两公司在Python补 [英] Two's Complement in Python

问题描述

有一个内置的Python功能将转换为二进制字符串，例如111111111111，到补整数 -1？

Is there a built in function in python which will convert a binary string, for example '111111111111', to the two's complement integer -1?

推荐答案

危险：gnibbler的回答（目前排名最高的）是不正确的结果。
可悲的是，我无法弄清楚如何评论添加到它。

DANGER: gnibbler's answer (currently the highest ranked) isn't correct.
Sadly, I can't figure out how to add a comment to it.

二的恭维减去了（1 LT;＆LT;位）如果最高位为1，以例如8位，这给-128一系列的127。

Two's compliment subtracts off (1<<bits) if the highest bit is 1. Taking 8 bits for example, this gives a range of 127 to -128.

一个为二进制补功能的int ...

A function for two's compliment of an int...

def twos_comp(val, bits):
    """compute the 2's compliment of int value val"""
    if (val & (1 << (bits - 1))) != 0: # if sign bit is set e.g., 8bit: 128-255
        val = val - (1 << bits)        # compute negative value
    return val                         # return positive value as is

这是一个二进制串去，这特别容易...

Going from a binary string is particularly easy...

binary_string = '1111' # or whatever... no '0b' prefix
out = twos_comp(int(binary_string,2), len(binary_string))

对我来说更有益位在从十六进制值去（在这个例子中32位）...

A bit more useful to me is going from hex values (32 bits in this example)...

hex_string = '0xFFFFFFFF' # or whatever... '0x' prefix doesn't matter
out = twos_comp(int(hex_string,16), 32)

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