Note</U> that ST(0) cannot be subtracted directly from a QWORD integer in memory. If such a subtraction becomes necessary, the QWORD value
must first be loaded to the FPU and then the subtraction performed with the FSUBR or <A HREF="fpuchap8.htm#fsubrp">FSUBRP</A> instruction.</BLOCKQUOTE>

An <B>I</B>nvalid operation exception is detected if the TOP data register ST(0) is empty or is a <A HREF="fpuchap2.htm#nans">NAN</A>, setting the related flag in the <A HREF="fpuchap1.htm#sword">Status Word</A>. The <A 