1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> 4<title>cpp<int C, int S, int I, int L, int LL></title> 5<link rel="stylesheet" href="../boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Safe Numerics"> 8<link rel="up" href="../promotion_policies.html" title="Promotion Policies"> 9<link rel="prev" href="automatic.html" title="automatic"> 10<link rel="next" href="../exception_safety.html" title="Exception Safety"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img href="index.html" height="164px" src="pre-boost.jpg" alt="Library Documentation Index"></td> 15<td><h2>Safe Numerics</h2></td> 16</tr></table> 17<div class="spirit-nav"> 18<a accesskey="p" href="automatic.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../promotion_policies.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="../exception_safety.html"><img src="../images/next.png" alt="Next"></a> 19</div> 20<div class="section"> 21<div class="titlepage"><div><div><h4 class="title"> 22<a name="safe_numerics.promotion_policies.cpp"></a>cpp<int C, int S, int I, int L, int LL></h4></div></div></div> 23<div class="section"> 24<div class="titlepage"><div><div><h5 class="title"> 25<a name="idm130202658416"></a>Description</h5></div></div></div> 26<p>This policy is used to promote safe types in arithmetic expressions 27 according to the rules in the C++ standard. But rather than using the 28 native C++ standard types supported by the compiler, it uses types whose 29 length in number of bits is specified by the template parameters.</p> 30<p>This policy is useful for running test programs which use C++ 31 portable integer types but which are destined to run on an architecture 32 which is different than the one on which the test program is being built 33 and run. This can happen when developing code for embedded systems. 34 Algorithms developed or borrowed from one architecture but destined for 35 another can be tested on the desktop.</p> 36<p>Note that this policy is only applicable to safe types whose base 37 type is a type fulfilling the type requirements of <a class="link" href="integer.html" title="Integer<T>">Integer</a>.</p> 38</div> 39<div class="section"> 40<div class="titlepage"><div><div><h5 class="title"> 41<a name="idm130202654880"></a>Template Parameters</h5></div></div></div> 42<div class="informaltable"><table class="table"> 43<colgroup> 44<col align="left"> 45<col align="left"> 46<col align="left"> 47</colgroup> 48<thead><tr> 49<th align="left">Parameter</th> 50<th align="left">Type</th> 51<th align="left">Description</th> 52</tr></thead> 53<tbody> 54<tr> 55<td align="left"><code class="computeroutput">C</code></td> 56<td align="left">int</td> 57<td align="left">Number of bits in a char</td> 58</tr> 59<tr> 60<td align="left"><code class="computeroutput">S</code></td> 61<td align="left">int</td> 62<td align="left">Number of bits in a short</td> 63</tr> 64<tr> 65<td align="left"><code class="computeroutput">I</code></td> 66<td align="left">int</td> 67<td align="left">Number of bits in an integer</td> 68</tr> 69<tr> 70<td align="left"><code class="computeroutput">L</code></td> 71<td align="left">int</td> 72<td align="left">Number of bits in a long</td> 73</tr> 74<tr> 75<td align="left"><code class="computeroutput">LL</code></td> 76<td align="left">int</td> 77<td align="left">Number of bits in a long long</td> 78</tr> 79</tbody> 80</table></div> 81</div> 82<div class="section"> 83<div class="titlepage"><div><div><h5 class="title"> 84<a name="idm130202637904"></a>Model of</h5></div></div></div> 85<p><a class="link" href="promotion_policy.html" title="PromotionPolicy<PP>">PromotionPolicy</a></p> 86</div> 87<div class="section"> 88<div class="titlepage"><div><div><h5 class="title"> 89<a name="idm130202636192"></a>Example of Use</h5></div></div></div> 90<p>Consider the following problem. One is developing software which 91 uses a very small microprocessor and a very limited C compiler. The chip 92 is so small, you can't print anything from the code, log, debug or 93 anything else. One debugs this code by using the "burn" and "crash" method 94 - you burn the chip (download the code), run the code, observe the 95 results, make changes and try again. This is a crude method which is 96 usually the one used. But it can be quite time consuming.</p> 97<p>Consider an alternative. Build and compile your code in testable 98 modules. For each module write a test which exercises all the code and 99 makes it work. Finally download your code into the chip and - voilà - 100 working product. This sounds great, but there's one problem. Our target 101 processor - in this case a PIC162550 from Microchip Technology is only an 102 8 bit CPU. The compiler we use defines INT as 8 bits. This (and a few 103 other problems), make our algorithm testing environment differ from our 104 target environment. We can address this by defining INT as a safe integer 105 with a range of 8 bits. By using a custom promotion policy, we can force 106 the evaluation of C++ expressions in the test environment to be the same 107 as that in the target environment. Also in our target environment, we can 108 trap any overflows or other errors. So we can write and test our code on 109 our desktop system and download the code to the target knowing that it 110 just has to work. This is a huge time saver and confidence builder. For an 111 extended example on how this is done, look at <a class="link" href="safety_critical_embedded_controller.html" title="Safety Critical Embedded Controller">Safety 112 Critical Embedded Controller</a> .</p> 113</div> 114<div class="section"> 115<div class="titlepage"><div><div><h5 class="title"> 116<a name="idm130202633184"></a>Header</h5></div></div></div> 117<p><code class="computeroutput"><a href="../../include/cpp.hpp" target="_top"><code class="computeroutput">#include 118 <boost/numeric/safe_numerics/cpp.hpp> </code></a></code></p> 119</div> 120</div> 121<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 122<td align="left"></td> 123<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 124 Software License</a></p> 125</div></td> 126</tr></table> 127<hr> 128<div class="spirit-nav"> 129<a accesskey="p" href="automatic.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../promotion_policies.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="../exception_safety.html"><img src="../images/next.png" alt="Next"></a> 130</div> 131</body> 132</html> 133
