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| <title>Using as: VAX-branch</title> |
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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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| <hr> |
| <a name="VAX-Branch-Improvement"></a> |
| <h4 class="subsection">9.48.5 VAX Branch Improvement</h4> |
| |
| <a name="index-VAX-branch-improvement"></a> |
| <a name="index-branch-improvement_002c-VAX"></a> |
| <a name="index-pseudo_002dops-for-branch_002c-VAX"></a> |
| <p>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>j</samp>’ for ‘<samp>b</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. |
| </p> |
| <dl compact="compact"> |
| <dt><code>jbsb</code></dt> |
| <dd><p>‘<samp>Jsb</samp>’ is already an instruction mnemonic, so we chose ‘<samp>jbsb</samp>’. |
| </p><dl compact="compact"> |
| <dt>(byte displacement)</dt> |
| <dd><p><kbd>bsbb …</kbd> |
| </p></dd> |
| <dt>(word displacement)</dt> |
| <dd><p><kbd>bsbw …</kbd> |
| </p></dd> |
| <dt>(long displacement)</dt> |
| <dd><p><kbd>jsb …</kbd> |
| </p></dd> |
| </dl> |
| </dd> |
| <dt><code>jbr</code></dt> |
| <dt><code>jr</code></dt> |
| <dd><p>Unconditional branch. |
| </p><dl compact="compact"> |
| <dt>(byte displacement)</dt> |
| <dd><p><kbd>brb …</kbd> |
| </p></dd> |
| <dt>(word displacement)</dt> |
| <dd><p><kbd>brw …</kbd> |
| </p></dd> |
| <dt>(long displacement)</dt> |
| <dd><p><kbd>jmp …</kbd> |
| </p></dd> |
| </dl> |
| </dd> |
| <dt><code>j<var>COND</var></code></dt> |
| <dd><p><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>. |
| </p><dl compact="compact"> |
| <dt>(byte displacement)</dt> |
| <dd><p><kbd>b<var>COND</var> …</kbd> |
| </p></dd> |
| <dt>(word displacement)</dt> |
| <dd><p><kbd>b<var>NOTCOND</var> foo ; brw … ; foo:</kbd> |
| </p></dd> |
| <dt>(long displacement)</dt> |
| <dd><p><kbd>b<var>NOTCOND</var> foo ; jmp … ; foo:</kbd> |
| </p></dd> |
| </dl> |
| </dd> |
| <dt><code>jacb<var>X</var></code></dt> |
| <dd><p><var>X</var> may be one of <code>b d f g h l w</code>. |
| </p><dl compact="compact"> |
| <dt>(word displacement)</dt> |
| <dd><p><kbd><var>OPCODE</var> …</kbd> |
| </p></dd> |
| <dt>(long displacement)</dt> |
| <dd><div class="example"> |
| <pre class="example"><var>OPCODE</var> …, foo ; |
| brb bar ; |
| foo: jmp … ; |
| bar: |
| </pre></div> |
| </dd> |
| </dl> |
| </dd> |
| <dt><code>jaob<var>YYY</var></code></dt> |
| <dd><p><var>YYY</var> may be one of <code>lss leq</code>. |
| </p></dd> |
| <dt><code>jsob<var>ZZZ</var></code></dt> |
| <dd><p><var>ZZZ</var> may be one of <code>geq gtr</code>. |
| </p><dl compact="compact"> |
| <dt>(byte displacement)</dt> |
| <dd><p><kbd><var>OPCODE</var> …</kbd> |
| </p></dd> |
| <dt>(word displacement)</dt> |
| <dd><div class="example"> |
| <pre class="example"><var>OPCODE</var> …, foo ; |
| brb bar ; |
| foo: brw <var>destination</var> ; |
| bar: |
| </pre></div> |
| </dd> |
| <dt>(long displacement)</dt> |
| <dd><div class="example"> |
| <pre class="example"><var>OPCODE</var> …, foo ; |
| brb bar ; |
| foo: jmp <var>destination</var> ; |
| bar: |
| </pre></div> |
| </dd> |
| </dl> |
| </dd> |
| <dt><code>aobleq</code></dt> |
| <dt><code>aoblss</code></dt> |
| <dt><code>sobgeq</code></dt> |
| <dt><code>sobgtr</code></dt> |
| <dd><dl compact="compact"> |
| <dt>(byte displacement)</dt> |
| <dd><p><kbd><var>OPCODE</var> …</kbd> |
| </p></dd> |
| <dt>(word displacement)</dt> |
| <dd><div class="example"> |
| <pre class="example"><var>OPCODE</var> …, foo ; |
| brb bar ; |
| foo: brw <var>destination</var> ; |
| bar: |
| </pre></div> |
| </dd> |
| <dt>(long displacement)</dt> |
| <dd><div class="example"> |
| <pre class="example"><var>OPCODE</var> …, foo ; |
| brb bar ; |
| foo: jmp <var>destination</var> ; |
| bar: |
| </pre></div> |
| </dd> |
| </dl> |
| </dd> |
| </dl> |
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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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