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.
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 3.44 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/.