[R-pkgs] new package 'bit64' - 1000x faster than 'int64' sponsored by Google

From: Jens Oehlschägel <Jens.Oehlschlaegel_at_truecluster.com>
Date: Tue, 21 Feb 2012 23:13:08 +0100


Dear R-Core team,
Dear Rcpp team and other package teams,
Dear R users,

The new package 'bit64' is available on CRAN for beta-testing and code-reviewing.

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.

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 Oehlschlägel
Munich, 21.2.2012



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