The bitmaps in SDSL are indexed to support rank and select queries: How many 1's are from the beginning until position i, and conversely, which is the position

The bitmaps in SDSL are indexed to support rank and select queries: How many 1's are from the beginning until position i, and conversely, which is the position of the j-th 1) [it uses popcount but is beyond it] So yes, the problems they are solving are different, even though the input data is the same.