def _translate_int(exp, length):
    """ Given an integer index, return a 3-tuple
        (start, count, step)
        for hyperslab selection
    """
    if exp < 0:
        exp = length+exp

    if not 0<=exp<length:
        raise ValueError("Index (%s) out of range (0-%s)" % (exp, length-1))

    return exp, 1, 1