Re: [Projects] [PATCH] Arithmetic overflow should wrap around - Projects

6 May 2014

On 06/04/2014 02:44, Pablo Oliveira wrote:

...
  Dear HAVM maintainers, 
Dear Pablo,

Sorry for this late answer! :/

...
  Tiger specifications do not precisely define the
expected behavior of an
 integer overflow. Currently, HAVM does not coerce its arithmetic
 computations to an Int32 type.
 To be consistent with nolimips, spim, and most current architectures, it
 would be nice that arithmetic operations in HAVM wrap around. 
Agreed.  We had a discussion in the Tiger Patches mailing list about
overflows in the code generated by the TC's MIPS backend a couple of
years ago and I was also in favor of wrapping arithmetic operators
(although I forgot to implement them!).

...
  The tentative attached patch fixes this. (I went for
the less intrusive
 fix, a more radical solution would be to redefine all Int types in HAVM
 to Int32.) 
Thank you for your patch!  As long as the semantics of the virtual
machine remain unclear regarding overflows, your solution is admittedly
better than migrating all Int values to Int32.

I'll apply it ASAP.

Kind regards,
Roland

-- 
Roland Levillain
EPITA Research and Development Laboratory (LRDE)
14-16, rue Voltaire - FR-94276 Le Kremlin-Bicêtre Cedex - France
Phone: +33 1 53 14 59 45 - Fax: +33 1 53 14 59 22 - www.lrde.epita.fr