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- From: jackc@vermont.mti.sgi.com (Jack Choquette)
- Newsgroups: comp.arch
- Subject: Re: Any use for Branch if Even/Odd ?
- Message-ID: <lihth9INNbpo@spim.mti.sgi.com>
- Date: 11 Dec 92 20:12:25 GMT
- References: <endecotp.723992157@cs.man.ac.uk> <1g8ub1INN8it@agate.berkeley.edu> <GJR.92Dec10233620@chamarti.ai.mit.edu>
- Organization: Mips Technologies, Inc.
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- In article <GJR.92Dec10233620@chamarti.ai.mit.edu>, gjr@zurich.ai.mit.edu (Guillermo J. Rozas) writes:
- |> In article <1g8ub1INN8it@agate.berkeley.edu> jbuck@forney.berkeley.edu (Joe Buck) writes:
- |>
- |> | From: jbuck@forney.berkeley.edu (Joe Buck)
- |> | Newsgroups: comp.arch
- |> | Date: 11 Dec 1992 02:27:45 GMT
- |> |
- |> | They are used heavily in VMS, since it encodes error status returns
- |> | that way (the LSB determines whether there is an error or not). The
- |> | Vax had an instruction that could do this, so so must the Alpha for
- |> | efficient VMS implementatation.
- |>
- |> Isn't this in fact how booleans are represented in BLISS, the language
- |> in which a lot of VMS was/is written?
-
-
- Since many programs use boolean variables for control flow but use integers
- as the boolean variable, I could see how this could be useful. However,
- if a int value is being used as a single boolean variable it would make
- more sense to use/have an instruction like branch on zero. It's more general
- purpose and useful. You can use it to test boolean values as well as
- count down (to zero) loops.
-
- /jack
-