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242 lines
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<title>pow</title>
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<basefont size="3"> <a name="pow"></a> <a name="tag_03_482"></a><!-- pow -->
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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_482_01"></a>NAME</h4>
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<blockquote>pow, powf, powl - power function</blockquote>
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<h4><a name="tag_03_482_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 pow(double</tt> <i>x</i><tt>, double</tt> <i>y</i><tt>);<br>
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float powf(float</tt> <i>x</i><tt>, float</tt> <i>y</i><tt>);<br>
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long double powl(long double</tt> <i>x</i><tt>, long double</tt> <i>y</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_482_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 the value of <i>x</i> raised to the power <i>y</i>, <i>x<sup><small>y</small></sup></i>. If
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<i>x</i> is negative, the application shall ensure that <i>y</i> is an integer value.</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_482_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, these functions shall return the value of <i>x</i> raised to the power <i>y</i>.</p>
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<p>For finite values of <i>x</i> < 0, and finite non-integer values of <i>y</i>, a domain error shall occur and <sup>[<a href=
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"javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> either a NaN
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(if representable), or <img src="../images/opt-end.gif" alt="[Option End]" border="0"> an implementation-defined value shall be
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returned.</p>
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<p>If the correct value would cause overflow, a range error shall occur and <i>pow</i>(), <i>powf</i>(), and <i>powl</i>() shall
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return HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.</p>
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<p>If the correct value would cause underflow, and is not representable, a range error may occur, and <sup>[<a href=
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"javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> either 0.0 (if
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supported), or <img src="../images/opt-end.gif" alt="[Option End]" border="0"> an implementation-defined value shall be
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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> or <i>y</i> is a NaN, a NaN shall be returned (unless specified elsewhere in this description).</p>
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<p>For any value of <i>y</i> (including NaN), if <i>x</i> is +1, 1.0 shall be returned.</p>
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<p>For any value of <i>x</i> (including NaN), if <i>y</i> is ±0, 1.0 shall be returned.</p>
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<p>For any odd integer value of <i>y</i> > 0, if <i>x</i> is ±0, ±0 shall be returned.</p>
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<p>For <i>y</i> > 0 and not an odd integer, if <i>x</i> is ±0, +0 shall be returned.</p>
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<p>If <i>x</i> is -1, and <i>y</i> is ±Inf, 1.0 shall be returned.</p>
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<p>For |<i>x</i>| < 1, if <i>y</i> is -Inf, +Inf shall be returned.</p>
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<p>For |<i>x</i>| > 1, if <i>y</i> is -Inf, +0 shall be returned.</p>
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<p>For |<i>x</i>| < 1, if <i>y</i> is +Inf, +0 shall be returned.</p>
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<p>For |<i>x</i>| > 1, if <i>y</i> is +Inf, +Inf shall be returned.</p>
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<p>For <i>y</i> an odd integer < 0, if <i>x</i> is -Inf, -0 shall be returned.</p>
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<p>For <i>y</i> < 0 and not an odd integer, if <i>x</i> is -Inf, +0 shall be returned.</p>
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<p>For <i>y</i> an odd integer > 0, if <i>x</i> is -Inf, -Inf shall be returned.</p>
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<p>For <i>y</i> > 0 and not an odd integer, if <i>x</i> is -Inf, +Inf shall be returned.</p>
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<p>For <i>y</i> < 0, if <i>x</i> is +Inf, +0 shall be returned.</p>
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<p>For <i>y</i> > 0, if <i>x</i> is +Inf, +Inf shall be returned.</p>
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<p>For <i>y</i> an odd integer < 0, if <i>x</i> is ±0, a pole error shall occur and ±HUGE_VAL, ±HUGE_VALF,
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and ±HUGE_VALL shall be returned for <i>pow</i>(), <i>powf</i>(), and <i>powl</i>(), respectively.</p>
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<p>For <i>y</i> < 0 and not an odd integer, if <i>x</i> is ±0, a pole error shall occur and HUGE_VAL, HUGE_VALF, and
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HUGE_VALL shall be returned for <i>pow</i>(), <i>powf</i>(), and <i>powl</i>(), respectively.</p>
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<p>If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be
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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_482_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 value of <i>x</i> is negative and <i>y</i> is a finite non-integer.
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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><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 zero and <i>y</i> is negative.
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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. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></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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<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>The result underflows.
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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.</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_482_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_482_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_482_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_482_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_482_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_482_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_482_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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</blockquote>
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<h4><a name="tag_03_482_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>powf</i>() and <i>powl</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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