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   logbl    ( 3 )

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)