estimation.py 文件源码

def primes_2_to_n(n):
    """
    Efficient algorithm to find and list primes from
    2 to `n'.

    Args:
        n (int): highest number from which to search for primes

    Returns:
        np array of all primes from 2 to n

    References:
        Robert William Hanks,
        https://stackoverflow.com/questions/2068372/fastest-way-to-list-all-primes-below-n/
    """
    sieve = np.ones(int(n / 3 + (n % 6 == 2)), dtype=np.bool)
    for i in range(1, int((n ** 0.5) / 3 + 1)):
        if sieve[i]:
            k = 3 * i + 1 | 1
            sieve[int(k * k / 3)::2 * k] = False
            sieve[int(k * (k - 2 * (i & 1) + 4) / 3)::2 * k] = False
    return np.r_[2, 3, ((3 * np.nonzero(sieve)[0][1:] + 1) | 1)]