Path: utzoo!mnetor!uunet!husc6!ut-sally!ut-emx!reeder
From: reeder@ut-emx.UUCP
Newsgroups: comp.arch
Subject: Re: Condition Codes in General Registers
Message-ID: <868@ut-emx.UUCP>
Date: 18 Feb 88 00:50:35 GMT
References: <191@telesoft.UUCP> <1556@gumby.mips.COM> <208@telesoft.UUCP> <6834@sol.ARPA>
Organization: The University of Texas at Austin, Austin, Texas
Lines: 23
Summary: that's how a Cray does it

In article <6834@sol.ARPA>, crowl@cs.rochester.edu (Lawrence Crowl) writes:
> using a general purpose register and slightly lower code density.  For example,
> 
>     compare R1 with R2 place condition code in R3
>     branch to ADDRESS if condition code in R3 is GREATER
>     branch to ADDRESS if condition code in R3 is EQUAL
>     branch to ADDRESS if condition code in R3 is LESS
> 
> Will this approach work?  Will the condition code comparison in the branch cost
> too much?  (It is an instruction constant.)  Comments please!

That is exactly how you do things on a Cray, for example:

          A0      A1-A2                 Compare A1 and A2
          JAP     addr1                 Branch to addr1 if A1 > A2
          JAZ     addr2                 Branch to addr2 if A1 = A2
          JAN     addr3                 Branch to addr3 if A1 < A2

William "Wills" Reeder

-- 

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