BitBuffer is a bit stream module implemented in pure Lua. Its purpose is to provide an easy way to write and read binary data down to the bit level. It first found life as a replacement for a module that performed rather poorly, and was primarily meant for use on Roblox.
However, no Roblox specific API is used in the main file or tests of this module. The module was written and tested using Lua 5.2, though any version of Lua that has a bit module should be able to run this module with a few modifications. It will probably perform best with LuaJIT, as Roblox's Lua VM is extremely fast compared to PUC-Rio and this module makes use of some specific optimizations (ipairs, as an example, is faster than a numeric for in Roblox).
Numbers take up a lot of space. Take the number 24930. When written out, it's 5 bytes. That's not an awful lot, but if you had to save hundreds of thousands of numbers of a similiar size, that's a lot of space spent on numbers alone.
When written with this BitBuffer though, 24930 only takes up 2 bytes and becomes ab.
Obviously, the two bytes taken up by ab is less than the 5 bytes taken up by 24930. This difference gets a lot more dramatic the bigger the number: 1633837924 is 10 bytes to write out but in binary is abcd, and 107075202213222 is 15 bytes but turns into abcdef. That's a difference of 9 bytes per number!
For more information, visit the documentation site!
For starters, they didn't exist when this module was written! They also don't exist until Lua 5.3, which is a huge downside.
They're also comparatively slow: BitBuffer does all of its calculations with pure arithmetic and bit32, which is always going to be faster than string creation.
The fact that you have to pass a format string to them is also a huge downside, as it means (un)serializing data that's dynamically generated is annoying.