pow, powf, powl - power functions
#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
These functions return the value of
x raised to the power of
y.
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.
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.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| pow (), powf (), powl () |
Thread safety |
MT-Safe |
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning
double also conforms to SVr4, 4.3BSD, C89.
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.
cbrt(3),
cpow(3),
sqrt(3)