bitwise negation operator for ulong returns uint

Question

I want to remove the last set bit of a ulong. Here's what I do:

ulong mydata;
...
ulong t = 1;
for (int i = 0; i < ulongSizeBits; i++)
{
    if ((myData&t)!=0)
    {
        mydata = mydata & (~t);
        break;
    }
    t <<= 1;
}

The problem is that this doesn't work as advertised. Let's do another experiment:

        var test = 1U;
        var t1 = ~test;
        var t = 1;
        for (int i = 0; i < 64; i++)
        {
            Console.Write((t&t1)!=0?1:0);
            t <<= 1;
        }

The output will be not 01111111111111111111111111111111111111111111111111111111111111 as expected, but 0111111111111111111111111111111100000000000000000000000000000000. It appears, that bitwise not converts ulong to uint or something.

What is the best way to work around this?

Answer 1

1U is not ulong. It's uint. Declare test and t as ulong and you'll get what you need:

var test = 1UL;
var t1 = ~test;
var t = 1UL;
for (int i = 0; i < 64; i++)
{
    Console.Write((t & t1) != 0 ? 1 : 0);
    t <<= 1;
}

prints

01111111111111111111111111111111111111111111111111111111111111