SIGNBIT(3) Linux Programmer's Manual SIGNBIT(3)
NAME
signbit - test sign of a real floating-point number
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
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 sign-
bit(-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; oth-
erwise it returns zero.
ERRORS
No errors occur.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
+----------+---------------+---------+
|Interface | Attribute | Value |
+----------+---------------+---------+
|signbit() | Thread safety | MT-Safe |
+----------+---------------+---------+
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).
SEE ALSO
copysign(3)
COLOPHON
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description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-09-15 SIGNBIT(3)