为什么右位移不产生负数 [英] why right bit shifting not producing negative number

问题描述

为什么右移不产生负数！

 Console.WriteLine（ 1 <<  2 ）;  //  结果是4-true我理解;  
 Console.WriteLine（ 4 >>  4 ）;  //  结果为0-为什么???????????? ???  

解决方案

简单。只需查看二进制值：

 1 == 00000001 
 2 == 00000010 
 3 == 00000011 
 4 = = 00000100 
 5 == 00000101 

使用移位运算符时，将二进制值n位向左或向右移动。

所以1 左移2个地方：

 0001变为0100 
 18 

和4 右移4个地方：

 0100变为0000 
 40 

因为所有1位都被移出价值和丢弃。

转移就是这样 - 它不会将值包裹回到值的顶部或底部。

这是右移的方式，即（来自 MSDN [ ^ ]）：

右移：

int operator>>（int x，int count）;

uint operator>>（uint x ，int count）;

long运算符>>（long x，int count）;

ulong运算符>>（ulong x，int count）;

>>运算符将x右移一个按如下所述计算的位数。

当x的类型为int或long时，丢弃x的低位，其余位向右移位，如果x为非负，则高位空位位置设置为零;如果x为负，则设置为1。

所以，十进制 4 ，即（二进制） 100b ，变为 0 ：

 100b>>  1  = 010b 
 100b>>  2  = 001b 
 100b>>  3  = 000b 
 100b>>  4  = 000b 
 ... 

why right bit shifting not producing negative number!

Console.WriteLine(1 << 2 );//result is 4-true i understand;
Console.WriteLine(4 >> 4);//result is 0-why??????????????

解决方案

Simple. Just look at the values in binary:

1 ==   00000001
2 ==   00000010
3 ==   00000011
4 ==   00000100
5 ==   00000101

When you use a shift operator, you move the binary value "n" bits to the left or right.
So "1" left shifted 2 places:

0001  becomes 0100
   1     "       8

And "4" right shifted 4 places:

0100 Becomes 0000
   4    "       0

because all the "1" bits are shifted out of teh value and discarded.
A "shift" is just that - it does not "wrap" bits back to teh top or bottom of the value.

That's the way right shift works, namely (from MSDN[^]):

Shift right:
int operator >>(int x, int count);
uint operator >>(uint x, int count);
long operator >>(long x, int count);
ulong operator >>(ulong x, int count);
The >> operator shifts x right by a number of bits computed as described below.
When x is of type int or long, the low-order bits of x are discarded, the remaining bits are shifted right, and the high-order empty bit positions are set to zero if x is non-negative and set to one if x is negative.

So, decimal 4, that is (binary) 100b, becomes 0:

100b >> 1 = 010b
100b >> 2 = 001b
100b >> 3 = 000b
100b >> 4 = 000b
...

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