c# - 可逆 [1..limit] -> [1..limit] 函数

Question

如果它存在于代码中，我正在寻找以下内容（任何语言都可以，但最好是 c#）：

a,b,limit,key : integers

0< a, b, < limit (fits in less than int32)

b = forth(a, limit, key)
a = back (b, limit, key)

我需要一些看起来有点随机的东西，(=)而且(xor)还不够好。

Now I looked into block ciphers and pseudorandom generators and like but it's always about encryption and security and speed and uses the whole size of the integer. I don't care about any of those. All I need is a bijection on the domain where average of forth(a+epsilon) >> b+epsilon

Answer 1

像下面这样简单的东西有什么问题吗？

int Forth(int a, int limit, int key)
{
    return (limit - a) ^ key;
}

int Back(int b, int limit, int key)
{
    return limit - (b ^ key);
}

编辑：改编自这里（虽然不使用密钥 - 这是必要的吗？）

int Forth(int a)
{
    return ((0x00FF & a)<<8) + ((0xFF00 & a)>>8);
}

int Back(int b)
{
    return ((0x00FF & b)<<8) + ((0xFF00 & b)>>8);
}

注意Back()和Forth()上面的功能相同......