旋转的任意整数位用C [英] Rotating bits of any integer in C

问题描述

传递一个整数2这个函数，然后返回一个整数，也就是4

  X = 2;
X = rotateInt（L中，x，1）;
 

（由1位左移）

例如：
00000010 - >旋转由左1 - > 00000100

但如果我通过这样的：

  X = rotateInt（'R'，X，3）;
 

将返回64，01000000

下面是code，有人可以纠正错误...谢谢

  INT rotateInt（字符方向，无符号整型的x，int y）对
{
    unsigned int类型面膜= 0;
    INT NUM = 0，结果为0;
    INT I;    对于（i = 0; I＆LT; Y;我++）
    {
        如果（方向=='R'）
        {
            如果（（X安培; 1）== 1）
                X =（X ^ 129）;
            其他
                X = X＆GT;＆GT; 1;
        }
        否则如果（方向=='L'）
        {
            如果（（X＆放大器; 128）== 1）
                X =（X ^ 129）;
            其他
                X = X＆所述;＆下; 1;
        }
    }
结果=（结果^ X）;
返回结果;
}
 

解决方案

所以，我假设你知道什么是左，右的变化是。并且知道算术和逻辑移位之间的差异。

仅C具有算术移位。它不这样做逻辑移位，也不做旋转。好吧，我撒谎了，C做逻辑移位无符号整数。

有一个旋转确实不错，正是：它是一样的，当你转移过去数的末尾，除了逻辑移位，数字环绕到另一边。例如：

0010 右键旋转时， 0001 。如果右键旋转一次，你会得到 1000 。你看，包裹 1 周围，或旋转，以整数的另一边。

左旋转是相似的： 0100 左旋 1000 左旋 0001 左旋 0010 等。

请注意，旋转不保留符号位的算术右移会。

所以，C只有算术移位。所以，你必须手动落实旋转的一部分。因此，采取左旋转。你会想：

1. 捕捉最左边的位的值。 （它是一个0或1？）


2. 请左移


3. 将最右边的位 - 这是我们在步骤1中（需要被围绕其旋转）为正确值的基础上，我们从步骤1中拍摄
谈到了一点。

您应该能够找出一个类似的方法右旋转。

好运！

Pass a integer 2 to this function and then return a integer which is 4

x = 2;
x = rotateInt('L', x, 1); 

(left shift the bits by 1)

Example: 00000010 -> rotate left by 1 -> 00000100

but if I pass this:

x = rotateInt('R', x, 3); 

it will return 64, 01000000

Here is the code, can someone correct the error... thanks

int rotateInt(char direction, unsigned int x, int y)
{
    unsigned int mask = 0;
    int num = 0, result = 0;
    int i;

    for (i = 0; i < y; i++)
    {     
        if (direction == 'R')
        {
            if ((x & 1) == 1)     
                x = (x ^ 129);
            else    
                x = x >> 1;
        }
        else if (direction == 'L')
        {
            if ((x & 128) == 1)  
                x = (x ^ 129);   
            else
                x = x << 1;
        }
    }
result = (result ^ x);
return result;   
}

解决方案

So, I'll assume you know what right and left shifts are. And that you know the difference between arithmetic and logical shifts.

C only has arithmetic shifts. It doesn't do logical shifts, nor does it do rotates. okay I lied, C does logical shifts on unsigned ints.

A rotate does, well, exactly that: it's the same as a logical shift, except when you shift past the end of the number, the digits "wrap around" to the other side. For example

0010 right-rotated is 0001. If you right-rotate again, you get 1000. See, the 1 wrapped around, or rotated, to the other side of the integer.

The left rotate is similar: 0100 left rotate 1000 left rotate 0001 left rotate 0010 etc.

Note that rotates don't keep the sign bit as an arithmetic right-shift would.

So, C only has arithmetic shifts. So you have to implement the "rotate" part manually. So, take a left-rotate. You would want to:

1. Capture the value of the left-most bit. (is it a 0 or 1?)
2. Do a left-shift
3. Set the right-most bit - which is the bit we talked about in step 1 (which needs to be rotated around) to the correct value, based on what we captured from step 1.

You should be able to figure out a similar method for right rotates.

good luck!

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