ruction executes as described in compatibility mode and legacy mode. It is not valid in 64-bit mode.</p>
<h2>Operation</h2>
<pre>IF 64-bit mode
    THEN
         #UD;
    ELSE
         IF ((AL AND 0FH) &gt; 9) or (AF = 1)
              THEN
                    AX ← AX – 6;
                    AH ← AH – 1;
                    AF ← 1;
                    CF ← 1;
                    AL ← AL AND 0FH;
              ELSE
                    CF ← 0;
                    AF ← 0;
                   