Function evlOverlay

src/jrd/SysFunction.cpp:5662–5843

dsc* evlOverlay(thread_db* tdbb, const SysFunction* function, const NestValueArray& args,
	impure_value* impure)
{
	fb_assert(args.getCount() >= 3);

	Request* request = tdbb->getRequest();

	const dsc* value = EVL_expr(tdbb, request, args[0]);
	if (request->req_flags & req_null)	// return NULL if value is NULL
		return NULL;

	const dsc* placing = EVL_expr(tdbb, request, args[1]);
	if (request->req_flags & req_null)	// return NULL if placing is NULL
		return NULL;

	const dsc* fromDsc = EVL_expr(tdbb, request, args[2]);
	if (request->req_flags & req_null)	// return NULL if fromDsc is NULL
		return NULL;

	const dsc* lengthDsc = NULL;
	ULONG length = 0;

	if (args.getCount() >= 4)
	{
		lengthDsc = EVL_expr(tdbb, request, args[3]);
		if (request->req_flags & req_null)	// return NULL if lengthDsc is NULL
			return NULL;

		const SLONG auxlen = MOV_get_long(tdbb, lengthDsc, 0);

		if (auxlen < 0)
		{
			status_exception::raise(Arg::Gds(isc_expression_eval_err) <<
										Arg::Gds(isc_sysf_argnmustbe_nonneg) <<
											Arg::Num(4) <<
											Arg::Str(function->name));
		}

		length = auxlen;
	}

	SLONG from = MOV_get_long(tdbb, fromDsc, 0);

	if (from <= 0)
	{
		status_exception::raise(Arg::Gds(isc_expression_eval_err) <<
									Arg::Gds(isc_sysf_argnmustbe_positive) <<
										Arg::Num(3) <<
										Arg::Str(function->name));
	}

	const USHORT resultTextType = DataTypeUtil::getResultTextType(value, placing);
	CharSet* cs = INTL_charset_lookup(tdbb, resultTextType);

	MoveBuffer temp1;
	UCHAR* str1;
	ULONG len1;