blob: a421ffafbafa224dca5d7cb105d9597562776fab (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
'\" t
.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: GPL-1.0-or-later
.\"
.\" Based on glibc infopages, copyright Free Software Foundation
.\"
.TH signbit 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
signbit \- test sign of a real floating-point number
.SH LIBRARY
Math library
.RI ( libm ", " \-lm )
.SH SYNOPSIS
.nf
.B "#include <math.h>"
.PP
.BI "int signbit(" x ");"
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR signbit ():
.nf
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
.fi
.SH DESCRIPTION
.BR signbit ()
is a generic macro which can work on all real floating-point types.
It returns a nonzero value if the value of
.I x
has its sign bit set.
.PP
This is not the same as
.IR "x < 0.0" ,
because IEEE 754 floating point allows zero to be signed.
The comparison
.I \-0.0\~<\~0.0
is false, but
.I signbit(\-0.0)
will return a nonzero value.
.PP
NaNs and infinities have a sign bit.
.SH RETURN VALUE
The
.BR signbit ()
macro returns nonzero if the sign of
.I x
is negative; otherwise it returns zero.
.SH ERRORS
No errors occur.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.BR signbit ()
T} Thread safety MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
POSIX.1-2001, C99.
.PP
This function is defined in IEC 559 (and the appendix with
recommended functions in IEEE 754/IEEE 854).
.SH SEE ALSO
.BR copysign (3)
|
