BN_window_bits_for_exponent_size
window = BN_window_bits_for_exponent_size(bits);
window = BN_window_bits_for_exponent_size(bits);
window = BN_window_bits_for_exponent_size(bits);
window1 = BN_window_bits_for_exponent_size(bits1);
window2 = BN_window_bits_for_exponent_size(bits2);