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; 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 positive 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 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 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
       For a pole error, errno is set to EDOM; POSIX.1 says it should be set to ERANGE.

       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  float-
       ing-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 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                                           2008-08-10                                                     POW(3)