protected override void Multiply64(DecodedInstruction inst)
{
    if (IsReserved(inst))
    {
        m_Exceptions |= ExceptionFlags.Reserved;
        return;
    }

    bool isUnsigned = (inst.Op.Flags & ExecutionFlags.Unsigned) == ExecutionFlags.Unsigned;
    ulong operandA = (ulong)ReadGPR(inst.Source);
    ulong operandB = (ulong)ReadGPR(inst.Target);

    /* MIPS document says no overflow exceptions, ever... */
    unchecked
    {
        /* Break the operands into four parts */
        ulong A_HI = (operandA >> 32);
        ulong A_LO = (uint)operandA;
        ulong B_HI = (operandB >> 32);
        ulong B_LO = (uint)operandB;
        ulong RESULT_LO = 0;
        ulong RESULT_HI = 0;

        if (!isUnsigned)
        {
            A_HI = (ulong)(int)(uint)A_HI;
            B_HI = (ulong)(int)(uint)B_HI;
        }

        /* Product parts */
        ulong P1 = A_LO * B_LO;
        ulong P2 = A_HI * B_LO;
        ulong P3 = A_LO * B_HI;
        ulong P4 = A_HI * B_HI;

        uint CARRY = (uint)(((P1 >> 32) + (uint)P2 + (uint)P3) >> 32);

        ulong TEMP = (P2 >> 32) + (P3 >> 32);

        if (!isUnsigned)
        {
            TEMP = (ulong)(int)(uint)TEMP;
        }

        RESULT_LO = P1 + (P2 << 32) + (P3 << 32);
        RESULT_HI = P4 + TEMP + CARRY;

        WriteHi(RESULT_HI);
        WriteLo(RESULT_LO);
    }
}