POW(3)                     POSIX Programmer's Manual                    POW(3)



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

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 .



IEEE/The Open Group                  2017                               POW(3)
