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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>scalbln</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="scalbln"></a> <a name="tag_03_616"></a><!-- scalbln --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_616_01"></a>NAME</h4><blockquote>scalbln, scalblnf, scalblnl, scalbn, scalbnf, scalbnl - compute exponent using FLT_RADIX</blockquote><h4><a name="tag_03_616_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/math.h.html">math.h</a>><br><br> double scalbln(double</tt> <i>x</i><tt>, long</tt> <i>n</i><tt>);<br> float scalblnf(float</tt> <i>x</i><tt>, long</tt> <i>n</i><tt>);<br> long double scalblnl(long double</tt> <i>x</i><tt>, long</tt> <i>n</i><tt>);<br> double scalbn(double</tt> <i>x</i><tt>, int</tt> <i>n</i><tt>);<br> float scalbnf(float</tt> <i>x</i><tt>, int</tt> <i>n</i><tt>);<br> long double scalbnl(long double</tt> <i>x</i><tt>, int</tt> <i>n</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_616_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>These functions shall compute <i>x</i> * FLT_RADIX<i><small><sup>n</sup></small></i> efficiently, not normally bycomputing FLT_RADIX<i><small><sup>n</sup></small></i> explicitly.</p><p>An application wishing to check for error situations should set <i>errno</i> to zero and call<i>feclearexcept</i>(FE_ALL_EXCEPT) before calling these functions. On return, if <i>errno</i> is non-zero or<i>fetestexcept</i>(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.</p></blockquote><h4><a name="tag_03_616_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, these functions shall return <i>x</i> * FLT_RADIX<i><small><sup>n</sup></small></i>.</p><p>If the result would cause overflow, a range error shall occur and these functions shall return ±HUGE_VAL,±HUGE_VALF, and ±HUGE_VALL (according to the sign of <i>x</i>) as appropriate for the return type of thefunction.</p><p>If the correct value would cause underflow, and is not representable, a range error may occur, and <sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> either 0.0 (ifsupported), or <img src="../images/opt-end.gif" alt="[Option End]" border="0"> an implementation-defined value shall bereturned.</p><p><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If<i>x</i> is NaN, a NaN shall be returned.</p><p>If <i>x</i> is ±0 or ±Inf, <i>x</i> shall be returned.</p><p>If <i>n</i> is 0, <i>x</i> shall be returned.</p><p>If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall bereturned. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_616_05"></a>ERRORS</h4><blockquote><p>These functions shall fail if:</p><dl compact><dt>Range Error</dt><dd>The result overflows. <p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If theinteger expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall beraised.</p></dd></dl><p>These functions may fail if:</p><dl compact><dt>Range Error</dt><dd>The result underflows. <p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If theinteger expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall beraised.</p></dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_616_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_616_07"></a>APPLICATION USAGE</h4><blockquote><p>On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent ofeach other, but at least one of them must be non-zero.</p></blockquote><h4><a name="tag_03_616_08"></a>RATIONALE</h4><blockquote><p>These functions are named so as to avoid conflicting with the historical definition of the <a href="../functions/scalb.html"><i>scalb</i>()</a> function from the Single UNIX Specification. The difference is that the <a href="../functions/scalb.html"><i>scalb</i>()</a> function has a second argument of <b>double</b> instead of <b>int</b>. The <a href="../functions/scalb.html"><i>scalb</i>()</a> function is not part of the ISO C standard. The three functions whose second typeis <b>long</b> are provided because the factor required to scale from the smallest positive floating-point value to the largestfinite one, on many implementations, is too large to represent in the minimum-width <b>int</b> format.</p></blockquote><h4><a name="tag_03_616_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_616_10"></a>SEE ALSO</h4><blockquote><p><a href="feclearexcept.html"><i>feclearexcept</i>()</a>, <a href="fetestexcept.html"><i>fetestexcept</i>()</a>, <a href="scalb.html"><i>scalb</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap04.html#tag_04_18">Section 4.18, Treatment of Error Conditions for Mathematical Functions</a>, <a href="../basedefs/math.h.html"><i><math.h></i></a></p></blockquote><h4><a name="tag_03_616_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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