Time for action – twiddling bits

We will go over three tricks—checking whether the signs of integers are different, checking whether a number is a power of two, and calculating the modulus of a number that is a power of two. We will show an operators-only notation and one using the corresponding NumPy functions:

1. The first trick depends on the XOR or ^ operator. The XOR operator is also called the inequality operator; so, if the sign bit of the two operands is different, the XOR operation will lead to a negative number. ^ corresponds to the bitwise_xor function. < corresponds to the less function.

   x = np.arange(-9, 9)
   y = -x
   print "Sign different?", (x ^ y) < 0
   print "Sign different?", np.less(np.bitwise_xor(x, y), 0)

   The result is shown as follows:

   Sign different? [ True  True  True  True  True  True  True  True  True False  True  True
     True  True  True  True  True  True]
   Sign different? [ True  True  True  True  True  True  True  True  True False  True  True
     True  True  True  True...