"Moving" parts of a RoaringBitmap

[llogiq]

Let's say I have a RoaringBitmap with the values 0, 1, 32, 35 and 70. Now I want to reduce all values > 6 and < 40 by, say, 2. Is there a thing I'm overlooking or would I have to remove and recreate the values via from_sorted_iter?

[Kerollmops]

Hey @llogiq 👋

Happy to see you there. Unfortunately, there is no direct operation to do the following. What I would do is create a second bitmap with numbers in between 7 (> 6) and 39 (<40), do an intersection to get the real numbers. Do the increment by 2 by by iterating on this subset and creating a new bitmap (yes, again). Using the RoaringBitmap::remove_range method to delete the range of values in between 7 and 39 then do the union with the previously shifted bitmap (using the BitOrAssign operator).

What are we Missing to be Efficient?

• A way to split a bitmap when doing an operation:
  fn extract_range(&self, impl Range) -> RoaringBitmap.
• A way to do different, simple, operations on a bitmap in-place:
  fn increment_all(&mut self, n: usize) -> u64.
• Or a way to directly do that on the bitmap itself:
  fn increment_range(&mut self, r: impl Range, n: usize) -> u64.

[llogiq]

Yeah, I guess having RoaringBitmap::{in, de}crement_range functions would probably get the most bang for the buck, and could also easily be SIMD-optimized.