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SystemVerilog——任务和函数(Tasks and Functions)

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发表于 2011-7-19 14:14:34 | 显示全部楼层 |阅读模式
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                      <h3 class="title pre fs1"><span class="tcnt">SystemVerilog——任务和函数(Tasks and Functions)</span><span class="bgc0 fc07 fw0 fs0"></span></h3>
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        <p>又翻译了一篇。</p>  <p>来源:<a href="http://systemverilog.co/wiki/Tasks_and_Functions">http://systemverilog.co/wiki/Tasks_and_Functions</a></p>  <p>&nbsp;</p>  <hr style="font-weight: bold; font-size: 13px; color: #007070; line-height: normal; font-family: verdana;">  <p><br></p><p>SystemVerilog从Verilog继承了任务和函数功能。任务和函数是两种用来定义子程序的方式。如果子程序需要消耗仿真时间,使用任务,否者子程序消耗仿真时间为0,则使用函数。另外,函数可以有返回值,而任务没有。</p>  <p>SystemVerilog给任务和函数增加了新的语义特性. 这些新的特性对高级抽象建模非常重要:</p>  <ul><li>静态和自动作用域 </li><li>参数传递 </li><li>线程 </li><li>参数化函数 </li></ul><br><br><br><br>  <hr style="font-weight: bold; font-size: 13px; color: #007070; line-height: normal; font-family: verdana;">  <h2><strong>静态和自动作用域</strong></h2>  <h2>   <hr style="font-weight: bold; font-size: 13px; color: #007070; line-height: normal; font-family: verdana;"></h2>  <h3><br><strong></strong></h3><h3><strong>Verilog中变量的作用域</strong></h3>  <p><br></p><p>Verilog
中,任务和函数中局部定义的变量是静态作用域。因此,如果多次调用函数/任务,则此局部变量将在多个函数执行线程中共享。在递归函数以及任务中通过
fork-join执行多线程的情况下发生。因此,Verilog的函数/任务仅仅只可能本地(native)递归。由于Verilog主要用来做RTL
级的设计,递归函数不是必须的。</p>  <p><br></p><p>【【译者查资料,猜想本地递归是指函数调用中没有变量,仅仅只有函数自己和参数的运算,举例如下:</p>  <blockquote>   <pre>fibonacci (n)
        if (n &lt;2) return n
        else return fibonacci(n-1)+fibonacci(n-2)</pre>
</blockquote>

<p>】】</p>

<h3><br><strong></strong></h3><h3><strong>静态和自动作用域</strong></h3><br>

<p>Statically静态作用域变量被绑定到应用程序的数据存储区域(在这里是指仿真器). 此存储区域将被所有的线程所共享. 而另一方面对于自动变量,将映射到栈区存储区, 对同一个函数进行多次调用,自动变量将映射到栈中互补相同的区域。</p>

<p>For 对于行为级建模,递归和多线程基本上都需要。为此,SystemVerilog允许变量以自动作用域绑定。为了在函数/任务中使用自动绑定功能,函数/任务需要声明为<em>automatic</em>.

另外,所有在program块中声明的函数/任务缺省都是自动作用域的。如果在自动作用域子程序中仍然需要使用静态变量,那么必须使用static关键字
显式声明此变量。注意在C/C++以及其他语言中,缺省就是这样的(类似program块中的样子: 缺省自动,显式声明静态)。</p><p><br></p>

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<blockquote class="webkit-indent-blockquote" style="padding-right: 0px; padding-left: 0px; padding-bottom: 0px; margin: 0px 0px 0px 40px; border-top-style: none; padding-top: 0px; border-right-style: none; border-left-style: none; border-bottom-style: none;">
  <p style="border-collapse: collapse;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana; border-collapse: separate;"><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">//Factorial using automatic binding</span></span></p>

  <p style="border-collapse: collapse;"><span class="Apple-style-span" style="line-height: normal; border-collapse: separate;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">function</span></span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">automatic</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">int</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">factorial</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">(</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">int</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">n</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">);</span></p>

  <p style="border-collapse: collapse;"><span class="Apple-style-span" style="line-height: normal; border-collapse: separate;"><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp; </span></span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">if</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">(</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">n</span></span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">=</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; font-family: verdana;">1</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">)</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">return</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; font-family: verdana;">1</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">;</span></p>

  <p style="border-collapse: collapse;"><span class="Apple-style-span" style="line-height: normal; border-collapse: separate;"><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp; </span></span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">else</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">return</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">n</span></span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">*</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">factorial</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">(</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">n</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">-</span><span class="S4" style="font-size: 10pt; color: #007f7f; font-family: verdana;">1</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">);</span></p>

  <p style="border-collapse: collapse;"><span class="Apple-style-span" style="line-height: normal; border-collapse: separate;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">endfunction</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">:</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">factorial</span></span></p>
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<h2><br><strong></strong></h2><h2><br></h2><h2><strong>参数传递</strong>

  <hr style="font-weight: bold; font-size: 13px; color: #007070; line-height: normal; font-family: verdana;"></h2>

<p><br></p><p>下面讲述使用函数的通用情况,大部分也是用于SystemVerilog的任务.</p>

<h3><br><strong></strong></h3><h3><br></h3><h3><strong>值传递</strong></h3><br>

<p>SystemVerilog中函数参数缺省是通过值传递,适用于所有的数据类型,包括容器类型。唯一一个例外是类对象,对象本身并没有绑定到变量描
述符,描述符所绑定的是对象的句柄(类似C/C++中的指针).
当一个类实例(实际上是它的句柄)被传递的时候,句柄本身是值传递,但是,因为句柄仅仅是指向真实数据,所以,被参数指向的真实的对象就和函数(任务)内
部看到的对象是一样的——等效于类对象看起来是通过引用来传递的.</p><p><br></p>

<p style="color: Red;">SystemVerilog提供了一个<tt>ref关键字作为函数参数的前缀。当使用ref时,表明参数是使用引用传递,'ref'语法类似C++中的引用.</tt></p><p><tt><br></tt> </p>

<p>有两种情况下使用'ref'做参数比较有意义。第一种情况,由于函数只能有一个返回值(不考虑传统Verilog上的input/output参数端口声明),任务没有返回值。当函数需要返回多个值或者任务需要返回一个以上值的时候,通过引用传递就用得上。</p><p><br></p>

<p>第二种情况是运行效率的考虑。当大量的数据需要作为参数传递的时候,值传递效率很低。所有的数据需要在每次函数调用的时候被复制。如果参数使用
'ref'前缀,可以不需要进行数据复制。但是这样会使得参数的数据容易被函数/任务中的代码修改。此危险可以通过声明ref参数为常量来解决.</p><p><br></p>

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<blockquote class="webkit-indent-blockquote" style="padding-right: 0px; padding-left: 0px; padding-bottom: 0px; margin: 0px 0px 0px 40px; border-top-style: none; padding-top: 0px; border-right-style: none; border-left-style: none; border-bottom-style: none;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana;"><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">// virtual base class
      <br></span></span><span class="Apple-style-span" style="line-height: normal;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">class</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">xactn</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">;
      <br></span></span><span class="Apple-style-span" style="line-height: normal;"><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp; </span><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">// user functions
      <br></span></span><span class="Apple-style-span" style="line-height: normal;"><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp; </span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">virtual</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">function</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">void</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">pack</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">(</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">ref</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">bytes</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">[]);
      <br></span></span><span class="Apple-style-span" style="line-height: normal;"><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp; </span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">virtual</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">function</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">void</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">unpack</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">(</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">const</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">ref</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px;">bytes</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">[]);
      <br></span></span><span class="Apple-style-span" style="line-height: normal;"><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp; </span><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">// other function declarations omitted
      <br></span></span><span class="Apple-style-span" style="line-height: normal;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">endclass</span></span></blockquote>
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<h3><br><strong></strong></h3><h3><strong>函数参数中的缺省值</strong></h3><br>

<p><span class="Apple-style-span" style=""><span class="Apple-style-span" style="line-height: 16px; border-collapse: collapse;"><span class="Apple-style-span" style="line-height: 18px;">SystemVerilog允许给函数设置缺省值。如果没有给参数指定值,并且参数有缺省值,那么函数将使用参数的缺省值。此指定缺省值的语法和C++类似.</span></span></span></p><p><span class="Apple-style-span" style="font-family: 'Verdana, Arial, 'trebuchet ms'';"><span class="Apple-style-span" style="line-height: 16px; border-collapse: collapse;"><span class="Apple-style-span" style="line-height: 18px;"><br></span></span></span></p>


<span class="Apple-style-span" style="line-height: normal;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana;"><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">
        <hr style="font-weight: bold; font-size: 13px; color: #007070; line-height: normal; font-family: verdana;"></span></span></span></span>

<blockquote class="webkit-indent-blockquote" style="padding-right: 0px; padding-left: 0px; padding-bottom: 0px; margin: 0px 0px 0px 40px; border-top-style: none; padding-top: 0px; border-right-style: none; border-left-style: none; border-bottom-style: none;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">task</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">void</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span>foo<span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">(</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">int</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span>x<span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">,</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">int</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span>y<span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">=</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; font-family: verdana;">10</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">);
      <br></span></span><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana;"><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp; </span><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">// the tasks implementation is not provided
      <br></span></span><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;">endtask</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; font-family: verdana;">:</span><span class="S0" style="font-size: 10pt; color: #808080; font-family: verdana;">&nbsp;</span>foo</span></blockquote>
<span class="Apple-style-span" style="line-height: normal;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana;"><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">
        <hr style="font-weight: bold; font-size: 13px; color: #007070; line-height: normal; font-family: verdana;"></span></span></span></span>

<p><span class="Apple-style-span" style=""><span class="Apple-style-span" style="border-collapse: collapse;"><br></span></span></p><p><span class="Apple-style-span" style=""><span class="Apple-style-span" style="border-collapse: collapse;">SystemVerilog
提供了额外的特征,不像C++,
SystemVerilog允许用户将使用指定值的参数放在使用缺省值的参数的后面。使用缺省的参数很简单的在函数调用的参数列表中不出现,后面指定值的
参数放在一个逗号后面,此逗号在一个空格之后,表示没有相应的参数。 <br></span></span></p><p><span class="Apple-style-span" style="font-family: 'Verdana, Arial, 'trebuchet ms'';"><span class="Apple-style-span" style="border-collapse: collapse;"><br></span></span></p>


<span class="Apple-style-span" style="line-height: normal;"><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal; font-family: verdana;"><span class="S2" style="font-size: 9pt; color: #007f00; font-family: 'Comic Sans MS';">
        <hr style="font-weight: bold; font-size: 13px; color: #007070; line-height: normal; font-family: verdana;"></span></span></span></span>



<blockquote class="webkit-indent-blockquote" style="padding-right: 0px; padding-left: 0px; padding-bottom: 0px; margin: 0px 0px 0px 40px; border-top-style: none; padding-top: 0px; border-right-style: none; border-left-style: none; border-bottom-style: none;">
  <p><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">function</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">void</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal;">foo</span></span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">(</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">int</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">first</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">=</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">1</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">,</span></p>

  <p><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; int</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal;">second</span></span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">=</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">2</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">,</span></p>

  <p><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">int</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal;">third</span></span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">=</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">3</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">,</span></p>

  <p><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">int</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">unsigned</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal;">fourth</span></span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">=</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">4</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">);</span></p>

  <p><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp; </span><span class="S2" style="font-size: 9pt; color: #007f00; line-height: normal; font-family: 'Comic Sans MS'; border-collapse: separate;">// function's code omitted</span></p>

  <p><span class="S5" style="font-weight: bold; font-size: 10pt; color: #00007f; line-height: normal; font-family: verdana; border-collapse: separate;">endfunction</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">:</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal;">foo</span></span></p>

  <p><span class="S2" style="font-size: 9pt; color: #007f00; line-height: normal; font-family: 'Comic Sans MS'; border-collapse: separate;">// foo函数的调用例子:</span></p>

  <p><span class="S2" style="font-size: 9pt; color: #007f00; line-height: normal; font-family: 'Comic Sans MS'; border-collapse: separate;">// 第3个和第4个参数使用缺省值</span></p>

  <p><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal;">foo</span></span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">(</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">10</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">,</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">20</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">);</span></p>

  <p><span class="S2" style="font-size: 9pt; color: #007f00; line-height: normal; font-family: 'Comic Sans MS'; border-collapse: separate;">// 第1个和第3个参数使用缺省值</span></p>

  <p><span class="Apple-style-span" style="font-size: small; font-family: verdana;"><span class="Apple-style-span" style="font-size: 13px; line-height: normal;">foo</span></span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">(</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">,</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">20</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">,</span><span class="S0" style="font-size: 10pt; color: #808080; line-height: normal; font-family: verdana; border-collapse: separate;">&nbsp;</span><span class="S10" style="font-weight: bold; font-size: 10pt; color: #007070; line-height: normal; font-family: verdana; border-collapse: separate;">,</span><span class="S4" style="font-size: 10pt; color: #007f7f; line-height: normal; font-family: verdana; border-collapse: separate;">40</span><span class="S10"><span class="Apple-style-span" style="font-size: medium; color: rgb(0, 112, 112); font-family: verdana;"><span class="Apple-style-span" style="font-size: 10pt; line-height: normal;"><b>);</b></span></span></span></p><p><br><span class="S10"><span class="Apple-style-span" style="font-size: medium; color: rgb(0, 112, 112); font-family: verdana;"><span class="Apple-style-span" style="font-size: 10pt; line-height: normal;"></span></span></span></p><p><br><span class="S10"><span class="Apple-style-span" style="font-size: medium; color: rgb(0, 112, 112); font-family: verdana;"><span class="Apple-style-span" style="font-size: 10pt; line-height: normal;"></span></span></span></p><p><br><span class="S10"><span class="Apple-style-span" style="font-size: medium; color: rgb(0, 112, 112); font-family: verdana;"><span class="Apple-style-span" style="font-size: 10pt; line-height: normal;"></span></span></span></p>
</blockquote>


from: http://electron64.blog.163.com/blog/static/106033970201010108713356/
发表于 2014-4-23 10:12:31 | 显示全部楼层
对C++中相关的内容与systemverilog的比较能够让熟悉C++的程序员很容易理解systemverilog中的程序机制,文章不错~
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