
POW(P) POSIX Programmer's Manual POW(P)
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 nega
tive, 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 nonzero,
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 noninteger values of y, a domain error shall occur
and either a NaN (if representable), or an implementationdefined 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 implementationdefined value shall be
returned.
If x or y is a NaN, a NaN shall be returned (unless specified elsewhere in this descrip
tion).
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(), respec
tively.
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 noninteger.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is nonzero,
then the invalid floatingpoint 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 nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the dividebyzero floatingpoint exception shall be raised.
Range Error
The result overflows.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the overflow floatingpoint exception shall be raised.
These functions may fail if:
Range Error
The result underflows.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the underflow floatingpoint 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 nonzero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
exp() , feclearexcept() , fetestexcept() , isnan() , the Base Definitions volume of
IEEE Std 1003.12001, Section 4.18, Treatment of Error Conditions for Mathematical Func
tions, <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) 20012003 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 orig
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 POW(P) 
