[R] binary coding of NA, Nan etc.

[Laurent Gautier]

Prof Brian Ripley wrote:

> How would you specify it?  You would need a way to specify the bit pattern
> (of the source or target endianness?) of Inf, -Inf, NA, the class of NaNs
> (there are many of them) for doubles and perhaps floats too.  And R
> has no type to represent such bit patterns.



I have no real knowledge of binary representation of these 'special'
numbers.
I was naively thinking a limited set of conventions were used by the
majority of the software/libraries. In this context having parameters
about endianess and type (as it is already the case for the actual
readBin and writeBin) plus the 'convention' (like IEEE-754 may be is).
For R things would remain the same, this would just be a choice in
encoding NA and friends on output (or input).

In my example I saw it as:


double:
	Java_representation (this is always 'big' endianess... a good thing
with java binary representation):
	0xef7f ffff ffff ffff

	IEEE-754
	0xffwhatever_it_is

and so on...

float:
	...and on...


But as you suggested things are (unfortunately) not that simple... I
guess for some type, NA and friends might be undefined...




I guess what I only have left to do is to wish everybody a good week-end
and run home....



Regards,




Laurent






 
> I would expect all compiled languages to be using the same representations
> on modern hardware.  However, Java is not in that sense compiled and may
> well be different: I have no idea.
> 
> One thing I did not say before: R's standard NA is the NaN with low word
> of 1954.  I have no idea how to generate that on another system except
> via the sort of sneaky tricks arithmetic.c plays.  The multiplicity
> of NaNs complicates this enormously.
> 
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272860 (secr)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595

-- 
Laurent Gautier			CBS, Building 208, DTU
PhD. Student			D-2800 Lyngby,Denmark	
tel: +45 45 25 24 85		http://www.cbs.dtu.dk/laurent
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