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pow.3

POW

Section: Linux Programmer's Manual (3)
Updated: 2008-08-10
Index Return to Main Contents
 

NAME

pow, powf, powl - power functions  

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);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

powf(), powl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99  

DESCRIPTION

The pow() function returns the value of x raised to the power of y.  

RETURN VALUE

On success, these functions return the value of x to the power of y.

If x is a finite value less than 0, and y is a finite non-integer, a domain error occurs, and a NaN is returned.

If the result overflows, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the mathematically correct sign.

If result underflows, and is not representable, a range error occurs, and 0.0 is returned.

Except as specified below, if x or y is a NaN, the result is a NaN.

If x is +1, the result is 1.0 (even if y is a NaN).

If y is 0, the result is 1.0 (even if x is a NaN).

If x is +0 (-0), and y is an odd integer greater than 0, the result is +0 (-0).

If x is 0, and y greater than 0 and not an odd integer, the result is +0.

If x is -1, and y is positive infinity or negative infinity, the result is 1.0.

If the absolute value of x is less than 1, and y is negative infinity, the result is positive infinity.

If the absolute value of x is greater than 1, and y is negative infinity, the result is +0.

If the absolute value of x is less than 1, and y is positive infinity, the result is +0.

If the absolute value of x is greater than 1, and y is positive infinity, the result is positive infinity.

If x is negative infinity, and y is an odd integer less than 0, the result is -0.

If x is negative infinity, and y less than 0 and not an odd integer, the result is +0.

If x is negative infinity, and y is an odd integer greater than 0, the result is negative infinity.

If x is negative infinity, and y greater than 0 and not an odd integer, the result is positive infinity.

If x is positive infinity, and y less than 0, the result is +0.

If x is positive infinity, and y greater than 0, the result is positive infinity.

If x is +0 or -0, and y is an odd integer less than 0, a pole error occurs and HUGE_VAL, HUGE_VALF, or HUGE_VALL, is returned, with the same sign as x.

If x is +0 or -0, and y is less than 0 and not an odd integer, a pole error occurs and +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, is returned.  

ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: x is negative, and y is a finite non-integer
errno is set to EDOM. An invalid floating-point exception (FE_INVALID) is raised.
Pole error: x is zero, and y is negative
errno is set to ERANGE (but see BUGS). A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.
Range error: the result overflows
errno is set to ERANGE. An overflow floating-point exception (FE_OVERFLOW) is raised.
Range error: the result underflows
errno is set to ERANGE. An underflow floating-point exception (FE_UNDERFLOW) is raised.
 

CONFORMING TO

C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.  

BUGS

For a pole error, errno is set to EDOM; POSIX.1 says it should be set to ERANGE.

If x is negative, then large negative or positive y values yield a NaN as the function result, with errno set to EDOM, and an invalid (FE_INVALID) floating-point exception. For example, with pow(), one sees this behavior when the absolute value of y is greater than about 9.223373e18.

In version 2.3.2 and earlier, when an overflow or underflow error occurs, glibc's pow() generates a bogus invalid floating-point exception (FE_INVALID) in addition to the overflow or underflow exception.  

SEE ALSO

cbrt(3), cpow(3), sqrt(3)  

COLOPHON

This page is part of release 3.21 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
BUGS
SEE ALSO
COLOPHON

 

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