Pocket Quake capabilities

[Lokas]

Hi,

I'm pretty new to the whole Pocket PC scene (although not to PC's and programming in general!) and I have only just come across Pocket Quake now. I must note that I was very impressed, it is certainly an accomplishment! I have a question though for anyone who is familiar with the source code and its development: I noticed that there seems to be a number of comments posted on the issue of fixed point conversions which would obviously greatly increase performance. Had Pocket Quake been written from the start with Pocket PCs in mind, i.e floating point calculus kept to a minimum and so on, roughly what kind of performance difference would there be?
I'm hoping to start developing for the platform soon and am trying to get an idea of the capabilities of the devices (only PocketPC 2002 machines really), especially with regards to 3D applications written especially for them. I've looked through the board but I couldn't really find a relevant answer so I thought I'd better post. I'd appreciate hearing any opinions on the subject.
(Great site, by the way! I hope to be coming here more frequently soon!)

Thanks in advance.

[Dan East]

It's very difficult to estimate, but my feeling is that if all floating point operations could be replaced with integer operations, one would see 20-30 FPS on a 206 mhz Pocket PC.

Dan East

[refractor]

Talking more generally here, on the PocketPC platforms without FPUs (AFAIK, that's all of them), carefully planned fixed-point operations will be several orders of magnitude faster than "floating point" operations.

The fixed point operations (except divide) all complete within a 5 or 6 cycles - an add/sub/multiply followed by a shift back to the correct position (or shifts in the case of a 64-bit intermediate result).

A floating point operation will likely mean at the very least a branch into an FP library, and at worst a processor exception and a branch to the FPU emulation code... not nice, and expensive computationally, cache-wise, etc.

Obviously for things like Pocket Quake it has to be retro-fitted quite carefully to avoid under and over-flow, but if you're designing a new graphics library I wouldn't (and don't) do anything but fixed point (on these FPU-less devices).

One "problem" with Quake is that the Intel processors of the time (and more recent AMD and Intels, of course) could do floating point operations in parallel (i.e. for free) with the integer operations, so some of Quake's "fast" Intel-specific code runs quite poorly on other processors (IIRC).

Cheers,

Refractor

[schmiddie]

[schmiddie]

[Dan East]