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+'\" t
+.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
+.\"
+.\" SPDX-License-Identifier: GPL-1.0-or-later
+.\"
+.\" Based on glibc infopages
+.\"
+.\" Corrections by aeb
+.\"
+.TH nan 3 (date) "Linux man-pages (unreleased)"
+.SH NAME
+nan, nanf, nanl \- return 'Not a Number'
+.SH LIBRARY
+Math library
+.RI ( libm ", " \-lm )
+.SH SYNOPSIS
+.nf
+.B #include <math.h>
+.P
+.BI "double nan(const char *" tagp );
+.BI "float nanf(const char *" tagp );
+.BI "long double nanl(const char *" tagp );
+.fi
+.P
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR nan (),
+.BR nanf (),
+.BR nanl ():
+.nf
+    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
+.fi
+.SH DESCRIPTION
+These functions return a representation (determined by
+.IR tagp )
+of a quiet NaN.
+If the implementation does not support
+quiet NaNs, these functions return zero.
+.P
+The call
+.I nan("char\-sequence")
+is equivalent to:
+.P
+.in +4n
+.EX
+strtod("NAN(char\-sequence)", NULL);
+.EE
+.in
+.P
+Similarly, calls to
+.BR nanf ()
+and
+.BR nanl ()
+are equivalent to analogous calls to
+.BR strtof (3)
+and
+.BR strtold (3).
+.P
+The argument
+.I tagp
+is used in an unspecified manner.
+On IEEE 754 systems, there are many representations of NaN, and
+.I tagp
+selects one.
+On other systems it may do nothing.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR nan (),
+.BR nanf (),
+.BR nanl ()
+T}	Thread safety	MT-Safe locale
+.TE
+.SH STANDARDS
+C11, POSIX.1-2008.
+.P
+See also IEC 559 and the appendix with
+recommended functions in IEEE 754/IEEE 854.
+.SH HISTORY
+glibc 2.1.
+C99, POSIX.1-2001.
+.SH SEE ALSO
+.BR isnan (3),
+.BR strtod (3),
+.BR math_error (7)