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Re: [STDS-754] after-rounding tininess detection and directed rounding
| The reason for allowing a choice is the need to accomodate existing
| implementations -- and where this was not an issue, rules could be
| tightened, and were. This also covers the new "reproducible mode"
| attribute.
In practical political terms, this is no doubt true. However, there is
in principle some intellectual benefit in allowing choice, because it
doesn't prematurely close off the space of possible future
implementations. I'd rather have kept a free choice for tininess
detection in both formats, at least in the main section.
In general this kind of nondeterminism may seem undesirable, but as
has been noted by others, there are already many other more
troublesome sources of dondeterminism. Tininess detection is one of
the more obscure, and one that doesn't directly affect numerical
results.
I think the consensus on the BRC was that -- as this discussion has shown
-- an issue like this, however obscure, is extremely expensive and
wasteful of many people's time. Consider how often this has come up in
754r discussions, let alone in engineers' discussions all over the world
-- and that's just for binary. Leaving a choice for decimal floating
point condemns implementers of decimal FP to the same fate for the next 20
years; the downside of that probably outweighs any possible advantage of
more implementation options.
Mike
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