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📁 建立《编译原理网络课程》的目的不仅使学生掌握构造编译程序的原理和技术
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<font class="title2"><b>9.7.7.2 强度削弱用于归纳变量的算法</b></font>            


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<font class = "definition">算法9.12 强度削弱用于归纳变量 </font><br>
    输入：循环L，附带到达_定值信息和算法9.11（寻找归纳变量）计算的<br>
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp归纳变量族。 <br>
    输出：强度削弱用于归纳变量后的循环。 <br>
    方法：依次对循环的每个基本归纳变量i执行：<br>
&nbsp&nbsp &nbsp&nbsp;  对i族的每个三元组为（i，c，d）的一般归纳变量j执行： <br>
 &nbsp&nbsp&nbsp&nbsp  (1) 建新变量s，但如果变量j1和j2有同样的三元组，则仅建一个<br>
&nbsp&nbsp&nbsp&nbsp;&nbsp;&nbsp&nbsp&nbsp&nbsp;新变量用于两者; <br>
 &nbsp&nbsp&nbsp&nbsp  (2) 用j:=s代替j 的赋值; <br>
 &nbsp&nbsp&nbsp&nbsp  (3) 在L中紧接在赋值语句i:=i+n的后面（n是常量）加上： <br>&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp &nbsp;&nbsp;            s:=s+r <br>
&nbsp&nbsp&nbsp&nbsp;&nbsp;&nbsp&nbsp;&nbsp; 	其中r=c*n,因为c和n是常量,所以c*n被计算为一个常量。把s<br>
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp;&nbsp;放入i族，三元组为（i，c，d）。 <br>
&nbsp&nbsp&nbsp&nbsp  (4) 还必须保证在循环的入口处s的初值为c*i+d，这个初始化工作<br>
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp;&nbsp;把下面<br>
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp     s:=c*i &nbsp&nbsp/*如果c为1，则s:=i*/ <br>
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp     s:=s+d &nbsp&nbsp /*如果d为0,则省略*/ <br>
&nbsp&nbsp&nbsp&nbsp&nbsp &nbsp;&nbsp;  的赋值放在前置块的末尾。<br>
 注意： s是i族的归纳变量。 </p>
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<td><font class="yanshi">&nbsp &nbsp观看演示&nbsp</font></td>
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