Question

I’m looking to convert this line of C code to C#:

const u64 a = 1, b = -a;

So my understanding is that both constants are unsigned 64-bit integers. If so, what is the result going to look like?

Or is the second constant actually promoted and therefore defined as a signed integer?

Answer 1

Due to the behaviour of negating unsigned integers, the representation of -(u64)1 is all 1s. So, after the following:

const u64 a = 1, b = -a;

// a is now 0x0000000000000001
// b is now 0xffffffffffffffff

Of course, 0xffffffffffffffff is also (2^64) -1, which is 18446744073709551615.

In my opinion, it would have been clearer for the original programmer to instead write:

const u64 a = 1, b = ~(u64)0;

I’m not a C# programmer, but I suspect the following will work for you:

const ulong b = ~(ulong)0;