1SIGNBIT(3)                 Linux Programmer's Manual                SIGNBIT(3)
2
3
4

NAME

6       signbit - test sign of a real floating-point number
7

SYNOPSIS

9       #include <math.h>
10
11       int signbit(x);
12
13       Link with -lm.
14
15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16
17       signbit():
18           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
19           _POSIX_C_SOURCE >= 200112L;
20           or cc -std=c99
21

DESCRIPTION

23       signbit() is a generic macro which can work on all real  floating-point
24       types.   It  returns a nonzero value if the value of x has its sign bit
25       set.
26
27       This is not the same as x < 0.0, because IEEE 754 floating point allows
28       zero  to  be  signed.   The  comparison  -0.0 < 0.0 is false, but sign‐
29       bit(-0.0) will return a nonzero value.
30
31       NaNs and infinities have a sign bit.
32

RETURN VALUE

34       The signbit() macro returns nonzero if the sign of x is negative;  oth‐
35       erwise it returns zero.
36

ERRORS

38       No errors occur.
39

ATTRIBUTES

41   Multithreading (see pthreads(7))
42       The signbit() macro is thread-safe.
43

CONFORMING TO

45       C99, POSIX.1-2001.  This function is defined in IEC 559 (and the appen‐
46       dix with recommended functions in IEEE 754/IEEE 854).
47

SEE ALSO

49       copysign(3)
50

COLOPHON

52       This page is part of release 3.53 of the Linux  man-pages  project.   A
53       description  of  the project, and information about reporting bugs, can
54       be found at http://www.kernel.org/doc/man-pages/.
55
56
57
58GNU                               2013-07-04                        SIGNBIT(3)
Impressum