Manpage of POW

POW

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

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():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
 

DESCRIPTION

These functions return the value of xraised to the power of y.  

RETURN VALUE

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

If xis a finite value less than 0, and yis a finite noninteger, 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 xor yis a NaN, the result is a NaN.

If xis +1, the result is 1.0 (even if yis a NaN).

If yis 0, the result is 1.0 (even if xis a NaN).

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

If xis 0, and ygreater than 0 and not an odd integer, the result is +0.

If xis -1, and yis positive infinity or negative infinity, the result is 1.0.

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

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

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

If the absolute value of xis greater than 1, and yis positive infinity, the result is positive infinity.

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

If xis negative infinity, and yless than 0 and not an odd integer, the result is +0.

If xis negative infinity, and yis an odd integer greater than 0, the result is negative infinity.

If xis negative infinity, and ygreater than 0 and not an odd integer, the result is positive infinity.

If xis positive infinity, and yless than 0, the result is +0.

If xis positive infinity, and ygreater than 0, the result is positive infinity.

If xis +0 or -0, and yis 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 xis +0 or -0, and yis 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 noninteger
errnois set to EDOM. An invalid floating-point exception (FE_INVALID) is raised.
Pole error: x is zero, and y is negative
errnois set to ERANGE(but see BUGS). A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.
Range error: the result overflows
errnois set to ERANGE. An overflow floating-point exception (FE_OVERFLOW) is raised.
Range error: the result underflows
errnois set to ERANGE. An underflow floating-point exception (FE_UNDERFLOW) is raised.
 

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
pow(), powf(), powl() Thread safetyMT-Safe
 

CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning doublealso conforms to SVr4, 4.3BSD, C89.  

BUGS

On 64-bits, pow() may be more than 10,000 times slower for some (rare) inputs than for other nearby inputs. This affects only pow(), and not powf() nor powl().

In glibc 2.9 and earlier, when a pole error occurs, errnois set to EDOMinstead of the POSIX-mandated ERANGE. Since version 2.10, glibc does the right thing.

If xis negative, then large negative or positive yvalues yield a NaN as the function result, with errnoset to EDOM, and an invalid (FE_INVALID) floating-point exception. For example, with pow(), one sees this behavior when the absolute value of yis 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)


 

Index

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

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