🚀 go-pugleaf

>One advantage of silently ignoring the low bits in unaligned accesses is
>that you can use the low order bits as free tag bits -- without runtime
>overhead when dereferencing the data if you don't care to type-check.  This
>contrasts with the use of alignment traps for run time error checking.
>
>I don't know if the CMU RT Common Lisp actually does this (I'm not a Lisp
>hacker), but it would be a reasonable thing to do.
>
>-bsy
>-- 
>Internet:  bsy@cs.cmu.edu		Bitnet:	 bsy%cs.cmu.edu%smtp@interbit
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>USPS:      Bennet Yee, CS Dept, CMU, Pittsburgh, PA 15213-3890
>Voice:     (412) 268-7571

Time yet again for expression of one of my favorite architectural "gimmicks":
provide a mask that is implicitly ANDed with any {instruction,data} address
before use -- this way you could place tag bits in the low bits, in the
high bits, or in any bit you wanted (and not have to rely on features like
"The 68000 only implements 24 address bits", etc.).

Yes, this is a gimmick...


Andy "Krazy" Glew   aglew@urbana.mcd.mot.com   uunet!uiucdcs!mcdurb!aglew
   Motorola Microcomputer Division, Champaign-Urbana Design Center
	   1101 E. University, Urbana, Illinois 61801, USA.
   
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