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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  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.
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  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 3.53 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/.

                                  2010-09-12                            POW(3)