Working with log math function

I want to output to calculate the following:

0 - (3/6)logbase2(3/6) = 1/2

I have this in my program:

Code :

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double ratio = 3/6;
x  = x - (ratio * (logbase2(ratio)));

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which should equal .5 but I keep getting 0.326634259978281

what am I doing wrong?

Edit: I figure it out. I should be using:
(ratio * Math.log(ratio)/Math.log(2))