Path: utzoo!attcan!uunet!snorkelwacker!paperboy!meissner From: meissner@osf.org (Michael Meissner) Newsgroups: comp.arch Subject: Re: Killer Micro II Message-ID: Date: 6 Sep 90 18:59:17 GMT References: <527@llnl.LLNL.GOV> <603@array.UUCP> <2482@l.cc.purdue.edu> <2497@l.cc.purdue.edu> <3755@osc.COM> <2493@crdos1.crd.ge.COM> Sender: news@OSF.ORG Organization: Open Software Foundation Lines: 40 In-reply-to: davidsen@crdos1.crd.ge.COM's message of 6 Sep 90 13:23:25 GMT In article <2493@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) writes: | In article <3755@osc.COM> jgk@osc.COM (Joe Keane) writes: | | | Our current programming languages have a strong influence. C has `float' and | | `double' types, and most machines have single-precision and double-precision | | floating point numbers. Coincidence? I think not. | | I miss this. Single and double precision came around before C by about | a decade. Yes they went into C when it was designed. If you are implying | that C was the reason manufacturers have double in hardware, the | timeline runs the wrong way. | | And the last time I checked, Cray C didn't do hardware double for the | double type, float and double were identical. As were short, long, and | int. There is no ANSI max size, just min size, so this is a conforming | implementation on that point. Note, C's promotions of floats into doubles is rather unique. Most languages that I'm familar with add two single precision floating point in single precision mode, rather than promoting both sides into double precision and doing a double precision add. This certainly simplifies the compiler/library, in that you only have to support one flavor of the math routines, and have less code patterns to deal with. It's interesting to note that some of the PDP-11 series floating point processors were actually faster doing double precision than doing single precision! On most other machines of that era, the reverse is true, and there was a big speedup in doing single precision (which is why most languages did not convert to double unless they needed to). Of course some of todays floating point processors, just do 80 bit floating point internally, and take the same amount of time (possibly being a little slower to convert a double precision value into internal format -- I don't know for sure). -- Michael Meissner email: meissner@osf.org phone: 617-621-8861 Open Software Foundation, 11 Cambridge Center, Cambridge, MA, 02142 Do apple growers tell their kids money doesn't grow on bushes?