Xref: utzoo comp.lang.fortran:821 comp.software-eng:648 Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!ucbvax!decwrl!labrea!sri-unix!garth!smryan 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.