RE: [GD-Consoles] PS2 floating point
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RE: [GD-Consoles] PS2 floating point
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From: <phi...@pl...> - 2003-02-28 19:11:31
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The PS2 fp support is indeed lacking denormals, also the various NAN's. Any
calculation involving them, tends to produce 0 in the results. This in
turn, tends to hide numerically catastrophic situations. The only other
thing I'm aware of, is that the FMAC units aren't symettrical at the lowest
bit. 1 x A != A x 1. This usually isn't a problem, but could potentially
cause otherwise inexplicable cracking.
Cheers
Phil
PS In their favour, there are 10 of them, and you can run them all at the
same time.
"Jacob Turner (Core Design Ltd)"
<Ja...@Co...> To: "'gam...@li...'"
Sent by: <gam...@li...>
gam...@li... cc:
eforge.net Fax to:
Subject: RE: [GD-Consoles] PS2 floating point
02/28/2003 02:22 AM
Please respond to gamedevlists-consoles
The one thing I do know is that on PC (don't know about GameCube) when
floating point numbers get very small it can switch to using de-normalised
mode (I think that is the term) which gives more accuracy.
I don't think the PS2 has this mode so it tends to just set everything to
0.0.
In my experience I have had it the other way i.e. PS2 is stable and fine
but
PC goes wrong.
-----Original Message-----
From: Research (GameBrains) [mailto:res...@ga...]
Sent: 28 February 2003 05:14
To: gam...@li...
Subject: Re: [GD-Consoles] PS2 floating point
We are still looking at the problem, but it seems that calculations
resulting in small numbers are the problem. On GameCube and PC the results
are correct but on the PS2 it's not. Still a good possibility that there
is
simply a bug in our code somewhere too :-) The cool thing about
multi-platform development is a lot of times different hardware and
different compilers help you find bugs you would have never found
otherwsie....
Cheers,
Brett
----- Original Message -----
From: "J. Grant" <jg-...@jg...>
To: <gam...@li...>
Sent: Thursday, February 27, 2003 10:33 PM
Subject: Re: [GD-Consoles] PS2 floating point
> Hi Brett,
>
> Out of interest what was the problem with your implementation? I found
> that -fshort-double stopped some of the problems I was having with one
> issue when I tested some float stuff a while ago. However, if the code
> is the problem then this would not solve that.
>
> JG
>
> Research (GameBrains) wrote:
> > Gareth,
> > Found it! (moved to chapter 8 in 6th edition). Thank you very much!
> > Brett
> >
> > ----- Original Message -----
> > From: "Gareth White" <gw...@ra...>
> > To: <res...@ga...>
> > Cc: <gam...@li...>
> > Sent: Thursday, February 27, 2003 2:49 PM
> > Subject: Re: [GD-Consoles] PS2 floating point
> >
> >
> >> There are indeed subtle differences between the PS2 and the IEEE
implementation.
> >>
> >> Try the 'EE Core User's Manual' (2nd Edition), Page 77, Chapter 4
> >> 'Floating-Point Unit (FPU)', section 4.8 'IEEE 754 Compatability'
> >>
> >> Cheers.
> >>
> >> ---
> >> Gareth White - Engine Programmer - Ratbag Pty Ltd
> >> Level 8, 63 Pirie Street, Adelaide, SA, Australia, 5000
> >> Ph: +61 8 8223 5830, Fax: +61 8 8223 5746, Mob: 0403 942668
> >> http://www.ratbaggames.com/
> >>
> >> ----- Original Message -----
> >> From: "Research (GameBrains)" <res...@ga...>
> >> To: <Gam...@li...>
> >> Sent: Thursday, February 27, 2003 4:46 PM
> >> Subject: [GD-Consoles] PS2 floating point
> >>
> >>
> >> Hello,
> >> Our physics engine is experiencing some odd behavior on the PS2. We
traced it
> >> to our resting contact force calculation where sometimes it seems the
result is
> >> not quite right, but it works fine on other platforms. I don't know
if
it's an
> >> urban legend or what, but I have heard that the PS2 has some quirks
with regard
> >> to floating point numbers and so I thought I would just ask and see if
this is
> >> something I need to look at or not. If so, what are the differences
between the
> >> PS2 IEEE implementation and is there a doc describing them?
> >> Thanks,
> >> Brett
>
>
>
>
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