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   signbit    ( 3 )

тестовый знак реального числа с плавающей запятой (test sign of a real floating-point number)

Имя (Name)

signbit - test sign of a real floating-point number

Синопсис (Synopsis)

#include <math.h>

int signbit(x);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

signbit(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L


Описание (Description)

signbit() is a generic macro which can work on all real floating-
       point types.  It returns a nonzero value if the value of x has
       its sign bit set.

This is not the same as x < 0.0, because IEEE 754 floating point allows zero to be signed. The comparison -0.0 < 0.0 is false, but signbit(-0.0) will return a nonzero value.

NaNs and infinities have a sign bit.


Возвращаемое значение (Return value)

The signbit() macro returns nonzero if the sign of x is negative;
       otherwise it returns zero.

Ошибки (Error)

No errors occur.

Атрибуты (Attributes)

For an explanation of the terms used in this section, see
       attributes(7).

┌──────────────────────────────────────┬───────────────┬─────────┐ │Interface Attribute Value │ ├──────────────────────────────────────┼───────────────┼─────────┤ │signbit() │ Thread safety │ MT-Safe │ └──────────────────────────────────────┴───────────────┴─────────┘


Стандарты (Conforming to)

POSIX.1-2001, POSIX.1-2008, C99.  This function is defined in IEC
       559 (and the appendix with recommended functions in IEEE 754/IEEE
       854).

Смотри также (See also)

copysign(3)