536 lines
7.6 KiB
HTML
536 lines
7.6 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of POW</TITLE>
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</HEAD><BODY>
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<H1>POW</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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pow, powf, powl - power functions
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/math.h">math.h</A>></B>
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<B>double pow(double </B><I>x</I><B>, double </B><I>y</I><B>);</B>
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<B>float powf(float </B><I>x</I><B>, float </B><I>y</I><B>);</B>
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<B>long double powl(long double </B><I>x</I><B>, long double </B><I>y</I><B>);</B>
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</PRE>
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<P>
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Link with <I>-lm</I>.
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>powf</B>(),
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<B>powl</B>():
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<DL COMPACT><DT id="1"><DD>
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_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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<BR> || /* Since glibc 2.19: */ _DEFAULT_SOURCE
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<BR> || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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These functions return the value of
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<I>x</I>
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raised to the
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power of
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<I>y</I>.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, these functions return the value of
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<I>x</I>
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to the power of
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<I>y</I>.
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<P>
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If
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<I>x</I>
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is a finite value less than 0, and
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<I>y</I>
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is a finite noninteger, a domain error occurs,
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and a NaN is returned.
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<P>
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If the result overflows,
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a range error occurs,
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and the functions return
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<B>HUGE_VAL</B>,
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<B>HUGE_VALF</B>,
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or
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<B>HUGE_VALL</B>,
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respectively, with the mathematically correct sign.
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<P>
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If result underflows, and is not representable,
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a range error occurs,
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and 0.0 is returned.
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<P>
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Except as specified below, if
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<I>x</I>
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or
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<I>y</I>
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is a NaN, the result is a NaN.
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<P>
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If
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<I>x</I>
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is +1, the result is 1.0 (even if
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<I>y</I>
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is a NaN).
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<P>
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If
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<I>y</I>
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is 0, the result is 1.0 (even if
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<I>x</I>
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is a NaN).
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<P>
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If
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<I>x</I>
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is +0 (-0),
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and
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<I>y</I>
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is an odd integer greater than 0,
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the result is +0 (-0).
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<P>
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If
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<I>x</I>
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is 0,
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and
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<I>y</I>
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greater than 0 and not an odd integer,
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the result is +0.
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<P>
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If
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<I>x</I>
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is -1,
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and
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<I>y</I>
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is positive infinity or negative infinity,
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the result is 1.0.
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<P>
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If the absolute value of
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<I>x</I>
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is less than 1,
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and
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<I>y</I>
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is negative infinity,
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the result is positive infinity.
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<P>
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If the absolute value of
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<I>x</I>
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is greater than 1,
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and
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<I>y</I>
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is negative infinity,
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the result is +0.
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<P>
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If the absolute value of
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<I>x</I>
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is less than 1,
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and
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<I>y</I>
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is positive infinity,
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the result is +0.
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<P>
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If the absolute value of
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<I>x</I>
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is greater than 1,
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and
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<I>y</I>
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is positive infinity,
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the result is positive infinity.
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<P>
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If
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<I>x</I>
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is negative infinity,
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and
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<I>y</I>
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is an odd integer less than 0,
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the result is -0.
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<P>
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If
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<I>x</I>
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is negative infinity,
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and
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<I>y</I>
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less than 0 and not an odd integer,
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the result is +0.
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<P>
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If
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<I>x</I>
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is negative infinity,
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and
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<I>y</I>
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is an odd integer greater than 0,
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the result is negative infinity.
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<P>
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If
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<I>x</I>
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is negative infinity,
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and
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<I>y</I>
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greater than 0 and not an odd integer,
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the result is positive infinity.
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<P>
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If
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<I>x</I>
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is positive infinity,
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and
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<I>y</I>
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less than 0,
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the result is +0.
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<P>
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If
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<I>x</I>
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is positive infinity,
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and
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<I>y</I>
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greater than 0,
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the result is positive infinity.
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<P>
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If
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<I>x</I>
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is +0 or -0,
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and
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<I>y</I>
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is an odd integer less than 0,
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a pole error occurs and
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<B>HUGE_VAL</B>,
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<B>HUGE_VALF</B>,
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or
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<B>HUGE_VALL</B>,
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is returned,
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with the same sign as
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<I>x</I>.
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<P>
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If
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<I>x</I>
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is +0 or -0,
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and
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<I>y</I>
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is less than 0 and not an odd integer,
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a pole error occurs and
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+<B>HUGE_VAL</B>,
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+<B>HUGE_VALF</B>,
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or
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+<B>HUGE_VALL</B>,
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is returned.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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See
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<B><A HREF="/cgi-bin/man/man2html?7+math_error">math_error</A></B>(7)
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for information on how to determine whether an error has occurred
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when calling these functions.
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<P>
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The following errors can occur:
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<DL COMPACT>
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<DT id="2">Domain error: <I>x</I> is negative, and <I>y</I> is a finite noninteger<DD>
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<I>errno</I>
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is set to
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<B>EDOM</B>.
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An invalid floating-point exception
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(<B>FE_INVALID</B>)
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is raised.
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<DT id="3">Pole error: <I>x</I> is zero, and <I>y</I> is negative<DD>
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<I>errno</I>
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is set to
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<B>ERANGE</B>
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(but see BUGS).
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A divide-by-zero floating-point exception
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(<B>FE_DIVBYZERO</B>)
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is raised.
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<DT id="4">Range error: the result overflows<DD>
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<I>errno</I>
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is set to
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<B>ERANGE</B>.
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An overflow floating-point exception
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(<B>FE_OVERFLOW</B>)
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is raised.
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<DT id="5">Range error: the result underflows<DD>
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<I>errno</I>
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is set to
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<B>ERANGE</B>.
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An underflow floating-point exception
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(<B>FE_UNDERFLOW</B>)
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is raised.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>pow</B>(),
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<B>powf</B>(),
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<B>powl</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe<BR></TD></TR>
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</TABLE>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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C99, POSIX.1-2001, POSIX.1-2008.
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<P>
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The variant returning
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<I>double</I>
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also conforms to
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SVr4, 4.3BSD, C89.
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<A NAME="lbAI"> </A>
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<H2>BUGS</H2>
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On 64-bits,
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<B>pow</B>()
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may be more than 10,000 times slower for some (rare) inputs
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than for other nearby inputs.
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This affects only
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<B>pow</B>(),
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and not
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<B>powf</B>()
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nor
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<B>powl</B>().
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<P>
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In glibc 2.9 and earlier,
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when a pole error occurs,
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<I>errno</I>
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is set to
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<B>EDOM</B>
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instead of the POSIX-mandated
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<B>ERANGE</B>.
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Since version 2.10,
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glibc does the right thing.
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<P>
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If
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<I>x</I>
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is negative,
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then large negative or positive
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<I>y</I>
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values yield a NaN as the function result, with
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<I>errno</I>
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set to
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<B>EDOM</B>,
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and an invalid
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(<B>FE_INVALID</B>)
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floating-point exception.
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For example, with
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<B>pow</B>(),
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one sees this behavior when the absolute value of
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<I>y</I>
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is greater than about 9.223373e18.
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<P>
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In version 2.3.2 and earlier,
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when an overflow or underflow error occurs, glibc's
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<B>pow</B>()
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generates a bogus invalid floating-point exception
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(<B>FE_INVALID</B>)
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in addition to the overflow or underflow exception.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+cbrt">cbrt</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+cpow">cpow</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sqrt">sqrt</A></B>(3)
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<A NAME="lbAK"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="6"><A HREF="#lbAB">NAME</A><DD>
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<DT id="7"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="8"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="9"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="10"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="11"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="12"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="13"><A HREF="#lbAI">BUGS</A><DD>
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<DT id="14"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="15"><A HREF="#lbAK">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:52 GMT, March 31, 2021
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</BODY>
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</HTML>
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