(number & (power_of_two - 1)) of course.
A bit more detail for non programmer?
Are you saying you want to program crypto algorythms in opencl without understanding "(number & (power_of_two - 1))"?
I kinda feel the same way, but I'll be a little gentler. BitmoreCoin, you may want to look up bitwise operators and things like that - an AND operation is far, far faster than modulus (modulus and division are ouch slow, as a general rule).
I think he means how to adjust the statements inside the case 0 and case 1.