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POW
Section: Linux Programmer's Manual (3)
Updated: 2010-09-12
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NAME
pow, powf, powl - power functions
SYNOPSIS
#include <math.h>
double pow(double x, double y);
float powf(float x, float y);
long double powl(long double x, long double y);
Link with -lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
powf(),
powl():
-
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99
DESCRIPTION
The
pow()
function returns the value of x raised to the
power of y.
RETURN VALUE
On success, these functions return the value of
x
to the power of
y.
If
x
is a finite value less than 0, and
y
is a finite noninteger, a domain error occurs,
and a NaN is returned.
If the result overflows,
a range error occurs,
and the functions return
HUGE_VAL,
HUGE_VALF,
or
HUGE_VALL,
respectively, with the mathematically correct sign.
If result underflows, and is not representable,
a range error occurs,
and 0.0 is returned.
Except as specified below, if
x
or
y
is a NaN, the result is a NaN.
If
x
is +1, the result is 1.0 (even if
y
is a NaN).
If
y
is 0, the result is 1.0 (even if
x
is a NaN).
If
x
is +0 (-0),
and
y
is an odd integer greater than 0,
the result is +0 (-0).
If
x
is 0,
and
y
greater than 0 and not an odd integer,
the result is +0.
If
x
is -1,
and
y
is positive infinity or negative infinity,
the result is 1.0.
If the absolute value of
x
is less than 1,
and
y
is negative infinity,
the result is positive infinity.
If the absolute value of
x
is greater than 1,
and
y
is negative infinity,
the result is +0.
If the absolute value of
x
is less than 1,
and
y
is positive infinity,
the result is +0.
If the absolute value of
x
is greater than 1,
and
y
is positive infinity,
the result is positive infinity.
If
x
is negative infinity,
and
y
is an odd integer less than 0,
the result is -0.
If
x
is negative infinity,
and
y
less than 0 and not an odd integer,
the result is +0.
If
x
is negative infinity,
and
y
is an odd integer greater than 0,
the result is negative infinity.
If
x
is negative infinity,
and
y
greater than 0 and not an odd integer,
the result is positive infinity.
If
x
is positive infinity,
and
y
less than 0,
the result is +0.
If
x
is positive infinity,
and
y
greater than 0,
the result is positive infinity.
If
x
is +0 or -0,
and
y
is an odd integer less than 0,
a pole error occurs and
HUGE_VAL,
HUGE_VALF,
or
HUGE_VALL,
is returned,
with the same sign as
x.
If
x
is +0 or -0,
and
y
is less than 0 and not an odd integer,
a pole error occurs and
+HUGE_VAL,
+HUGE_VALF,
or
+HUGE_VALL,
is returned.
ERRORS
See
math_error(7)
for information on how to determine whether an error has occurred
when calling these functions.
The following errors can occur:
- Domain error: x is negative, and y is a finite noninteger
-
errno
is set to
EDOM.
An invalid floating-point exception
(FE_INVALID)
is raised.
- Pole error: x is zero, and y is negative
-
errno
is set to
ERANGE
(but see BUGS).
A divide-by-zero floating-point exception
(FE_DIVBYZERO)
is raised.
- Range error: the result overflows
-
errno
is set to
ERANGE.
An overflow floating-point exception
(FE_OVERFLOW)
is raised.
- Range error: the result underflows
-
errno
is set to
ERANGE.
An underflow floating-point exception
(FE_UNDERFLOW)
is raised.
CONFORMING TO
C99, POSIX.1-2001.
The variant returning
double
also conforms to
SVr4, 4.3BSD, C89.
BUGS
In glibc 2.9 and earlier,
when a pole error occurs,
errno
is set to
EDOM
instead of the POSIX-mandated
ERANGE.
Since version 2.10,
glibc does the right thing.
If
x
is negative,
then large negative or positive
y
values yield a NaN as the function result, with
errno
set to
EDOM,
and an invalid
(FE_INVALID)
floating-point exception.
For example, with
pow(),
one sees this behavior when the absolute value of
y
is greater than about 9.223373e18.
In version 2.3.2 and earlier,
when an overflow or underflow error occurs, glibc's
pow()
generates a bogus invalid floating-point exception
(FE_INVALID)
in addition to the overflow or underflow exception.
SEE ALSO
cbrt(3),
cpow(3),
sqrt(3)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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