From: Gabriel Dos Reis (gdr_at_[hidden])
Date: 2003-07-16 16:45:46
"Paul A. Bristow" <boost_at_[hidden]> writes:
| | Signalling NaNs are used to indicate missing initialization values.
|
| This is OK for catching missing initialization by mistake - but not
| for OK for deliberately missing because there really is no value
| (measurement missing).
There is not just one qNaN (nor just one sNaN). There is a range for
NaNs. And most of the systems I worked with, the pattern bits in a
NaN is used to communicate the reason of being of the NaN. For
example, it may output sNaN("missing-value").
Note: C99 provides a pseudo-standard way to produce NaNs, through the
functions
double nan(const char*);
float nanf(const char*);
long double nanl(const char*);
|
| In this case, for example calculating the mean, you want to test if the value is
| present/valid 'is_not_missing' before you add it to the sum and increment the
| count.
|
| Testing !is_nan is possible solution but I'm not sure it is ideal.
Indeed, it is no good.
| Suggestions?
I would first make a summary of the usage of the bit patterns for NaNs
and decide on one and document it.