.\"	$OpenBSD: nan.3,v 1.6 2016/04/26 19:49:22 tb Exp $
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.\" Copyright (c) 2007 David Schultz <das@FreeBSD.org>
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.\" $FreeBSD: src/lib/msun/man/nan.3,v 1.1 2007/12/16 21:19:28 das Exp $
.\"
.Dd $Mdocdate: April 26 2016 $
.Dt NAN 3
.Os
.Sh NAME
.Nm nan ,
.Nm nanf ,
.Nm nanl
.Nd quiet NaNs
.Sh SYNOPSIS
.In math.h
.Ft double
.Fn nan "const char *s"
.Ft float
.Fn nanf "const char *s"
.Ft long double
.Fn nanl "const char *s"
.Sh DESCRIPTION
The
.Dv NAN
macro expands to a quiet NaN (Not A Number).
Similarly both the
.Fn nan ,
.Fn nanf
and
.Fn nanl
functions generate a quiet NaN value without raising an invalid exception.
The argument
.Fa s
should point to either an empty string or a hexadecimal representation
of a non-negative integer (e.g. 0x1234).
In the latter case, the integer is encoded in some free bits in the
representation of the NaN, which sometimes stores
machine-specific information about why a particular NaN was generated.
There are 22 such bits available for
.Vt float
variables, 51 bits for
.Vt double
variables, and at least 51 bits for a
.Vt long double .
If
.Fa s
is improperly formatted or represents an integer that is too large,
then the particular encoding of the quiet NaN that is returned
is indeterminate.
.Sh COMPATIBILITY
Calling these functions with a non-empty string isn't portable.
Another operating system may translate the string into a different
NaN encoding, and furthermore, the meaning of a given NaN encoding
varies across machine architectures.
If you understood the innards of a particular platform well enough to
know what string to use, then you would have no need for these functions
anyway, so don't use them.
Use the
.Dv NAN
macro instead.
.Sh SEE ALSO
.Xr isnan 3 ,
.Xr strtod 3
.Sh STANDARDS
The
.Fn nan ,
.Fn nanf
and
.Fn nanl
functions and the
.Dv NAN
macro conform to
.St -isoC-99 .