powf(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
   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.

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   ┌──────────────────────┬───────────────┬─────────┐
   │InterfaceAttributeValue   │
   ├──────────────────────┼───────────────┼─────────┤
   │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
   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 4.09 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/.

                              2016-03-15                            POW(3)





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