[m-rev.] for review: define <<u and >>u

[Peter Wang]

On Tue, 06 Dec 2022 16:53:33 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> 
> As for const_prop, I have just done the required updates.
> I found the existing code strange, in that uint_emu.m reduces
> the unchecked shift ops to the checked ones,
> which I think is the right thing to do, while int_emu.m does not.
> And unchecked_{left,right}_shift in int_enu.m check their arguments
> using code that is (a) different from the checks in {left,right}_shift
> in int_emu.m, but (b) similar to the checks in {left,right}_shift in
> uint_emu.m.
> 
> Peter, you wrote the original int_emu.m. Do you remember the
> reason for (a)?

The additional checks in int_emu.unchecked_{left,right}_shift
are to ensure that they only succeed when the behaviour of
int.unchecked_{left,right}_shift is defined.

Peter