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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang.f77
Subject: Re: Wanted: Ultra-fast fortran compiler for UNIX
Message-ID: <1022@umcp-cs.UUCP>
Date: Sat, 27-Jul-85 17:52:16 EDT
Article-I.D.: umcp-cs.1022
Posted: Sat Jul 27 17:52:16 1985
Date-Received: Mon, 29-Jul-85 07:29:35 EDT
References: <621@astrovax.UUCP> <9871@Glacier.ARPA> <624@astrovax.UUCP> <867@oddjob.UUCP> <10068@Glacier.ARPA>
Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 24

>Can anyone explain to me why the comparison comes out so different
>on the 780/FPA and the 750, for instance?

(Fools rush in...)

I believe that the VMS compiler goes to great pains to avoid using
the floating point instructions when another instruction will (at
least 95% of the time) achieve the same result.  The original 4.2
f77 used "movf" and "movd" to copy real*4 and real*8 variables back
and forth; VMS Fortran uses "movl" and "movq".

Amusing anecdote: this apparently caused someone grief when a
program using real*8 datatypes to move integer or string values
around ``worked just fine under VMS, and gives me a "Floating
exception (core dumped)" under Unix.  What's wrong with the Unix
compiler?''  The problem, of course, was that the values being
moved were illegal floating point numbers, and were causing reserved
operand faults when "movd" tried to read them.

The f77 compiler that will be in 4.3BSD now uses movl and movq....
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@maryland