Subroutines to reverse the byte order of integer and real variables.
This is useful when reading binary data from a file intended for use
on a compute whose byte order is opposite that of the computer on
which the Fortran program is to be run.
Adopted from Fortran 90 routines written by David G. Simpson, NASA
Goddard Space Flight Center (https://caps.gsfc.nasa.gov/simpson/).
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