On Mon, 19 Aug 2002 12:27:24 EDT, "Thomas" <tho### [at] gmxnet> wrote:

>Erkki.Sondergaard wrote:
>>the time. Ok, I also have to check if we have the right compiler for
>>my usual platform, IBM Z-series mainframes, I know we're at the right
>>OS level to have 64-bit support, I belive we have at least the
>>run-time libs, but it's no good without the right compiler.
>
>I heard somewhere that mainframes are not particular good at floating point
>stuff and if I remember correctly the IBM one's are only IEEE (floating
>point standard(can't remember the number)) compitable since a few
>generation (S/390 G3 or G4?).

You're right, if you don't have the right hardware floating point
calculations are emulated in software, not in hardware (in other
words, slow as molasses). When I ported POV-Ray 1.0 to S/370 I didn't
do it for the speed (at that time about 7 times faster than a
486/50MHz, _with_FP_emulated_) but for the memory as we had 256 MB on
the mainframe and I only had 4 MB on my 386 workstation. Actually I
think my first port was DBW-Render, it had fractal subdivision
surfaces, they ate storage _very_ fast (4* for each level of
subdivision.

>I tried to run 3.1 in 64 bits sometime ago on IBM Power machines. no speed
>difference. And I never tried to let pov use more then 4 gigs of memory
>either.

The main advantage in running POV-Ray (or other sw) in 64 bits isn't
speed but the available memory space. In other words, it's only
interesting if your scene takes more than 2 GB storage to trace. I
belive that G. Tran has passed the 1 GB mark on some of his scenes and
I think that some of the IRTC images has come close to hitting the 2
GB limit. As for speed, well, all your pointers double in length and
that isn't good for speed as you have to load twice as much data. 

>Also there are two bugs at least in 64 bit versions of pov 3.1: The time at
>the end of the render is negative  and radiosity does not work at all. I
>tried to report it as a bug, but the Pov-team wasn't interested.

Well, if the POV-Team doesn't have the hardware to test on they can't
do much. Remember that the POV-Team mostly only have our personal
hardware to test on and 64-bit systems aren't that common (yet). I
have access to 64-bit hw at work (IBM, newest Z-Series), but I still
have to check if we have the right compiler. 

In my first raytracing test on S/370 I bombed out on the 16 MB limit
until I learned how to compile/link in 31-bit mode, in 64-bit mode I
better warn the performance guys before I allocate a couple of GB
storage (virtual or real).

/Erkki

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