boost-react-native-bundle

<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Sign Manipulation Functions</title> <link rel="stylesheet" href="../math.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../index.html" title="Math Toolkit 2.1.0"> <link rel="up" href="../utils.html" title="Chapter 2. Floating Point Utilities"> <link rel="prev" href="fpclass.html" title="Floating-Point Classification: Infinities and NaNs"> <link rel="next" href="fp_facets.html" title="Facets for Floating-Point Infinities and NaNs"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> <td align="center"><a href="../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <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> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="math_toolkit.sign_functions"></a><a class="link" href="sign_functions.html" title="Sign Manipulation Functions">Sign Manipulation Functions</a> </h2></div></div></div> <h5> <a name="math_toolkit.sign_functions.h0"></a> <a name="math_toolkit.sign_functions.synopsis"></a><a class="link" href="sign_functions.html#math_toolkit.sign_functions.synopsis">Synopsis</a> </h5> <pre class="programlisting">#include <boost/math/special_functions/sign.hpp> </pre> <pre class="programlisting">namespace boost{ namespace math{ template<class T> int signbit(T x); template <class T> int sign (const T& z); template <class T, class U> T copysign (const T& x, const U& y); template <class T> <a class="link" href="result_type.html" title="Calculation of the Type of the Result">calculated-result-type</a> changesign (const T& z); }} // namespaces </pre> <h5> <a name="math_toolkit.sign_functions.h1"></a> <a name="math_toolkit.sign_functions.description"></a><a class="link" href="sign_functions.html#math_toolkit.sign_functions.description">Description</a> </h5> <pre class="programlisting">template<class T> int signbit(T x); </pre> Returns a non-zero value if the sign bit is set in variable x, otherwise <code class="computeroutput">0</code>. <div class="important"><table border="0" summary="Important"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td> <th align="left">Important</th> </tr> <tr><td align="left" valign="top"> The return value from this function is zero or not-zero and not zero or one. </td></tr> </table></div> <pre class="programlisting">template <class T> int sign (const T& z); </pre> Returns <code class="computeroutput">1</code> if x <code class="computeroutput">> 0</code>, <code class="computeroutput">-1</code> if x <code class="computeroutput">< 0</code>, and <code class="computeroutput">0</code> if x is zero. <pre class="programlisting">template <class T, class U> <a class="link" href="result_type.html" title="Calculation of the Type of the Result">calculated-result-type</a> copysign (const T& x, const U& y); </pre> Sets the sign of x to be the same as the sign of y. See <a href="http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf" target="_top">C99 7.12.11.1 The copysign functions</a> for more detail. <pre class="programlisting">template <class T> T changesign (const T& z); </pre> Returns a floating point number with a binary representation where the signbit is the opposite of the sign bit in x, and where the other bits are the same as in x. This function is widely available, but not specified in any standards. Rationale: Not specified by TR1, but <code class="computeroutput">changesign(x)</code> is both easier to read and more efficient than <pre class="programlisting">copysign(x, signbit(x) ? 1.0 : -1.0); </pre> For finite values, this function has the same effect as simple negation, the assignment z = -z, but for nonfinite values, <a href="http://en.wikipedia.org/wiki/Infinity#Computing" target="_top">infinities</a> and <a href="http://en.wikipedia.org/wiki/NaN" target="_top">NaNs</a>, the <code class="computeroutput">changesign(x)</code> function may be the only portable way to ensure that the sign bit is changed. <h6> <a name="math_toolkit.sign_functions.h2"></a> <a name="math_toolkit.sign_functions.sign_bits"></a><a class="link" href="sign_functions.html#math_toolkit.sign_functions.sign_bits">Sign bits</a> </h6> One of the bits in the binary representation of a floating-point number gives the sign, and the remaining bits give the absolute value. That bit is known as the sign bit. The sign bit is set = 1 for negative numbers, and is not set = 0 for positive numbers. (This is true for all binary representations of floating point numbers that are used by modern microprocessors.) <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">C++ TR1</a> specifies <code class="computeroutput">copysign</code> functions and function templates for accessing the sign bit. For user-defined types (UDT), the sign may be stored in some other way. They may also not provide infinity or NaNs. To use these functions with a UDT, it may be necessary to explicitly specialize then for UDT type T. <h6> <a name="math_toolkit.sign_functions.h3"></a> <a name="math_toolkit.sign_functions.examples"></a><a class="link" href="sign_functions.html#math_toolkit.sign_functions.examples">Examples</a> </h6> <pre class="programlisting">signbit(3.5) is zero (or false) signbit(-7.1) is 1 (or true) copysign(4.2, 7.9) is 4.2 copysign(3.5 -1.4) is -3.5 copysign(-4.2, 1.0) is 4.2 copysign(-8.6, -3.3) is -8.6 changesign(6.9) is -6.9 changesign(-1.8) is 1.8 </pre> <h6> <a name="math_toolkit.sign_functions.h4"></a> <a name="math_toolkit.sign_functions.portability"></a><a class="link" href="sign_functions.html#math_toolkit.sign_functions.portability">Portability</a> </h6> The library supports the following binary floating-point formats: <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> IEEE 754 single precision </li> <li class="listitem"> IEEE 754 double precision </li> <li class="listitem"> IEEE 754 extended double precision with 15 exponent bits </li> <li class="listitem"> Intel extended double precision </li> <li class="listitem"> PowerPC extended double precision </li> <li class="listitem"> Motorola 68K extended double precision </li> </ul></div> The library does not support the VAX floating-point formats. (These are available on VMS, but the default on VMS is the IEEE 754 floating-point format.) The main portability issues are: <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> Unsupported floating point formats </li> <li class="listitem"> The library depends on the header boost/detail/endian.hpp </li> <li class="listitem"> Code such as <code class="computeroutput">#if defined(__ia64) || defined(__ia64__) || defined(_M_IA64)</code> is used to determine the processor type. </li> </ul></div> The library has passed all tests on the following platforms: <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> Win32 / MSVC 7.1 / 10.0 / x86 </li> <li class="listitem"> Win32 / Intel C++ 7.1, 8.1, 9.1 / x86 </li> <li class="listitem"> Mac OS X / GCC 3.3, 4.0 / ppc </li> <li class="listitem"> Linux / Intel C++ 9.1 / x86, ia64 </li> <li class="listitem"> Linux / GCC 3.3 / x86, x64, ia64, ppc, hppa, mips, m68k </li> <li class="listitem"> Linux / GCC 3.4 / x64 </li> <li class="listitem"> HP-UX / aCC, GCC 4.1 / ia64 </li> <li class="listitem"> HP-UX / aCC / hppa </li> <li class="listitem"> Tru64 / Compaq C++ 7.1 / alpha </li> <li class="listitem"> VMS / HP C++ 7.1 / alpha (in IEEE floating point mode) </li> <li class="listitem"> VMS / HP C++ 7.2 / ia64 (in IEEE floating point mode) </li> </ul></div> </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 © 2006-2010, 2012-2014 Nikhar Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert Holin, Bruno Lalande, John Maddock, Johan Råde, Gautam Sewani, Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang Distributed under the Boost Software License, Version 1.0. (See accompanying 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>) </div></td> </tr></table> <hr> <div class="spirit-nav"> <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> </div> </body> </html>