Question

I’m trying to generate a fixed length hash using the code below.

public int GetStableHash(string s)
        {
            string strKey = "myHashingKey";
            UnicodeEncoding UE = new UnicodeEncoding();
            byte[] key = UE.GetBytes(strKey);
            byte[] contentBuffer = UE.GetBytes(s);
            // Initialize the keyed hash object.
            HMACSHA256 myhmacsha256 = new HMACSHA256(key);
            byte[] hashValue = myhmacsha256.ComputeHash(contentBuffer);
            return BitConverter.ToInt32(hashValue,0);
        }

It gives me output like this.

-1635597425

I need a positive number fixed length (8 digits). Can someone plz tell me how to do that.

Thanks in advance.

Answer 1

unchecked
{
    int num = BitConverter.ToInt32(hashValue,0);

    if (num < 0)
    {
        num = -num;
    }

    num %= 100000000;
}

I’m using the unchecked because otherwise -int.MinValue would break (but note that normally programs are compiled with the unchecked “flag” “on”)

The code means:

    unchecked

don't do overflow controls

    if (num < 0)
    {
        num = -num;
    }

make the number positive if negative

    num %= 100000000;

take the remainder (that has 0-8 digits)

much shorter:

return unchecked((int)((uint)BitConverter.ToInt32(hashValue,0) % 100000000));