Bitarray is a NIF library to provide an alternative to hipe_bifs:bitarray* functions, which become unusable in certain circumstances (platform doesn't support HiPE, halfword emulator).
./rebar compile
./rebar get-deps compile && ./rebar ct skip_deps=true
The bitarrays are 0-indexed (based on HiPE's bitarrays), and run with three functions: new/2, update/3, and sub/2:
%% 20 bits array, initialized to false
Bits = bitarray:new(20, false),
%% flips the bits 0, 13 and 19 to true
bitarray:update(Bits, 0, true), % lower boundary
bitarray:update(Bits, 13, true),
bitarray:update(Bits, 19, true), % max boundary for 20 bits
%% Reads the 6th and 13th bits:
false = bitarray:sub(Bits, 6),
true = bitarray:sub(Bits, 13).
Note that there is also a new/1 function that defaults to new(N, false).
The bitarray application is, depending on the test run, on par with HiPE bitarrays in the best cases, and nearly twice as slow in the worst case. Initial allocation for a bitarray is the worst part, being nearly 10x slower than their HiPE counterparts.
Note that they're generally much faster than any in-Erlang attempt at things, such as using binaries if you need to update rather frequently.
This application may therefore be seen as a backup plan for the HiPE bitarrays, not a performance improvement.