This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

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.

Copyright

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                           POW(3POSIX)

Description

       The  functionality  described  on  this  reference  page is aligned with the ISO C standard. Any conflict
       between the requirements described  here  and  the  ISO C  standard  is  unintentional.  This  volume  of
       POSIX.1‐2017 defers to the ISO C standard.

       These  functions  shall  compute  the  value  of  x  raised  to  the  power y, xy.  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.

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:

       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 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.

       Thefollowingsectionsareinformative.

Examples

       None.

Future Directions

       None.

Name

       pow, powf, powl — power function

Prolog

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

Rationale

       None.

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 pow(),
       powf(), and powl() shall return 0.0, or (if IEC 60559 Floating-Point is not supported) an implementation-
       defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

       For  y  <  0,  if x is zero, a pole error may occur and pow(), powf(), and powl() shall return ±HUGE_VAL,
       ±HUGE_VALF, and ±HUGE_VALL, respectively.  On systems that support the IEC 60559  Floating-Point  option,
       if  x  is  ±0, a pole error shall occur and pow(), powf(), and powl() shall return ±HUGE_VAL, ±HUGE_VALF,
       and ±HUGE_VALL, respectively if y is an odd integer, or HUGE_VAL, HUGE_VALF, and HUGE_VALL,  respectively
       if y is not an odd integer.

       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.

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

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);