Re: [hatari-devel] FPU update

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Andreas Grabher schrieb:

> Did you ever hear about
> this difference between x87/IEEE and 6888x? It seems this behavior
> does not comply with the IEEE standard. 

It doesn't? From what I understand, IEEE 754-1985 only specifies very
little about extended formats which are said to be
"implementation-dependent". I can't find neither the bias nor the
specific encoding of (de-normalized) numbers in the standard document
for extended formats.

In particular, in Motorola's implementation with the explicit integer
bit it would lead to redundant/ambiguous encoding of some numbers if the
bias changed either for de-normalized numbers or generally when the
unbiased exponent becomes 0. So I can see why Motorola has implemented
it the way they did.

> Or might this even be a
> mistake in the data sheets (i checked different versions of it, they
> all tell the same)?

Wouldn't the easiest way be to check this on actual hardware?

Christian Zietz  -  CHZ-Soft  -  czietz@xxxxxxx
PGP/GnuPG-Key-ID: 0x52CB97F66DA025CA / 0x6DA025CA

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