Re: Any use for Branch if Even/Odd ?

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Article #10851

#10851

From: Guillermo J. Rozas
Date: Fri, 11 Dec 1992 23:11

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In article <MOSS.92Dec11172728@CRAFTY.cs.cmu.edu> moss@cs.cmu.edu (Eliot Moss) writes:

|   Many garbage collected / dynamic languages use tagging to distinguish pointers
|   from non-pointers. If one uses the low bit to implement that tag, the branch
|   has obvious utility ....					ELiot

Another place where it is useful is to test packed booleans.
On most machines, the word containing the packed boolean would have to
be masked, but the mask generation might take multiple instructions.
Having branch-on-low-bit, you only need to shift before branching.

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References: <endecotp.723992157@cs.man.ac.uk> <MOSS.92Dec11172728@CRAFTY.cs.cmu.edu>

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Path: arc1-ca.pugleaf.net!sparky!uunet!stanford.edu!snorkelwacker.mit.edu!ai-lab!zurich.ai.mit.edu!gjr
From: gjr@zurich.ai.mit.edu (Guillermo J. Rozas)
Newsgroups: comp.arch
Subject: Re: Any use for Branch if Even/Odd ?
Date: 11 Dec 92 23:11:16
Organization: M.I.T. Artificial Intelligence Lab.
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Message-ID: <GJR.92Dec11231116@chamarti.ai.mit.edu>
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