These functions shall determine the maximum numeric value of their arguments.
NaN arguments shall be treated as missing data: if one argument is a NaN and
the other numeric, then these functions shall choose the numeric value.
Upon successful completion, these functions shall return the maximum numeric
value of their arguments.
If just one argument is a NaN, the other argument shall be returned.
If x and y are NaN, a NaN shall be returned.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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