On Wed, 24 Aug 2005, Colin A. Smith wrote:
On Aug 22, 2005, at 3:38 , Prof Brian Ripley wrote:
Unfortunately, R sometimes hits the 2GB memory limit of Win32.
The rw-FAQ explains why that is _not_ the limit!
Sorry to be uninformed, I see from the Microsoft documentation that the limit
can be increased to 3GB when you change the boot parameters of Windows and a
flag in the R binary.
Why via "raw"?
I believe the intention is that this sort of thing be done via external
references, but as float and int are the same size on all current
platforms, I would have considered R integers for storage. Then for example
subsetting would work and you had a 4x larger size limit on 64-bit
platforms. (You would also have got automatic handling of endianness.)
I was concerned that on some platforms (particularly 64 bit ones) an integer
may actually be 64 bits. However, if all current platforms have standardized
on float and int being the same size, then using the integer data type would
be more elegant and solve any endian issues. (Is that really the case?)
Yes, configure tests for int being 32 bit, and R if set to fail to compile
it not. As we assume IEC60559 arithmetic, a float is 32-bit.
Another motivation for using raw was so other R functions (particularly
internal ones) wouldn't assume the data was integer and produce erroneous
results. I'd rather have user-visible error thrown.
To have the best of both worlds, I'm now using an S4 class with a single slot
(f) that stores the float data as an integer vector. It uses the extensible
conversion mechanism created by Duncan Lang to allow the .C() function to
handle float objects. (The custom converter also allows proper checking for
single-precision NA values, which don't get caught if passed as integers.)
At some point, I would like to release this for others to use. Before I get
too far into it, I would greatly appreciate it if anyone had any ideas,
unforeseen caveats, or other suggestions about my current direction. My
implementation is available here:
http://abagyan.scripps.edu/~csmith/float.R
http://abagyan.scripps.edu/~csmith/float.c
http://abagyan.scripps.edu/~csmith/float_0.1.0.tar.gz
I've run into a limitation with the .C() function where it does not
handle raw vectors, which it will do in 2.2.0.
That is just not true!
I should have been a bit more explicit and said that R 2.1.x doesn't
have RAWSXP handlers in either RObjToCPtr() or CPtrToRObj(), so all the C
code gets is a SEXP. R-devel does and passes raw vectors as unsigned char *.
Of course that doesn't matter now that I'm using an extensible converter.
Cheers.
-Colin
--
Brian D. Ripley, [EMAIL PROTECTED]
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 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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