mirror of
https://github.com/boostorg/safe_numerics.git
synced 2026-02-09 23:32:37 +00:00
1bc0b94e65
a) made trap_exception work b) updated manual and examples to show how to use library to eliminate runtime penalty c) added in safe_literal d) made corrections of various types
89 lines
4.8 KiB
HTML
89 lines
4.8 KiB
HTML
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
|
|
<title>Eliminating Runtime Penalty</title>
|
|
<link rel="stylesheet" href="../boostbook.css" type="text/css">
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.76.1">
|
|
<link rel="home" href="../index.html" title="Safe Numerics">
|
|
<link rel="up" href="../index.html" title="Safe Numerics">
|
|
<link rel="prev" href="7.html" title="Programming by Contract is Too Slow">
|
|
<link rel="next" href="../8.html" title="Using Automatic Type Promotion">
|
|
</head>
|
|
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
|
|
<table cellpadding="2" width="100%"><tr>
|
|
<td valign="top"><img href="index.html" height="164px" src="pre-boost.jpg" alt="Library Documentation Index"></td>
|
|
<td><h2>Safe Numerics</h2></td>
|
|
</tr></table>
|
|
<div class="spirit-nav">
|
|
<a accesskey="p" href="7.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="../8.html"><img src="../images/next.png" alt="Next"></a>
|
|
</div>
|
|
<div class="section">
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
<a name="safe_numerics.tutorial.8"></a>Eliminating Runtime Penalty</h2></div></div></div>
|
|
<div class="toc"><dl>
|
|
<dt><span class="section"><a href="../8.html">Using Automatic Type Promotion</a></span></dt>
|
|
<dt><span class="section"><a href="../8.html">Using safe_range</a></span></dt>
|
|
<dt><span class="section"><a href="../8.html"></a></span></dt>
|
|
</dl></div>
|
|
<p>Up until now, we've focused on detecting when incorrect results are
|
|
produced and handling these occurances either by throwing an exception or
|
|
invoking some designated function. We've achieved our goal of enforcing
|
|
arithmetically correct behavior - but at what cost. For many C++ programers
|
|
any runtime penalty is unacceptable. Whether or not one agrees with this
|
|
tradeoff, its a fact that many C++ programmers feel this way. So the
|
|
question arises as to how we alter our program to minimize or eliminate any
|
|
runtime penalty.</p>
|
|
<p>The first step is to determine what parts of a program might invoke
|
|
exceptions. The following program is similar to previous examples but uses a
|
|
special exception policy: <a class="link" href=""><code class="computeroutput">trap_exception</code></a>.</p>
|
|
<pre class="programlisting">#include <iostream>
|
|
|
|
#include "../include/safe_integer.hpp"
|
|
#include "../include/exception.hpp" // include exception policies
|
|
#include "safe_format.hpp" // prints out range and value of any type
|
|
|
|
using safe_t = boost::numeric::safe<
|
|
int,
|
|
boost::numeric::native,
|
|
boost::numeric::trap_exception // note use of "trap_exception" policy!
|
|
>;
|
|
|
|
safe_t f(const safe_t & x, const safe_t & y){
|
|
// each statement below will fail to compile !
|
|
safe_t z = x + y;
|
|
std::cout << "(x + y)" << safe_format(x + y) << std::endl;
|
|
std::cout << "(x - y)" << safe_format(x - y) << std::endl;
|
|
return z;
|
|
}
|
|
|
|
int main(int argc, const char * argv[]){
|
|
std::cout << "example 81:\n";
|
|
safe_t x(INT_MAX); // will fail to compile
|
|
safe_t y(2); // will fail to compile
|
|
std::cout << "x" << safe_format(x) << std::endl;
|
|
std::cout << "y" << safe_format(y) << std::endl;
|
|
std::cout << "z" << safe_format(f(x, y)) << std::endl;
|
|
return 0;
|
|
}
|
|
</pre>
|
|
<p>Now,
|
|
any expression which <span class="emphasis"><em><span class="bold"><strong>MIGHT</strong></span></em></span> fail at runtime is flagged with a
|
|
compile time error. There is no longer any need for <code class="computeroutput">try/catch
|
|
blocks</code>. Since this program does not compile, the <span class="bold"><strong>library absolutely <span class="bold"><strong>guarantees that no
|
|
arithmetic expression</strong></span> will yield incorrect results</strong></span> .
|
|
This is our original goal. Now all we need to do is make the program work.
|
|
There are a couple of ways to do this.</p>
|
|
</div>
|
|
<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 Robert Ramey<p><a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">Subject to Boost
|
|
Software License</a></p>
|
|
</div></td>
|
|
</tr></table>
|
|
<hr>
|
|
<div class="spirit-nav">
|
|
<a accesskey="p" href="7.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="../8.html"><img src="../images/next.png" alt="Next"></a>
|
|
</div>
|
|
</body>
|
|
</html>
|