[datatable-help] New package bit64 over package int64

[Branson Owen]

FYI, I remembered we raised an idea awhile ago for data.table leveraging on
int64 package. Now we seem to have a better alternative? If we are indeed
considering to support int64 package, maybe you should take a look at this
(though 90% chance you already did :p).

[Copy from R-packages Digest, Vol 101, Issue 3]

Package 'bit64' provides fast serializable S3 atomic 64bit (signed)
integers that can be used in vectors, matrices, arrays and data.frames.
Methods are available for coercion from and to logicals, integers,
doubles, characters as well as many elementwise and summary functions.

Package 'bit64' has the following advantages over package 'int64' (which
was sponsored by Google):
- true atomic vectors usable with length, dim, names etc.
- only S3, not S4 class system used to dispatch methods
- less RAM consumption by factor 7 (under 64 bit OS)
- faster operations by factor 4 to 2000 (under 64 bit OS)
- no slow-down of R's garbage collection (as caused by the pure
existence of 'int64' objects)
- pure GPL, no copyrights from transnational commercial company

While the advantage of the atomic S3 design over the complicated S4
object design is obvious, it is less obvious that an external package is
the best way to enrich R with 64bit integers. An external package will
not give us literals such as 1LL or directly allow us to address larger
vectors than possible with base R. But it allows us to properly address
larger vectors in other packages such as 'ff' or 'bigmemory' and it
allows us to properly work with large surrogate keys from external
databases. An external package realizing just one data type also makes a
perfect test bed to play with innovative performance enhancements.
Performance tuned sorting and hashing are planned for the next release,
which will give us fast versions of sort, order, merge, duplicated,
unique, and table - for 64bit integers.

For those who still hope that R's 'integer' will be 64bit some day, here
is my key learning: migrating R's 'integer' from 32 to 64 bit would be
RAM expensive. It would most likely require to also migrate R's 'double'
from 64 to 128 bit - in order to again have a data type to which we can
lossless coerce. The assumption that 'integer' is a proper subset of
'double' is scattered over R's semantics. We all expect that binary and
n-ary functions such as '+' and 'c' do return 'double' and do not
destroy information. With solely extending 64bit integers but not 128bit
doubles, we have semantic changes potentially disappointing such
expectations: integer64+double returns integer64 and does kill decimals.
I did my best to make operations involving integer64 consistent and
numerically stable - please consult the documentation at ?bit64 for details.

Since this package is 'at risk' to create a lot of dependencies from
other packages, I'd appreciate serious  beta-testing and also
code-review, ideally from the R-Core team. Please check the
'Limitations' sections at the help page and the numerics involving "long
double" in C. If the conclusion is that this should be better done in
Base R - I happly donate the code and drop this package. If we have to
go with an external package for 64bit integers, it would be great if
this work could convince the Rcpp team including Romain about the
advantages of this approach. Shouldn't we join forces here?

Best regards

Jens Oehlschl?gel
Munich, 21.2.2012
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