Re: Signed integer to modular type conversion

[Mark Johnson <mark_h_johnson@raytheon.com>]

Robert Dewar wrote:
> 
> adam@irvine.com (Adam Beneschan) wrote in message news:<b4682ab7.0205151602.3c564c9e@posting.google.com>...
> 
> > Would you still use something like Z := X + ToModType(Y) [where
> > ToModType is an instance of Unchecked_Conversion]?
> 
> No, I would use a 64-bit type to compute. If you have a deficient
> compiler that does not support 64-bit integers, then you have trouble,
> but so what? You could have equally asked to deal with numbers in the
> range 2**44, and then you would have needed a larger type anyway.
> 
> These days, all compilers should support 64-bit integers.

That's a little heavy if all he wants is a 32 bit value computed using
modular arithmetic. I sent a separate reply showing the alternative by
defining the mixed type arithmetic that should get the results he is
looking for.
  --Mark
PS: A long time ago, in the days of fixed point arithmetic, we used this
kind of trick to do a lot of our calculations. (e.g., represent the
angles of a circle as the range 0 .. 1-(1/2**15) which allowed natural
ways to add angles yet preserve good precision)