Re: [Squeak-VMdev] DING! End of Round One

[Ian P. <ian...@in...>]

Hi Ian,

On 09 Apr 2004, at 01:27, Ian Piumarta wrote:

>> Hm... this would actually be a strong argument against introducing 
>> more
>> immediates. They would have similar properties wouldn't they?
>
> Yes, absolutely.  (At least in the lower magnitudes of the 
> price/performance equation.)

No, not necessarily.

We have an array containing the classes for each tag combination (init 
from splObj at startup, ensure remap during GC) then (for a 2-bit tag 
field):

   Interp
     instVars: '... immediateClasses ...'

   Interp>>classOf: anObj
     | tag |
     self inline: true.
     ^(tag _ anObj bitAnd: 3) == 0
       ifTrue: [self classHeaderOf: anObj]
       ifFalse: [immediateClasses at: tag]

or something similar.  Costs the same as if we only had one tag bit 
(with ClassSmallInt sucked out of splObj).

Cheers,
Ian