It looks like having BitArray is a good approach. Is there a MIT compatible version? I could add it to my collection collection :) Containers I should migrate it to github.
Stef On Mon, Mar 5, 2018 at 2:52 PM, Richard O'Keefe <rao...@gmail.com> wrote: > As I understand it, the OP's problem is that he wants to > count bits from the high end, and Integers don't *have* > a finite high end. > > PL/I has bit strings. Common Lisp has bit strings. > Some Schemes have copied Lisp. Eiffel _had_ bit strings, > more or less, but dropped them. > > Smalltalk/X has a BitArray class; see > http://live.exept.de/ClassDoc/classDocOf:,BitArray > for documentation. > > My own Smalltalk also has a BitArray class with a > somewhat different interface. Although developed > independently, both are implemented as byte arrays > with an associated count. It's not terribly hard. > For selecting small numbers of bits out of long > bit strings, this is more efficient than shifting > and masking a large integer. > > I rather wonder whether it might be possible to do > better by thinking in a somewhat less C-like style. > For example, Erlang handles unpacking network > packets and the like by letting you write bit-string > *patterns*, which the compiler can then generate > special-case code for. > > Run-time generation of small amounts of code is > somewhat easier in Smalltalk. (Most Smalltalks.) > What would it be like if you had a BitArray class > where you could say > extractor := BitArray extractorForBits: 3 to: 7 of: 256. > ... > extractor value: thisPacket > and extractor was a block (possibly cached) with > code specialised for just that case?
