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- <td><h2>Safe Numerics</h2></td>
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- <a name="safe_numerics.promotion_policies.cpp"></a>cpp<int C, int S, int I, int L, int LL></h4></div></div></div>
- <div class="section">
- <div class="titlepage"><div><div><h5 class="title">
- <a name="idm130202658416"></a>Description</h5></div></div></div>
- <p>This policy is used to promote safe types in arithmetic expressions
- according to the rules in the C++ standard. But rather than using the
- native C++ standard types supported by the compiler, it uses types whose
- length in number of bits is specified by the template parameters.</p>
- <p>This policy is useful for running test programs which use C++
- portable integer types but which are destined to run on an architecture
- which is different than the one on which the test program is being built
- and run. This can happen when developing code for embedded systems.
- Algorithms developed or borrowed from one architecture but destined for
- another can be tested on the desktop.</p>
- <p>Note that this policy is only applicable to safe types whose base
- type is a type fulfilling the type requirements of <a class="link" href="integer.html" title="Integer<T>">Integer</a>.</p>
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- <div class="titlepage"><div><div><h5 class="title">
- <a name="idm130202654880"></a>Template Parameters</h5></div></div></div>
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- <col align="left">
- <col align="left">
- <col align="left">
- </colgroup>
- <thead><tr>
- <th align="left">Parameter</th>
- <th align="left">Type</th>
- <th align="left">Description</th>
- </tr></thead>
- <tbody>
- <tr>
- <td align="left"><code class="computeroutput">C</code></td>
- <td align="left">int</td>
- <td align="left">Number of bits in a char</td>
- </tr>
- <tr>
- <td align="left"><code class="computeroutput">S</code></td>
- <td align="left">int</td>
- <td align="left">Number of bits in a short</td>
- </tr>
- <tr>
- <td align="left"><code class="computeroutput">I</code></td>
- <td align="left">int</td>
- <td align="left">Number of bits in an integer</td>
- </tr>
- <tr>
- <td align="left"><code class="computeroutput">L</code></td>
- <td align="left">int</td>
- <td align="left">Number of bits in a long</td>
- </tr>
- <tr>
- <td align="left"><code class="computeroutput">LL</code></td>
- <td align="left">int</td>
- <td align="left">Number of bits in a long long</td>
- </tr>
- </tbody>
- </table></div>
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- <div class="section">
- <div class="titlepage"><div><div><h5 class="title">
- <a name="idm130202637904"></a>Model of</h5></div></div></div>
- <p><a class="link" href="promotion_policy.html" title="PromotionPolicy<PP>">PromotionPolicy</a></p>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h5 class="title">
- <a name="idm130202636192"></a>Example of Use</h5></div></div></div>
- <p>Consider the following problem. One is developing software which
- uses a very small microprocessor and a very limited C compiler. The chip
- is so small, you can't print anything from the code, log, debug or
- anything else. One debugs this code by using the "burn" and "crash" method
- - you burn the chip (download the code), run the code, observe the
- results, make changes and try again. This is a crude method which is
- usually the one used. But it can be quite time consuming.</p>
- <p>Consider an alternative. Build and compile your code in testable
- modules. For each module write a test which exercises all the code and
- makes it work. Finally download your code into the chip and - voilà -
- working product. This sounds great, but there's one problem. Our target
- processor - in this case a PIC162550 from Microchip Technology is only an
- 8 bit CPU. The compiler we use defines INT as 8 bits. This (and a few
- other problems), make our algorithm testing environment differ from our
- target environment. We can address this by defining INT as a safe integer
- with a range of 8 bits. By using a custom promotion policy, we can force
- the evaluation of C++ expressions in the test environment to be the same
- as that in the target environment. Also in our target environment, we can
- trap any overflows or other errors. So we can write and test our code on
- our desktop system and download the code to the target knowing that it
- just has to work. This is a huge time saver and confidence builder. For an
- extended example on how this is done, look at <a class="link" href="safety_critical_embedded_controller.html" title="Safety Critical Embedded Controller">Safety
- Critical Embedded Controller</a> .</p>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h5 class="title">
- <a name="idm130202633184"></a>Header</h5></div></div></div>
- <p><code class="computeroutput"><a href="../../include/cpp.hpp" target="_top"><code class="computeroutput">#include
- <boost/numeric/safe_numerics/cpp.hpp> </code></a></code></p>
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- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <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
- Software License</a></p>
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