded array */
+
+	/* Fields used when we have an expanded array */
+	Datum	   *datumptr;		/* Pointer to Datum array */
+	bool	   *isnullptr;		/* Pointer to isnull array */
+
+	/* Fields used when we have a flat array */
+	char	   *dataptr;		/* Current spot in the data area */
+	bits8	   *bitmapptr;		/* Current byte of the nulls bitmap, or NULL */
+	int			bitmask;		/* mask for current bit in nulls bitmap */
+} array_iter;
+
+
+static inline void
+array_iter_setup(array_iter *it, AnyArrayType *a)
+{
+	if (VARATT_IS_EXPANDED_HEADER(a))
+	{
+		if (a->xpn.dvalues)
+		{
+			it->datumptr = a->xpn.dvalues;
+			it->isnullptr = a->xpn.dnulls;
+			/* we must fill all fields to prevent compiler warnings */
+			it->dataptr = NULL;
+			it->bitmapptr = NULL;
+		}
+		else
+		{
+			/* Work with flat array embedded in the expanded datum */
+			it->datumptr = NULL;
+			it->isnullptr = NULL;
+			it->dataptr = ARR_DATA_PTR(a->xpn.fvalue);
+			it->bitmapptr = ARR_NULLBITMAP(a->xpn.fvalue);
+		}
+	}
+	else
+	{
+		it->datumptr = NULL;
+		it->isnullptr = NULL;
+		it->dataptr = ARR_DATA_PTR((ArrayType *) a);
+		it->bitmapptr = ARR_NULLBITMAP((ArrayType *) a);
+	}
+	it->bitmask = 1;
+}
+
+static inline Datum
+array_iter_next(array_iter *it, bool *isnull, int i,
+				int elmlen, bool elmbyval, char elmalign)
+{
+	Datum		ret;
+
+	if (it->datumptr)
+	{
+		ret = it->datumptr[i];
+		*isnull = it->isnullptr ? it->isnullptr[i] : false;
+	}
+	else
+	{
+		if (it->bitmapptr && (*(it->bitmapptr) & it->bitmask) == 0)
+		{
+			*isnull = true;
+			ret = (Datum) 0;
+		}
+		else
+		{
+			*isnull = false;
+			ret = fetch_att(it->dataptr, elmbyval, elmlen);
+			it->dataptr = att_addlength_pointer(it->dataptr, elmlen,
+												it->dataptr);
+			it->dataptr = (char *) att_align_nominal(it->dataptr, elmalign);
+		}
+		it->bitmask <<= 1;
+		if (it->bitmask == 0x100)
+		{
+			if (it->bitmapptr)
+				it->bitmapptr++;
+			it->bitmask = 1;
+		}
+	}
+
+	return ret;
+}
+
+#endif							/* ARRAYACCESS_H */