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
       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 posi‐
       tive 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 pos‐
       itive 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.

CONFORMING TO
       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  over‐
       flow or underflow exception.

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

COLOPHON
       This  page  is  part of release 3.74 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/.



                                            2010-09-12                                     POW(3)