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Re: bignum branch


From: Achim Gratz
Subject: Re: bignum branch
Date: Sat, 04 Aug 2018 12:43:17 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Tom Tromey writes:
> Paul> min and max propagate any NaNs they find.
>
> This part I don't understand, since my mental mode of min/max is that
> they are iteratively applying < or >

The point of having NaN at all is to set aside a tiny bit of the symbol
space for floating point numbers to encode certain error conditions and
propagate them in-band.  Otherwise they'd need to be signalled via side
channels like traps and exceptions, which usually significantly slow
down the error-free cases also or complicate the code even further.
Getting an NaN indicates that your computation has left the domain it
was defined in.  So no matter what you do, after you get an NaN this
indication must be preserved, hence all results must propagate NaN until
you get to the point where you do error handling.


Regards,
Achim.
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