/*--------------------------------------------------------------------
 * Symbols referenced in this file:
 * - DatumGetEOHP
 * - EOH_get_flat_size
 * - EOH_flatten_into
 *--------------------------------------------------------------------
 */

/*-------------------------------------------------------------------------
 *
 * expandeddatum.c
 *	  Support functions for "expanded" value representations.
 *
 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/utils/adt/expandeddatum.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "utils/expandeddatum.h"
#include "utils/memutils.h"

/*
 * DatumGetEOHP
 *
 * Given a Datum that is an expanded-object reference, extract the pointer.
 *
 * This is a bit tedious since the pointer may not be properly aligned;
 * compare VARATT_EXTERNAL_GET_POINTER().
 */
ExpandedObjectHeader *
DatumGetEOHP(Datum d)
{
	varattrib_1b_e *datum = (varattrib_1b_e *) DatumGetPointer(d);
	varatt_expanded ptr;

	Assert(VARATT_IS_EXTERNAL_EXPANDED(datum));
	memcpy(&ptr, VARDATA_EXTERNAL(datum), sizeof(ptr));
	Assert(VARATT_IS_EXPANDED_HEADER(ptr.eohptr));
	return ptr.eohptr;
}

/*
 * EOH_init_header
 *
 * Initialize the common header of an expanded object.
 *
 * The main thing this encapsulates is initializing the TOAST pointers.
 */


/*
 * EOH_get_flat_size
 * EOH_flatten_into
 *
 * Convenience functions for invoking the "methods" of an expanded object.
 */

Size
EOH_get_flat_size(ExpandedObjectHeader *eohptr)
{
	return (*eohptr->eoh_methods->get_flat_size) (eohptr);
}

void
EOH_flatten_into(ExpandedObjectHeader *eohptr,
				 void *result, Size allocated_size)
{
	(*eohptr->eoh_methods->flatten_into) (eohptr, result, allocated_size);
}

/*
 * Does the Datum represent a writable expanded object?
 */


/*
 * If the Datum represents a R/W expanded object, change it to R/O.
 * Otherwise return the original Datum.
 */


/*
 * Transfer ownership of an expanded object to a new parent memory context.
 * The object must be referenced by a R/W pointer, and what we return is
 * always its "standard" R/W pointer, which is certain to have the same
 * lifespan as the object itself.  (The passed-in pointer might not, and
 * in any case wouldn't provide a unique identifier if it's not that one.)
 */


/*
 * Delete an expanded object (must be referenced by a R/W pointer).
 */