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
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 either 0.0 (if supported), or an
implementation-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 Conditions 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 .