199 lines
7.6 KiB
HTML
199 lines
7.6 KiB
HTML
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<title>lgamma</title>
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<basefont size="3"> <a name="lgamma"></a> <a name="tag_03_332"></a><!-- lgamma -->
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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_332_01"></a>NAME</h4>
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<blockquote>lgamma, lgammaf, lgammal - log gamma function</blockquote>
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<h4><a name="tag_03_332_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 lgamma(double</tt> <i>x</i><tt>);<br>
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float lgammaf(float</tt> <i>x</i><tt>);<br>
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long double lgammal(long double</tt> <i>x</i><tt>);<br>
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</tt></code></p>
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> extern int signgam; <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_332_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
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<br>
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<img src="../images/lgamma.gif">
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<br>
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The argument <i>x</i> need not be a non-positive integer (<img src="../images/lgamma2.gif"> is defined over the reals,
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except the non-positive integers).</p>
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<p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The sign of <img src="../images/lgamma2.gif"> is returned in the external integer <i>signgam</i>. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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These functions need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></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_332_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, these functions shall return the logarithmic gamma of <i>x</i>.</p>
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<p>If <i>x</i> is a non-positive integer, a pole error shall occur and <i>lgamma</i>(), <i>lgammaf</i>(), and <i>lgammal</i>()
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shall return +HUGE_VAL, +HUGE_VALF, and +HUGE_VALL, respectively.</p>
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<p>If the correct value would cause overflow, a range error shall occur and <i>lgamma</i>(), <i>lgammaf</i>(), and <i>lgammal</i>()
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shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (having the same sign as the correct value),
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respectively.</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 1 or 2, +0 shall be returned.</p>
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<p>If <i>x</i> is ±Inf, +Inf shall be returned. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_332_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>Pole Error</dt>
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<dd>The <i>x</i> argument is a negative integer or zero.
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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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<dt>Range Error</dt>
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<dd>The result overflows.
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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 overflow 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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</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_332_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_332_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_332_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_332_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_332_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="exp.html"><i>exp</i>()</a> , <a href="feclearexcept.html"><i>feclearexcept</i>()</a> , <a href=
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"fetestexcept.html"><i>fetestexcept</i>()</a> , <a href="isnan.html"><i>isnan</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap04.html#tag_04_18">Section 4.18, Treatment of Error Conditions for
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Mathematical Functions</a>, <a href="../basedefs/math.h.html"><i><math.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_332_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 3.</p>
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</blockquote>
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<h4><a name="tag_03_332_12"></a>Issue 5</h4>
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<blockquote>
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<p>The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the
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APPLICATION USAGE section.</p>
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<p>A note indicating that this function need not be reentrant is added to the DESCRIPTION.</p>
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</blockquote>
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<h4><a name="tag_03_332_13"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>lgamma</i>() function is no longer marked as an extension.</p>
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<p>The <i>lgammaf</i>() and <i>lgammal</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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<p>XSI extensions are marked.<br>
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</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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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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