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<br>

<h2>17.8 How to convert _AX pseudo-registers?</h2>

<p><em><strong>Q</strong>: Since DJGPP doesn't recognize Borland-style pseudo-register
variables like <code>_AX</code>, how should I port code which uses them to
DJGPP?</em>

<br><p>
<p><strong>A</strong>:  These pseudo-variables are typically used in two different
contexts:

<ul>
<li>When calling real-mode interrupt services.

<p>To port such code to DJGPP, use the fields of the <code>__dpmi_regs</code>
structure (declared on the <code>dpmi.h</code> header file) to set the
register values, and library function <code>__dpmi_int</code> to invoke the
interrupt service.  For example, consider the following code snippet:

<pre>  #include &lt;dos.h&gt;
  void _highcolor (void)
  {
    _AH = 0x10;
    _AL = 0x03;
    _BL = 0;
    geninterrupt (0x10);
  }
</pre>

<p>Here's one way to express this in DJGPP<a rel=footnote href="faq25.html"><sup>30</sup></a>:

<pre>  #include &lt;dpmi.h&gt;
  void _highcolor (void)
  {
    __dpmi_regs r;

    r.h.ah = 0x10;
    r.h.al = 0x03;
    r.h.bl = 0;
    __dpmi_int (0x10, &amp;r);
  }
</pre>

<p>Please read <a href="faq18_1.html">how to call real-mode interrupt functions</a>, elsewhere in this document, for further
details on how call real-mode services from DJGPP programs.

</p><li>Immediately before or after an inline assembly code.

<p>GCC features extensive inline assembly facilities which allow you to
assign values to, or read values from registers from the inline assembly
code.  Since you will have to rewrite your inline assembly code anyway,
make it refer directly to your C variables, instead of referencing
pseudo-register variables from C.  See <a href="faq18_12.html">description of inline assembly</a>, for further info. 
</ul>

<p><hr>
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