POW(3) Linux Programmer's Manual POW(3)
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():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
These functions return 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 do-
main 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 mathemati-
cally 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 infin-
ity, 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 infin-
ity, the result is positive infinity.
If x is negative infinity, and y is an odd integer less than 0, the re-
sult 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 oc-
curs 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 float-
ing-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.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌──────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────┼───────────────┼─────────┤
│pow(), powf(), powl() │ Thread safety │ MT-Safe │
└──────────────────────┴───────────────┴─────────┘
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
BUGS
Historical bugs (now fixed)
Before glibc 2.28, on some architectures (e.g., x86-64) pow() may be
more than 10,000 times slower for some inputs than for other nearby in-
puts. This affects only pow(), and not powf() nor powl(). This prob-
lem was fixed in glibc 2.28.
A number of bugs in the glibc implementation of pow() were fixed in
glibc version 2.16.
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.
In version 2.3.2 and earlier, when an overflow or underflow error oc-
curs, 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 5.10 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2020-06-09 POW(3)
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