Integer to byte with given number of bits set

Question

I don't know what to call this, which makes googling harder.

I have an integer, say 3, and want to convert it to 11100000, that is, a byte with the value of the integers number of bits set, from the most significantly bit.

I guess it could be done with:

byte result = 0;
for(int i = 8; i > 8 - 3; i--)
    result += 2 ^ i;

but is there anything faster / more nice or, preferably, standard library included in .net?

Answer 1

int n = 3; // 0..8 
int mask = 0xFF00;
byte result  = (byte) (mask >> n);