On Tuesday, 5 December 2023 at 19:47:38 UTC, confuzzled wrote:
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?
ulong.sizeof is 8, like double.sizeof. So F.init.lo should have
the same bit pattern as F.init.x because they share storage
exactly. F.init.hi should be 0 and it is on my system. (*"If the
union is larger than the first field, the remaining bits are set
to 0"*). I don't know why you don't get zero for that.
