A Class for Vectors of 1-Bit Booleans
Description
True boolean datatype (no NAs),
coercion from and to logicals, integers and integer subscripts;
fast boolean operators and fast summary statistics.
With 'bit' vectors you can store true binary booleans {FALSE,TRUE} at the
expense of 1 bit only, on a 32 bit architecture this means factor 32 less
RAM and ~ factor 32 more speed on boolean operations. Due to overhead of
R calls, actual speed gain depends on the size of the vector: expect gains
for vectors of size > 10000 elements. Even for one-time boolean operations
it can pay-off to convert to bit, the pay-off is obvious, when such
components are used more than once.
Reading from and writing to bit is approximately as fast as accessing
standard logicals - mostly due to R's time for memory allocation. The package
allows to work with pre-allocated memory for return values by calling .Call()
directly: when evaluating the speed of C-access with pre-allocated vector
memory, coping from bit to logical requires only 70% of the time for copying
from logical to logical; and copying from logical to bit comes at a
performance penalty of 150%. the package now contains further classes for
representing logical selections: 'bitwhich' for very skewed selections and
'ri' for selecting ranges of values for chunked processing. All three index
classes can be used for subsetting 'ff' objects (ff-2.1-0 and higher).