Re: Can I use CRoaring library in Git?

[Derrick Stolee <derrickstolee@github.com>]

On 7/16/22 9:50 AM, Abhradeep Chakraborty wrote:
> Hello,
> 
> I need the CRoaring[1] library to use roaring bitmaps. But it has
> Apache license v2 which is not compatible with GPLv2[2].
> 
> Is there a way to use the CRoaring library in Git? Taylor told me that
> contrib/persistent-https tree is also licensed under Apache License
> version 2.
> 
> [1] https://github.com/RoaringBitmap/CRoaring
> [2] https://www.apache.org/licenses/GPL-compatibility.html

I know that working around a license would be the the optimal way to get a
battle-tested implementation. Its API should be close enough to the EWAH
bitmap implementation that we can transition between the formats easily.
Continue pursuing that for now.

However, we always have the option of implementing a version from scratch
based on the description in the paper [3]. The benefit there is that we
would only need to implement what we need from the format and logic, and
we could even get some benefits from exposing some of the internals to the
rest of Git's codebase.

[3] https://arxiv.org/pdf/1603.06549.pdf

I mention this because I made an independent C# implementation of
Roaring+Run for the Azure Repos back-end. The way that the bitmaps are
split into "chunks" of 65k positions was helpful with how the object order
was set up: older objects were in early chunks and so deltas only needed
the later chunks. When using a chunk, we could lazy-load and unload each
chunk as we went through the object order.

So, if we really want to try this, an independent implementation might be
the way to start, at least as a prototype while pursuing the licensing
angle.

Thanks,
-Stolee