Underlying type of sum of constants

[abgs]

Consider:

namespace {
typedef unsigned short ui16;
const ui16 x = 1U;
const ui16 y = 2U;
const ui16 z = x + y;
}

Page 55 of MISRA C++ states:

"The underlying type of an integer constant expression is therefore defined as follows: 1. If the actual type of the expression is signed integral, the underlying type is defined as the smallest signed integer type that is capable of representing its value."

* The actual type of x + y is int
* The value of x + y is three
* The smallest signed type capable of representing three is signed char
* The underlying type of x + y is signed char

This also seems to match the behavior on page 60:

"The underlying type for a constant expression “e” with a value “v” will have the same signedness as “e”, and a magnitude given by the underlying type of a single integer-literal with the same value as “v”." (referring to page 58 "The underlying type of an integral literal is the smallest fundamental type of the appropriate sign required to store its value.")

where:

* "e" is x + y
* The actual type of "e" is int (determining signedness)
* "v" is three
* The underlying type of an integer literal with the value three is signed char (determining magnitude)
* The underlying type of x + y is signed char

Is this interpretation correct?