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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

<div class="Element13"><div class="Element12" id="code00420"><pre class="Element12"><span style="color: #008000">//    1  2  3         3    4      1   2   -&gt; Dimension numbers</span>
<span style="color: #0000FF">int</span> A<span style="color: #800080">[</span><span style="color: #FF0000">2</span><span style="color: #800080">][</span><span style="color: #FF0000">3</span><span style="color: #800080">][</span><span style="color: #FF0000">4</span><span style="color: #800080">];</span> <span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">3</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">][</span><span style="color: #FF0000">2</span><span style="color: #800080">:</span><span style="color: #FF0000">1</span><span style="color: #800080">]</span> B<span style="color: #800080">[</span><span style="color: #FF0000">5</span><span style="color: #800080">:</span><span style="color: #FF0000">1</span><span style="color: #800080">][</span><span style="color: #FF0000">4</span><span style="color: #800080">];</span>
<span style="color: #0000FF">foreach</span><span style="color: #800080">(</span>A<span style="color: #800080">[</span>i<span style="color: #800080">,</span>j<span style="color: #800080">,</span>k<span style="color: #800080">])</span> ...
<span style="color: #0000FF">foreach</span><span style="color: #800080">(</span>B<span style="color: #800080">[</span>q<span style="color: #800080">,</span>r<span style="color: #800080">, ,</span>s<span style="color: #800080">])</span> ...</pre></div></div>
<p class="Element10">
第一个<span style="color: #0000FF">foreach</span>引起<i>i</i>从0到1迭代，<i>j</i>从0到2迭代，<i>k</i>从0到3迭代。第二个<span style="color: #0000FF">foreach</span>引起<i>q</i>从5到1迭代，<i>r</i>从0到3迭代，<i>s</i>从2到1迭代。&nbsp;</p>
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&nbsp;</p>
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迭代约束可以包含判定条件。例如： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00421');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00421"><pre class="Element12"><span style="color: #0000FF">class</span> C<span style="color: #800080">;</span>
    <span style="color: #0000FF">rand int</span> A<span style="color: #800080">[];</span>
    <span style="color: #0000FF">constraint</span> c1 <span style="color: #800080">{</span>arr<span style="color: #800080">.</span><span style="color: #0000FF">size</span> <span style="color: #0000FF">inside</span> <span style="color: #800080">{[</span><span style="color: #FF0000">1</span><span style="color: #800080">:</span><span style="color: #FF0000">10</span><span style="color: #800080">]};}</span>
    <span style="color: #0000FF">constraint</span> c2 <span style="color: #800080">{</span><span style="color: #0000FF">foreach</span> <span style="color: #800080">(</span>A<span style="color: #800080">[</span>k<span style="color: #800080">]) (</span>k<span style="color: #800080"> &lt; </span>A<span style="color: #800080">.</span><span style="color: #0000FF">size</span><span style="color: #800080">-</span><span style="color: #FF0000">1</span><span style="color: #800080">) -&gt; </span>A<span style="color: #800080">[</span>k<span style="color: #800080">+</span><span style="color: #FF0000">1</span><span style="color: #800080">] &gt; </span>A<span style="color: #800080">[</span>k<span style="color: #800080">];}</span>
<span style="color: #0000FF">endclass</span></pre></div></div>
<p class="Element10">
第一个约束，<i>c1</i>将数组<i>A</i>的尺寸约束在1到10之间。第二个约束，<i>c2</i>将每一个数组值约束成大于前面一个的值，也就是数组按降序排列。&nbsp;</p>
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&nbsp;</p>
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在一个<span style="color: #0000FF">foreach</span>结构内，仅包含常量、状态变量、对象句柄比较、循环变量、正在被迭代的数组的尺寸的判定表达式的作用是作为产生约束的守卫者，而不是作为逻辑关系操作。例如，上面例子中约束<i>c2</i>中的蕴涵仅包括一个循环变量和正在被迭代的数组的尺寸，它仅当k<span style="color: #800080"> &lt; </span>A<span style="color: #800080">.</span><span style="color: #0000FF">size</span><span style="color: #800080">-</span><span style="color: #FF0000">1</span>时才允许产生一个约束，这样可以阻止约束中的越界访问。有关约束守卫的更多细节在<a href="00071.html" target="topic">12.4.12节</a>中描述。&nbsp;</p>
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&nbsp;</p>
<p class="Element10">
索引表达式可以包含循环变量、常量、和状态变量。无效或越界的数组索引不会被自动地消除；用户必须使用判定条件来显式地排除这些索引。&nbsp;</p>
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动态数组或联合数组的<span style="color: #0000FF">size</span>方法可以被用来约束数组的尺寸（参见上面例子中的<i>c1</i>）。如果一个数组既被尺寸约束所约束也被迭代约束所约束，那么尺寸约束首先被解析，然后才是迭代约束。作为尺寸约束和迭代约束间隐含排序的结果，<span style="color: #0000FF">size</span>方法应该被当作对应数组的<span style="color: #0000FF">foreach</span>块内的状态变量。例如，表达式<i>A<span style="color: #800080"></i>.</span><span style="color: #0000FF">size</span>被当作约束<i>c1</i>中的一个随机变量，并被作为约束<i>c2</i>中的一个状态变量。这个隐含的排序在某些情况下会导致求解器失败。</p></div>
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