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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.

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

       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.

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.

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.

       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 POSIX.1‐2017, Section 4.20, Treatment of  Error  Conditions
       for Mathematical Functions, <math.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, 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 .