pow, powf, powl - power functions
Math library (libm
, -lm
)
#include <math.h>
double pow(double x, double y);
float powf(float x, float y);
long double powl(long double x, long double y);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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 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 with the appropriate sign is returned.
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.
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 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 a finite value less than 0, and y
is a
finite noninteger, a domain error occurs, and a NaN is returned.
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.
Except as specified above, if x
or y
is a NaN, the
result is a NaN.
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.
The following errors can occur:
x
is negative, and y
is a finite
nonintegererrno
is set to EDOM. An invalid
floating-point exception (FE_INVALID) is raised.
x
is zero, and y
is negativeerrno
is set to ERANGE (but see BUGS). A
divide-by-zero floating-point exception (FE_DIVBYZERO)
is raised.
errno
is set to ERANGE. An overflow
floating-point exception (FE_OVERFLOW) is raised.
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 |
Thread safety | MT-Safe |
C11, POSIX.1-2008.
C99, POSIX.1-2001.
The variant returning double
also conforms to SVr4, 4.3BSD,
C89.
Before glibc 2.28, on some architectures (e.g., x86-64) pow() may be more than 10,000 times slower for some inputs than for other nearby inputs. This affects only pow(), and not powf() nor powl(). This problem was fixed in glibc 2.28.
A number of bugs in the glibc implementation of pow() were fixed in glibc 2.16.
In glibc 2.9 and earlier, when a pole error occurs, errno
is
set to EDOM instead of the POSIX-mandated
ERANGE. Since glibc 2.10, glibc does the right
thing.
In glibc 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.