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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
       These functions shall compute the value of x raised  to  the  power  y,
       x**y. If x is negative, the application shall ensure that y is an inte-
       ger 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 implemen-
       tation-defined value shall be returned.
       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.
       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(), respectively.
       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 Condi-
       tions for Mathematical Functions, <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 original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                              POW(3P)