如何在VB.net中实现数组的哈希函数 [英] How to implement a hash function for an array in VB.net

问题描述

C＃中用于从数组创建哈希值的经典函数看起来像这样或类似：

The classic function in C# to create a hash value from an array looks like this or similar:

public int GetHashCode(T[] array)
    {
        unchecked
        {
            if (array == null)
            {
                return 0;
            }
            int hash = 17;
            foreach (T item in array)
            {
                hash = hash * 31 + item.GetHashCode;
            }
            return hash;
        }
    }

但是由于未选中在VB.Net中不可用，因此当溢出时我会很快收到异常。

我以为我可以使用位移来解决它，但是在VB中它只有算术而不是圆形所以每一个被移出的位都会被丢弃。



虽然我无法相信这在VB中从未解决过，但我的google foo让我失望。



获取哈希值的标准解决方案是什么？ VB中的数组？

But since unchecked is not available in VB.Net I will quickly get an exception when it overflows.
I thought I could solve it using bitshifting, but in VB its only arithmetic and not circular so every bit that is shifted out is dropped.

And while I can't believe this has never been solved in VB my google foo is failing me.

What is the standard solution for getting a hash value for an array in VB?

推荐答案

你难道不能将哈希声明为 Int64 并清除上半部分需要？

Couldn't you just declare hash as Int64 and clear the upper part when needed?

为了将来参考，这就是我的解决方案的样子：

For future reference, this is how my solution looks like:

Public Overrides Function GetHashCode() As Integer
     Dim hash As Int64 = 19
     For Each Item As T In Me
         hash = hash * 31 + Item.GetHashCode
         hash = ((hash << 32) >> 32) + hash >> 32
     Next
     hash = ((hash << 32) >> 32)
     Return CInt(hash)
 End Function

有一些改善性能的空间，溢出只需要每6次迭代处理一次，例如

There is some room for improving performance, the overflow only needs to be handled every 6 iterations for example

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