.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\" Distributed under GPL
.\" Based on glibc infopages
.TH SIGNBIT 3 2002-08-10 "GNU" "Linux Programmer's Manual"
.SH NAME
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.
.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
.IR "-0.0 < 0.0"
is false, but
.IR "signbit(\-0.0)"
will return a nonzero value.
.SH "CONFORMING TO"
C99.
This function is defined in IEC 559 (and the appendix with
recommended functions in IEEE 754/IEEE 854).
.SH "SEE ALSO"
.BR copysign (3)