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Re: differences between implementations of IEEE-754 basic operators

Michel Hack <hack@xxxxxxxxxxxxxx> wrote:

If we're talking 754-1985, that's it for basic operations (taking
Vincent's addition of "don't look at the bits" into account.  The
latter also covers issues of NaN propagation and NaN signs.

Not quite.  There's the ambiguity about when the underflow flag
must be set.  I think that the new standard closes that one, but I
haven't a clue how many current hardware (and software, if any)
implementations conform.  It's a pretty arcane issue, anyway.

If we are talking practicabilities, then things are very different,
and expecting repeatable results in real programs is crying for the
moon.  But we have been there before, and let's not go there again.

Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:  nmm1@xxxxxxxxx
Tel.:  +44 1223 334761    Fax:  +44 1223 334679

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