Python中按位运算如何工作? [英] How do bitwise operations work in Python?

问题描述

我今天已经在学习按位运算，并且我知道Not(〜)将所有位取反，例如:

I have been learning about Bitwise operations today and I learned that Not (~) inverses all bits, e.g.:

01010
to
10101

这意味着〜10应该是-5，但我已经看到它是-11(按照python命令行)是

which means ~10 should be -5 but instead I have seen that it is -11 (per the python command line) which is

01010
to
11011

只有两个位被反转了.谁能解释为什么它不是10101?

only two of the bits have been inverted. Can anybody explain why it isn't 10101?

看完我的计算器后，我对它的理解有所提高，但是我自己的用于确定二进制和整数的代码仍然令人困惑.以字节模式输入11110101会给我-11，但在我的代码中输入的却是-117:

After looking on my calculator I understand it a little better, But my own code for determining binary and ints is still being confused. Entering in (in byte mode) 11110101 gives me -11 but the same entered in my code gives -117:

def binaryToInt(biNum, bUnsigned = False):
    iNum = 0
    bSign = int(biNum[0]) if not (bUnsigned or biNum[-1] == "u") else 0
    biNum = biNum[(1 if not (bUnsigned or biNum[-1] == "u") else 0):(len(biNum) if biNum[-1] != "u" else -1)]
    for i in xrange(len(biNum)):
        iNum += int(biNum[i]) * 2**(len(biNum) - 1 - i)
    return (iNum if not bSign else -iNum)

def intToBinary(iNum, bUnsigned = False):
    bSign = "1" if iNum < 0 else "0"
    iLoopNum = int((iNum ** 2) ** 0.5) #make positive!
    biNum = ""
    while iLoopNum:
        biNum += str(iLoopNum%2)
        iLoopNum /= 2
    return bSign + biNum[::-1] if not bUnsigned else biNum[::-1] + "u"

你们中的一个可以解释吗?

can one of you explain that?

推荐答案

11011不是 -11.您对负数的编码方案有误解.

11011 is not -11. You have a misunderstanding of the encoding scheme for negative numbers.

在二进制补码中，-11是10101，这是正确的位求反.

In two's complement, -11 is 10101 which is the correct bit inversion.

要对二进制补码求反，请将所有位取反并加一个:

To negate a two's complement number, you invert all bits and add one:

01011 eleven
10100 invert
10101 add one gives negative eleven

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