Re: [Discuss-gnuradio] new to GNUradio: AFSK and codec2 gmsk modem

[Marcus D. Leech]

O
> I've looked around a little bit and teh interwebs say, "never test
> floating point for equality", which is the way we are headed here.
> Aside from NEON not being fully IEEE 754 compliant as Doug mentioned,
> it looks like x86 (this statement not true for x86_64) has excess
> precision inside the floating point registers so you may get different
> results comparing a recently computed value with one loaded from
> memory. I haven't found any suggestions for a threshold.
>
> On a fun note, you can see there's a bazillion bug reports to GCC
> based on this: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323
>
> Nathan
I learned, back in the Pleistocene Era, never to test floating-point 
values for exact equality.  Anyone who is doing so is living in a state 
of sin.

But my surprise was in learning that two modern-CPU floating-point 
implementations, starting from the same starting conditions, would produce
  slightly different answers, and the reason, is that not everybody 
supports IEEE-754, or not, perhaps, all the rounding rules of IEEE-754, 
while
  perhaps supporting the format.

It's not like there's non-determinism going on.  The same CPU will 
always produce the same floating-point result, given the same starting
  conditions, and the same chain of floating-point operations.







--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org