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():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

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.

SEE ALSO
       cbrt(3), cpow(3), sqrt(3)

COLOPHON
       This  page  is  part of release 4.04 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
       http://www.kernel.org/doc/man-pages/.

                                  2015-04-19                            POW(3)
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