relibc_openlibm/man/nan.3

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.\" $FreeBSD: src/lib/msun/man/nan.3,v 1.1 2007/12/16 21:19:28 das Exp $
.\"
.Dd December 16, 2007
.Dt NAN 3
.Os
.Sh NAME
.Nm nan ,
.Nm nanf ,
.Nm nanl
.Nd quiet \*(Nas
.Sh LIBRARY
.Lb libm
.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 \*(Na (Not A Number).
Similarly, each of the
.Fn nan ,
.Fn nanf ,
and
.Fn nanl
functions generate a quiet \*(Na 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 \*(Na, which sometimes store
machine-specific information about why a particular \*(Na 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 \*(Na 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
\*(Na encoding, and furthermore, the meaning of a given \*(Na 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 fenv 3 ,
.Xr ieee 3 ,
.Xr isnan 3 ,
.Xr math 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 .