countOneBits

uint[] bits = [0, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1];
SuccinctBitVector bitvector = new SuccinctBitVector();
foreach(uint bit; bits) {
    bitvector.append(bit);
}

///bitvector.bitarray[0] = [0, 1, 1, 0, 1, 1, 0, 0]
//countOneBits(bitvector.bitarray[0], 2) should return the number of 1 bits
//in [0, 1]
assert(countOneBits(bitvector.bitarray[0], 2) == 1);

//countOneBits(bitvector.bitarray[0], 3) should return the number of 1 bits
//in [0, 1, 1]
assert(countOneBits(bitvector.bitarray[0], 3) == 2);

///bitvector.bitarray[1] = [1, 0, 0, 0, 0, 0, 0, 1]
//countOneBits(bitvector.bitarray[1], 2) should return the number of 1 bits
//in [1, 0]
assert(countOneBits(bitvector.bitarray[1], 2) == 1);
//countOneBits(bitvector.bitarray[1], 8) should return the number of 1 bits
//in [1, 0, 0, 0, 0, 0, 0, 1]
assert(countOneBits(bitvector.bitarray[1], 8) == 2);