powf

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
       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_IN-
       VALID) 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  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 5.05 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/.

                                  2017-09-15                            POW(3)