SYNOPSIS: Added feature test macro requirements.

SYNOPSIS: Remove unneeded "Compile with" piece.
Added RETURN VALUE section.
Added (null) ERRORS section.
CONFORMING TO: Added POSIX.1-2001.

man3/signbit.3

@@ -1,15 +1,28 @@
 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
+.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
+.\"     <mtk.manpages@gmail.com>
 .\" Distributed under GPL
 .\" Based on glibc infopages
-.TH SIGNBIT 3 2002-08-10 "GNU" "Linux Programmer's Manual"
+.TH SIGNBIT 3 2008-07-29 "GNU" "Linux Programmer's Manual"
 .SH NAME
-signbit \- test sign of a real floating point number
+signbit \- test sign of a real floating-point number
 .SH SYNOPSIS
 .B "#include <math.h>"
 .sp
 .BI  "int signbit(" x ");"
 .sp
-Compile with \fI\-std=c99\fP; link with \fI\-lm\fP.
+Link with \fI\-lm\fP.
+.sp
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.sp
+.ad l
+.BR signbit ():
+_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
+.I cc\ -std=c99
+.ad b
 .SH DESCRIPTION
 .BR signbit ()
 is a generic macro which can work on all real floating-point types.
@@ -19,15 +32,24 @@ 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.
+because IEEE 754 floating point allows zero to be signed.
 The comparison
 .IR "-0.0 < 0.0"
 is false, but
 .IR "signbit(\-0.0)"
 will return a non-zero value.
+
+NaNs and infinities have a sign bit.
+.SH RETURN VALUE
+The
+.BR signbit ()
+macro returns non-zero if the sign of
+.x
+is negative; otherwise it returns zero.
+.SH ERRORS
+No errors occur.
 .SH "CONFORMING TO"
-C99.
+C99, POSIX.1-2001.
 This function is defined in IEC 559 (and the appendix with
 recommended functions in IEEE 754/IEEE 854).
 .SH "SEE ALSO"