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📁 这是一本关于verilog编程语言的教程,对学习verilog语言有帮助
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<span style="color: #0000FF">endcase</span></pre></div></div>
<p class="Element10">
如果<i>instr</i>保存了一个<i>Add</i>指令，那么第一个模式形成匹配，标识符<i>r1</i>、<i>r2</i>和<i>rd</i>被绑定到嵌套结构体值得三个寄存器域。右侧的语句对寄存器文件rf执行这个指令。如果标签为<i>Jmp</i>，我们不可能访问这些寄存器域。如果<i>instr</i>保存了一个<i>Jmp</i>指令，那么第二个模式形成匹配，并且标识符<i>j</i>被绑定到嵌套的标签联合体值。内层的case语句轮流地将这个值与<i>JmpU</i>和<i>JmpC</i>模式进行匹配，依次类推。&nbsp;</p>
<p class="Element10">
&nbsp;</p>
<p class="Element10">
下面的例子与前一个例子相同，但使用通佩符和常量模式来排除<i>rd=0</i>的情况（在某些处理器中，寄存器0是一个特殊的“丢弃”寄存器）： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00270');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00270"><pre class="Element12"><span style="color: #0000FF">case</span> <span style="color: #800080">(</span>instr<span style="color: #800080">)</span> <span style="color: #0000FF">matches</span>
    <span style="color: #0000FF">tagged</span> Add <span style="color: #800080">{.*,.*, .0} : ;</span>   <span style="color: #008000">// 无操作</span>
    <span style="color: #0000FF">tagged</span> Add <span style="color: #800080">{</span>r1<span style="color: #800080">,</span>r2<span style="color: #800080">,</span>rd<span style="color: #800080">} :</span> rf<span style="color: #800080">[</span>rd<span style="color: #800080">] = </span>rf<span style="color: #800080">[</span>r1<span style="color: #800080">] +</span> rf<span style="color: #800080">[</span>r2<span style="color: #800080">];</span>
    <span style="color: #0000FF">tagged</span> Jmp j <span style="color: #800080">:</span> <span style="color: #0000FF">case</span> <span style="color: #800080">(</span>j<span style="color: #800080">)</span> <span style="color: #0000FF">matches</span>
                       <span style="color: #0000FF">tagged</span> JmpU a <span style="color: #800080">:</span> pc <span style="color: #800080">=</span> pc <span style="color: #800080">+</span> a<span style="color: #800080">;</span>
                       <span style="color: #0000FF">tagged</span> JmpC <span style="color: #800080">{</span>c<span style="color: #800080">,</span>a<span style="color: #800080">}:</span> <span style="color: #0000FF">if</span> <span style="color: #800080">(</span>rf<span style="color: #800080">[</span>c<span style="color: #800080">])</span> pc <span style="color: #800080">=</span> a<span style="color: #800080">;</span>
                   <span style="color: #0000FF">endcase</span>
<span style="color: #0000FF">endcase</span></pre></div></div>
<p class="Element10">
下面的例子与前一个例子相同，但第一个内层case语句仅包含结构体和常量，但不包括标签联合体： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00271');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00271"><pre class="Element12"><span style="color: #0000FF">case</span> <span style="color: #800080">(</span>instr<span style="color: #800080">)</span> <span style="color: #0000FF">matches</span>
    <span style="color: #0000FF">tagged</span> Add s<span style="color: #800080">:</span> <span style="color: #0000FF">case</span> <span style="color: #800080">(</span>s<span style="color: #800080">)</span> <span style="color: #0000FF">matches</span>
                      <span style="color: #800080">{.*,.*, .0} : ;</span>   <span style="color: #008000">// 无操作</span>
                      <span style="color: #800080">{</span>r1<span style="color: #800080">,</span>r2<span style="color: #800080">,</span>rd<span style="color: #800080">} :</span> rf<span style="color: #800080">[</span>rd<span style="color: #800080">] = </span>rf<span style="color: #800080">[</span>r1<span style="color: #800080">] +</span> rf<span style="color: #800080">[</span>r2<span style="color: #800080">];</span>
                  <span style="color: #0000FF">endcase</span>
    <span style="color: #0000FF">tagged</span> Jmp j <span style="color: #800080">:</span> <span style="color: #0000FF">case</span> <span style="color: #800080">(</span>j<span style="color: #800080">)</span> <span style="color: #0000FF">matches</span>
                       <span style="color: #0000FF">tagged</span> JmpU a <span style="color: #800080">:</span> pc <span style="color: #800080">=</span> pc <span style="color: #800080">+</span> a<span style="color: #800080">;</span>
                       <span style="color: #0000FF">tagged</span> JmpC <span style="color: #800080">{</span>c<span style="color: #800080">,</span>a<span style="color: #800080">}:</span> <span style="color: #0000FF">if</span> <span style="color: #800080">(</span>rf<span style="color: #800080">[</span>c<span style="color: #800080">])</span> pc <span style="color: #800080">=</span> a<span style="color: #800080">;</span>
                   <span style="color: #0000FF">endcase</span>
<span style="color: #0000FF">endcase</span></pre></div></div>
<p class="Element10">
下面的例子与前一个相同，但使用嵌套的标签联合体模式： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00272');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00272"><pre class="Element12"><span style="color: #0000FF">case</span> <span style="color: #800080">(</span>instr<span style="color: #800080">)</span> <span style="color: #0000FF">matches</span>
    <span style="color: #0000FF">tagged</span> Add <span style="color: #800080">{</span>r1<span style="color: #800080">,</span>r2<span style="color: #800080">,</span>rd<span style="color: #800080">}</span> <span style="color: #800080">&amp;&amp; (</span>rd <span style="color: #800080">!=</span> <span style="color: #FF0000">0</span><span style="color: #800080">):</span> rf<span style="color: #800080">[</span>rd<span style="color: #800080">] =</span> rf<span style="color: #800080">[</span>r1<span style="color: #800080">] + </span>rf<span style="color: #800080">[</span>r2<span style="color: #800080">];</span>
    <span style="color: #0000FF">tagged</span> Jmp <span style="color: #800080">(</span><span style="color: #0000FF">tagged</span> JmpU a<span style="color: #800080">) :</span> pc <span style="color: #800080">=</span> pc <span style="color: #800080">+</span> a<span style="color: #800080">;</span>
    <span style="color: #0000FF">tagged</span> Jmp <span style="color: #800080">(</span><span style="color: #0000FF">tagged</span> JmpC <span style="color: #800080">{</span>c<span style="color: #800080">,</span>a<span style="color: #800080">}) :</span> <span style="color: #0000FF">if</span> <span style="color: #800080">(</span>rf<span style="color: #800080">[</span>c<span style="color: #800080">])</span> pc <span style="color: #800080">=</span> a<span style="color: #800080">;</span>
<span style="color: #0000FF">endcase</span></pre></div></div>
<p class="Element10">
下面的例子与前一个相同，但使用命名的结构体组件： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00273');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00273"><pre class="Element12"><span style="color: #0000FF">case</span> <span style="color: #800080">(</span>instr<span style="color: #800080">)</span> <span style="color: #0000FF">matches</span>
    <span style="color: #0000FF">tagged</span> Add <span style="color: #800080">{</span>reg2<span style="color: #800080">:</span>r2<span style="color: #800080">,</span>regd<span style="color: #800080">:</span>rd<span style="color: #800080">,</span>reg1<span style="color: #800080">:</span>r1<span style="color: #800080">}</span> <span style="color: #800080">&amp;&amp; (</span>rd <span style="color: #800080">!=</span> <span style="color: #FF0000">0</span><span style="color: #800080">):</span> rf<span style="color: #800080">[</span>rd<span style="color: #800080">] =</span> rf<span style="color: #800080">[</span>r1<span style="color: #800080">] + </span>rf<span style="color: #800080">[</span>r2<span style="color: #800080">];</span>
    <span style="color: #0000FF">tagged</span> Jmp <span style="color: #800080">(</span><span style="color: #0000FF">tagged</span> JmpU a<span style="color: #800080">) :</span> pc <span style="color: #800080">=</span> pc <span style="color: #800080">+</span> a<span style="color: #800080">;</span>
    <span style="color: #0000FF">tagged</span> Jmp <span style="color: #800080">(</span><span style="color: #0000FF">tagged</span> JmpC <span style="color: #800080">{</span>addr<span style="color: #800080">:</span>a,cc<span style="color: #800080">:</span>c<span style="color: #800080">}) :</span> <span style="color: #0000FF">if</span> <span style="color: #800080">(</span>rf<span style="color: #800080">[</span>c<span style="color: #800080">])</span> pc <span style="color: #800080">=</span> a<span style="color: #800080">;</span>
<span style="color: #0000FF">endcase</span></pre></div></div>
<p class="Element10">
<span style="color: #0000FF">casez</span>和<span style="color: #0000FF">casex</span>关键字同样可以用来替代<span style="color: #0000FF">case</span>关键字，并具有相同的语义。换句话说，在模式匹配过程中，无论两个位在哪里比较（无论它们是标签位还是成员位），<span style="color: #0000FF">casez</span>都会忽略<span style="color: #FF0000">z</span>位，<span style="color: #0000FF">casex</span>会忽略<span style="color: #FF0000">z</span>和<span style="color: #FF0000">x</span>位。&nbsp;</p>
<p class="Element10">
&nbsp;</p>
<p class="Element10">
<span style="color: #0000FF">priority</span>和<span style="color: #0000FF">unique</span>限定符扮演它们原本的角色。<span style="color: #0000FF">priority</span>意味着某个case条目必须被选择。<span style="color: #0000FF">unique</span>也同样意味着仅仅可以选择一个case条目，所以他们可以并行计算。&nbsp;</p></div>
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