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| <h5 class="subsubsection">9.23.6.1 Branch Improvement</h5> |
| |
| <p><a name="index-pseudo_002dopcodes_002c-M68HC11-1512"></a><a name="index-M68HC11-pseudo_002dopcodes-1513"></a><a name="index-branch-improvement_002c-M68HC11-1514"></a><a name="index-M68HC11-branch-improvement-1515"></a> |
| Certain pseudo opcodes are permitted for branch instructions. |
| They expand to the shortest branch instruction that reach the |
| target. Generally these mnemonics are made by prepending ‘<samp><span class="samp">j</span></samp>’ to |
| the start of Motorola mnemonic. These pseudo opcodes are not affected |
| by the ‘<samp><span class="samp">--short-branches</span></samp>’ or ‘<samp><span class="samp">--force-long-branches</span></samp>’ options. |
| |
| <p>The following table summarizes the pseudo-operations. |
| |
| <pre class="smallexample"> Displacement Width |
| +-------------------------------------------------------------+ |
| | Options | |
| | --short-branches --force-long-branches | |
| +--------------------------+----------------------------------+ |
| Op |BYTE WORD | BYTE WORD | |
| +--------------------------+----------------------------------+ |
| bsr | bsr <pc-rel> <error> | jsr <abs> | |
| bra | bra <pc-rel> <error> | jmp <abs> | |
| jbsr | bsr <pc-rel> jsr <abs> | bsr <pc-rel> jsr <abs> | |
| jbra | bra <pc-rel> jmp <abs> | bra <pc-rel> jmp <abs> | |
| bXX | bXX <pc-rel> <error> | bNX +3; jmp <abs> | |
| jbXX | bXX <pc-rel> bNX +3; | bXX <pc-rel> bNX +3; jmp <abs> | |
| | jmp <abs> | | |
| +--------------------------+----------------------------------+ |
| XX: condition |
| NX: negative of condition XX |
| |
| </pre> |
| <dl> |
| <dt><code>jbsr</code><dt><code>jbra</code><dd>These are the simplest jump pseudo-operations; they always map to one |
| particular machine instruction, depending on the displacement to the |
| branch target. |
| |
| <br><dt><code>jb</code><var>XX</var><dd>Here, ‘<samp><span class="samp">jb</span><var>XX</var></samp>’ stands for an entire family of pseudo-operations, |
| where <var>XX</var> is a conditional branch or condition-code test. The full |
| list of pseudo-ops in this family is: |
| <pre class="smallexample"> jbcc jbeq jbge jbgt jbhi jbvs jbpl jblo |
| jbcs jbne jblt jble jbls jbvc jbmi |
| </pre> |
| <p>For the cases of non-PC relative displacements and long displacements, |
| <code>as</code> issues a longer code fragment in terms of |
| <var>NX</var>, the opposite condition to <var>XX</var>. For example, for the |
| non-PC relative case: |
| <pre class="smallexample"> jb<var>XX</var> foo |
| </pre> |
| <p>gives |
| <pre class="smallexample"> b<var>NX</var>s oof |
| jmp foo |
| oof: |
| </pre> |
| </dl> |
| |
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