Unix/Linux Go Back    


Linux 2.6 - man page for pow (linux section 3posix)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


POW(P)				    POSIX Programmer's Manual				   POW(P)

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 nega-
       tive, 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  descrip-
       tion).

       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(),  respec-
       tively.

       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 Func-
       tions, <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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					   POW(P)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 12:17 AM.