Re: RT/PC Unaligned Accesses

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Article #20619

#20619

From: Flexi-thumbs
Date: Mon, 03 Apr 1989 16:46

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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
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!bbn!rochester!pt.cs.cmu.edu!PLAY.MACH.CS.CMU.EDU!bsy
From: bsy@PLAY.MACH.CS.CMU.EDU (Flexi-thumbs)
Newsgroups: comp.arch
Subject: Re: RT/PC Unaligned Accesses
Keywords: lisp, tag bits
Message-ID: <4636@pt.cs.cmu.edu>
Date: 3 Apr 89 16:46:31 GMT
References: <4618@pt.cs.cmu.edu> <oYBLMhy00jaRA1ZlFZ@andrew.cmu.edu> <16420@winchester.mips.COM>
Organization: Cranberry Melon
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