Hi Dan,
Thanks for the explanation.  That's why I asked and didn't assume; I'm 
fairly new to Squeak/Smalltalk and thought I should find out instead of 
just dropping the call in ;-)  thanks.  Does this mean once Jitter is 2x 
that you're going to rewrite the VM to get rid of the "warts"? ;-)

Cheers,
S

----- Dan Ingalls said:

>>Pouring over the source VM code, it looks like the primitiveBitXOr routine
>>needs a failSpecialPrim(16) after the end of the routine if the pop is 
>>not successful and after the unPop.
>>
>>This sound reasonable?
>
>Entirely.  However, it is not the case ;-)
>
>My guess is that you looked at primitiveBitOr (or similar), and reasoned 
>that primitiveBitXOr should work the same way.  However, note that bitOr: 
>is compiled as a special bytecode (see Smalltalk specialSelectors), and 
>therefore enters its primitive method earlier than most other primitives.  
>If you look at the comment in failSpecialPrim, you'll see that this is 
>explained somewhat:
>
>	"Used only for failing from a primitive that was entered as a special
>	bytecode.  This routine will look up the real method and, only if its
>	primitiveIndex is different, then it will run that primitive, otherwise
>	it will simply activate to run the fail code"
>
>Why is OR a special primitve but XOR is not?  It was just a speed/space 
>issue many years ago when the special integer ops were parcelled out, and 
>there wasn't room for every common function.
>
>What is such a crufty mechanism doing in a nice clean system like Squeak?  
>Chalk it up to many hours spent trying to make an interpreter run as fast 
>as a compiler.  My hope is that when jitter passes the 2x mark, we can 
>back the interpreter off to being a thing of elegance and beauty.  'Til 
>then, warts like this are mostly paying their way.
>
>Hope this helps
>
>	- Dan
>
>
>


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