197 lines
7.6 KiB
HTML
197 lines
7.6 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>log1p</title>
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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<basefont size="3"> <a name="log1p"></a> <a name="tag_03_345"></a><!-- log1p -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_345_01"></a>NAME</h4>
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<blockquote>log1p, log1pf, log1pl - compute a natural logarithm</blockquote>
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<h4><a name="tag_03_345_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/math.h.html">math.h</a>><br>
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<br>
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double log1p(double</tt> <i>x</i><tt>);<br>
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float log1pf(float</tt> <i>x</i><tt>);<br>
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long double log1pl(long double</tt> <i>x</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_345_03"></a>DESCRIPTION</h4>
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<blockquote>
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<div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
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requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
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the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div>
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<p>These functions shall compute log<sub><small>e</small></sub>(1.0 + <i>x</i>).</p>
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<p>An application wishing to check for error situations should set <i>errno</i> to zero and call
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<i>feclearexcept</i>(FE_ALL_EXCEPT) before calling these functions. On return, if <i>errno</i> is non-zero or
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<i>fetestexcept</i>(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.</p>
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</blockquote>
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<h4><a name="tag_03_345_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, these functions shall return the natural logarithm of 1.0 + <i>x</i>.</p>
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<p>If <i>x</i> is -1, a pole error shall occur and <i>log1p</i>(), <i>log1pf</i>(), and <i>log1pl</i>() shall return -HUGE_VAL,
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-HUGE_VALF, and -HUGE_VALL, respectively.</p>
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<p>For finite values of <i>x</i> that are less than -1, <sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src=
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"../images/opt-start.gif" alt="[Option Start]" border="0"> or if <i>x</i> is -Inf, <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"> a domain error shall occur, and <sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src=
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"../images/opt-start.gif" alt="[Option Start]" border="0"> either a NaN (if supported), or <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"> an implementation-defined value shall be returned.</p>
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<p><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If
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<i>x</i> is NaN, a NaN shall be returned.</p>
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<p>If <i>x</i> is ±0, or +Inf, <i>x</i> shall be returned.</p>
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<p>If <i>x</i> is subnormal, a range error may occur and <i>x</i> should be returned. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_345_05"></a>ERRORS</h4>
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<blockquote>
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<p>These functions shall fail if:</p>
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<dl compact>
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<dt>Domain Error</dt>
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<dd>The finite value of <i>x</i> is less than -1, <sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src=
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"../images/opt-start.gif" alt="[Option Start]" border="0"> or <i>x</i> is -Inf. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0">
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<p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [EDOM]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be
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raised.</p>
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</dd>
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<dt>Pole Error</dt>
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<dd>The value of <i>x</i> is -1.
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<p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be
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raised.</p>
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</dd>
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</dl>
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<p>These functions may fail if:</p>
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<dl compact>
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<dt>Range Error</dt>
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<dd><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The value of <i>x</i> is subnormal.
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<p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be
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raised. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_345_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_345_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of
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each other, but at least one of them must be non-zero.</p>
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</blockquote>
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<h4><a name="tag_03_345_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_345_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_345_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="feclearexcept.html"><i>feclearexcept</i>()</a> , <a href="fetestexcept.html"><i>fetestexcept</i>()</a> , <a href=
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"log.html"><i>log</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/xbd_chap04.html#tag_04_18">Section 4.18, Treatment of Error Conditions for Mathematical Functions</a>, <a href=
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"../basedefs/math.h.html"><i><math.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_345_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4, Version 2.</p>
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</blockquote>
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<h4><a name="tag_03_345_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE.</p>
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</blockquote>
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<h4><a name="tag_03_345_13"></a>Issue 6</h4>
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<blockquote>
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<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
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<p>The <i>log1p</i>() function is no longer marked as an extension.</p>
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<p>The <i>log1pf</i>() and <i>log1pl</i>() functions are added for alignment with the ISO/IEC 9899:1999 standard.</p>
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<p>The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999
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standard.</p>
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<p>IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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]</font></center>
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