Actually "&" used here means Bitwise.

binary value of 0xf is 0000 1111

Example:

Bitwise A & B

A = 0000 1111

B = 0000 0011

-------------------

then: 0000 0011

"sysstat & 0xf =3" will guarantee that sysstat value is 3.

See MSDN site: http://msdn.microsoft.com/en-us/library/ms174965.aspx

Hope this can help! 😀