NAME

       pow, powf, powl - power function

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);

DESCRIPTION

       These  functions  shall  compute  the  value  of  x  raised  to the power y, x**y. If x is
       negative, the application shall ensure that y is an integer value.

       An application wishing to check for error situations should set errno  to  zero  and  call
       feclearexcept(FE_ALL_EXCEPT)  before calling these functions.  On return, if errno is non-
       zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is  non-zero,
       an error has occurred.

RETURN VALUE

       Upon  successful  completion,  these  functions  shall return the value of x raised to the
       power y.

       For finite values of x < 0, and finite non-integer values of y, a domain error shall occur
       and     either  a  NaN  (if  representable),  or  an implementation-defined value shall be
       returned.

       If the correct value would cause overflow, a range error shall occur  and  pow(),  powf(),
       and powl() shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively, with the same
       sign as the correct value of the function.

       If the correct value would cause underflow, and is not representable, a  range  error  may
       occur,  and     either  0.0  (if supported), or   an implementation-defined value shall be
       returned.

       If x or y is a  NaN,  a  NaN  shall  be  returned  (unless  specified  elsewhere  in  this
       description).

       For any value of y (including NaN), if x is +1, 1.0 shall be returned.

       For any value of x (including NaN), if y is ±0, 1.0 shall be returned.

       For any odd integer value of y > 0, if x is ±0, ±0 shall be returned.

       For y > 0 and not an odd integer, if x is ±0, +0 shall be returned.

       If x is -1, and y is ±Inf, 1.0 shall be returned.

       For |x| < 1, if y is -Inf, +Inf shall be returned.

       For |x| > 1, if y is -Inf, +0 shall be returned.

       For |x| < 1, if y is +Inf, +0 shall be returned.

       For |x| > 1, if y is +Inf, +Inf shall be returned.

       For y an odd integer < 0, if x is -Inf, -0 shall be returned.

       For y < 0 and not an odd integer, if x is -Inf, +0 shall be returned.

       For y an odd integer > 0, if x is -Inf, -Inf shall be returned.

       For y > 0 and not an odd integer, if x is -Inf, +Inf shall be returned.

       For y < 0, if x is +Inf, +0 shall be returned.

       For y > 0, if x is +Inf, +Inf shall be returned.

       For  y an odd integer < 0, if x is ±0, a pole error shall occur and ±HUGE_VAL, ±HUGE_VALF,
       and ±HUGE_VALL shall be returned for pow(), powf(), and powl(), respectively.

       For y < 0 and not an odd integer, if x is ±0, a  pole  error  shall  occur  and  HUGE_VAL,
       HUGE_VALF, and HUGE_VALL shall be returned for pow(), powf(), and powl(), respectively.

       If  the correct value would cause underflow, and is representable, a range error may occur
       and the correct value shall be returned.

ERRORS

       These functions shall fail if:

       Domain Error
              The value of x is negative and y is a finite non-integer.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set  to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
       then the invalid floating-point exception shall be raised.

       Pole Error
              The value of x is zero and y is negative.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set  to  [ERANGE].  If  the integer expression (math_errhandling & MATH_ERREXCEPT) is non-
       zero, then the divide-by-zero floating-point exception shall be raised.

       Range Error
              The result overflows.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set  to  [ERANGE].  If  the integer expression (math_errhandling & MATH_ERREXCEPT) is non-
       zero, then the overflow floating-point exception shall be raised.

       These functions may fail if:

       Range Error
              The result underflows.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set  to  [ERANGE].  If  the integer expression (math_errhandling & MATH_ERREXCEPT) is non-
       zero, then the underflow floating-point exception shall be raised.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       On  error,  the  expressions  (math_errhandling  &  MATH_ERRNO)  and  (math_errhandling  &
       MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       exp()  ,  feclearexcept()  ,  fetestexcept()  ,  isnan()  , the Base Definitions volume of
       IEEE Std 1003.1-2001,  Section  4.18,  Treatment  of  Error  Conditions  for  Mathematical
       Functions, <math.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .