def max_value_bits(b):
    """
    Get maximum (unsigned) value of a given integer bit size variable.

    Parameters
    ----------
    b : int
        Number of bits (binary values) that are used to describe a putative variable.

    Returns
    -------
    max_value : int
        Maximum value that putative variable can hold (integer unsigned).

    """
    return (2 ** b) - 1