# pow

```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);

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
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 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
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  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
attributes(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
On 64-bits, pow() may be more than 10,000 times slower for some  (rare)
inputs  than for other nearby inputs.  This affects only pow(), and not
powf() nor powl().

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 excep-
tion (FE_INVALID) in addition to the overflow or underflow exception.