huschi.net

POW(3P)                    POSIX Programmer's Manual                   POW(3P)
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.1-2008
       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,  respec-
       tively.   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,  respec-
       tively 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.1-2008, Section 4.19, 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, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) 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.unix.org/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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                              POW(3P)