first() and last() methods like RoaringBitmap in Roaring64Bitmap

[nareshv]

Is your feature request related to a problem? Please describe.
RoaringBitmap provides first() and last() methods to determine the start and end values present in the bitmap. These methods are not present in the latest release. There are couple of alternatives which available are Roaring64Bitmap.toArray() and then get the first/last values in the array. There is also a Roaring64Bitmap.query(j), with query() function can we use .cardinatliy to get the first/last values in the bitmap ?

Describe the solution you'd like
Whats the most efficient way to get the first() and last() values in the bitmap without iterating over the entire dataset ?

Please note that this is a community-based project. Consider proposing a fix (code, documentation) as a pull request.

[lemire]

You can use getReverseLongIterator() and getLongIterator() to get the last() and first() value respectively.

[nareshv]

Thanks. I was also reading the code,

                long all = bitmap.getLongCardinality();
                long start = bitmap.select(0);
                long end = bitmap.select(all - 1);

also seem to work.
In terms of performance between select() vs *Iterator whats preferred ?

[richardstartin]

Select is linear in the number of bits, the reverse iterator is constant time. Specialised first and last methods would be more efficient though, if someone wants to add them.

[lemire]

@richardstartin is correct. The iterators are better, but we could do even better with specialized functions.