问题描述
我是一名学生，我写在C函数符号扩展一个给定的位字段。我与32位工作。
I am a student and I am writing a function in C to sign extend a given bit field. I'm working with 32 bits.
我看了这个答案在谷歌，但没有发现什么，我一直在寻找。
I looked this answer up on Google but didn't find what I was looking for.
我在写函数返回一个或多个连续位三三两两complemnt重新presentation从32 INT拉动。最左边位为符号位。
I'm writing function that returns the twos complemnt representation of one or more consecutive bits pulled from a 32 int. The leftmost bit is the sign bit.
我怎么返回，如果我拉一个位？你如何重新present单位作为签署三三两两complment多少？
What do I return if I pull a single bit? How do you represent a single bit as a signed twos complment number?
推荐答案
这是没有多大意义谈了1位二进制补码。如果你只有1位是0或1。
It doesn't make much sense to talk a 1-bit two's complement number. If you only have 1 bit, it is either 0 or 1.
在一般情况下，如果你有N位二进制补码数的最高值前pressible是 2 ^（N-1）-1 和最低值为 -2 ^（N-1）。如果我们想成为愚蠢的，我们可以应用此N = 1，我们发现1位二进制补码数的范围从-1到0。
In general, if you have a two's complement number with N bits, the highest value expressible is 2^(N-1)-1 and the lowest value is -2^(N-1). If we want to be silly we can apply this to N=1 and we find that a 1-bit two's complement number can range from -1 to 0.
编辑：您写道：
我在写函数返回一个或多个连续位三三两两complemnt重新presentation从32 INT拉动。最左边位为符号位。
我不认为这是很好的界定。的两补的是，可以让你重新present某个整数作为一系列比特的编码。给定一个整数，它会告诉你什么位来存储。我不知道二的补再一个位序列的presentation将是什么。这就像你问我给你一个系列任意字节的ASCII编码，或者你问我从法国的葛底斯堡演说翻译成英文。
I don't think this is well defined. Two's complement is an encoding that lets you represent a mathematical integer as a series of bits. Given an integer, it tells you what bits to store. I don't know what the two's complement representation of a series of bits would be. It's like you're asking me to give you the ASCII encoding of a series of arbitrary bytes, or you are asking me to translate the Gettysburg Address from French to English.
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