Rtwobitlib is an R package that contains a trimmed down copy of
the kent-core source tree turned into a C library for manipulation
of .2bit files. See https://genome.ucsc.edu/FAQ/FAQformat.html#format7
for a quick overview of the 2bit format.
The kent-core source tree can be found
here.
Only the .c and .h files from the source tree that are related
to manipulation of .2bit files were kept.
Note that the package is primarily useful to developers of other R packages
who wish to use the 2bit C library in their own C/C++ code.