def ceilpow2(n):
    """convenience function to determine a power-of-2 upper frequency limit"""
    signif,exponent = frexp(n)
    if (signif < 0):
        return 1;
    if (signif == 0.5):
        exponent -= 1;
    return (1) << exponent;
convenience function to determine a power-of-2 upper frequency limit