Integer bits can be addressed using array syntax:

    n = 21
    n[0] # => 1
    n[1] # => 0
    n[2] # => 1
    # etc..

To generate an array of bits from an integer:

    number_of_bits = Math.sqrt(n).ceil
    # => 5

    number_of_bits.times.map { |i| n[i] }
    # => [1, 0, 1, 0, 1]

lib/methods/bitmask.rb

@@ -9,8 +9,9 @@ def initialize(base, column_name, options)
 
       base.send :define_method, :_roles do
         states = base.const_get(column_name.upcase.to_sym)
+        masked_integer = self[column_name.to_sym] || 0
 
-        states.reject { |r| ((self[column_name.to_sym] || 0) & 2**states.index(r)).zero? }
+        states.reject.with_index { |r,i| masked_integer[i].zero? }
       end
 
       base.send :define_method, :has_role? do |role|