степенные функции (power functions)
Имя (Name)
pow, powf, powl - power functions
Синопсис (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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Описание (Description)
These functions return the value of x raised to the power of y.
Возвращаемое значение (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.
Ошибки (Error)
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.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│pow(), powf(), powl() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
Ошибки (баги) (Bugs)
Historical bugs (now fixed)
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 version 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 version
2.10, glibc does the right thing.
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.
Смотри также (See also)
cbrt(3), cpow(3), sqrt(3)
