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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) 2001-2003 The Open Group, All Rights Reserved --><title>scalb</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="scalb"></a> <a name="tag_03_615"></a><!-- scalb --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_615_01"></a>NAME</h4><blockquote>scalb - load exponent of a radix-independent floating-point number</blockquote><h4><a name="tag_03_615_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('OB XSI')">OB XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/math.h.html">math.h</a>><br><br> double scalb(double</tt> <i>x</i><tt>, double</tt> <i>n</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_615_03"></a>DESCRIPTION</h4><blockquote><p>The <i>scalb</i>() function shall compute <i>x</i>*<i>r<sup><small>n</small></sup></i>, where <i>r</i> is the radix of themachine's floating-point arithmetic. When <i>r</i> is 2, <i>scalb</i>() shall be equivalent to <a href="ldexp.html"><i>ldexp</i>()</a> . The value of <i>r</i> is FLT_RADIX which is defined in <a href="../basedefs/float.h.html"><i><float.h></i></a>.</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_615_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, the <i>scalb</i>() function shall return <i>x</i>*<i>r<sup><small>n</small></sup></i>.</p><p>If <i>x</i> or <i>n</i> is NaN, a NaN shall be returned.</p><p>If <i>n</i> is zero, <i>x</i> shall be returned.</p><p>If <i>x</i> is ±Inf and <i>n</i> is not -Inf, <i>x</i> shall be returned.</p><p>If <i>x</i> is ±0 and <i>n</i> is not +Inf, <i>x</i> shall be returned.</p><p>If <i>x</i> is ±0 and <i>n</i> is +Inf, a domain error shall occur, and either a NaN (if supported), or animplementation-defined value shall be returned.</p><p>If <i>x</i> is ±Inf and <i>n</i> is -Inf, a domain error shall occur, and either a NaN (if supported), or animplementation-defined value shall be returned.</p><p>If the result would cause an overflow, a range error shall occur and ±HUGE_VAL (according to the sign of <i>x</i>) shallbe returned.</p><p>If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall bereturned.</p><p>If the correct value would cause underflow, and is not representable, a range error may occur, and 0.0 shall be returned.</p></blockquote><h4><a name="tag_03_615_05"></a>ERRORS</h4><blockquote><p>The <i>scalb</i>() function shall fail if:</p><dl compact><dt>Domain Error</dt><dd>If <i>x</i> is zero and <i>n</i> is +Inf, or <i>x</i> is Inf and <i>n</i> is -Inf. <p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [EDOM]. If theinteger expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall beraised.</p></dd><dt>Range Error</dt><dd>The result would overflow. <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>The <i>scalb</i>() function 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_615_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_615_07"></a>APPLICATION USAGE</h4><blockquote><p>Applications should use either <a href="../functions/scalbln.html"><i>scalbln</i>()</a>, <a href="../functions/scalblnf.html"><i>scalblnf</i>()</a>, or <a href="../functions/scalblnl.html"><i>scalblnl</i>()</a> in preference tothis function.</p><p>IEEE Std 1003.1-2001 only defines the behavior for the <i>scalb</i>() function when the <i>n</i> argument is aninteger, a NaN, or Inf. The behavior of other values for the <i>n</i> argument is unspecified.</p><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_615_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_615_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_615_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="ilogb.html"><i>ilogb</i>()</a> , <a href="ldexp.html"><i>ldexp</i>()</a> , <a href="logb.html"><i>logb</i>()</a> , <a href="scalbln.html"><i>scalbln</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/float.h.html"><i><float.h></i></a>, <a href="../basedefs/math.h.html"><i><math.h></i></a></p></blockquote><h4><a name="tag_03_615_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4, Version 2.</p></blockquote><h4><a name="tag_03_615_12"></a>Issue 5</h4><blockquote><p>Moved from X/OPEN UNIX extension to BASE.</p><p>The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in theAPPLICATION USAGE section.</p></blockquote><h4><a name="tag_03_615_13"></a>Issue 6</h4><blockquote><p>This function is marked obsolescent.</p><p>Although this function is not part of the ISO/IEC 9899:1999 standard, the RETURN VALUE and ERRORS sections are updated toalign with the error handling in the ISO/IEC 9899:1999 standard.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><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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