powl (3)
Leading comments
Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpages@gmail.com>
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NAME
pow, powf, powl - power functionsSYNOPSIS
#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 ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTION
These functions return 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 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 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 noninteger
- 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| pow(), powf(), powl() | Thread safety | MT-Safe |
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.The variant returning double also 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, errno is set to EDOM instead of the POSIX-mandated ERANGE. Since version 2.10, glibc does the right thing.
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.