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279 lines
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<title>SafeNumeric<T></title>
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<td valign="top"><img href="index.html" height="164px" src="pre-boost.jpg" alt="Library Documentation Index"></td>
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<td><h2>Safe Numerics</h2></td>
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<a accesskey="p" href="integer.html"><img src="images/prev.png" alt="Prev"></a><a accesskey="u" href="concepts.html"><img src="images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="images/home.png" alt="Home"></a><a accesskey="n" href="promotion_policy.html"><img src="images/next.png" alt="Next"></a>
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<div class="titlepage"><div><div><h3 class="title">
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<a name="safe_numerics.safe_numeric_concept"></a>SafeNumeric<T></h3></div></div></div>
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<div class="toc"><dl class="toc">
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<dt><span class="section"><a href="safe_numeric_concept.html#idm130203881648">Description</a></span></dt>
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<dt><span class="section"><a href="safe_numeric_concept.html#idm130203880192">Refinement of</a></span></dt>
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<dt><span class="section"><a href="safe_numeric_concept.html#idm130203877840">Notation</a></span></dt>
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<dt><span class="section"><a href="safe_numeric_concept.html#idm130203860368">Valid Expressions</a></span></dt>
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<dt><span class="section"><a href="safe_numeric_concept.html#idm130203788608">Invariants</a></span></dt>
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<dt><span class="section"><a href="safe_numeric_concept.html#idm130203787008">Models</a></span></dt>
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<dt><span class="section"><a href="safe_numeric_concept.html#idm130203782672">Header</a></span></dt>
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</dl></div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="idm130203881648"></a>Description</h4></div></div></div>
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<p>This holds an arithmetic value which can be used as a replacement
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for built-in C++ arithmetic values. These types differ from their built-in
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counter parts in that the are guaranteed not to produce invalid arithmetic
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results. These operations return safe types rather than built-in
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types.</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="idm130203880192"></a>Refinement of</h4></div></div></div>
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<p><a class="link" href="numeric.html" title="Numeric<T>">Numeric</a> or <a class="link" href="integer.html" title="Integer<T>">Integer</a></p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="idm130203877840"></a>Notation</h4></div></div></div>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col align="left">
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<col align="left">
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</colgroup>
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<thead><tr>
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<th align="left">Symbol</th>
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<th align="left">Description</th>
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</tr></thead>
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<tbody>
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<tr>
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<td align="left"><code class="computeroutput">T, U</code></td>
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<td align="left">Types fulfilling <a class="link" href="numeric.html" title="Numeric<T>">Numeric</a> or <a class="link" href="integer.html" title="Integer<T>">Integer</a> type
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requirements.</td>
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</tr>
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<tr>
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<td align="left">t, u</td>
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<td align="left">objects of types T, U</td>
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</tr>
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<tr>
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<td align="left">S</td>
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<td align="left">A type fulfilling SafeNumeric type requirements</td>
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</tr>
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<tr>
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<td align="left">s, s1, s2</td>
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<td align="left">objects of types S</td>
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</tr>
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<tr>
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<td align="left">op</td>
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<td align="left">C++ infix operator supported by underlying type T</td>
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</tr>
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<tr>
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<td align="left">prefix_op</td>
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<td align="left">C++ prefix operator: -, +, ~, ++, -- supported by
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underlying type T</td>
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</tr>
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<tr>
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<td align="left">postfix_op</td>
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<td align="left">C++ postfix operator:++, -- supported by underlying type
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T</td>
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</tr>
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<tr>
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<td align="left">assign_op</td>
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<td align="left">C++ assignment operator</td>
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</tr>
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</tbody>
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</table></div>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="idm130203860368"></a>Valid Expressions</h4></div></div></div>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col align="left">
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<col align="left">
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<col align="left">
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</colgroup>
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<thead><tr>
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<th align="left">Expression</th>
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<th align="left">Result Type</th>
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<th align="left">Description</th>
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</tr></thead>
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<tbody>
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<tr>
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<td align="left"><code class="computeroutput">s op t</code></td>
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<td align="left">unspecified S</td>
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<td align="left"><p>invoke C++ operator op and return another
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SafeNumeric type.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">t op s</code></td>
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<td align="left">unspecified S</td>
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<td align="left"><p>invoke C++ operator op and return another
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SafeNumeric type.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">s1 op s2</code></td>
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<td align="left">unspecified S</td>
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<td align="left"><p>invoke C++ operator op and return another
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SafeNumeric type.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">prefix_op S</code></td>
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<td align="left">unspecified S</td>
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<td align="left"><p>invoke C++ operator <code class="computeroutput">prefix_op</code> and
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return another SafeNumeric type.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">S postfix_op</code></td>
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<td align="left">unspecified S</td>
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<td align="left"><p>invoke C++ operator <code class="computeroutput">postfix_op</code> and
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return another SafeNumeric type.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">s assign_op t</code></td>
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<td align="left">S &</td>
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<td align="left"><p>convert t to type S and assign it to s.
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</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">t assign_op s</code></td>
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<td align="left">T &</td>
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<td align="left"><p>convert s to type T and assign it to s. If the
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value t cannot be represented as an instance of type S, it is an
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error.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">S(t)</code></td>
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<td align="left">S</td>
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<td align="left"><p>construct an instance of S from a value of type T.
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In this case, T is referred to as the base type of S. If the
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value t cannot be represented as an instance of type S, it is an
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exception condition is invoked. </p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">S</code></td>
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<td align="left">S</td>
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<td align="left"><p>construct an uninitialized instance of
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S.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">T(s)</code></td>
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<td align="left">T</td>
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<td align="left"><p>implicit conversion of the value of s to type T. If
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the value of s cannot be correctly represented as a type T, an
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exception condition is invoked.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">static_cast<T>(s)</code></td>
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<td align="left">T</td>
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<td align="left"><p>convert the value of s to type T. If the value of s
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cannot be correctly represented as a type T, an exception
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condition is invoked. </p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">is_safe<S></code></td>
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<td align="left"><code class="computeroutput">std::true_type</code></td>
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<td align="left"><p>type trait to query whether any type S fulfills the
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requirements for a SafeNumeric type.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">base_type<S>::type</code></td>
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<td align="left">T</td>
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<td align="left"><p>Retrieve the base type of a given safe
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type.</p></td>
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</tr>
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<tr>
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<td align="left"><code class="computeroutput">base_value(s)</code></td>
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<td align="left">T</td>
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<td align="left"><p>Retrieve the value of an instance of a safe type.
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This is equivalent to
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<code class="computeroutput">static_cast<base_type<S>>(s)</code>.</p></td>
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</tr>
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</tbody>
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</table></div>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem"><p>The result of any binary operation where one or both of the
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operands is a SafeNumeric type is also a SafeNumeric type.</p></li>
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<li class="listitem"><p>All the expressions in the above table are
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<code class="computeroutput">constexpr</code> expressions.</p></li>
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<li class="listitem"><p>Binary expressions which are not assignments and whose operands
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are both safe types require that promotion and exception policies of
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the operands be identical.</p></li>
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<li class="listitem"><p><code class="computeroutput">Operations on safe types are supported if and only if the
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same operation is supported on the underlying types. For example, the
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binary operations |</code>, <code class="computeroutput">&</code>, <code class="computeroutput">^</code> and
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<code class="computeroutput">~</code> operations defined for safe unsigned integer types. But
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they are not defined for floating point types. Currently the are also
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defined for signed integer types. It's not clear that this is the
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correct decision. On one hand, usage of these operators on signed
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types is almost certainly an error in program logic. But trapping this
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as an error conflicts with the goal of making safe types "drop-in"
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replacements for the corresponding built-in types. In light of this,
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these operators are currently supported as they are for normal
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built-in types.</p></li>
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<li class="listitem">
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<p>Safe Numeric types will be implicitly converted to built-in
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types when appropriate. Here's an example:</p>
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<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="keyword">int</span><span class="special">)</span><span class="special">;</span>
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<span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="special">)</span><span class="special">{</span>
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<span class="keyword">long</span> <span class="identifier">x</span><span class="special">;</span>
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<span class="identifier">f</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span><span class="special">;</span> <span class="comment">// OK - builtin implicit version</span>
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<span class="identifier">safe</span><span class="special"><</span><span class="keyword">long</span><span class="special">></span> <span class="identifier">y</span><span class="special">;</span>
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<span class="identifier">f</span><span class="special">(</span><span class="identifier">y</span><span class="special">)</span><span class="special">;</span>
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<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
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<span class="special">}</span></pre>
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<p>This behavior supports the concept of
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<code class="computeroutput">safe<T></code> as being a "drop-in" replacement for a
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<code class="computeroutput">T</code>.</p>
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</li>
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</ul></div>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="idm130203788608"></a>Invariants</h4></div></div></div>
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<p>The fundamental requirement of a SafeNumeric type is that it
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implements all C++ operations permitted on its base type in a way the
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prevents the return of an incorrect arithmetic result. Various
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implementations of this concept may handle circumstances which produce
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such results differently (throw exception, compile time trap, etc..). But
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no implementation should return an arithmetically incorrect result.</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="idm130203787008"></a>Models</h4></div></div></div>
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<p><code class="computeroutput">safe<T></code></p>
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<p><code class="computeroutput">safe_signed_range<-11, 11></code></p>
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<p><code class="computeroutput">safe_unsigned_range<0, 11></code></p>
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<p><code class="computeroutput">safe_signed_literal<4></code></p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="idm130203782672"></a>Header</h4></div></div></div>
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<p><a href="../../include/concept/safe_numeric.hpp" target="_top"><code class="computeroutput">#include
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<boost/numeric/safe_numerics/concepts/safe_numeric.hpp></code></a></p>
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</div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2012-2018 Robert Ramey<p><a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">Subject to Boost
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Software License</a></p>
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</div></td>
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</tr></table>
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