WHERE IS THE TWEAK

The Tweak, as explained in the documentation, consists solely on the change
of one part of the DIFFUSION macro. Therefore, the files here are the same as
the original ones, except where the DIFFUSION macro appears.
Namely, on the Reference version, in the files encrypt256.c and encrypt512.c.
The Optimized versions for 32 and 64 bits do not use encrypt*.c files,
since everything was put on the same files for some speed tricks.
Therefore, on the Optimized versions the files changed are
inupfin256.c and inupfin512.c

In every case only the DIFFUSION macro is changed, and
for ease of comparison just above the new macro the original DIFFUSION macro is left
in the file  (commented, of course, and just in case with a name
change to DIFFUSIONoriginal).