RE: [fpu] FPU operations

["Rudolf Usselmann" <russelmann@hotmail.com>]

>From: owner-fpu@opencores.org [mailto:owner-fpu@opencores.org]On Behalf
>Of Damjan Lampret
>
>
...
>Sure. You can include 'undetermined' also since it is one of the status
>signals. Anyway 'undetermined' isn't evaluted by branch insns but
>always triggers exception (is my interpretation right: SNAN triggers
>exception and QNAN doesn't?).

Ahm, no, yes.
Undetermined is only the output of the comparator. There is a separate
output (SNAN) that is asserted when the result is a signaling NAN, in
which case a exception is triggered (or a trap is taken). Undetermined
only says that one of the operators to a compare was a NAN, signaling
or quiet.

Hmm, this is interesting, so what should happen if a compare instruction
has a SNAN as an input ? Do we assert the SNAN exception, or do we remain
quiet ?

At this point I'm thinking we should not generate an exception, to give SW
a chance to deal with potential exception causing data, without generating
exception.
What do you think ?

...
>
>--damjan

rudi
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