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extreme exponent spill definitions
The opposite extreme definition is:
the numerical result rounded to the destination format differs from the
numerical result rounded to a hypothetical format with the same precision
as the destination format but unbounded exponent range.
Could you detail a situation where [this] definition will not
satisfy everybody? It seems like this is the definition that any user
actually expects. For example, if a developer checks the sticky flags
(or trap exceptions) in order to ensure that a sequence of operations
did not go astray (bounded relative error as predicted by the model),
then both definitions work. But only the second one has the advantage of
never raising a false positive.
1) This definition does not signal an exact subnormal result.
Some people want underflow signaled in that case, in order to wrap exponents
for instance, or to implement abrupt underflow in software.
2) This definition is actually rather hard to translate from words into
efficient hardware. It's never been implemented as far as I know.
The problem is excluding the cases that round to the same value that they
would have rounded to in the hypothetical format.