Convert String to 64bit Integer

static Int64 GetInt64HashCode(string strText)
{
    Int64 hashCode = 0;
    if (!string.IsNullOrEmpty(strText))
    {
          byte[] byteContents = Encoding.Unicode.GetBytes(strText);
        System.Security.Cryptography.SHA256 hash = 
  new System.Security.Cryptography.SHA256CryptoServiceProvider();
        byte[] hashText = hash.ComputeHash(byteContents);
        Int64 hashCodeStart = BitConverter.ToInt64(hashText, 0);
        Int64 hashCodeMedium = BitConverter.ToInt64(hashText, 8);
        Int64 hashCodeEnd = BitConverter.ToInt64(hashText, 24);
        hashCode = hashCodeStart ^ hashCodeMedium ^ hashCodeEnd;
    }
    return (hashCode);
}