’s operation is the same in non-64-bit modes and 64-bit mode.</p>
<h2>Operation</h2>
<pre>IF Instruction = FIADD
    THEN
         DEST ← DEST + ConvertToDoubleExtendedPrecisionFP(SRC);
    ELSE (* Source operand is floating-point value *)
         DEST ← DEST + SRC;
FI;
IF Instruction = FADDP
    THEN
         PopRegisterStack;
FI;</pre>
<h2>FPU Flags Affected</h2>
<table class="exception-table">
<tr>
<td>C1</td>
<td>
<p>Set to 0 if stack underflow occurred.</p>
<p>Set if result was rounded up; clear