.\"	$NetBSD: signbit.3,v 1.3 2008/04/30 13:10:50 martin Exp $
.\"
.\" Copyright (c) 2003 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Klaus Klein.
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.Dd October 29, 2003
.Dt SIGNBIT 3
.Os
.Sh NAME
.Nm signbit
.Nd test sign
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In math.h
.Ft int
.Fn signbit "real-floating x"
.Sh DESCRIPTION
The
.Fn signbit
macro determines whether the sign of its argument value
.Fa x
is negative.
An argument represented in a format wider than its semantic type is
converted to its semantic type first.
The determination is then based on the type of the argument.
.Ss IEEE754
The sign is determined for all values, including infinities, zeroes,
and NaNs
.Ss VAX
The sign is determined for finites, true zeros, and dirty zeroes;
for ROPs the sign is reported negative.
.Sh RETURN VALUES
The
.Fn signbit
macro returns a non-zero value if the sign of its value
.Fa x
is negative.
Otherwise 0 is returned.
.Sh ERRORS
No errors are defined.
.Sh SEE ALSO
.Xr fpclassify 3 ,
.Xr isfinite 3 ,
.Xr isnormal 3 ,
.Xr math 3
.Sh STANDARDS
The
.Fn signbit
macro conforms to
.St -isoC-99 .