Re: Fun-O Basic Edition Compiler

[Jeffrey Siegal <address@hidden>]

Bruce Hoult wrote:

>>Not exactly.  What I was getting at would use the "natural" limits of a 
>>machine integer (like the native <integer> but with overflow checking). 
>>Is there a way of specifying that?
>>
> 
> I don't know what FunctionalDeveloper does.  We don't have such a type 
> in Gwydion Dylan.
> 
> More than that, I don't know how to efficiently implement one in 
> portable ANSI C, otherwise I'd be happy to add one.  Which would also 
> allow us to make our bignum support a lot more efficient (it currently 
> works on 16 bit "digits").

A first cut would be to implement it the exact same way as 
limited(<integer>, from: -2^31, to: 2^31-1), but without

> How can you do it for multiplication, other than by dividing afterwards 
> and comparing, or pre-classifying the operands?

Well, sometimes you can preclassify at compile time...

> OTOH, maybe it's time for Gwydion to have just a *little* assembler.  
> That's not nice given that it runs on a number of different CPUs, but 
> maybe it's not *too* bad: x86 and PPC will cover most people.  SPARC and 
> MIPS and HPPA and IA64 would probably get the rest.

What's wrong with a little assembler on systems you chose to support and 
standard C elsewhere?

On systems with 32x32->64 multiplication, this becomes very easy. (I 
think that's what you were getting at.)

By the way, I just looked in the DRM and <integer> is *not* defined to 
wrap there.  The overflow behavior is left implementation-defined.  So 
programs which rely on <integer> wrapping are non-portable.  That 
suggests some merit in a compile-time option to trap such things, and it 
also suggests some merit in having a class which is defined to wrap and 
one which is defined to trap, for when the programmer explicitly wants 
one behavior or the other.