负数与正数之间按位与(&)? [英] Bitwise AND (&) between negative and positive numbers?

问题描述

我一直在学习如何使用位操作将两个数相加，但是在理解如何用Python处理负数时遇到了一些问题.例如，如果我尝试&以下内容:

I've been learning about adding two numbers using bit manipulation and I am having issues understanding how it is done in Python for negative numbers. For example, if I am trying to & the following:

-0b1111010 (-122) & 0b11011110 (222)

应该不是:

   0b1111010 
& 0b11011110
------------
  0b01011010

因为只有1的结果与1的组合?

since only a combination of 1's results in 1's?

现在python给出0b10000110

Right now python gives 0b10000110

特别是当使用python将负数添加到正数时，我找不到任何资源.

I couldn't find any resources specifically when a negative number is added to a positive number using python.

推荐答案

这是因为Python使用二进制补码二进制有符号整数表示形式.这是一段代码，其输出显示实际的字节数据并说明 为什么 ，您将得到的结果是

It's because Python uses a two's complement binary signed integer representation. Here a snippet of code whose output shows the actual byte data and illustrates why you're getting the results that you are:

import math

def bin_format(integer):
    num_bytes = math.ceil(integer.bit_length()/8)  # Number required to represent value.
    ba = integer.to_bytes(num_bytes, 'big', signed=integer<0)
    return ''.join('{:08b}'.format(b) for b in ba) + ' ({:4d})'.format(integer)

print('  ' + bin_format(-122))
print('& ' + bin_format(222))
print('=' * 17)
print('  ' + bin_format(-122 & 222))

输出:

  10000110 (-122)
& 11011110 ( 222)
=================
  10000110 ( 134)

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