]> git.proxmox.com Git - ceph.git/blame - ceph/src/boost/libs/math/doc/html/math_toolkit/sign_functions.html
projects / ceph.git / blame
? search:
summary | shortlog | log | commit | commitdiff | tree
blob | blame (incremental) | history | HEAD
bump version to 12.2.2-pve1
[ceph.git] / ceph / src / boost / libs / math / doc / html / math_toolkit / sign_functions.html
CommitLineData
7c673cae
FG		 1<html>
2<head>
3<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
4<title>Sign Manipulation Functions</title>
5<link rel="stylesheet" href="../math.css" type="text/css">
6<meta name="generator" content="DocBook XSL Stylesheets V1.77.1">
7<link rel="home" href="../index.html" title="Math Toolkit 2.5.1">
8<link rel="up" href="../utils.html" title="Chapter&#160;2.&#160;Floating Point Utilities">
9<link rel="prev" href="fpclass.html" title="Floating-Point Classification: Infinities and NaNs">
10<link rel="next" href="fp_facets.html" title="Facets for Floating-Point Infinities and NaNs">
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 alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
15<td align="center"><a href="../../../../../index.html">Home</a></td>
16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
19<td align="center"><a href="../../../../../more/index.htm">More</a></td>
20</tr></table>
21<hr>
22<div class="spirit-nav">
23<a accesskey="p" href="fpclass.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../utils.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="fp_facets.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
24</div>
25<div class="section">
26<div class="titlepage"><div><div><h2 class="title" style="clear: both">
27<a name="math_toolkit.sign_functions"></a><a class="link" href="sign_functions.html" title="Sign Manipulation Functions">Sign Manipulation Functions</a>
28</h2></div></div></div>
29<h5>
30<a name="math_toolkit.sign_functions.h0"></a>
31 <span class="phrase"><a name="math_toolkit.sign_functions.synopsis"></a></span><a class="link" href="sign_functions.html#math_toolkit.sign_functions.synopsis">Synopsis</a>
32 </h5>
33<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">/</span><span class="identifier">sign</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
34</pre>
35<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span>
36
37<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
38<span class="keyword">int</span> <span class="identifier">signbit</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">x</span><span class="special">);</span>
39
40<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
41<span class="keyword">int</span> <span class="identifier">sign</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">z</span><span class="special">);</span>
42
43<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span>
44<span class="identifier">T</span> <span class="identifier">copysign</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">U</span><span class="special">&amp;</span> <span class="identifier">y</span><span class="special">);</span>
45
46<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
47<a class="link" href="result_type.html" title="Calculation of the Type of the Result"><span class="emphasis"><em>calculated-result-type</em></span></a> <span class="identifier">changesign</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">z</span><span class="special">);</span>
48
49<span class="special">}}</span> <span class="comment">// namespaces</span>
50</pre>
51<h5>
52<a name="math_toolkit.sign_functions.h1"></a>
53 <span class="phrase"><a name="math_toolkit.sign_functions.description"></a></span><a class="link" href="sign_functions.html#math_toolkit.sign_functions.description">Description</a>
54 </h5>
55<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
56<span class="keyword">int</span> <span class="identifier">signbit</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">x</span><span class="special">);</span>
57</pre>
58<p>
59 Returns a non-zero value if the sign bit is set in variable <span class="emphasis"><em>x</em></span>,
60 otherwise <code class="computeroutput"><span class="number">0</span></code>.
61 </p>
62<div class="important"><table border="0" summary="Important">
63<tr>
64<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
65<th align="left">Important</th>
66</tr>
67<tr><td align="left" valign="top"><p>
68 The return value from this function is zero or <span class="emphasis"><em>not-zero</em></span>
69 and <span class="bold"><strong>not</strong></span> zero or one.
70 </p></td></tr>
71</table></div>
72<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
73<span class="keyword">int</span> <span class="identifier">sign</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">z</span><span class="special">);</span>
74</pre>
75<p>
76 Returns <code class="computeroutput"><span class="number">1</span></code> if <span class="emphasis"><em>x</em></span>
77 <code class="computeroutput"><span class="special">&gt;</span> <span class="number">0</span></code>,
78 <code class="computeroutput"><span class="special">-</span><span class="number">1</span></code>
79 if <span class="emphasis"><em>x</em></span> <code class="computeroutput"><span class="special">&lt;</span> <span class="number">0</span></code>, and <code class="computeroutput"><span class="number">0</span></code>
80 if <span class="emphasis"><em>x</em></span> is zero.
81 </p>
82<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span>
83<a class="link" href="result_type.html" title="Calculation of the Type of the Result"><span class="emphasis"><em>calculated-result-type</em></span></a> <span class="identifier">copysign</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">U</span><span class="special">&amp;</span> <span class="identifier">y</span><span class="special">);</span>
84</pre>
85<p>
86 Sets the sign of <span class="emphasis"><em>x</em></span> to be the same as the sign of <span class="emphasis"><em>y</em></span>.
87 </p>
88<p>
89 See <a href="http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf" target="_top">C99
90 7.12.11.1 The copysign functions</a> for more detail.
91 </p>
92<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
93<span class="identifier">T</span> <span class="identifier">changesign</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">z</span><span class="special">);</span>
94</pre>
95<p>
96 Returns a floating-point number with a binary representation where the signbit
97 is the opposite of the sign bit in <span class="emphasis"><em>x</em></span>, and where the other
98 bits are the same as in <span class="emphasis"><em>x</em></span>.
99 </p>
100<p>
101 This function is widely available, but not specified in any standards.
102 </p>
103<p>
104 Rationale: Not specified by TR1, but <code class="computeroutput"><span class="identifier">changesign</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code>
105 is both easier to read and more efficient than
106 </p>
107<pre class="programlisting"><span class="identifier">copysign</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">signbit</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="number">1.0</span> <span class="special">:</span> <span class="special">-</span><span class="number">1.0</span><span class="special">);</span>
108</pre>
109<p>
110 For finite values, this function has the same effect as simple negation, the
111 assignment z = -z, but for nonfinite values, <a href="http://en.wikipedia.org/wiki/Infinity#Computing" target="_top">infinities</a>
112 and <a href="http://en.wikipedia.org/wiki/NaN" target="_top">NaNs</a>, the <code class="computeroutput"><span class="identifier">changesign</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> function
113 may be the only portable way to ensure that the sign bit is changed.
114 </p>
115<h6>
116<a name="math_toolkit.sign_functions.h2"></a>
117 <span class="phrase"><a name="math_toolkit.sign_functions.sign_bits"></a></span><a class="link" href="sign_functions.html#math_toolkit.sign_functions.sign_bits">Sign
118 bits</a>
119 </h6>
120<p>
121 One of the bits in the binary representation of a floating-point number gives
122 the sign, and the remaining bits give the absolute value. That bit is known
123 as the sign bit. The sign bit is set = 1 for negative numbers, and is not set
124 = 0 for positive numbers. (This is true for all binary representations of floating-point
125 numbers that are used by modern microprocessors.)
126 </p>
127<p>
128 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">C++
129 TR1</a> specifies <code class="computeroutput"><span class="identifier">copysign</span></code>
130 functions and function templates for accessing the sign bit.
131 </p>
132<p>
133 For user-defined types (UDT), the sign may be stored in some other way. They
134 may also not provide infinity or NaNs. To use these functions with a UDT, it
135 may be necessary to explicitly specialize them for UDT type T.
136 </p>
137<h6>
138<a name="math_toolkit.sign_functions.h3"></a>
139 <span class="phrase"><a name="math_toolkit.sign_functions.examples"></a></span><a class="link" href="sign_functions.html#math_toolkit.sign_functions.examples">Examples</a>
140 </h6>
141<pre class="programlisting"><span class="identifier">signbit</span><span class="special">(</span><span class="number">3.5</span><span class="special">)</span> <span class="identifier">is</span> <span class="identifier">zero</span> <span class="special">(</span><span class="keyword">or</span> <span class="keyword">false</span><span class="special">)</span>
142<span class="identifier">signbit</span><span class="special">(-</span><span class="number">7.1</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">1</span> <span class="special">(</span><span class="keyword">or</span> <span class="keyword">true</span><span class="special">)</span>
143<span class="identifier">copysign</span><span class="special">(</span><span class="number">4.2</span><span class="special">,</span> <span class="number">7.9</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">4.2</span>
144<span class="identifier">copysign</span><span class="special">(</span><span class="number">3.5</span> <span class="special">-</span><span class="number">1.4</span><span class="special">)</span> <span class="identifier">is</span> <span class="special">-</span><span class="number">3.5</span>
145<span class="identifier">copysign</span><span class="special">(-</span><span class="number">4.2</span><span class="special">,</span> <span class="number">1.0</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">4.2</span>
146<span class="identifier">copysign</span><span class="special">(-</span><span class="number">8.6</span><span class="special">,</span> <span class="special">-</span><span class="number">3.3</span><span class="special">)</span> <span class="identifier">is</span> <span class="special">-</span><span class="number">8.6</span>
147<span class="identifier">changesign</span><span class="special">(</span><span class="number">6.9</span><span class="special">)</span> <span class="identifier">is</span> <span class="special">-</span><span class="number">6.9</span>
148<span class="identifier">changesign</span><span class="special">(-</span><span class="number">1.8</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">1.8</span>
149</pre>
150<h6>
151<a name="math_toolkit.sign_functions.h4"></a>
152 <span class="phrase"><a name="math_toolkit.sign_functions.portability"></a></span><a class="link" href="sign_functions.html#math_toolkit.sign_functions.portability">Portability</a>
153 </h6>
154<p>
155 The library supports the following binary floating-point formats:
156 </p>
157<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
158<li class="listitem">
159 IEEE 754 single precision
160 </li>
161<li class="listitem">
162 IEEE 754 double precision
163 </li>
164<li class="listitem">
165 IEEE 754 extended double precision with 15 exponent bits
166 </li>
167<li class="listitem">
168 Intel extended double precision
169 </li>
170<li class="listitem">
171 PowerPC extended double precision
172 </li>
173<li class="listitem">
174 Motorola 68K extended double precision
175 </li>
176</ul></div>
177<p>
178 The library does not support the VAX floating-point formats. (These are available
179 on VMS, but the default on VMS is the IEEE 754 floating-point format.)
180 </p>
181<p>
182 The main portability issues are:
183 </p>
184<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
185<li class="listitem">
186 Unsupported floating-point formats.
187 </li>
188<li class="listitem">
189 The library depends on the header <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">detail</span><span class="special">/</span><span class="identifier">endian</span><span class="special">.</span><span class="identifier">hpp</span></code>
190 to detemine endianness.
191 </li>
192<li class="listitem">
193 Code such as <code class="computeroutput"><span class="preprocessor">#if</span> <span class="identifier">defined</span><span class="special">(</span><span class="identifier">__ia64</span><span class="special">)</span> <span class="special">||</span> <span class="identifier">defined</span><span class="special">(</span><span class="identifier">__ia64__</span><span class="special">)</span> <span class="special">||</span> <span class="identifier">defined</span><span class="special">(</span><span class="identifier">_M_IA64</span><span class="special">)</span></code> is used to determine the processor type.
194 </li>
195</ul></div>
196<p>
197 The library has passed all tests on the following platforms:
198 </p>
199<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
200<li class="listitem">
201 Win32 / MSVC 7.1 / 10.0 / x86 32 and 64-bit, and later Win32
202 </li>
203<li class="listitem">
204 Win32 / Intel C++ 7.1, 8.1, 9.1 / x86
205 </li>
206<li class="listitem">
207 Mac OS X / GCC 3.3, 4.0 / ppc
208 </li>
209<li class="listitem">
210 Linux / Intel C++ 9.1 / x86, ia64
211 </li>
212<li class="listitem">
213 Linux / GCC 3.3 / x86, x64, ia64, ppc, hppa, mips, m68k
214 </li>
215<li class="listitem">
216 Linux / GCC 3.4 / x64
217 </li>
218<li class="listitem">
219 HP-UX / aCC, GCC 4.1 / ia64
220 </li>
221<li class="listitem">
222 HP-UX / aCC / hppa
223 </li>
224<li class="listitem">
225 Tru64 / Compaq C++ 7.1 / alpha
226 </li>
227<li class="listitem">
228 VMS / HP C++ 7.1 / alpha (in IEEE floating-point mode)
229 </li>
230<li class="listitem">
231 VMS / HP C++ 7.2 / ia64 (in IEEE floating-point mode)
232 </li>
233</ul></div>
234</div>
235<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
236<td align="left"></td>
237<td align="right"><div class="copyright-footer">Copyright &#169; 2006-2010, 2012-2014 Nikhar Agrawal,
238 Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
239 Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan R&#229;de, Gautam Sewani,
240 Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p>
241 Distributed under the Boost Software License, Version 1.0. (See accompanying
242 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
243 </p>
244</div></td>
245</tr></table>
246<hr>
247<div class="spirit-nav">
248<a accesskey="p" href="fpclass.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../utils.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="fp_facets.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
249</div>
250</body>
251</html>
Ceph