Xref: utzoo comp.lang.fortran:821 comp.software-eng:648
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From: smryan@garth.UUCP (Steven Ryan)
Newsgroups: comp.lang.fortran,comp.software-eng
Subject: Re: Fortran follies
Message-ID: <821@garth.UUCP>
Date: 27 Jun 88 22:54:30 GMT
References: <5377@cup.portal.com> <2852@mmintl.UUCP> <1005@cresswell.quintus.UUCP> <701@garth.UUCP> <2157@sugar.UUCP> <1555@kalliope.rice.edu> <809@garth.UUCP>
Reply-To: smryan@garth.UUCP (Steven Ryan)
Organization: INTERGRAPH (APD) -- Palo Alto, CA
Lines: 12

>The Cyber 205's breakeven vector length is from 20 to 50 elements.

[A person asked where this number came from. I really don't know how to respond
personally (I only learned about *f* and *F* by accidents) through this strange
network, so....]

That is the number Arden Hills always gave us. Where did they get? I'm not
sure, but I think it was murkily derived from benchmark tests.

The vector math library routines are rather arcane. They start by checking the
vector length. If less than 20, they use scalar loops unrolled by a factor
of three (the memory handles up to three concurrent load/stores). Otherwise
they use vector instructions.