def percentile(values, percent):
    """Find the percentile of a list of values.

    :parameter values: list of numbers
    :parameter percent: float value from 0.0 to 1.0

    :returns: the percentile of values
    """
    if not values:
        return None
    values.sort()
    k = (len(values) - 1) * percent
    f = math.floor(k)
    c = math.ceil(k)
    if f == c:
        return values[int(k)]
    d0 = values[int(f)] * (c - k)
    d1 = values[int(c)] * (f - k)
    return (d0 + d1)
dataset/ETHPy150Open openstack/rally/rally/task/processing/utils.py/percentile/swapped operands of `-`