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- Path: sparky!uunet!olivea!sgigate!odin!mash.wpd.sgi.com!mash
- From: mash@mash.wpd.sgi.com (John R. Mashey)
- Newsgroups: comp.sys.sgi.misc
- Subject: Re: any update on plans for {fortran,C} support of 128-bit floats?
- Message-ID: <1993Jan6.005916.800@odin.corp.sgi.com>
- Date: 6 Jan 93 00:59:16 GMT
- References: <BzGLB0.90v@helios.physics.utoronto.ca> <1992Dec20.004150.14551@sol.ctr.columbia.edu> <3236@contex.contex.com>
- Sender: news@odin.corp.sgi.com (Net News)
- Organization: Silicon Graphics, Inc.
- Lines: 55
- Nntp-Posting-Host: mash.wpd.sgi.com
-
- In article <3236@contex.contex.com>, frank@marvin.contex.com (Frank Perdicaro) writes:
- |> In article <1992Dec20.004150.14551@sol.ctr.columbia.edu> penev@venezia.rockefeller.edu writes:
- |> >Mark Bartelt (sysmark@helios.physics.utoronto.ca) wrote:
- |> >: Nearly a year ago I groused a bit about the fact that neither C nor
- |> >: fortran (under IRIX 4.0.x) support 128-bit floats, and that (worse!)
-
- |> Perhaps the next chip? No. The FPX, and the low power R4000 ( I
- |> forget its name ) are the two next chips. Though I go not concrete
- |> answers, I got a solid feeling that these would also have only SP and
- |> DP. And the chip after that, the R5000? I have no idea. Call your
- |> salesman today.
-
- Well ... this probably won't help you much (calling your salesman,
- that is), since the sales folks are fairly far away from chip architecture
- decisions for several years out.
-
- As it happens, the 128-bit FP issue is generally reviewed for each major
- new round of chip design, and we tend to ask customers and industry experts
- what they think, and the answers tend to go as follows:
-
- Q: Would you like to have 128-bit FP?
- A: Yes, of course.
- Q: Would you like to have faster 64-bit FP?
- A: Yes, of course.
- Q: If, for the next design, we only have chip die area (and it is *always*
- limited) to give you 128-bit OR faster 64-bit, which should we do?
- A: Faster 64-bit.
-
- 1) When you allocate the space on a chip, there is a large range of
- floating-point solutions where using more space gets more performance, by having
- space-intensive FP units with lower latencies and higher repeat rates,
- and/or by duplicating FP units, which is far more useful for FP performance
- than it is for integer work, so far. With current-sized chips, this is
- still a tradeoff; 128-bit FP is not free.
-
- 2) As a result, I suspect it will be a while before 128-bit FP is
- frequently found in microprocessors. It will happen as chip features sizes
- shrink (and *must* happen, for some classes of programs),
- but it will take a while. Of course, doing it all (or mostly) in software
- can precede fast support in hardware, and there are ways to help this.
-
- 3) Given the lead-times involved, don't expect a 128-bit FP Rxxx in 1993
- or 1994; 1995 may well be impossible also. Maybe later.
-
- 4) IF you think you really need 128-bit FP, it would probably help us to
- post/email what you're doing. Of course, if you were to post that you would
- buy $100Ms of computers because of this feature, more attention would
- be attracted :-).... but seriously, we're interested in this area and willing
- to listen to people on it.
-
- --
- -john mashey DISCLAIMER: <generic disclaimer, I speak for me only, etc>
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