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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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下面要介绍的是P.J.Weinberger的C编译程序中实际用到的散列函数hashpjw,如图6.29所示。 
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(1) <font color="#0000FF">#define</font> PRIME 211 <br>     
        &nbsp;&nbsp;&nbsp;  (2) <font color="#0000FF">#define</font> EOS '＼0'<br>    
        &nbsp;&nbsp;&nbsp;  (3) <font color="#0000FF"> int</font> hashpjw(s) <br>     
        &nbsp;&nbsp;&nbsp;  (4) <font color="#0000FF"> char</font> *s； <br>     
        &nbsp;&nbsp;&nbsp;  (5)｛ <br>     
        &nbsp;&nbsp;&nbsp;  (6) &nbsp;&nbsp;&nbsp;<font color="#0000FF">char</font> *p; <br>     
        &nbsp;&nbsp;&nbsp;  (7) &nbsp;&nbsp;&nbsp;<font color="#0000FF">unsigned</font> h＝0，g; <br>     
        &nbsp;&nbsp;&nbsp;  (8) &nbsp;&nbsp;&nbsp;<font color="#0000FF">for</font>(p=s;*p!=EOS；p=p+1)｛ <br>    
        &nbsp;&nbsp;&nbsp;  (9) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;h=(h<<4)+(*p)； <br>     
        &nbsp;&nbsp;&nbsp;  (10)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <font color="#0000FF">if</font>（g＝h＆0xf0000000）｛     
        <br>    
        &nbsp;&nbsp;&nbsp;  (11)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  h= h^(g>>24)； <br>     
        &nbsp;&nbsp;&nbsp;  (12) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;h＝h^g;      
        <br>    
        &nbsp;&nbsp;&nbsp;  (13)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;｝ <br>     
        &nbsp;&nbsp;&nbsp;  (14)&nbsp;&nbsp;&nbsp;｝ <br>     
        &nbsp;&nbsp;&nbsp;  (15) &nbsp;&nbsp;<font color="#0000FF">return</font> h％PRIME； <br>     
        &nbsp;&nbsp;&nbsp;&nbsp; (16) } </p>     
      <p> &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp; 
      <b>图6.29</b> 散列函数hashpjw </p>    
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函数hashpjw是从h＝0开始计算的。对每一个字符c，将h左移4位，并加上c，得到新的h。如果在32位的h的四位高序位（最左边的四位）中有1存在的话，那么把这四位提取出来并右移24位，把它与h进行模2相加，然后将四位高序位中曾是1的那些位置为0。经试验证明散列函数hashpiw对于用它建立的各种长度不同的符号表都取得了很好的效果。即在这样的符号表中字符串能均匀的落人到各个链表中去。不但如此，haShpjw本身的计算既快速又简洁。
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