import math


def days_to_hmsm(days):
    """
    Convert fractional days to hours, minutes, seconds, and microseconds.
    Precision beyond microseconds is rounded to the nearest microsecond.

    Parameters
    ----------
    days : float
        A fractional number of days. Must be less than 1.

    Returns
    -------
    hour : int
        Hour number.

    min : int
        Minute number.

    sec : int
        Second number.

    micro : int
        Microsecond number.

    Raises
    ------
    ValueError
        If `days` is >= 1.

    Examples
    --------
    >>> days_to_hmsm(0.1)
    (2, 24, 0, 0)

    """
    hours = days * 24.
    hours, hour = math.modf(hours)

    mins = hours * 60.
    mins, min = math.modf(mins)

    secs = mins * 60.
    secs, sec = math.modf(secs)

    micro = round(secs * 1.e6)

    return int(hour), int(min), int(sec), int(micro)