Re: [squeak-dev] Re: [ANN] Number comparison, hash, NaN, Point, and other partially ordered sets

>
> On Jan 8, 2009, at 9:30 AM, Hans-Martin Mosner wrote:
>
>> AFAIK, the Croquet project needs to have exactly reproducible float
>> arithmetics on all platforms. Would these rounding effects on the x86
>> affect that goal (perhaps with denormal intermediate results)?
>
> Yes.
>
>> Maybe it would be nice to write a unit test which would uncover
>> different rounding behaviors between purely-double-precision FP  
>> hardware
>> and extended-precision hardware.
>
> I'd have to play around a bit to get this into a Squeak unit test,  
> but here's a test vector which shows the effect:
>
> 3ff3208a25e04e87 * 000316dd1d02d1ae
>
> x86 result: 0003b16ef930a76e
> powerPC result: 0003b16ef930a76f
>
> These are IEEE double-precision floating-point numbers, specified in  
> hex (big-endian) so that they are bit exact (no conversion error  
> from a decimal representation).  The first number is between 1.0 and  
> 2.0, while the second number is a denormal value.  The product shows  
> an lsb difference between an x86 platform (extended-precision FPU)  
> and a PPC platform (double-precision FPU), even when the x86  
> floating-point control word is set to use double-precision rounding  
> for all results.