signbit
Section: C Library Functions (3)
Updated: 2022-12-15
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NAME
signbit - test sign of a real floating-point number
LIBRARY
Math library
(libm, -lm)
SYNOPSIS
#include <math.h>
int signbit(x);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
signbit():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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.
RETURN VALUE
The
signbit()
macro returns nonzero if the sign of
x
is negative; otherwise it returns zero.
ERRORS
No errors occur.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
signbit()
| Thread safety | MT-Safe
|
STANDARDS
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).
SEE ALSO
copysign(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- SEE ALSO
-
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