Bug in floating-point addition: is anyone else seeing this?

[Carl Banks]

On May 21, 11:27 pm, Dave Parker <davepar... at flamingthunder.com>
wrote:
> On May 21, 7:01 pm, Carl Banks <pavlovevide... at gmail.com> wrote:
>
> > The crucial thing is not to slow down the calculations with useless
> > bells and whistles.
>
> Are you running your simulations on a system that does or does not
> support the "useless bell and whistle" of correct rounding?  If not,
> how do you prevent regression towards 0?

The "useless bell and whistle" is switching to multiprecision.

I'm not sure whether our hardware has a rounding bias or not but I
doubt it would matter if it did.


> For example, one of the things that caused the PS3 to be in 3rd place
> behind the Wii and XBox 360 is that to save a cycle or two, the PS3
> cell core does not support rounding of single precision results -- it
> truncates them towards 0.  That led to horrible single-pixel errors in
> the early demos I saw, which in term helped contribute to game release
> delays, which has turned into a major disappointment for Sony.

And you believe that automatically detecting rounding errors and
switching to multi-precision in software would have saved Sony all
this?


Carl Banks