How do I check, if bitmask contains bit?

well

if (8 & bitmask == 8 ) {
}

will check if the bitmask contains 8.

more complex

int mask = 8 | 12345;
if (mask & bitmask == mask) {
   //true if, and only if, bitmask contains 8 | 12345
}

if (mask & bitmask != 0) {
   //true if bitmask contains 8 or 12345 or (8 | 12345)
}

may be interested by enum and more particularly FlagsAttibute.

I'm pretty sure (A & B)==B where A is the bitmask and B is whatever you want to check should do.

Example:

if((18358536 & 8) == 8) 
{
    // mask contains 8
}