You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
132 lines
6.0 KiB
HTML
132 lines
6.0 KiB
HTML
4 years ago
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>VAX-branch - Using as</title>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<meta name="description" content="Using as">
|
||
|
|
<meta name="generator" content="makeinfo 4.13">
|
||
|
|
<link title="Top" rel="start" href="index.html#Top">
|
||
|
|
<link rel="up" href="Vax_002dDependent.html#Vax_002dDependent" title="Vax-Dependent">
|
||
|
|
<link rel="prev" href="VAX_002dopcodes.html#VAX_002dopcodes" title="VAX-opcodes">
|
||
|
|
<link rel="next" href="VAX_002doperands.html#VAX_002doperands" title="VAX-operands">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
This file documents the GNU Assembler "as".
|
||
|
|
|
||
|
|
Copyright (C) 1991-2015 Free Software Foundation, Inc.
|
||
|
|
|
||
|
|
Permission is granted to copy, distribute and/or modify this document
|
||
|
|
under the terms of the GNU Free Documentation License, Version 1.3
|
||
|
|
or any later version published by the Free Software Foundation;
|
||
|
|
with no Invariant Sections, with no Front-Cover Texts, and with no
|
||
|
|
Back-Cover Texts. A copy of the license is included in the
|
||
|
|
section entitled ``GNU Free Documentation License''.
|
||
|
|
|
||
|
|
-->
|
||
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
||
|
|
<style type="text/css"><!--
|
||
|
|
pre.display { font-family:inherit }
|
||
|
|
pre.format { font-family:inherit }
|
||
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallexample { font-size:smaller }
|
||
|
|
pre.smalllisp { font-size:smaller }
|
||
|
|
span.sc { font-variant:small-caps }
|
||
|
|
span.roman { font-family:serif; font-weight:normal; }
|
||
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
||
|
|
--></style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<div class="node">
|
||
|
|
<a name="VAX-branch"></a>
|
||
|
|
<a name="VAX_002dbranch"></a>
|
||
|
|
<p>
|
||
|
|
Next: <a rel="next" accesskey="n" href="VAX_002doperands.html#VAX_002doperands">VAX-operands</a>,
|
||
|
|
Previous: <a rel="previous" accesskey="p" href="VAX_002dopcodes.html#VAX_002dopcodes">VAX-opcodes</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="Vax_002dDependent.html#Vax_002dDependent">Vax-Dependent</a>
|
||
|
|
<hr>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h4 class="subsection">9.48.5 VAX Branch Improvement</h4>
|
||
|
|
|
||
|
|
<p><a name="index-VAX-branch-improvement-2358"></a><a name="index-branch-improvement_002c-VAX-2359"></a><a name="index-pseudo_002dops-for-branch_002c-VAX-2360"></a>Certain pseudo opcodes are permitted. They are for branch
|
||
|
|
instructions. They expand to the shortest branch instruction that
|
||
|
|
reaches the target. Generally these mnemonics are made by
|
||
|
|
substituting ‘<samp><span class="samp">j</span></samp>’ for ‘<samp><span class="samp">b</span></samp>’ at the start of a DEC mnemonic.
|
||
|
|
This feature is included both for compatibility and to help
|
||
|
|
compilers. If you do not need this feature, avoid these
|
||
|
|
opcodes. Here are the mnemonics, and the code they can expand into.
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><code>jbsb</code><dd>‘<samp><span class="samp">Jsb</span></samp>’ is already an instruction mnemonic, so we chose ‘<samp><span class="samp">jbsb</span></samp>’.
|
||
|
|
<dl>
|
||
|
|
<dt>(byte displacement)<dd><kbd>bsbb ...</kbd>
|
||
|
|
<br><dt>(word displacement)<dd><kbd>bsbw ...</kbd>
|
||
|
|
<br><dt>(long displacement)<dd><kbd>jsb ...</kbd>
|
||
|
|
</dl>
|
||
|
|
<br><dt><code>jbr</code><dt><code>jr</code><dd>Unconditional branch.
|
||
|
|
<dl>
|
||
|
|
<dt>(byte displacement)<dd><kbd>brb ...</kbd>
|
||
|
|
<br><dt>(word displacement)<dd><kbd>brw ...</kbd>
|
||
|
|
<br><dt>(long displacement)<dd><kbd>jmp ...</kbd>
|
||
|
|
</dl>
|
||
|
|
<br><dt><code>j</code><var>COND</var><dd><var>COND</var> may be any one of the conditional branches
|
||
|
|
<code>neq</code>, <code>nequ</code>, <code>eql</code>, <code>eqlu</code>, <code>gtr</code>,
|
||
|
|
<code>geq</code>, <code>lss</code>, <code>gtru</code>, <code>lequ</code>, <code>vc</code>, <code>vs</code>,
|
||
|
|
<code>gequ</code>, <code>cc</code>, <code>lssu</code>, <code>cs</code>.
|
||
|
|
<var>COND</var> may also be one of the bit tests
|
||
|
|
<code>bs</code>, <code>bc</code>, <code>bss</code>, <code>bcs</code>, <code>bsc</code>, <code>bcc</code>,
|
||
|
|
<code>bssi</code>, <code>bcci</code>, <code>lbs</code>, <code>lbc</code>.
|
||
|
|
<var>NOTCOND</var> is the opposite condition to <var>COND</var>.
|
||
|
|
<dl>
|
||
|
|
<dt>(byte displacement)<dd><kbd>b</kbd><var>COND</var><kbd> ...</kbd>
|
||
|
|
<br><dt>(word displacement)<dd><kbd>b</kbd><var>NOTCOND</var><kbd> foo ; brw ... ; foo:</kbd>
|
||
|
|
<br><dt>(long displacement)<dd><kbd>b</kbd><var>NOTCOND</var><kbd> foo ; jmp ... ; foo:</kbd>
|
||
|
|
</dl>
|
||
|
|
<br><dt><code>jacb</code><var>X</var><dd><var>X</var> may be one of <code>b d f g h l w</code>.
|
||
|
|
<dl>
|
||
|
|
<dt>(word displacement)<dd><var>OPCODE</var><kbd> ...</kbd>
|
||
|
|
<br><dt>(long displacement)<dd>
|
||
|
|
<pre class="example"> <var>OPCODE</var> ..., foo ;
|
||
|
|
brb bar ;
|
||
|
|
foo: jmp ... ;
|
||
|
|
bar:
|
||
|
|
</pre>
|
||
|
|
</dl>
|
||
|
|
<br><dt><code>jaob</code><var>YYY</var><dd><var>YYY</var> may be one of <code>lss leq</code>.
|
||
|
|
<br><dt><code>jsob</code><var>ZZZ</var><dd><var>ZZZ</var> may be one of <code>geq gtr</code>.
|
||
|
|
<dl>
|
||
|
|
<dt>(byte displacement)<dd><var>OPCODE</var><kbd> ...</kbd>
|
||
|
|
<br><dt>(word displacement)<dd>
|
||
|
|
<pre class="example"> <var>OPCODE</var> ..., foo ;
|
||
|
|
brb bar ;
|
||
|
|
foo: brw <var>destination</var> ;
|
||
|
|
bar:
|
||
|
|
</pre>
|
||
|
|
<br><dt>(long displacement)<dd>
|
||
|
|
<pre class="example"> <var>OPCODE</var> ..., foo ;
|
||
|
|
brb bar ;
|
||
|
|
foo: jmp <var>destination</var> ;
|
||
|
|
bar:
|
||
|
|
</pre>
|
||
|
|
</dl>
|
||
|
|
<br><dt><code>aobleq</code><dt><code>aoblss</code><dt><code>sobgeq</code><dt><code>sobgtr</code><dd>
|
||
|
|
<dl>
|
||
|
|
<dt>(byte displacement)<dd><var>OPCODE</var><kbd> ...</kbd>
|
||
|
|
<br><dt>(word displacement)<dd>
|
||
|
|
<pre class="example"> <var>OPCODE</var> ..., foo ;
|
||
|
|
brb bar ;
|
||
|
|
foo: brw <var>destination</var> ;
|
||
|
|
bar:
|
||
|
|
</pre>
|
||
|
|
<br><dt>(long displacement)<dd>
|
||
|
|
<pre class="example"> <var>OPCODE</var> ..., foo ;
|
||
|
|
brb bar ;
|
||
|
|
foo: jmp <var>destination</var> ;
|
||
|
|
bar:
|
||
|
|
</pre>
|
||
|
|
</dl>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
</body></html>
|
||
|
|
|