For historical accuracy, I'll add a few comments to what Paul said.
 
> We did distribute DIFF with our 'Qlib' contributed library.
                       ^
                       It was really called DIF.
> But we didn't have the source and it generated stack overflows on larger
> tasks.
 
We did have the source code and I spent quite a bit of time studying
it.  However the stack space management was a fundamental part of how
the code worked and it wasn't easy/possible to change.  Because of
customer complaints we stopped distributing Dif with our products
several years ago.
 
In Pascal News #18 (published around 1979) was a program called
Compare.  I typed this program in and used it extensively as an
internal tool for many years.  It was also distributed as part of
Pascal/Robelle (a Pascal compiler for MPE V).
 
I felt that the output from Compare was vastly better than the output
from either Dif or Scompare (or the UNIX diff tool).  Compare was
written in standard Pascal using fixed-size buffers, so it had even
worse stack problems than Dif.  I believe that Scompare for MPE V
didn't use the stack for storage of differences so that it didn't have
the problems of Dif and Compare.
 
> Dave Lo of our programming staff re-wrote it in Pascal.
>
 
Because I really liked Compare, I asked Dave Lo to work on it.  Dave
spent a lot of time seeing if we could produce a version for MPE V
that didn't use the stack.  While Dave worked hard on the problem, we
never ended up with a version that ran fast enough.  Dave did many
other enhancements, wrote a test suite, user manual, and generally
made Compare into a bonus product.
 
> It is now called COMPARE and it only works on MPE/iX. It is a BONUS program
> that is on every license tape that we send to our customers.
 
If you are a Robelle customer and are on MPE/iX, you have a comparison
tool in compare.pub.robelle.  If you are not a Robelle customer, you
can obtain Compare by purchasing our bonus products (available at a
low price).  Contact [log in to unmask] for more information on the
bonus products.
 
Scompare has many more features than our Compare program.  For
example, if you want to automatic source-code updates using
comparisons between versions, you want Scompare from Aldon (you might
need another product from them too).  But if you are a Robelle
customer, you should give Compare a try.
 
Cheers,
 
David Greer    <[log in to unmask]>