代码中的&符，它做什么 [英] ampersand in code, what does it do

问题描述

我在网上找到了我想了解的代码。但是，在以下代码中，谷歌搜索并没有发现与号的含义。

I found this code online that i'd like to understand. However, googling didn't turn up any results as to the meaning of the ampersand in the following code

return ( 1.0 - ( (x * (x * x * 15731 + 789221) + 1376312589) & 7fffffff) / 1073741824.0); 

我从以下页面获得它： http://freespace.virgin.net/hugo.elias/models/m_perlin.htm

I got it from the following page: http://freespace.virgin.net/hugo.elias/models/m_perlin.htm

是的，有人指出这不是真正的perlin，但我不在乎，我现在想知道基本知识。

and yes, it has been pointed out that it is not real perlin, but I don't care, I want to know the basics for now.

问候

推荐答案

&符是按位AND。这意味着您是在位级别进行比较。
对于且仅当2个输入位均为1时，结果位为1。

The ampersand is a bitwise AND. It means that you're comparing on the bit level. For each bit, the resulting bit is 1 if and only if the 2 incoming bits are 1.

1 & 2 = 0

因为：

1 = 00000001

1 = 00000001

2 = 00000010

2 = 00000010

但是

2 & 3 = 2

因为我们有：

2 = 000000 1 0

2 = 000000 1 0

3 = 000000 1 1

3 = 000000 1 1

结果= 000000 1 0

result = 000000 1 0

在您的情况下，按位与用于将0的第一位强制为0结果（如果结果为32位，在您的示例中就是这种情况），因为：

In your case, the bitwise AND is used to force a 0 on the first bit of the result (if the the result is in 32 bits, which is the case in your example), because :

7fffffff = (0111) (1111) (1111) etc...

所以无论您与什么

鉴于结果是一个有符号整数，因此将第一位设置为0的作用是确保结果始终为正。

Given that the result is a signed integer, the effect of putting the first bit to 0 is to ensure that the result is always positive.

这是由于以下事实：在cpp中，有符号整数的第一位用于设置符号。 1表示数字为负数，0表示数字为正数。

This is due to the fact that in cpp, the first bit of a signed integer is used to set the sign. A 1 means the number is negative, a 0 means it is positive.

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