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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

float A<span style="color: #800080">,</span> B<span style="color: #800080">,</span> C<span style="color: #800080">,</span> D<span style="color: #800080">;</span>
<span style="color: #0000FF">assign</span> A <span style="color: #800080">=</span> B <span style="color: #800080">+</span> C<span style="color: #800080">;</span>   <span style="color: #008000">// 等价于A = faddff(B, C);</span>
<span style="color: #0000FF">assign</span> D <span style="color: #800080">=</span> A <span style="color: #800080">+</span> <span style="color: #FF0000">1.0</span><span style="color: #800080">;</span> <span style="color: #008000">// 等价于A = faddfr(A, 1.0);</span></pre></div></div>
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根据过载表达式中等价的自变量类型，过载声明将<span style="color: #800080">+</span>操作符链接到每一个函数原型。通常，这种过载需要自变量具有精确的类型匹配。然而，一个例外是：如果真实参数具有integral类型，并且只有一个函数原型具有对应的integral类型的自变量，那么真实参数会被隐式地强制转换到原型中的类型。&nbsp;</p>
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注意：函数原型不需要精确地匹配于真实的函数声明。如果没有，那么在调用函数的时候应用普通的隐式强制类型转换。例如，<i>fcopyi</i> 函数可以被定义成具有一个<span style="color: #0000FF">int</span>类型的自变量： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00242"><pre class="Element12"><span style="color: #0000FF">function</span> float fcopyi <span style="color: #800080">(</span><span style="color: #0000FF">int</span> i<span style="color: #800080">);</span>
    float o<span style="color: #800080">;</span>

    o<span style="color: #800080">.</span>sign <span style="color: #800080">=</span> i<span style="color: #800080">[</span><span style="color: #FF0000">31</span><span style="color: #800080">];</span>
    o<span style="color: #800080">.</span>exponent <span style="color: #800080">=</span> <span style="color: #FF0000">0</span><span style="color: #800080">;</span>
    o<span style="color: #800080">.</span>mantissa <span style="color: #800080">=</span> <span style="color: #FF0000">0</span><span style="color: #800080">;</span>
    …
<span style="color: #0000FF">    return</span> o;
<span style="color: #0000FF">endfunction</span></pre></div></div>
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对赋值操作符的过载也会过载隐式赋值或强制类型转换。Here these are using the same functions as the unary <span style="color: #800080">+</span>. </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00243"><pre class="Element12"><span style="color: #0000FF">bind</span> <span style="color: #800080">=</span> <span style="color: #0000FF">function</span> float fcopyi<span style="color: #800080">(</span><span style="color: #0000FF">int</span><span style="color: #800080">);</span>       <span style="color: #008000">// 将int强制转换成float</span>
<span style="color: #0000FF">bind</span> <span style="color: #800080">=</span> <span style="color: #0000FF">function</span> float fcopyr<span style="color: #800080">(</span><span style="color: #0000FF">real</span><span style="color: #800080">);</span>      <span style="color: #008000">// 将real强制转换成float</span>
<span style="color: #0000FF">bind</span> <span style="color: #800080">=</span> <span style="color: #0000FF">function</span> float fcopyr<span style="color: #800080">(</span><span style="color: #0000FF">shortreal</span><span style="color: #800080">);</span> <span style="color: #008000">// 将shortreal强制转换成float</span></pre></div></div>
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可以被过载的操作符有算术操作符、关系操作符、以及赋值操作符。注意，在这里从<i>float</i>到<i>float</i>的赋值操作符不能被过载，因为这种赋值本来就是合法的。类似的，在<i>float</i>之间的相等和不等操作符也不能被过载。&nbsp;</p>
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对于<span style="color: #FF0000">0</span>或<span style="color: #FF0000">1</span>来说，我们不能假定它的格式，所以用户不能依靠减法来得出是否相等的结论，也不能使用加法来获得递增的操作结果。类似地，对于正数或负数也不能假定它的格式，因此，比较操作必须被显式地编码。&nbsp;</p>
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诸如<span style="color: #800080">+=</span>之类的赋值操作符从连续的<span style="color: #800080">+</span>和<span style="color: #800080">=</span>操作符自动构建，其中，<span style="color: #800080">=</span>操作符具有标准含义。例如： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00244"><pre class="Element12">float A<span style="color: #800080">,</span> B<span style="color: #800080">;</span>

<span style="color: #0000FF">bind</span> <span style="color: #800080">+</span> <span style="color: #0000FF">function</span> float faddff<span style="color: #800080">(</span>float<span style="color: #800080">,</span> float<span style="color: #800080">);</span>

<span style="color: #0000FF">always</span> <span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clock<span style="color: #800080">)</span> A <span style="color: #800080">+=</span> B<span style="color: #800080">;</span>  <span style="color: #008000">// 等价于A = A + B</span></pre></div></div>
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过载声明的作用范围和可视性与数据声明遵从相同的搜索规则。在过载声明的可视范围内，过载声明必须在其使用之前声明。The function bound by the overload declaration uses the same scope search rules as a function enable from the scope where the operator is invoked.</p></div>
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<a href="00860.html" target="topic">第七章 操作符与表达式</a></p></div>
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<a href="00860.html" target="topic">第七章 操作符与表达式</a></div>
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