On 2009-03-03 23:23, Thomas Stover wrote:
> -I'm curious what NaNAware is, but I haven't found a good link
> explaining it.
NaNAware refers to one of the special "numbers" in IEEE arithmetics:
NaN is the acronym of Not-a-Number, it is used to represent the
result of 0.0/0.0, sqrt(-1) etc. Using such special numbers (Infinity
is another one) makes the floating arithmetical system a closed system,
that is: every possible combination of x, y and +,-,*,/, etc. has
a value. (The upshot of that characteristic of IEEE arithmetics is that
the underlying hardware does not have to raise exceptions.)
One peculiar property of NaN is that it is unequal to any number,
even unequal to itself: NaN != NaN.
That said, NaNs can be used to represent missing values, as is done
in the CSA and NN libraries. But software support for dealing with NaNs
is not always obvious, hence the test for NaNs in the CMake files.
(I do not know of a concise publication that explains these features
and more, but with the keywords above you can probably dig up tons
of stuff :))
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