получить показатель степени значения с плавающей запятой (get exponent of a floating-point value)
Имя (Name)
logb, logbf, logbl - get exponent of a floating-point value
Синопсис (Synopsis)
#include <math.h>
double logb(double x);
float logbf(float x);
long double logbl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
logb():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
logbf(), logbl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Описание (Description)
These functions extract the exponent from the internal floating-
point representation of x and return it as a floating-point
value. The integer constant FLT_RADIX, defined in <float.h>,
indicates the radix used for the system's floating-point
representation. If FLT_RADIX is 2, logb(x) is equal to
floor(log2(x)), except that it is probably faster.
If x is subnormal, logb() returns the exponent x would have if it
were normalized.
Возвращаемое значение (Return value)
On success, these functions return the exponent of x.
If x is a NaN, a NaN is returned.
If x is zero, then a pole error occurs, and the functions return
-HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
If x is negative infinity or positive infinity, then positive
infinity 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:
Pole error: x is 0
A divide-by-zero floating-point exception (FE_DIVBYZERO)
is raised.
These functions do not set errno.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│logb(), logbf(), logbl() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
C99, POSIX.1-2001, POSIX.1-2008.
Смотри также (See also)
ilogb(3), log(3)
