}

                fun String.isValidIndex(index: Int) = index in indices

                check(text.isValidIndex(offset))

                val realStartIndex = offset + offsetRelativeIndexRange.first
                check(text.isValidIndex(realStartIndex))

                val realEndIndex = offset + offsetRelativeIndexRange.last
                check(text.isValidIndex(realEndIndex))

	}

	// 0 <= v [ && v < max ]
	return x.typ, v
}

// isValidIndex checks whether operand x satisfies the criteria for integer
// index values. If allowNegative is set, a constant operand may be negative.
// If the operand is not valid, an error is reported (using what as context)
// and the result is false.
func (check *Checker) isValidIndex(x *operand, code Code, what string, allowNegative bool) bool {
	if x.mode == invalid {

func (check *Checker) index(index ast.Expr, max int64) (typ Type, val int64) {
	typ = Typ[Invalid]
	val = -1

	var x operand
	check.expr(nil, &x, index)
	if !check.isValidIndex(&x, InvalidIndex, "index", false) {
		return
	}

	if x.mode != constant_ {
		return x.typ, -1
	}

	if x.val.Kind() == constant.Unknown {
		return
	}

		check.verifyVersionf(call.Fun, go1_17, "unsafe.Add")

		check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
		if x.mode == invalid {
			return
		}

		y := args[1]
		if !check.isValidIndex(y, InvalidUnsafeAdd, "length", true) {
			return
		}

		x.mode = value
		x.typ = Typ[UnsafePointer]
		if check.recordTypes() {
			check.recordBuiltinType(call.Fun, makeSig(x.typ, x.typ, y.typ))
		}

		check.verifyVersionf(call.Fun, go1_17, "unsafe.Add")

		check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
		if x.mode == invalid {
			return
		}

		y := args[1]
		if !check.isValidIndex(y, InvalidUnsafeAdd, "length", true) {
			return
		}

		x.mode = value
		x.typ = Typ[UnsafePointer]
		if check.recordTypes() {
			check.recordBuiltinType(call.Fun, makeSig(x.typ, x.typ, y.typ))
		}