union default initialization values

[confuzzled]

On 12/6/23 4:28 AM, Adam D Ruppe wrote:
> On Tuesday, 5 December 2023 at 19:24:51 UTC, confuzzled wrote:
>> Given the following union
>>
>> union F
>> {
>>     double x;
>>     struct {
>>         ulong lo;
>>         ulong hi;
>>     }
>> }
> 
> The default value of this would be `double.init`, since the first member 
> of the union is a `double`, which is a kind of NaN. This is non-zero.
> 

Correct. So I expected a NaN output for x. However, I wasn't expecting 
lo == 13835058055282163712 and hi == 32767 where x is of type real, or 
lo == 9221120237041090560 and hi = 0 where x is of type double. Based on 
the default initialization rules, I expected both lo and hi to have a 
value of zero regardless if x is of type double or real. This is what 
I'm trying to understand, how are these values derived?

Thanks again,
--confuzzled