C＃不安全的代码翻译？

Question

I have some code that I'm using in a standard C# application.

I'm sharing the library in a Silverlight project that doesn't allow unsafe code. I don't know much at all about unsafe/pointer logic/arithmetic and was wondering if someone could translate the following code snippet so that it will run without /unsafe. I don't care about the performance drop since the code won't be called often on the client. Thanks in advance for any assistance.

    public static unsafe int GeStableHash(string name)
    {
        fixed (char* str = name)
        {
            char* chPtr = str;
            int num = 352654597;
            int num2 = num;
            int* numPtr = (int*)chPtr;
            for (int i = name.Length; i > 0; i -= 4)
            {
                num = (((num << 5) + num) + (num >> 27)) ^ numPtr[0];
                if (i <= 2)
                {
                    break;
                }
                num2 = (((num2 << 5) + num2) + (num2 >> 27)) ^ numPtr[1];
                numPtr += 2;
            }
            return (num + (num2 * 1566083941));
        }
    }

As per reply below, I looked into the Silverlight implementation of this function.

Now I'm even more confused. The code I see in the SL mscorlib.dll string.GetHashCode function looks like this (it uses the unsafe keyword and gives syntax errors in Visual Studio!):

[SecuritySafeCritical, ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
public unsafe override int GetHashCode()
{
    IntPtr arg_0F_0;
    IntPtr expr_06 = arg_0F_0 = this;
    if (expr_06 != 0)
    {
        arg_0F_0 = (IntPtr)((int)expr_06 + RuntimeHelpers.OffsetToStringData);
    }
    char* ptr = arg_0F_0;
    int num = 352654597;
    int num2 = num;
    int* ptr2 = (int*)ptr;
    int i;
    for (i = this.Length; i > 2; i -= 4)
    {
        num = ((num << 5) + num + (num >> 27) ^ *ptr2);
        num2 = ((num2 << 5) + num2 + (num2 >> 27) ^ ptr2[(IntPtr)4 / 4]);
        ptr2 += (IntPtr)8 / 4;
    }
    if (i > 0)
    {
        num = ((num << 5) + num + (num >> 27) ^ *ptr2);
    }
    return num + num2 * 1566083941;
}

The solution can be found here: https://codereview.stackexchange.com/questions/7661/c-unsafe-code-translation

Answer 1

It looks like this is the implementation of GetHashCode

So perhaps you don't need to do anything "datatohash".GetHashCode(); will suffice

Answer 2

The hash code implementations you posted use pointer arithmetic for better performance. It compiles in Visual Studio if you put it in a .NET Framework project with the "allow unsafe code" option.

It would be possible to compute the same result by using the same logic, but indexing the string directly. For example, the expression "Hello, World"[7] evaluates to 'W' .

I'll leave the translation itself as the proverbial exercise for the reader.

Answer 3

Why don't you do something like an MD5 hash? It's stable, and is implemented in various places.