  We present efficient algorithms to generate a bit string in which each bit is
set with arbitrary probability. By adopting a hybrid algorithm, i.e., a
finite-bit density approximation with correction techniques, we achieve 3.8
times faster random bit generation than the simple algorithm for the 32-bit
case and 6.8 times faster for the 64-bit case. Employing the developed
algorithm, we apply the multispin coding technique to one-dimensional
bond-directed percolation. The simulations are accelerated by up to a factor of
14 compared with an optimized scalar implementation. The random bit string
generation algorithm proposed here is applicable to general Monte Carlo
methods.
