Reverse Engineering String.GetHashCode

Question

String.GetHashCode\'s behavior is depend on the program architecture. So it will return one value in x86 and one value on x64. I have a test application which must run in x8

Answer 1

While all of the warnings given here are valid, they don't answer the question. I had a situation in which GetHashCode() was unfortunately already being used for a persisted value in production, and I had no choice but to re-implement using the default .NET 2.0 32-bit x86 (little-endian) algorithm. I re-coded without unsafe as shown below, and this appears to be working. Hope this helps someone.

// The GetStringHashCode() extension method is equivalent to the Microsoft .NET Framework 2.0
// String.GetHashCode() method executed on 32 bit systems.
public static int GetStringHashCode(this string value)
{
    int hash1 = (5381 << 16) + 5381;
    int hash2 = hash1;

    int len = value.Length;
    int intval;
    int c0, c1;
    int i = 0;
    while (len > 0)
    {
        c0 = (int)value[i];
        c1 = (int)value[i + 1];
        intval = c0 | (c1 << 16);
        hash1 = ((hash1 << 5) + hash1 + (hash1 >> 27)) ^ intval;
        if (len <= 2)
        {
            break;
        }
        i += 2;
        c0 = (int)value[i];
        c1 = len > 3 ? (int)value[i + 1] : 0;
        intval = c0 | (c1 << 16);
        hash2 = ((hash2 << 5) + hash2 + (hash2 >> 27)) ^ intval;
        len -= 4;
        i += 2;
    }

    return hash1 + (hash2 * 1566083941);
}