man pages section 3: Extended Library Functions, Volume 2

Updated: Thursday, June 13, 2019

powl(3M)

Name

pow, powf, powl - power function

Synopsis

c99 [ flag... ] file... –lm [ library... ]
#include <math.h>

double pow(double x, double y);
float powf(float x, float y);
long double powl(long double x, long double y);
cc [ flag... ] file... –lm [ library... ]
#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 compute the value of x raised to the power y, xy>. If x is negative, y must be an integer value.

Return Values

Upon successful completion, these functions 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 occurs and either a NaN (if representable), or an implementation-defined value is returned.

If the correct value would cause overflow, a range error occurs and pow(), powf(), and powl() return HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.

If x or y is a NaN, a NaN is returned unless:

• If x is +1 and y is NaN and the application was compiled with the c99 compiler driver and is therefore SUSv3–conforming (see standards(7)), 1.0 is returned.

• For any value of x (including NaN), if y is +0, 1.0 is returned.

For any odd integer value of y > 0, if x is ±0, ±0 is returned.

For y > 0 and not an odd integer, if x is ±0, +0 is returned.

If x is ±1 and y is ±Inf, and the application was compiled with the cc compiler driver, NaN is returned. If, however, the application was compiled with the c99 compiler driver and is therefore SUSv3-conforming (seestandards(7)), 1.0 is returned.

For |x| < 1, if y is −Inf, +Inf is returned.

For |x| > 1, if y is −Inf, +0 is returned.

For |x| < 1, if y is +Inf, +0 is returned.

For |x| > 1, if y is +Inf, +Inf is returned.

For y an odd integer < 0, if x is −Inf, −0 is returned.

For y < 0 and not an odd integer, if x is −Inf, +0 is returned.

For y an odd integer > 0, if x is −Inf, −Inf is returned.

For y > 0 and not an odd integer, if x is −Inf, +Inf is returned.

For y < 0, if x is +Inf, +0 is returned.

For y > 0, if x is +Inf, +Inf is returned.

For y an odd integer < 0, if x is ±0, a pole error occurs and ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL are returned for pow(), powf(), and powl(), respectively.

For y < 0 and not an odd integer, if x is ±0, a pole error occurs and HUGE_VAL, HUGE_VALF, and HUGE_VALL are returned for pow(), powf(), and powl(), respectively.

For exceptional cases, matherr(3M) tabulates the values to be returned by pow() as specified by SVID3 and XPG3.

Errors

These functions will fail if:

Domain Error

The value of x is negative and y is a finite non-integer.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the invalid floating-point exception is raised.

The pow() function sets errno to EDOM if the value of x is negative and y is non-integral.

Pole Error

The value of x is 0 and y is negative.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the divide-by-zero floating-point exception is raised.

Range Error

The result overflows.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the overflow floating-point exception is raised.

The pow() function sets errno to EDOM if the value to be returned would cause overflow.

Usage

An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

An application can also set errno to 0 before calling pow(). On return, if errno is non-zero, an error has occurred. The powf() and powl() functions do not set errno.

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
Availability
system/library/math
MT-Level
MT-Safe
Standard