Equality == comparisons with floating point numbers

[Joseph Rushton Wakeling]

On 07/12/13 09:29, Abdulhaq wrote:
> Some time ago in a test I had written (C++) apparently identical floating point
> operations were returning different answers (in the 17th/18th sign fig), when
> re-running the same code with the same data. The paper described how the result
> could change if the numbers remained in the FPU (which had a few bits extra
> precision over the normal register size) during the course of the calculation as
> a opposed to being swapped in and out of the main registers. Depending on when
> numbers could get flushed out of the FPU (task swapping I suppose) you would get
> slightly different answers.
>
> Could this be a factor?

Yes, I think you are right.  In fact monarch_dodra had already pointed me 
towards this, but I slightly missed the point as I assumed this was about real 
vs. double (for example) comparisons, rather than type vs. FPU cache.

Interestingly, it appears to only hit 32-bit D.  There's a bug report related to 
this here:
http://d.puremagic.com/issues/show_bug.cgi?id=8745

Anyway, I think I now have a firm idea how to move forward; I thought I'd ask 
around here first just to see if there was anything I'd missed or that I 
otherwise wasn't aware of.  So thanks to everybody for your input! :-)