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From: slackey@bbn.com (Stan Lackey)
Newsgroups: comp.arch
Subject: Re: isamax and instruction set design
Message-ID: <64739@bbn.BBN.COM>
Date: 18 Jun 91 20:27:36 GMT
References: <396@validgh.com> <1991Jun13.234834.22970@neon.Stanford.EDU> <1991Jun14.134338.4673@linus.mitre.org> <1991Jun14.163141.17728@rice.edu>
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In article <1991Jun14.163141.17728@rice.edu> preston@asta.rice.edu (Preston Briggs) writes:
>bs@frieda.mitre.org (Robert D. Silverman) writes:
>
>>:	    ibig  = absdx .le. dmax
>>	    ^^^^^^^^^^^^^^^^^^^^^^^^
>>
>>I would be very interested in seeing the assembler code that gets
>>emitted for this line of Fortran. How can this statement get executed
>>WITHOUT a branch??
>
>Don't know of any conditional assignments, though we might
>use a skip instruction to accomplish the purpose.

I once worked on a machine that had instructions like x=min(y,z) in hardware.
Also there were vector instructions that would elementwise compare vectors
and build a vector of logicals which could be applied to a subsequent vector
op.  So a loop of the form

  where (a(i) .lt. b(i)) c(i) = d(i) + e(i)

could be done with two vector instructions and no branches (other than
loop control, of course).

-Stan