ideas from https://www.zhihu.com/question/20180484/answer/79886771

confuseids.py

"""实在是对位运算不熟，甚是麻烦，直接操作字符串了。
"""

def test_rev_encode():
    for i in range(500):
        encode = rev_encode(i)
        if rev_encode(encode) != i:
            print('{0}>{1} {1}>{2}'.format(i,encode,rev_encode(encode)))


def rev_encode(n):
    bits = list(bin(n)[2:])[::-1]
    odd = bits[::2]
    even = bits[1::2][::-1]
    for i, e in enumerate(even):
        odd.insert(2*i+1,e)
    return int('0b{}'.format(''.join(odd[::-1])),2)

def reverse32bits(n):
    ''' 32bit '''
    n = ((n & 0xAAAAAAAA) >> 1) | ((n & 0x55555555) << 1)
    n = ((n & 0xCCCCCCCC) >> 2) | ((n & 0x33333333) << 2)
    n = ((n & 0xF0F0F0F0) >> 4) | ((n & 0x0F0F0F0F) << 4)
    n = ((n & 0xFF00FF00) >> 8) | ((n & 0x00FF00FF) << 8)
    n = ((n & 0xFFFF0000) >> 16) | ((n & 0x0000FFFF) << 16)
    return n

def encode(n):
    # print bin(n)
    odd = n & 0x55555555
    # print('odd', bin(odd))
    even = n & 0xAAAAAAAA
    # print('even', bin(even))
    reverse_even = reverse32bits(even)
    # print('reverse_even', bin(reverse_even))
    result = odd | reverse_even
    # print bin(result)
    return result

def odd_rev(n):
    even = n & 0xAAAAAAAA
    odd = n & 0x55555555
    odd = ((odd & 0x33333333) << 2) | ((odd & 0xCCCCCCCC) >> 2)
    odd = ((odd & 0x0F0F0F0F) << 4) | ((odd & 0xF0F0F0F0) >> 4)
    odd = ((odd & 0x00FF00FF) << 8) | ((odd & 0xFF00FF00) >> 8)
    odd = ((odd & 0x0000FFFF) << 16) | ((odd & 0xFFFF0000) >> 16)
    return even | odd

def even_rev(n):
    even = n & 0xAAAAAAAA
    odd = n & 0x55555555
    even = ((even & 0x33333333) << 2) | ((even & 0xCCCCCCCC) >> 2)
    even = ((even & 0x0F0F0F0F) << 4) | ((even & 0xF0F0F0F0) >> 4)
    even = ((even & 0x00FF00FF) << 8) | ((even & 0xFF00FF00) >> 8)
    even = ((even & 0x0000FFFF) << 16) | ((even & 0xFFFF0000) >> 16)
    return even | odd

def test_func(func, n):   
    for i in range(n):
        encode = func(i)
        if func(encode) != i:
            print('{0}>{1} {1}>{2}'.format(i, encode, func(encode)))

if __name__ == '__main__':
    test_func(even_rev, 1000000)

wow，好长。

我给个实现吧

def odd_rev(n):
    even = n & 0xAAAAAAAA  # 偶数位
    odd = n & 0x55555555
    odd = ((odd & 0x33333333) << 2) | ((odd & 0xCCCCCCCC) >> 2)
    odd = ((odd & 0x0F0F0F0F) << 4) | ((odd & 0xF0F0F0F0) >> 4)
    odd = ((odd & 0x00FF00FF) << 8) | ((odd & 0xFF00FF00) >> 8)
    odd = ((odd & 0x0000FFFF) << 16) | ((odd & 0xFFFF0000) >> 16)
    return even | odd

嗯，翻转的过程出错了。这行可以去掉 https://gist.github.com/xavierskip/c89604d084397ecb62f412147e6e6d65#file-confuseids-py-L21