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214 lines
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HTML
214 lines
7.5 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>VAX-branch (Using as)</title>
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<meta name="description" content="VAX-branch (Using as)">
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<meta name="keywords" content="VAX-branch (Using as)">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Vax_002dDependent.html#Vax_002dDependent" rel="up" title="Vax-Dependent">
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<link href="VAX_002doperands.html#VAX_002doperands" rel="next" title="VAX-operands">
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</head>
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<body lang="en">
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<a name="VAX_002dbranch"></a>
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<div class="header">
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<p>
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Next: <a href="VAX_002doperands.html#VAX_002doperands" accesskey="n" rel="next">VAX-operands</a>, Previous: <a href="VAX_002dopcodes.html#VAX_002dopcodes" accesskey="p" rel="prev">VAX-opcodes</a>, Up: <a href="Vax_002dDependent.html#Vax_002dDependent" accesskey="u" rel="up">Vax-Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="VAX-Branch-Improvement"></a>
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<h4 class="subsection">9.49.5 VAX Branch Improvement</h4>
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<a name="index-VAX-branch-improvement"></a>
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<a name="index-branch-improvement_002c-VAX"></a>
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<a name="index-pseudo_002dops-for-branch_002c-VAX"></a>
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<p>Certain pseudo opcodes are permitted. They are for branch
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instructions. They expand to the shortest branch instruction that
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reaches the target. Generally these mnemonics are made by
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substituting ‘<samp>j</samp>’ for ‘<samp>b</samp>’ at the start of a DEC mnemonic.
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This feature is included both for compatibility and to help
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compilers. If you do not need this feature, avoid these
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opcodes. Here are the mnemonics, and the code they can expand into.
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</p>
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<dl compact="compact">
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<dt><code>jbsb</code></dt>
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<dd><p>‘<samp>Jsb</samp>’ is already an instruction mnemonic, so we chose ‘<samp>jbsb</samp>’.
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</p><dl compact="compact">
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<dt>(byte displacement)</dt>
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<dd><p><kbd>bsbb …</kbd>
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</p></dd>
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<dt>(word displacement)</dt>
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<dd><p><kbd>bsbw …</kbd>
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</p></dd>
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<dt>(long displacement)</dt>
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<dd><p><kbd>jsb …</kbd>
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</p></dd>
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</dl>
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</dd>
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<dt><code>jbr</code></dt>
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<dt><code>jr</code></dt>
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<dd><p>Unconditional branch.
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</p><dl compact="compact">
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<dt>(byte displacement)</dt>
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<dd><p><kbd>brb …</kbd>
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</p></dd>
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<dt>(word displacement)</dt>
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<dd><p><kbd>brw …</kbd>
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</p></dd>
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<dt>(long displacement)</dt>
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<dd><p><kbd>jmp …</kbd>
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</p></dd>
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</dl>
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</dd>
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<dt><code>j<var>COND</var></code></dt>
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<dd><p><var>COND</var> may be any one of the conditional branches
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<code>neq</code>, <code>nequ</code>, <code>eql</code>, <code>eqlu</code>, <code>gtr</code>,
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<code>geq</code>, <code>lss</code>, <code>gtru</code>, <code>lequ</code>, <code>vc</code>, <code>vs</code>,
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<code>gequ</code>, <code>cc</code>, <code>lssu</code>, <code>cs</code>.
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<var>COND</var> may also be one of the bit tests
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<code>bs</code>, <code>bc</code>, <code>bss</code>, <code>bcs</code>, <code>bsc</code>, <code>bcc</code>,
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<code>bssi</code>, <code>bcci</code>, <code>lbs</code>, <code>lbc</code>.
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<var>NOTCOND</var> is the opposite condition to <var>COND</var>.
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</p><dl compact="compact">
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<dt>(byte displacement)</dt>
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<dd><p><kbd>b<var>COND</var> …</kbd>
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</p></dd>
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<dt>(word displacement)</dt>
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<dd><p><kbd>b<var>NOTCOND</var> foo ; brw … ; foo:</kbd>
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</p></dd>
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<dt>(long displacement)</dt>
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<dd><p><kbd>b<var>NOTCOND</var> foo ; jmp … ; foo:</kbd>
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</p></dd>
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</dl>
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</dd>
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<dt><code>jacb<var>X</var></code></dt>
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<dd><p><var>X</var> may be one of <code>b d f g h l w</code>.
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</p><dl compact="compact">
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<dt>(word displacement)</dt>
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<dd><p><kbd><var>OPCODE</var> …</kbd>
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</p></dd>
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<dt>(long displacement)</dt>
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<dd><div class="example">
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<pre class="example"><var>OPCODE</var> …, foo ;
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brb bar ;
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foo: jmp … ;
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bar:
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</pre></div>
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</dd>
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</dl>
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</dd>
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<dt><code>jaob<var>YYY</var></code></dt>
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<dd><p><var>YYY</var> may be one of <code>lss leq</code>.
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</p></dd>
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<dt><code>jsob<var>ZZZ</var></code></dt>
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<dd><p><var>ZZZ</var> may be one of <code>geq gtr</code>.
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</p><dl compact="compact">
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<dt>(byte displacement)</dt>
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<dd><p><kbd><var>OPCODE</var> …</kbd>
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</p></dd>
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<dt>(word displacement)</dt>
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<dd><div class="example">
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<pre class="example"><var>OPCODE</var> …, foo ;
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brb bar ;
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foo: brw <var>destination</var> ;
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bar:
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</pre></div>
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</dd>
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<dt>(long displacement)</dt>
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<dd><div class="example">
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<pre class="example"><var>OPCODE</var> …, foo ;
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brb bar ;
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foo: jmp <var>destination</var> ;
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bar:
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</pre></div>
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</dd>
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</dl>
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</dd>
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<dt><code>aobleq</code></dt>
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<dt><code>aoblss</code></dt>
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<dt><code>sobgeq</code></dt>
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<dt><code>sobgtr</code></dt>
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<dd><dl compact="compact">
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<dt>(byte displacement)</dt>
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<dd><p><kbd><var>OPCODE</var> …</kbd>
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</p></dd>
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<dt>(word displacement)</dt>
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<dd><div class="example">
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<pre class="example"><var>OPCODE</var> …, foo ;
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brb bar ;
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foo: brw <var>destination</var> ;
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bar:
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</pre></div>
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</dd>
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<dt>(long displacement)</dt>
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<dd><div class="example">
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<pre class="example"><var>OPCODE</var> …, foo ;
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brb bar ;
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foo: jmp <var>destination</var> ;
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bar:
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</pre></div>
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</dd>
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</dl>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="VAX_002doperands.html#VAX_002doperands" accesskey="n" rel="next">VAX-operands</a>, Previous: <a href="VAX_002dopcodes.html#VAX_002dopcodes" accesskey="p" rel="prev">VAX-opcodes</a>, Up: <a href="Vax_002dDependent.html#Vax_002dDependent" accesskey="u" rel="up">Vax-Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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