Каталог требований LSB Core 3.1

Standard	ID	Description
SUSv3	__isnan.isnan.01	The isnan() macro shall determine whether its argument value is a NaN.
SUSv3	__isnan.isnan.02	The isnan() macro shall return a non-zero value if and only if its argument has a NaN value.
LSB	__isnan.30	__isnan() has the same specification as isnan() in ISO POSIX (2003), except that the argument type for __isnan() is known to be double.

The text in the Description column of SUSv3 requirements is reproduced from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html