public Guid(byte[] b)
{
    if (b==null)
        throw new ArgumentNullException("b");
    if (b.Length != 16)
        throw new ArgumentException(Environment.GetResourceString("Arg_GuidArrayCtor", "16"));

    Contract.EndContractBlock();
    _a = ((int)b[3] << 24) | ((int)b[2] << 16) | ((int)b[1] << 8) | b[0];
    _b = (short)(((int)b[5] << 8) | b[4]);
    _c = (short)(((int)b[7] << 8) | b[6]);
    _d = b[8];
    _e = b[9];
    _f = b[10];
    _g = b[11];
    _h = b[12];
    _i = b[13];
    _j = b[14];
    _k = b[15];
}