bitwise

I have just started learning PHP . I am new to it. i have read of logical and bitwise negation in the book that i have bought. I am not able to understand it and following php code. <?php $num1=25.59; $num2=30; $num3=(~$num1)+(!$num2); echo "The sum of Bitwise number 25.59...

can anyone tell me how to implement the function to calculate power of 2 with the help of bitwise operations.