🚀 go-pugleaf

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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