x = c * (2**p)   # the value you want to express
   c                # the coefficient
   p = -n           # the smallest power of two that goes into x; 
                    # negative, since it's a binary fraction
   
   x = c*(2**p) = c*(2**-n) = ...
                                
               [  1   ]     [  1   ] [ 5**n ]     [  5**n ]
     = ... = c*[------] = c*[------]*[------] = c*[-------] = ...
               [ 2**n ]     [ 2**n ] [ 5**n ]     [ 10**n ]
                                
     = ... = c * (5**n) * (10**-n) = c * (5**n) ** (10**p)
   
   k = c * (5**n)   # k integer, so exactly representable in decimal
   
   x = k * (10**-n) # since n is finite and k is an integer, 
                    # x is exactly representable in decimal