[Vm-dev] Re: [ANN] 7061 = Squeak 3.9 final

[Andreas Raab]

David Griswold wrote:
> Sorry, I'm not familiar with the Squeak VM, but why does Slang translate
> into untagged C arithmetic?  

Because Slang is a subset that has been specifically chosen for 
translation to C. In other words it was choice made way back when the 
first version of the translator was written.

> To ensure the same semantic subset, why can't
> you generate C that uses tagged arithmetic that traps on overflow, rather
> than enlarging?  Low-bit tags are not that slow!  You could still represent
> up to 512MB with 2 tag bits and signed arithmetic.  And if you need more you
> just generate 64bit tagged integers, which would be fast on all new
> machines.
> 
> Then you should get the same semantics in Slang and in the simulator, modulo
> traps.

That would be a fun project (I wonder how different/similar it is to 
Ian's statically compiled idst version) but nothing I'm too eager to 
take on ;-)

Cheers,
   - Andreas