SandForce Firmware Developer, Junior interview questions

I'm a new college graduate. They asked me a few questions about my background and resume. Next, told me about their products and where the company is going. There was a technical coding quiz on a shared Google Doc. int func(int y) { int result=0; while(y) { y &= y - 1; result++; } return result; } -- what does this function do? --what's another way to write this?