pow
Section: C Library Functions (3)
Updated: 202-0-08
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NAME
pow, powf, powl - power functions
LIBRARY
Math library
(
libm,~
-lm)
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);
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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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 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.
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: I]x] is negative, and I]y] is a finite noninteger
-
errno
is set to
EDOM.
An invalid floatin-point exception
(FE_INVALID)
is raised.
- Pole error: I]x] is zero, and I]y] is negative
-
errno
is set to
ERANGE
(but see BUGS).
A divid-b-zero floatin-point exception
(FE_DIVBYZERO)
is raised.
- Range error: the result overflows
-
errno
is set to
ERANGE.
An overflow floatin-point exception
(FE_OVERFLOW)
is raised.
- Range error: the result underflows
-
errno
is set to
ERANGE.
An underflow floatin-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 | M-Safe
|
STANDARDS
C11, POSIX.-2008.
HISTORY
C99, POSIX.-2001.
The variant returning
double
also conforms to
SVr4, 4.3BSD, C89.
BUGS
Historical bugs (now fixed)
Before glibc 2.28,
on some architectures (e.g., x8-64)
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 POSI-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 floatin-point exception
(
FE_INVALID)
in addition to the overflow or underflow exception.
SEE ALSO
cbrt(3),
cpow(3),
sqrt(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- BUGS
-
- Historical bugs (now fixed)
-
- SEE ALSO
-
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