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通过一遍扫描得到目标代码的布尔表达式的翻译模式如图7．14所示。在翻译模式中用到如下三个函数：<br>
1．makelist(i),它将创建一个仅包含i的新表，i
是四元式数组的一个索引（下标），或说i是四元式代码序列的一个标号。<br>
2．merge(p<span class="down"><sub>1</sub></span>，p<span class="down"><sub>2</sub></span>)，它将连接由指针p<span
class="down">1</span>和p2指向的两个表并且返回一个指向连接后的表的指针。<br>
3．backpatch（p，i），它将把i作为目标标号回填到p所指向的表中的每一个转移指令中去。<br>
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<td vAlign="top" width="41%"> (1) E -> E<span class="down"><sub>1</sub></span>
<b>or</b> M E<span class="down"><sub>2</sub></span><p><br>
<br>
<br>
<br>
</p>
<p>(2) E -> E<span class="down"><sub>1</sub></span> <b>and</b> M E<span class="down"><sub>2</sub></span></p>
<p><br>
<br>
<br>
</p>
<p>(3) E -> <b>not</b> E<span class="down"><sub>1</sub></span></p>
<p><br>
<br>
</p>
<p>(4) E -> (E<span class="down"><sub>1</sub></span>)</p>
<p><br>
</p>
<p>(5) E -> <b>id</b><span class="down"><sub>1</sub></span><br>
<b>relop id</b><span
class="down"><sub>2</sub></span></p>
<p><br>
<br>
<br>
<br>
</p>
<p>(6) E -> <b>true</b></p>
<p><br>
</p>
<p>(7) E -> <b>false</b></p>
<p><br>
</p>
<p>(8) E -> ε</td>
<td vAlign="top" width="59%">{ backpatch(E<span class="down"><sub>1</sub></span>.falselist,M.quad);<br>
E.truelist := merge(E<span class="down"><sub>1</sub></span>.truelist,E<span
class="down"><sub>2</sub></span>.truelist);<br>
E.falselist := E<span class="down"><sub>2</sub></span>.falselist }<br>
<br>
{ backpatch(E<span class="down"><sub>1</sub></span>.truelist,M.quad);<br>
E.truelist := E<span class="down"><sub>2</sub></span>.truelist;<br>
E.falselist := merge(E<span class="down"><sub>1</sub></span>.falselist,E<span
class="down"><sub>2</sub></span>.falselist) }<br>
<br>
{ E.truelist := E<span class="down"><sub>1</sub></span>.falselist;<br>
E.falselist := E<span class="down"><sub>1</sub></span>.truelist }<br>
<br>
{ E.truelist := E<span class="down"><sub>1</sub></span>.truelist;<br>
E.falselist := E<span class="down"><sub>1</sub></span>.falselist }<br>
<br>
{ E.truelist := makelist(nextquad);<br>
E.falselist<br>
:= makelist(nextquad + 1);<br>
emit('if' <b>id</b><span class="down"><sub>1</sub></span>.place <b>relop.</b>op <b>id</b><span
class="down"><sub>2</sub></span>.place 'goto --')<br>
emit('goto --') }<br>
<br>
{ E.truelist := makelist(nextquad);<br>
emit('goto --') }<br>
<br>
{ E.falselist := makelist(nextquad);<br>
emit('goto --') }<br>
<br>
{ M.quad := nextquad }</td>
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<p align="center"><br>
图7.14 使用一遍扫描的布尔表达式的翻译模式 </p>
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